Terpenoids’ anti‑cancer effects: focus on autophagy

Chirine El‑Baba1 · Amro Baassiri2 · Georges Kiriako3 · Batoul Dia2 · Sukayna Fadlallah2 · Sara Moodad2 · Nadine Darwiche1

Accepted: 28 June 2021
© The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021

Terpenoids are the largest class of natural products, most of which are derived from plants. Amongst their numerous bio- logical properties, their anti-tumor effects are of interest for they are extremely diverse which include anti-proliferative, apoptotic, anti-angiogenic, and anti-metastatic activities. Recently, several in vitro and in vivo studies have been dedicated to understanding the ‘terpenoid induced autophagy’ phenomenon in cancer cells. Light has already been shed on the intri- cacy of apoptosis and autophagy relationship. This latter crosstalk is driven by the delicate balance between activating or silencing of certain proteins whereby the outcome is expressed via interrelated signaling pathways. In this review, we focus on nine of the most studied terpenoids and on their cell death and autophagic activity. These terpenoids are grouped in three classes: sesquiterpenoid (artemisinin, parthenolide), diterpenoids (oridonin, triptolide), and triterpenoids (alisol, betulinic acid, oleanolic acid, platycodin D, and ursolic acid). We have selected these nine terpenoids among others as they belong to the different major classes of terpenoids and our extensive search of the literature indicated that they were the most studied in terms of autophagy in cancer. These terpenoids alone demonstrate the complexity by which these secondary metabolites induce autophagy via complex signaling pathways such as MAPK/ERK/JNK, PI3K/AKT/mTOR, AMPK, NF-kB, and reac- tive oxygen species. Moreover, induction of autophagy can be either destructive or protective in tumor cells. Nevertheless, should this phenomenon be well understood, we ought to be able to exploit it to create novel therapies and design more effective regimens in the management and treatment of cancer.
Keywords Terpenoids · Autophagy · Cancer · Cell death
Cancer is the leading cause of mortality worldwide and is considered as one of the major obstacles hindering the increase in life expectancy [1, 2]. The rapid identification of numerous potential therapeutic targets for different cancer types is setting a high demand for the development of new drugs. Due to the side effects of chemotherapy, the need for alternative anticancer agents from natural sources is increasing.

 Nadine Darwiche [email protected]
1 Department of Biochemistry and Molecular Genetics, American University of Beirut, Beirut, Lebanon
2 Department of Biomedical Sciences, American University of Beirut, Beirut, Lebanon
3 Department of Biomedical Engineering, American University of Beirut, Beirut, Lebanon

The unparalleled chemical diversity of compounds har- bored within millions of plant species is the epitome of nature’s ingenuity [3]. Structural variety complemented with multifunctional activity makes plant-extracted natural products auspicious [4–8]. Currently, these plant products account for more than 60% of the Food and Drug Adminis- tration (FDA; USA) approved commercially available drugs that target cancer [9]. Terpenoids, the largest class of natural products, includes more than 40,000 structures that are used in flavor, fragrances, chemical, and pharmaceutical indus- tries [10–14]. Terpenoids, composed of five carbon isoprene units, are divided into subclasses based on their structures and include hemiterpenoids, monoterpenoids, sesquiterpe- noids, diterpenoids, sesterterpenoids, triterpenoids, tetrater- penoids, and polyterpenoids [15]. Each terpenoids’ subclass has its own set of diverse biological properties. Terpenoids have anticancer activities as they target several stages of cancer development such as cell proliferation, cell death, angiogenesis, and metastasis [8]. Many terpenoids affect

epigenetic and cellular death mechanisms through targeting nuclear factor kB (NF-kB), Janus kinases-signal transducer and activated of transcription proteins (JAK-STAT), acti- vator protein-1 (AP-1), metalloproteinases (MMPs), DNA topoisomerase I and II, blocking the endoplasmic reticulum (ER) calcium ATPase pump, inhibiting proteasome, activat- ing p53, and modulating DNA minor grooves [14–16].
The major mechanism of cell death induced by terpenoids is apoptosis [17, 18]. However, recent studies indicate that terpenoids can result in other forms of cell death, specifi- cally autophagy, as highlighted in this review. Autophagy is a self-eating process that involves the formation of double-membrane vacuoles, autophagosomes, which then merge with lysosomes [19, 20]. Autophagy is regulated by numerous players, namely the autophagy genes (ATG) [21]. This leads to the degradation and recycling of large protein molecules and dysfunctional organelles [22, 23]. In eukaryotes, autophagy is important in preventing cellular damage and aging, maintaining homeostasis, and enhancing cell survival during stressful conditions [24]. On the other hand, autophagy can play a role in pathological conditions including neurodegenerative diseases, infection, and cancer [23, 25–29]. The emerging role of autophagy in cancer is one of a double-edged sword [30–32]. In fact, autophagy enables cancer cell survival during stressful events such as starvation and hypoxic conditions or may lead to apoptotic or non-apoptotic cell death.
This review summarizes nine different terpenoids
among the various subclasses  and their cell death

mechanisms of action with an emphasis on autophagy . These latter plant terpenoids were selected as they present with several antitumor mechanism involving autophagy. In addition, we have chosen these nine terpenoids among others as they belong to the different major classes of terpenoids and our extensive search of the literature indi- cated that they were the most studied in terms of autophagy in cancer. Furthermore, the cross-talk between apoptosis and autophagy will be addressed since they share several signal- ing pathways [23, 33–35]. We will first cover the different mechanisms of cell death and autophagy of the representa- tive sesquiterpenoids (artemisinin, parthenolide) followed by the diterpenoids (oridonin, triptolide) and will end up with the triterpenoids (alisol, betulinic acid, oleanolic acid, platycodin D, ursolic acid) as summarized in Tables 1 and 2.

Artemisinin and its derivatives and anticancer activities

Artemisinin, a sesquiterpene lactone, was first isolated from the sweet wormwood Artemisia annua L. by the Nobel Prize winner Youyou Tu [36, 37]. Artemisinin is mostly used in anti- malarial treatments and along its derivatives such as dihydroar- temisinin (DHA), and artesunate (ARS) have proven to harbor antitumor properties [38]. Artemisinin activity was established in vitro and in vivo and induces caspase 3-dependent apoptosis in tumor cells while exhibiting low toxicity to normal cells [16, 39]. Artemisinin was shown to induce ferroptosis in several

1 Chemical structures of selected terpenoids divided into three subclasses: sesquiter- penoids (artemisinin, parthe- nolide), diterpenoids (oridonin, triptolide), and triterpenoids (alisol, betulinic acid, oleanolic acid, platycodin D, and ursolic acid)


2 The effect of terpenoids on the autophagic signaling pathways. These terpenoids alone (blue oval) demonstrate the complexity by which these secondary metabolites induce autophagy via complex signaling pathways such as MAPK/ERK/JNK, PI3K/AKT/mTOR, AMPK, NF-kB, and reactive oxygen species. AKT protein kinase B; AMPK AMP-activated kinase; ATG autophagy-related gene; c-met hepatocyte growth factor receptor. ER sarcoplasmic/endoplasmic

reticulum; ERK extracellular signal-regulated kinase; Glut-1 glucose transporter 1; HSF1 heat shock factor 1; HSP70 heat shock protein 70; JNK c-jun N-terminal kinase; LC3 microtubule-associated protein light chain 3; MAPK mitogen-activated protein kinase; mTOR mecha- nistic target of rapamycin; NF-kB nuclear factor-kB; PI3K phospho- inositide 3-kinase; ROS reactive oxygen species
cancer cells by increasing intracellular ROS activity and trig- gering degradation of lysosomes [40]. ARS is water soluble, inhibits cell growth through inducing cell cycle arrest [41, 42] and causes tumor cell death through apoptosis, ferroptosis, and autophagy [43, 44]. Recently, ARS was reported to induce G1 arrest without DNA damage induction in 2 dimensional (2D) and 3D breast cancer models [45].
DHA is the most potent derivative of artemisinin and has been emerging as an anticancer agent with a cytotoxic effect on a wide range of human cancer cell lines [8, 39, 46–56]. In addition, DHA has a significantly lower cytotoxicity on normal cells which makes it an ideal chemotherapeutic agent [8].
DHA has a diverse set of cell death mechanisms which include apoptosis, autophagy, cell cycle arrest, reactive oxygen species (ROS) generation, iron involvement, and T-helper type 1 (Th1) immune response shift [41, 47, 49,

Artemisinin and its derivatives in autophagy
The past few years have witnessed great interest in study- ing autophagy on artemisinin and its derivatives and have been shown to induce autophagic cell death in tumors [64,

65]. Artemisinin and ARS induce G2/M cell cycle arrest, increase in cyclins B1, D1, and E and apoptosis in breast cancer cells, and result in autophagic cell death via Bec- lin1 upregulation, LC3 aggregation, and LC3-II conversion [42, 66]. A hallmark of autophagy induction was measured, namely the conversion of LC3-I to LC3-II [67]. It is worth noting that there is a close correlation between the amount of LC3-II and the number of autophagosomes [68]. Inhibit- ing autophagy by 3-methyladenine (3-MA) abrogated the latter observed cell death. ARS treatment of human bladder cancer cells (T24 and EJ) resulted in autophagy-dependent apoptosis, ROS increase, and activation of AMPK-mTOR- ULK1 [69]. On the other hand, artemisinin in combination with chemotherapeutic drugs synergize to induce caspase 3-dependent apoptosis by inhibiting autophagy [39, 70]. Studies have shown that DHA can induce autophagy in a number of human cancer cell lines, namely ovarian (SKOV3/ DDP) [61, 71], multiple myeloma (RPMI 8226), promyelo- cytic leukemia (NB4), colorectal (HCT116), cervical (HeLa) [63, 67, 72, 73], esophageal (Eca109 and Ec9706) [62, 74], pancreatic (BxPC-3 and PANC-1) [75], hepatic (HepG2, HepG2215) [73, 76, 77], chronic myelogenous leukemia (K562) [59], glioma (SKMG-4) [78], LN-Z308, T98G
and LN-229 [79], and tongue squamous cell carcinoma

Table 1 Sesquiterpenoids and diterpenoids anticancer compounds as autophagic regulators
Terpenoids Cancer model Autophagy mechanism and effects Reference


Artemisinin MCF-7 and MDA-MB-231 human breast cancer cells ↑Beclin 1
LC3-I to LC3-II conversion → LC3 aggregation
→ Autophagic cell death
T24 and EJ human bladder cancer cells ↑ROS
→ Autophagic cell death

SKOV3 and SKOV3/DDP human ovarian cancer cells ↑pmTOR [71]

SKOV3 and primary EOC human ovarian cancer cells ↓NFkB
→ Autophagic cell death

RPMI 8226 human multiple myeloma, NB4 promyelo- cytic leukemia, HCT116 colorectal, and HeLa cervical cancer cells
HeLa, HCT116, HepG2 and SKOV3
in vitro and in vivo
HL60 human acute promyelocytic leukemia, KG1 acute myeloid leukemia, and THP-1 acute monocytic leuke- mia cell lines

↓NFkB, ↑ ROS, ↓p62
LC3-I to LC3-II conversion → LC3 aggregation
→ Autophagic cell death
↑Stress-regulated protein p8, ↑ATF4, ↑CHOP
→ Autophagic cell survival
↑ROS, ↓ferritin
→ Autophagic cell death

HeLa cervical cancer cells LC3-I to LC3-II conversion → LC3 aggregation
↑ROS, ↑p-Bcl-2, ↑p-JNK1/2, ↑Beclin 1, ↓pmTOR
→ Atophagic cell death

Eca109 and Ec9706 human esophageal cancer cells LC3-I to LC3-II conversion [74]

Eca109 human esophageal cancer in vitro and in vivo ↑ROS,
↓TRF2→ DNA damage response
→ Autophagic cell death
BxPC-3 and PANC-1 pancreatic cancer ↑LC3-II, ↑ROS, ↑Beclin 1, ↑MAPK/JNK
→Autophagic cell survival
HepG2215 hepatic ↑ ROS → DNA damage response, ↑autophagosomes,
↑AIM2/caspase-1 inflammasome, ↑Beclin 1, ↓p62 LC3-I to LC3-II conversion

HepG2.2.15 HBV positive hepatocellular carcinoma cells in vitro and in vivo

LC3-I to LC3-II conversion, ↓AKT/mTOR
→Autoagic cell survival

K562 chronic myelogenous leukemia ↑ROS, ↑LC3-II
→ Autophagic cell death

MGR1, MGR3, SF295, SKMG-1, SKMG-4, T98G,
U251, U251/CP2, U373 and U87 human glioma cell lines in vitro and in vivo

↑Beclin 1, ↑LC3-II
→ Autophagic cell death

T29 primary human glioblastoma cell line, LN-Z308, T98G and LN-229 human glioma cell lines in vitro and in vivo

↑ROS, ↑LC3-II [79]

Cal-27 tongue squamous cell carcinoma cells ↑LC3-II, ↑Beclin 1, ↑autophagosomes
↑ ROS→ DNA double strand breaks
→ Autophagic cell death

A549 human adenocarcinoma epithelial cells in vitro and in vivo

LC3-I to LC3-II conversion, ↑MAPK
→ Autophagic cell death

HUVEC Human umbilical vein endothelial cells ↑autophagosomes, ↑ROS, ↑LC3-II
Parthenolide Saos-2 and MG-63 Osteosarcoma cells ↑PINK1, mitochondrial translocation of Parkin →
mitophagy, ↑ROS
→ Autophagic cell death
MDA-MB231 breast cancer in vitro and in vivo ↑ROS, ↑JNK, ↓NFkB, ↑Beclin 1,
LC3-I to LC3-II conversion
→ Autophagic cell death
MCF-7 and MCF-10A breast cancer cells ↑ROS, ↑AMPK pathway
→Autophagic cell survival

Table 1 (continued)

Terpenoids Cancer model Autophagy mechanism and effects Reference

MCF7 and MDA-MB231 breast cancer cells ↓p62/SQSTM1, ↑Beclin 1, ↑ATG13, ↑ATG14
→Autophagic cell survival
Panc-1 and BxPC3 pancreatic cancer cells ↑autophagosomes, ↑LC3-II, ↑p62/SQSTM1, ↑Beclin 1,
→ Autophagic cell death
HeLa cervical cancer ↑Beclin 1, ↑ATG5, ↑ATG3, ↓PI3K/AKT/mTOR, ↑ ROS
→ mitochondrial membrane potential loss
→ Autophagic cell death
HepG2 human hepatocellular carcinoma cells ↑MSD uptake, acidic vesicular organelle cytoplasmic
→ Autophagic cell death


MDA-T32 human papillary thyroid carcinoma cells in vitro and in vivo
HL-60 human promyelocytic leukemia cell line, HeLa human epithelial carcinoma cell line, and HEK293T primary embryonic human kidney cells

↑LC3-II, ↑Beclin 1, ↓PI3K/AKT/mTOR
→ Autophagic cell death
↑ROS, ↓translation initiation factor eIF4E binding protein 1 (4E-BP1)
→ Autophagic cell death

Oridonin SW480, HCT-15 colorectal cancer cells in vitro and in vivo
↓GLUT1, ↓MCT1, ↑LC3-II, ↓p-AMPK,
↑Beclin 1, ↑ATG5
→Autophagic cell death

MDA-MB-436 and MDA-MB-231 breast cancer ↑LC3-II, ↑Beclin 1
→Autophagic cell death
cervical cancer Hela cells ↑ROS, ↑Beclin 1, LC3-I to LC3-II conversion
→Autophagic cell survival
A549 lung cancer LC3-I to LC3-II conversion, ↑ Beclin1
↓c-met → ↑ERK pathway
→ Autophagic cell death
PC3 and LNCaP prostate cancer ↑autophagosomes, acidic vesicular organelle cytoplasmic accumulation,
LC3-I to LC3-II conversion
→Autophagic cell survival
RPMI8266 human multiple myeloma ↑Beclin 1, ↑ROS, ↓sirtuin 1
→Autophagic cell survival
U937 human histiocytic lymphoma ↑p-ERK, ↑pro IL-1β
↑ Beclin1, ↑LC3-II, ↑ATG4B
Triptolide WEHI-3 murine leukemia cells in vitro and in vivo ↑ROS, ↑mitochondrial membrane potential, ↑intracel-
lular calcium,↑acidic vacuoles, ↑MSD uptake, ↑ATG5,
↑ATG7, and ↑ATG12,
→autophagic cell death
MCF-7 human breast cancer ↓p62, ↑p38/ERK/mTOR pathway
→autophagic cell death

S2-013, S2-VP10, and Hs766T metastatic pancreatic cancer cells

MIA, PaCa-2, and PANC pancreatic cancer cells in vitro and in vivo
↑ATG5, ↑Beclin 1, ↓AKT/mTOR/p70S6K,
↑ERK pathway
→Autophagic cell death
↑autophagosomes, ↑LC3-II, ↑ATG5, ↑ULK1, ↑VPS34,
→Autophagic cell death

MG-6 human osteosarcoma cells ↑Beclin 1, ↑LC3-II, ↓p62, ↓VEGF, ↓HIF-1α,

↓Wnt/β catenin
→Autophagic cell death
SiHa Cervical cancer ↑p38, ↑MAPK, ↓PI3k/AKT/mTOR
→Autophagic cell survival
SKOV3/DDP ovarian cancer cells in vitro and in vivo ↑ROS, ↓ JAK2/STAT3
→ Autophagic cell deathSH-SY5Y and IMR-32 neuroblastoma cells ↑intracellular calcium, ↑LC3-II, ↓NFkB, ↓HSF1, ↓HSP70 [167]

Table 1 (continued)
Terpenoids Cancer model Autophagy mechanism and effects Reference

PC-3, LNCaP and C4-2 pancreatic cancer cells ↑intracellular calcium → ER stress, ↓mTOR, ↑ULK1,
↑Beclin 1, ↑CaMKKβ/AMPK
→Autophagic cell survival

AIM2 absent in melanoma 2; AKT protein kinase B; AMPK AMP-activated kinase; ATF4 Activating transcription factor 4; ATG autophagy- related gene; Bcl-2 B-cell lymphoma 2; CaMKKβ Ca2 + /CaM-dependent protein kinase kinase β; CHOP Cytoxan, Hydroxyrubicin,, Oncovin, Prednisone); ERK extracellular signal-regulated kinase; JAK2 Janus Kinase 2 gene; JNK c-jun N-terminal kinase; HIF-1α, hypoxia-inducible factor 1-alpha; HSF1 heat shock factor 1; HSP70 heat shock protein 70; IL-1β Interleukin 1 beta; LC3 microtubule-associated protein light chain 3; MCT1 monocarboxylate transporter 1; mTOR mechanistic target of rapamycin; NFkB nuclear factor-kB; p- phosphorylated; p70S6K riboso- mal protein S6 kinase beta-1; PINK1 PTEN-induced kinase 1; PI3K phosphoinositide 3-kinase; PUMA p53 upregulated modulator of apoptosis; ROS reactive oxygen species; STAT3 signal transducer and activator of transcription 3; TRF2 telomeric repeat binding factor 2; ULK1 Unc-51 like autophagy activating kinase; VEGF vascular endothelial growth factor; VPS34 phosphatidylinositol 3-kinase
(Cal-27) cells [80]. DHA-treated cells presented with acidic vesicular organelles (autophagosomes and autolysosomes), increased expression of LC3-II protein, decreased p62 pro- tein aggregation, and increased Beclin1 levels compared to control cells [59, 71–75, 78–80]. Furthermore, the MAPK/ JNK signaling pathway was studied whereby it showed an increase in JNK phosphorylation that was dose- and time- dependent. JNK activation was decreased in cells that were pretreated with N-acetyl-L-cysteine (NAC, a ROS inhibitor) which suggests this process is ROS-dependent [67, 75, 81]. DHA promoted autophagy in tumor cells by suppressing the phosphorylation and activation of AKT/mTOR pathway [82]. On the other hand, NF-kB activation was suppressed in DHA-treated myeloma and ovarian cells in a dose-dependent manner and induced autophagic cell death [61, 72]. DHA- induced autophagy in cancer cells was ROS-dependent [62, 76]. Finally, Zhang et al. have demonstrated that co-treat- ment of glioma SKMG-4 cells with DHA and Temozolo- mide induced autophagy and was more effective at tumor inhibition efficacy in vitro and in vivo than in cells treated with Temozolomide alone [78].

Parthenolide and anticancer activities
Parthenolide, a 15-C terpenoids known as sesquiterpene lac- tone, is found in the feverfew tree (Tanacetum parthenium). It has many pharmacological effects such as anti-inflamma- tory, anti-bacterial, and anticancer and it is widely used for the treatment of headache, fever, and arthritis [83–85]. Par- thenolide was found to target cancer stem cell (CSC) which drove the development of an analogue with more favorable pharmacological properties, the dimethylaminoparthenolide (DMAPT) [86, 87]. Parthenolide displays anticancer activi- ties against many tumor types such as colorectal, melanoma, pancreatic, breast, prostate, cervical, renal, and thyroid [88–94]. It usually induces apoptosis through increasing oxi- dative stress, mitochondrial dysfunction, inhibiting NF-kB and mTOR/PI3K/AKT pathways, stimulating p53 signaling,

regulating MAPK and JNK, interfering with STAT3, and controlling Bcl-2 family members [86, 93, 95–97].

Parthenolide and autophagy
Parthenolide administration in osteosarcoma cells resulted in ROS generation followed by autophagic cell death, sug- gesting a role of parthenolide in inducing autophagy and not apoptosis [98]. Similarly, treatment of MDA-MB231 breast cancer cells with parthenolide and DMAPT resulted in ROS generation, activation of JNK, downregulation of NF-kB, and autophagic cell death as indicated by enhanced Beclin1 expression and the conversion of LC3-I to LC3-II [99]. At a more advanced stage, ROS resulted in dissolu- tion of the mitochondrial membrane and necrotic cell death. In a study done on pancreatic cancer cells, it was demon- strated that parthenolide induced autophagy as manifested by autophagosomes production and increase in LC3-II levels [100]. Additionally, blocking autophagy inhibited parthe- nolide-induced apoptosis, indicating that this drug inhibited proliferation of cancer cells by prompting autophagy-medi- ated apoptosis. On the other hand, parthenolide treatment of MCF-7 breast cancer cells resulted in activation of apoptosis pathway and ROS production leading to AMPK-autophagy pathway; a protective-survival mechanism rather than a cell death mechanism [92, 101]. In another study, parthenolide induced apoptosis as well as autophagy and inhibited pro- liferation of HepG2 human hepatocellular carcinoma cells
[102] and breast cancer cells through inhibition of PI3K/
AKT/mTOR pathway [103]. Treatment of human leukemic HL-60 and Jurkat cells with parthenolide resulted in atypical apoptosis briefly after caspase activation denoted by plasma membrane destruction [104]. Similarly, this sesquiterpene lactone also led to atypical necrosis that was indicated by prompt membrane rupture [104]. Parthenolide and several sesquiterpene lactones alter membrane integrity by affect- ing lipid oxidation and disruption [105]. Thyroid carci- noma cells treated with parthenolide resulted in induction

Table 2 Triterpenoids anticancer compounds as autophagic regulators


→Autophagic cell death AKT/mTOR,
→ Autophagic cell death

↓cytochrome c, mitochondrial damage

→Inhibits autophagy

→Inhibits autophagy

v Autophagic cell death

→ Autophagic cell survival

→Autophagic cell death

→Inhibits autophagy Autophagic cell survival
→ Autophagic cell survival

→ Autophagic cell death

↑ROS,concentration, ↓p-AKT,

→ Autophagic cell death v Autophagic cell survival
↑Bid, ↑autophagic vesicles

↑ERK1/2 pathway,

↓PI3K/AKT/mTOR, ↑JNK/p38MAPK,adenocarcinoma epithelial cells, and MCF7 human breast adenocarcinoma cells
→ Autophagic cell death

Table 2 (continued)
Terpenoid Cancer models Autophagy mechanism and effects Reference

BEL-7402 hepatoma cells in vitro and in vivo ↑cytoplasmic vacuoles, ↑LC3-II, ↑MSD uptake, ↓Bcl-2,
↑apoptosis, ↑ERK/JNK pathways,
→ Autophagic cell survival
glioblastoma multiforme cells ↓autophagosomes degradation
→Inhibits autophagy
Ursolic acid T47D, MCF-7, and MDA-MB-231 breast cancer cells ↓PI3K/AKT, ↑GSK activity, ↓NFkB, ↑LC3-II,
→ Autophagic cell death
MCF-7, MDA-MB-231, and SK-BR-3 breast cancer cells ↓p-ERK1/2, ↑ROS, ↓p-AKT and ↑-pATM, ↑AMPK,
→ Autophagic cell death

TC-1 mouse hybridoma lymphoblast derived cervical cancer cells

↑cytoplasmic vacuoles, ↑LC3-II, ↑ATG5
→ Autophagic cell death

MCF-7 breast cancer cells ↑ER stress, ↑MAPK1/3 pathway
→ Autophagic cell death
PC-3 prostate cancer cells ↑LC3-II, ↑MSD uptake, ↑autophagosomes, ↑Beclin 1,
→ Autophagic cell survival
AKT protein kinase B; AMPK AMP-activated protein kinase; ATG autophagy-related gene; ATM ataxia-telangiectasia mutated Serine/Threonine Kinase; Bcl2 B-cell lymphoma 2; Bid BH3-interacting domain death agonist; CaMKK calcium/calmodulin-dependent protein kinase; ER, sarco- plasmic/endoplasmic reticulum; ERK extracellular signal-regulated kinase; GSK glycogen synthase kinase; JNK c-jun N-terminal kinase; LC3 microtubule-associated protein light chain 3; MAPK mitogen-activated protein kinase; MSD monodansylcadaverine; mTOR mechanistic target of rapamycin; NF-kB nuclear factor-kB; p- phosphorylated; PI3K phosphoinositide 3-kinase; PINK PTEN (Phosphatase and tensin homolog)- induced kinase; ROS reactive oxygen species; SQSTM1 sequestosome 1; ULK1 Unc-51 like autophagy activating kinase 1
of autophagy through an increase in LC3-II and Beclin1 [93] inhibiting autophagy by blocking ATG5 abrogated apoptosis [106].

Oridonin and anticancer activities
Oridonin is a natural tetracyclic diterpenoid extracted mainly from Rabdosia rubescens that exhibits potent anti- tumor properties in various types of human cancer cells [8, 107–111]. Oridonin was shown to act as an anti-inflamma- tory, anti-bacterial and anti-proliferative compound [112]. In vitro and in vivo studies revealed its antitumor effect on a variety of solid tumors including liver, pancreas, cervix, prostate, breast, lung, and colorectal cancers, fibrosar- coma, melanoma, and osteoma [107, 113–120]. Oridonin exhibited antitumor effects in different forms of leukemia, lymphoma, and multiple myeloma as well [110, 121]. This diterpenoid was shown to influence several cellular events such as cell cycle arrest, apoptosis, ferroptosis, autophagy, differentiation, angiogenesis, and metastasis [15, 122–124]. The major oridonin-induced cancer cell death mechanism is apoptosis [110]. Several studies reported that this diter- penoid was able to block the NF-kB pathway by disrupting NF-kB protein/DNA interaction [15, 110]. Moreover, the blockade of NF-kB and p38 pathways was preceded by AP-1 downregulation in response to oridonin treatment contribut- ing to apoptosis in a colorectal cancer model [15]. Oridonin induced apoptosis in tumor cells through the suppression of

PI3K/AKT signaling, forkhead box class O (FOXO) tran- scription factor expression, and glycogen synthase kinase 3 (GSK3) [15]. This diterpenoid inhibited epithelial mesen- chymal transition (EMT) and halted metastasis by abrogat- ing the AKT/STAT3 pathway in nasopharyngeal carcinoma cells [125]. Oridonin effect was p53-depended as a reversal in oridonin anti-proliferative activity was observed upon p53 inhibition by pifithrin-α in gastric cancer cells [109]. These findings were further supported by a study show- ing that apoptosis was the adopted cell death mechanism in wild-type p53 colorectal cancer (CRC) cells while other mechanisms were prompted in mutant p53 cancer cells such as autophagy [108]. Other studies revealed the contribution of caspase 3, caspase 8, Bcl-2/Bax, ROS, and cytochrome c in oridonin-induced apoptosis [107, 120, 126]. However, the detailed mechanism of the antitumor effect of this dit- erpenoid is yet to be elucidated, especially after the emerg- ing indication regarding its influence on autophagy and its association with apoptosis.

Oridonin and autophagy
Reports in the literature described that autophagy is another cell death mechanism adopted by oridonin-treated cancer cells besides apoptosis [15, 108, 112, 127, 128]. However, the relationship between these two mechanisms remains controversial. [15, 112]. A study by Yao et al. stated an interesting finding that no significant apoptotic

activity was observed in oridonin-treated CRC SW480 cells, despite of its clear anti-proliferative effect [108]. The same report indicated that oridonin deactivated AMPK which downregulated the glucose transporter 1 (GLUT1) and the monocarboxylate transporter 1 (MCT1) both in vitro and in vivo, thus inhibiting glucose uptake and lactate export. However, ATP levels were not affected which suggests that oridonin is triggering autophagy: the major source of ATP in cancer cells. Others reported these two models of cell death frequently occur in parallel in tumor progression [74, 129]. Oridonin was shown to induce autophagy and apoptosis acting in synergy in fibro- sarcoma [15] and breast cancer cells [112]. On the con- trary, it was suggested that oridonin induced autophagy by activating PI3K/AKT, a signaling pathway that suppresses apoptosis. These observations were further supported by a study on CRC cells detecting LC3-II concomitant with rapid deactivation of p-AMPK upon oridonin treatment which confirmed the presence of autophagy and the inhibi- tion of apoptosis [108].
Various studies demonstrated that oridonin induced pro-
apoptotic autophagy in A549 lung cancer and PC3 prostate cancer cells [130, 131]. This was indicated by a decrease in the LC3B-1/LC3B-2 ratio and by an increase in Beclin 1 levels. Furthermore, the inhibition of autophagy by 3-MA led to a decrease in apoptotic bodies. This elucidates that autophagy acts in synergy with apoptosis in oridonin- treated cells. Additionally, the induction of autophagy was mainly through the inhibition of c-met (hepatocyte growth factor receptor) which is a potent inhibitor of the ERK signaling pathway. By this means, ERK pathway is induced which in turn activates the autophagic signaling pathways [130]. In normal liver cells THLE-2, oridonin activated autophagy and protected against steatosis [132]. In addition, co-treatment of oridonin with other thera-
peutics such as NVP-BEZ235 (inhibitor of AKT/mTOR pathway) and c-tocotrienol led to higher levels of LC3B-2 and Bcl-1 which highlights the importance of using com- bined treatments for cancer therapy [133, 134]. In fact, combining oridonin to chemotherapy and immunotherapy sensitized cancer cells to oridonin-induced apoptosis and activated autophagy [135–137].
In contrast with previous findings, oridonin induced anti-apoptotic autophagy in human multiple myeloma through the regulation of ROS and sirtuin 1 suggesting that autophagy acted as a protective mechanism against apoptosis [138]. This concurs with another study where autophagy, induced by this compound, inhibited apoptosis of human histiocytic lymphoma U937 cells through the regulation of inflammation [139]. Finally, further studies need to investigate the dichotomous effects of oridonin on autophagy and the signaling pathways involved.

Triptolide and anticancer activities
Triptolide, a compound found in the Chinese herb Trip- terygium wilfordii Hook F [140], is a diterpene triepoxide that is mainly used in Chinese cultures for treating inflam- mation [141–143], fibrosis [144–146], kidney, neurologi- cal, and autoimmune diseases [8, 147–150]. This diter- pene has anti-inflammatory and antioxidant characteristics which makes it an attractive drug for cancer therapy [151].
Triptolide inhibits growth of various cancer cell lines in vitro and in vivo, namely in prostate LNCaP and PC-3 [152, 153], pancreatic cancer PANC1, ASPC1, and SW1990 [154, 155], breast cancer MCF7 cells [156], and osteosarcoma MG63 cells [157], leukemia WEHI-3 [158], lung cancer A549 [143] and NSCLC NCI-H1299 and NCI- H460 [159], and CRC HCT116, CT26, HT29, CT16, and
Raw264.7 cells [154, 160, 161]. Triptolide was shown to result in apoptosis by intrinsic and extrinsic mechanisms, triggering cellular stress and DNA damage, in evad- ing immune surveillance [162], remodeling the immune microenvironment [161], and prompting tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) [163]. In addition, triptolide was shown to inhibit angiogenesis through HIF-1α and VEGF suppression [157] and metas- tasis through B-catenin reduction, therefore targeting EMT [159].
Triptolide and autophagy
The antitumor effects of triptolide were initially demon- strated to be only apoptotic. However, recent studies have shown that triptolide also induces autophagy in several cancer types [150]. Compelling evidence showed that this compound induced autophagy in in vitro and in vivo tumor models, in murine leukemia, breast cancer, pancreatic can- cer [156, 158, 163, 164], osteosarcoma [157], and cervical cancer [165]. When treated with triptolide, tumor cells exhibited high levels of LC3B-II, Beclin 1, and autophago- lysosomes. In addition, an increase in autophagic markers such as ATG5, ATG7, and ATG12 was detected. Impor- tantly, it was reported that triptolide-induced autophagy activates ERK1/2 and inhibits AKT/mTOR pathway [156, 165]. Furthermore, triptolide activated p38, p53, and MAPK while inhibiting forkhead box O3 (Foxo3a). In osteosarcoma cells, triptolide triggered autophagy by reducing the Wnt/βcatenin signaling [157]. Interestingly, in the presence of the autophagy inhibitor 3-MA, apoptosis was triggered which indicates one more time the presence of a cross-talk between autophagy and apoptosis [164]. In ovarian cancer cells SKOV3/DDP that are resistant to

cisplatin, triptolide inhibited JAK2/STAT3 pathway, and induced ROS which resulted in lethal autophagy [166]. Another study demonstrated that triptolide increased intra- cellular calcium (Ca2+) in SY5Y neuroblastoma cells by inhibiting NF-κB pathway and by decreasing heat shock factor 1 (HSF1) and HSP70. The high levels of intracel- lular Ca2+ [167] and the inhibition of mTOR triggered cell death by autophagy [160]. On the other hand, the inhibition of autophagy in triptolide-treated PC-3 cells increased the cytotoxicity of this compound suggesting that autophagy was triggered as a protective survival mechanism against the cytotoxic effect of triptolide [164]. Therefore, new studies have shown the possibility consid- ering the combination of triptolide with autophagy inhibi- tors to surpass its induced chemoresistance.

Alisol and anticancer activities
Alisol and derivatives are natural triterpenoids of protos- tane-type extracted from the Chinese medical herb, rhizomes of Alisma orientale [15, 168, 169]. Wide range of physi- ological activities were reported by alisol including treat- ment of hypertension, hyperlipidemia, osteoporotic, and uro- logical disorders [15]. Importantly, these compounds have anti-metabolic, anti-viral, anti-bacterial, anti-inflammatory, immunomodulatory, and anticancer activities [152, 154]. Alisol has shown antitumor activities in breast, prostate, gastric, CRC, liver, and ovarian cancers [168–174]. Alisol mediated cell cycle arrest at either G1 phase, via CDK4, 6 and cyclin D1 downregulation [168, 169], or G2/M phase
[15] followed by cell death. Inhibiting PI3K/AKT pathway was also shown to be involved in the apoptosis induction of cancer cells [15, 170, 171].This triterpenoid caused PARP, caspase-3, and caspase-9 cleavage, increased Bax/Bcl2 [175], increased ROS [174], and induced Apaf-1 in cancer cells [171]. It also decreased MMP2 and MMP9, resulting in reduced migration and invasion. Finally, alisol chemosensi- tized tumor cells by blocking P-glycoprotein-mediated drug resistance [176, 177].

Alisol and autophagy
Studies have shown that alisol induced Ca2+ mobilization from internal stores [168] causing endoplasmic reticulum stress [15]. This also triggered autophagy through the acti- vation of CaMKK-AMPK-mTOR pathway [168]. Concomi- tantly, the disruption of calcium homeostasis activated apop- tosis in alisol-treated cells [15, 168]. Notably, this compound targets and blocks the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) leading to the above-mentioned con- sequences [15, 168]. A study in CRC revealed that upon

treatment with alisol, an increase in the LC3-II was observed simultaneously with a degradation of p62/QSTM1 [168] and thus leading to the activation of autophagy [129, 178–180]. These results were further supported as 3-MA inhibition of autophagy led to apoptosis abrogation as well [169]. The same study demonstrated that inhibiting ROS or phospho- rylation of JNK, that are induced by alisol treatment, attenu- ated autophagy. Alisol-treated breast cancer cells increased LC3-II and ROS production, induced DNA damage, and promoted autophagy-dependent apoptosis [172, 173]. All these findings indicate that in cancer cells, alisol leads to apoptotic cell death induced by autophagy.

Betulinic acid and anticancer activities
Betulinic acid is a pentacyclic triterpene with lupane skel- eton extracted generally from the bark of the white birch tree [35, 181–185]. This compound has been reported to have a plethora of bioactivities against the human immunodefi- ciency virus (HIV), herpes simplex viruses-1 (HSV-1), bac- teria, malaria, helminths, pain, inflammation, immunomodu- lation, angiogenesis, metastasis [184, 185], and anticancer activities [35, 181–185]. This antitumor activity is believed to be mediated mainly through the mitochondrial pathway of apoptosis leading to the death of cancer cells [35, 181, 182, 185]. Betulinic acid showed high selectivity to tumor versus normal cells [186]. Hela cells treated with betulinic acid triggered ER pathway and ROS-mediated mitochondrial pathways leading to apoptosis [187]. Using caspase inhibi- tors failed to block apoptosis in the same treated cells [182]. Additional features of apoptosis were prominent upon betu- linic acid treatment in different cancer types, such as DNA fragmentation [188, 189], upregulation of Bak and Bax protein levels [182], augmentation of cytochrome c release, caspases 3, 8, and 9 activation, ROS generation [190], and inhibition of migration and invasion [191]. Furthermore, the apoptotic activity of betulinic acid was enhanced by hypoxic conditions in NSCLC cells [192]. Several animal models of human cancers confirmed the antitumor potential of betu- linic acid [185].

Betulinic acid and autophagy
Autophagy was shown to have a great impact in several betulinic acid-treated tumor cells; however, it was inhib- ited by cyclosporine A (CsA), an inhibitor of the mito- chondrial membrane permeability transition pore. Block- ing cytochrome c release from mitochondria, inhibited autophagy, thus implying that the latter occurred via mitochondrial damage [182]. However, caspase 3 induc- tion resulted in a decrease in Beclin 1 levels showing that

betulinic acid treatment in multiple myeloma KM3 cells blocked autophagy while enhancing apoptosis [193]. Betu- linic acid induced cell death by autophagy-independent apoptosis in hepatocellular carcinoma cells [194]. A semisynthetic derivative of betulinic acid inhibited the phosphorylation of AKT and induced autophagy in glio- blastoma cells [195]. Inhibiting autophagy by RNAi of ATG7, ATG5, or Beclin 1 led to inhibition of lysosomal cell death and caspase-3 mediated apoptosis. Similar results were obtained in different tumor cells where betu- linic acid inhibited cellular growth, triggered apoptosis, and induced autophagy via blocking PI3K/AKT/mTOR signaling pathway [186, 196]. Betulinic acid treatment of microglial BV-2 cells led to the increase of LC3-II levels and the formation of autophagosomes [189]. However, the observed accumulation of p62 indicates a blockade of autophagy, meanwhile apoptosis was still taking place.
Oleanolic acid and anticancer activities
Oleanolic acid, a multifunctional pentacyclic triterpenoid, has been isolated from several fruits and medicinal herbs [197–201]. It has numerous biological activities which include anti-inflammatory [202], antioxidant [203], anti-
diabetic [204], anti-HIV [205], hepato-protective [206, 207], and prevents cardiovascular disease progression [208, 209]. In addition, it has a marked anticancer activ- ity in several types of tumors [210–216]. Its antitumor activity affects initiation, proliferation, cell cycle arrest, apoptotic induction, ferroptosis, angiogenesis, invasion, migration, and metastasis [178, 179, 215, 217–229]. Many studies have shown that oleanolic acid and its deriva- tives have anticancer effects through the activation of the intrinsic and extrinsic cell death pathways in breast can- cer cells [178], induction of cell cycle arrest in human leukemia K562 cells [179], and attenuation of the NF-ĸB pathway and thus cytokine production and cell survival in human liver cancer Huh7 cells [230]. Oleanolic acid mainly causes cell death through apoptosis by increas- ing the ratio of Bax to Bcl-2, releasing cytochrome c, and leading to mitochondrial cell death [230, 231]. Further- more, oleanolic acid reduced PDL1 and DNA demethylase TET3 expression, and NF-κB activity in gastric cancer cells suggesting that this triterpenoid can be further con- sidered as an epigenetic and immunotherapy modulator [232]. Oleanolic acid enhanced apoptosis and reduced multi-drug resistance in lung cancer cells by nanoparticle formulation with cisplatin [233]. However, the non-spec- ificity, side effects, and poor water solubility has driven research into creating oleanolic acid synthetic derivatives

that would enhance its efficacy and pharmacological prop- erties [234, 235].

Oleanolic acid and autophagy
Recently, several studies reported yet another oleanolic acid antitumor mechanism which involves a dose and time- dependent autophagy induction in a wide panel of human cancer cell lines: lung A549, breast MCF-7, osteosarcoma U2OS, pancreatic BXPC3, prostate PANC-1 and PC-3 [236, 237], gastric SGC-7901, MGC-803, and BGC-823 cells [238], hepatocellular carcinoma HepG2 and SMC7721 [239, 240], Lv-KRAS12V-infected MCF10A and gastric mucosal cells [241]. Interestingly, oleanolic acid can induce autophagy in normal cells as well but without cytotoxicity, as such cell survival is not affected [241]. Moreover, inhibition of certain cancer cells proliferation and invasiveness was pri- marily via an autophagy-dependent mechanism, for this inhi- bition was abolished in the presence of an autophagy inhibi- tor which was demonstrated in vitro and in vivo [238, 239, 241, 242]. Meanwhile, in other cancer cell lines, autophagy inhibition potentiated the apoptotic death of cancer cells treated with this triterpenoid [236, 238]. Concerning the signaling pathways involved, it was shown that oleanolic acid-induced autophagy is mediated via JNK activation and mTOR suppression, whereby an increase in phosphorylated c-Jun with a dose-dependent decrease in the expression of phosphorylated RPS6KB1, RPS6 (ribosomal protein S6), 4EBP1 (eukaryotic translation initiation factor 4E binding protein 1), PI3K, and AKT were observed [236, 239, 241]. Furthermore, ROS plays a pivotal role in autophagy induc- tion by oleanolic acid [243–245]. A dose-dependent early increase in ROS was reported in Oleanolic acid HepG2 cells. ROS, such as superoxide (O2−), hydroxyl radical (HO−), and hydrogen peroxide (H2O2) causes buildup of the ATG8- phosphoethanolamine precursor for autophagosome for- mation by inactivating the cysteine protease ATG4, hence directly activating autophagy [244]. NAC pretreated cells resulted in a significant decrease in LC3-II production and cell death. Therefore, oleanolic acid-induced autophagy in HepG2 cells is ROS dependent [239]. On the other hand, this compound can initiate autophagy as a protective mechanism and inhibit the pro-apoptotic effect of this drug in cancer cells either through the activation of JNK pathway in a num- ber of cancer cells or alteration of the AMPK-mTOR-ULK-1 signaling pathway [236, 240, 242, 246]. Therefore, combin- ing oleanolic acid with autophagy inhibitors may enhance the antitumor properties of this compound. Mitophagy is a mechanism by which autophagy targets and degrades mito- chondria, resulting in cell survival or death [247]. In lung cancer A541 oleanolic acid-treated cells, mitophagy was observed dependent on PINK1 activation [237].

Platycodin D and anticancer activities
Platycodin D, isolated from the Chinese medicinal herb Platycodonis Radix, is a triterpenoid saponin with an eclectic variety of activities, namely anti-inflammatory [248, 249], anti-nociceptive [250], anti-obesity [251, 252], anti-atherogenic [253], immune-stimulatory [254], and neuroprotective [255]. In addition, it exhibits antitumor activity on diverse cancer types both in vitro and in vivo. The broad spectrum of cytotoxicity it has on tumor cells occurs via multiple mechanisms of action that involve proliferation suppression [256–259], cell cycle arrest, and apoptosis induction through inhibition of NF-ĸB, PI3K/ AKT, and JAK2/STAT3 pathways [256, 257, 260–264],
angiogenesis, invasion, and metastasis inhibition [263, 265, 266]. Platycodin D reversed chemotherapy resistance via histone deacetylase inhibitor (HDACi) and ERK1/2 inhibition in hepatocellular carcinoma cells [267].
Platycodin D and autophagy
Morphological features such as cytoplasmic vacuole accu- mulation is often observed in cells undergoing autophagy [268]. Several studies demonstrated how various human cancer dosages of platycodin D in prostate PC-12 [269], hepatocellular HepG2 and Hep3B, breast MCF-7, MDA- MB-231, lung A549 and 95D [270], and NCI-H460 [271],
CRC RKO cells [272], and CML K562 cells [273]. Results showed that LC3-II levels increased in a concentration- and time-dependent manner in hepatoma BEL-7402 cells in addition to all the previously mentioned cancer cell lines [269–271, 274]. However, platycodin D-triggered autophagy seems to be a universal phenomenon, for non- cancer cell lines as LO-2 and H9c2 formed cytoplasmic vacuoles in association with up-regulation of LC3-II as well, however without being cytotoxic [270].
AKT/mTOR pathway is a one of the crucial regula- tory pathways of autophagy [275]. However, platycodin D-induced autophagy in HepG2, NCI-H460, and A549 cells was shown to be independent of this pathway. Instead, autophagy was mediated through MAPK signaling pathway in the hepatocellular and lung carcinoma cancer cells [270, 271]. Moreover, in BEL-7402 cells, ERK and JNK pathways cooperate to regulate platycodin D- trig- gered autophagy. This triterpenoid increased c-Jun phos- phorylation at Ser73 which is the site of JNK regulation [276]. Pretreatment with SP600125, an inhibitor of JNK [277], blocked c-Jun phosphorylation which resulted in a decrease of LC3-II. Co- and pre-treatment of cells with SP600126 and U0126 (inhibitor of MEK) [278] blocked

both ERK and JNK pathways, resulting in suppression of platycodin D-induced LC3-II expression [274]. In therapy regimen that combines platycodin D and chloroquine or bafilomycin A1, both autophagy inhibitors, is a promising regimen for hepatocellular carcinoma treatment since it enhanced platycodin D-induced cytotoxicity and apoptosis in HepG2 and BEL-7402 cells [270, 274]. Recently, Plat- ycodin D treatment was shown to inhibit autophagy while promoting cell death in glioblastoma cells [279].

Ursolic acid and anticancer activities
Ursolic acid is a pentacyclic triterpenoid which is extracted from medicinal herbs such as Rosmarinns officinalis, Oci- mum sanctum, and Eriobotrya japonica [235, 280]. It is known that ursolic acid has low toxicity, anti-proliferative [281–283], anti-inflammatory [284, 285], and immuno-mod- ulatory properties [286]. In addition, ursolic acid selectively inhibits the growth of numerous cancer cell types via cell cycle arrest, increase in p21, and promotion of oxidative stress and DNA damage [287], increase in JNK-dependent lysosomal associated cell death [288], activation of p53 [289], and induction of apoptosis [290], mainly through intrinsic mechanism [291]. The key immune checkpoints programmed cell death protein 1 (PD-1) and its ligand PDL-1 were downregulated by ursolic acid in treated tumor cells [292, 293]. Recently, ursolic acid was shown to sup- press Wnt signaling in breast cancer stem cells [294].

Ursolic acid and autophagy
Recently, it was shown that ursolic acid induced cell death of cancer cells via autophagy through the PI3K-AKT-GSK signaling pathway [295]. In T47D breast cancer cells, urso- lic acid downregulated PI3K/AKT which in turn increased GSK levels. Activation of GSK downregulated cyclin D1 which is an essential inhibitor of autophagy [296]. A simi- lar study demonstrated that ursolic acid induced oxidative stress which decreased phosphorylated AKT and increased phosphorylated ATM. This led to a high elevation of AMPK which triggered cytotoxic autophagy [287]. Similarly, this triterpenoid induced autophagy in TC-1 cervical cancer cells by the regulation of ATG5 and through the PI3K signaling pathway [297]. However, ursolic acid induced autophagy in MCF-7 human breast cancer cells through the activation of MAPK1/3 pathway and not through the inhibition of mTOR which highlights the ubiquitous effects of this compound [298]. In addition, ursolic acid can be a potent stimula- tor of autophagy when combined with other molecules. A study indicated that the synergistic effects of ursolic acid and ZOL (inhibitor of osteoclast-mediated bone resorption)

induced autophagy in osteosarcoma cells, whereas this trit- erpenoid alone did not show any effects [299]. In contrast with previous results, ursolic acid can also induce protective autophagy against apoptosis. A study conducted on prostate cancer PC3 cells showed that treatment with a low dose of ursolic acid increased the levels of LC3B-II and the num- ber of autophagolysosomes [300]. It was reported also that Beclin 1 and ATG5 played a major role in the induction of autophagy which was mediated through the AKT/mTOR pathway. However, when inhibiting autophagy, there was a reduction in cell viability and enhanced apoptosis postulat- ing that autophagy acted as a protective mechanism against cell death [300–303]. Combining ursolic acid to chemother- apy promoted ER stress induced apoptosis and sensitized tumor cells [304].

Evading cell death is one of the crucial hallmarks of can- cer whereby a wide range of therapeutics are now target- ing these latter signaling pathways [305]. Accumulating evidence suggests that autophagy plays an important role in carcinogenesis; therefore, targeting autophagic signaling pathways could be a novel therapeutic potential against can- cer. Interestingly, terpenoids have been demonstrated to trig- ger molecular mechanisms by which cell death by autophagy is induced in cancer cells. These natural compounds have been studied for their role in treating inflammation, auto- immune diseases, and cancer. Studies report apoptosis as the major mechanism through which terpenoids induce cell death. However, the role of autophagy remained elusive. In this review, we highlighted the importance of representa- tive terpenoids in inducing autophagic cell death in cancer cells, alongside their use as cancer therapeutics. It was dem- onstrated that the discussed terpenoids induced autophagy via many signaling pathways such as MAPK/ERK/JNK, PI3K/AKT/mTOR, AMPK, NF-kB, and ROS
This highlights the numerous mechanisms by which terpe-
noids induce autophagy. In fact, combining terpenoids with chemotherapeutics sensitized tumor cells to cell death. In addition, this review sheds light on the intricate relationship between apoptosis and autophagy. Even though these two processes have their own molecular and physiological path- ways, they seem to crosstalk under certain circumstances. It was shown that autophagy can counteract apoptosis as a tumor survival mechanism, while in other cases it pro- moted apoptotic cell death in a synergistic way. Therefore, due to the complex dichotomy of autophagy, deciphering its role in tumorigenesis would open new possibilities in can- cer therapeutics. Activating autophagy in some cancer cells may increase their sensitivity to apoptosis while inhibiting autophagy in others may enhance apoptotic cell death. This

review highlighted the major contribution of triterpenoids in plant-derived autophagic modulators. It remains to be deter- mined whether any chemical structure in this terpenoid sub- class enhanced autophagy induction in treated tumor cells. In conclusion, the effects of terpenoids on autophagy need more investigation to fully understand the complexity of the signaling pathways involved and to build a more effective therapeutic strategy against cancer.
Acknowledgements The authors thank Lamis El Aaraj and Ali Yousef for their help with

Authors’ contribution All authors have contributed to the write up and revision of the final manuscript.

Funding None.


Conflict of interest Disclosure of conflict of interest none.

1. Ferlay J, Colombet M, Soerjomataram I et al (2021) Cancer sta- tistics for the year 2020: an overview. Int J Cancer
2. Siegel RL, Miller KD, Fuchs HE, Jemal A (2021) Cancer statis- tics, 2021. CA Cancer J Clin 71:7–33
3. Newman DJ, Cragg GM (2020) Natural products as sources of new drugs over the nearly four decades from 01/1981 to 09/2019. J Nat Prod 83:770–803
4. Millimouno FM, Dong J, Yang L, Li J, Li X (2014) Targeting apoptosis pathways in cancer and perspectives with natural com- pounds from mother nature. Cancer Prev Res 7:1081–1107
5. Cragg GM, Newman DJ (2005) Plants as a source of anti-cancer agents. J Ethnopharmacol 100:72–79
6. Balunas MJ, Kinghorn AD (2005) Drug discovery from medici- nal plants. Life Sci 78:431–441
7. Chin Y-W, Balunas MJ, Chai HB, Kinghorn AD (2006) Drug discovery from natural sources. AAPS J 8:E239–E253
8. Luo H, Vong CT, Chen H et al (2019) Naturally occurring anti- cancer compounds: shining from Chinese herbal medicine. Chin Med 14:48
9. Dall’Acqua S (2014) Natural products as antimitotic agents. Curr Top Med Chem 14:2272–2285
10. Gershenzon J, Dudareva N (2007) The function of terpene natural products in the natural world. Nat Chem Biol 3:408–414
11. Withers ST, Keasling JD (2007) Biosynthesis and engineer- ing of isoprenoid small molecules. Appl Microbiol Biotechnol 73:980–990
12. Rabi T, Bishayee A (2009) Terpenoids and breast cancer chemo- prevention. Breast Cancer Res Treat 115:223–239
13. Wagner K-H, Elmadfa I (2003) Biological relevance of terpe- noids. Ann Nutr Metab 47:95–106
14. Ashrafizadeh M, Ahmadi Z, Mohammadinejad R, Kaviyani N, Tavakol S (2019) Monoterpenes modulating autophagy: a review study. Basic Clin Pharmacol Toxicol
15. Huang M, Lu JJ, Huang MQ, Bao JL, Chen XP, Wang YT (2012) Terpenoids: natural products for cancer therapy. Expert Opin Investig Drugs 21:1801–1818

16. Ghantous A, Gali-Muhtasib H, Vuorela H, Saliba NA, Dar- wiche N (2010) What made sesquiterpene lactones reach can- cer clinical trials? Drug Discovery Today 15:668–678
17. Yang H, Dou QP (2010) Targeting apoptosis pathway with natural terpenoids: implications for treatment of breast and prostate cancer. Curr Drug Targets 11:733–744
18. Kuttan G, Pratheeshkumar P, Manu KA, Kuttan R (2011) Inhi- bition of tumor progression by naturally occurring terpenoids. Pharm Biol 49:995–1007
19. Mizushima N (2007) Autophagy: process and function. Genes Dev 21:2861–2873
20. Sun CY, Zhang QY, Zheng GJ, Feng B (2019) Autophagy and its potent modulators from phytochemicals in cancer treatment. Cancer Chemother Pharmacol 83:17–26
21. Levine B, Kroemer G (2019) Biological functions of autophagy genes: a disease perspective. Cell 176:11–42
22. Klionsky DJ, Emr SD (2000) Autophagy as a regulated pathway of cellular degradation. Science (New York, NY) 290:1717–1721
23. Mulcahy Levy JM, Thorburn A (2020) Autophagy in cancer: moving from understanding mechanism to improving therapy responses in patients. Cell Death Differ 27:843–857
24. Kroemer G, Mariño G, Levine B (2010) Autophagy and the inte- grated stress response. Mol Cell 40:280–293
25. Levine B, Kroemer G (2008) Autophagy in the pathogenesis of disease. Cell 132:27–42
26. Guo JY, Xia B, White E (2013) Autophagy-mediated tumor pro- motion. Cell 155:1216–1219
27. Deretic V, Saitoh T, Akira S (2013) Autophagy in infection, inflammation and immunity. Nat Rev Immunol 13:722–737
28. Choi KS (2012) Autophagy and cancer. Exp Mol Med 44:109–120
29. Klionsky DJ (2020) Autophagy participates in, well, just about everything. Cell Death Differ 27:831–832
30. Colhado Rodrigues BL, Lallo MA, Perez EC (2020) The con- troversial role of autophagy in tumor development: a systematic review. Immunol Invest 49:386–396
31. White E, DiPaola RS (2009) The double-edged sword of autophagy modulation in cancer. Clin Cancer Res 15:5308–5316
32. Apel A, Zentgraf H, Büchler MW, Herr I (2009) Autophagy-A double-edged sword in oncology. Int J Cancer 125:991–995
33. Tormo D, Chęcińska A, Alonso-Curbelo D et al (2009) Tar- geted activation of innate immunity for therapeutic induction of autophagy and apoptosis in melanoma cells. Cancer Cell 16:103–114
34. Kang R, Zeh H, Lotze M, Tang D (2011) The Beclin 1 network regulates autophagy and apoptosis. Cell Death Differ 18:571–580
35. Gali-Muhtasib H, Hmadi R, Kareh M, Tohme R, Darwiche N (2015) Cell death mechanisms of plant-derived anticancer drugs: beyond apoptosis. Apoptosis 20:1531–1562
36. Klayman DL (1985) Qinghaosu (artemisinin): an antimalarial drug from China. Science (New York, NY) 228:1049–1055
37. Cheng C, Wang T, Song Z et al (2018) Induction of autophagy and autophagy-dependent apoptosis in diffuse large B-cell lym- phoma by a new antimalarial artemisinin derivative, SM1044. Cancer Med 7:380–396
38. Li Y, Zhou X, Liu J, Yuan X, He Q (2020) Therapeutic potentials and mechanisms of artemisinin and its derivatives for tumorigen- esis and metastasis. Anticancer Agents Med Chem 20:520–535
39. Hou J, Wang D, Zhang R, Wang H (2008) Experimental therapy of hepatoma with artemisinin and its derivatives: in vitro and in vivo activity, chemosensitization, and mechanisms of action. Clin Cancer Res 14:5519–5530
40. Zhu S, Yu Q, Huo C et al (2021) Ferroptosis: a novel mechanism of artemisinin and its derivatives in cancer therapy. Curr Med Chem 28:329–345

41. Jiang Z, Chai J, Chuang HH et al (2012) Artesunate induces G0/ G1 cell cycle arrest and iron-mediated mitochondrial apoptosis in A431 human epidermoid carcinoma cells. Anticancer Drugs 23:606–613
42. Chen K, Shou LM, Lin F et al (2014) Artesunate induces G2/M cell cycle arrest through autophagy induction in breast cancer cells. Anticancer Drugs 25:652–662
43. Jiang F, Zhou JY, Zhang D, Liu MH, Chen YG (2018) Artesu- nate induces apoptosis and autophagy in HCT116 colon cancer cells, and autophagy inhibition enhances the artesunate-induced apoptosis. Int J Mol Med 42:1295–1304
44. Chen GQ, Benthani FA, Wu J, Liang D, Bian ZX, Jiang X (2020) Artemisinin compounds sensitize cancer cells to ferroptosis by regulating iron homeostasis. Cell Death Differ 27:242–254
45. McDowell A, Jr., Hill KS, McCorkle JR et al (2021) Preclinical evaluation of artesunate as an antineoplastic agent in ovarian cancer treatment. Diagnostics (Basel, Switzerland) 11
46. Lu YY, Chen TS, Wang XP, Li L (2010) Single-cell analysis of dihydroartemisinin-induced apoptosis through reactive oxygen species-mediated caspase-8 activation and mitochondrial path- way in ASTC-a-1 cells using fluorescence imaging techniques. J Biomed Opt 15:046028
47. Noori S, Hassan ZM (2011) Dihydroartemisinin shift the immune response towards Th1, inhibit the tumor growth in vitro and in vivo. Cell Immunol 271:67–72
48. Chen H, Sun B, Wang S et al (2010) Growth inhibitory effects of dihydroartemisinin on pancreatic cancer cells: involvement of cell cycle arrest and inactivation of nuclear factor-kappaB. J Cancer Res Clin Oncol 136:897–903
49. Chen H, Sun B, Pan S, Jiang H, Sun X (2009) Dihydroarte- misinin inhibits growth of pancreatic cancer cells in vitro and in vivo. Anticancer Drugs 20:131–140
50. Lu JJ, Chen SM, Zhang XW, Ding J, Meng LH (2011) The anti- cancer activity of dihydroartemisinin is associated with induc- tion of iron-dependent endoplasmic reticulum stress in colorectal carcinoma HCT116 cells. Invest New Drugs 29:1276–1283
51. Huang XJ, Li CT, Zhang WP, Lu YB, Fang SH, Wei EQ (2008) Dihydroartemisinin potentiates the cytotoxic effect of temozo- lomide in rat C6 glioma cells. Pharmacology 82:1–9
52. Huang XJ, Ma ZQ, Zhang WP, Lu YB, Wei EQ (2007) Dihy- droartemisinin exerts cytotoxic effects and inhibits hypoxia inducible factor-1alpha activation in C6 glioma cells. J Pharm Pharmacol 59:849–856
53. He Q, Shi J, Shen XL et al (2010) Dihydroartemisinin upregu- lates death receptor 5 expression and cooperates with TRAIL to induce apoptosis in human prostate cancer cells. Cancer Biol Ther 9:819–824
54. Morrissey C, Gallis B, Solazzi JW et al (2010) Effect of arte- misinin derivatives on apoptosis and cell cycle in prostate cancer cells. Anticancer Drugs 21:423–432
55. Lai H, Singh NP (1995) Selective cancer cell cytotoxicity from exposure to dihydroartemisinin and holotransferrin. Cancer Lett 91:41–46
56. Singh NP, Lai H (2001) Selective toxicity of dihydroartemisinin and holotransferrin toward human breast cancer cells. Life Sci 70:49–56
57. Hamacher-Brady A, Stein HA, Turschner S et al (2011) Artesu- nate activates mitochondrial apoptosis in breast cancer cells via iron-catalyzed lysosomal reactive oxygen species production. J Biol Chem 286:6587–6601
58. Gao W, Xiao F, Wang X, Chen T (2013) Artemisinin induces A549 cell apoptosis dominantly via a reactive oxygen species- mediated amplification activation loop among caspase-9, -8 and
-3. Apoptosis 18:1201–1213
59. Wang Z, Hu W, Zhang JL, Wu XH, Zhou HJ (2012) Dihydroarte- misinin induces autophagy and inhibits the growth of iron-loaded

human myeloid leukemia K562 cells via ROS toxicity. FEBS Open Bio 2:103–112
60. Handrick R, Ontikatze T, Bauer KD et al (2010) Dihydroarte- misinin induces apoptosis by a Bak-dependent intrinsic pathway. Mol Cancer Ther 9:2497–2510
61. Li B, Bu S, Sun J, Guo Y, Lai D (2018) Artemisinin derivatives inhibit epithelial ovarian cancer cells via autophagy-mediated cell cycle arrest. Acta Biochim Biophys Sin 50:1227–1235
62. Ma Q, Liao H, Xu L et al (2020) Autophagy-dependent cell cycle arrest in esophageal cancer cells exposed to dihydroartemisinin. Chin Med 15:37
63. Du J, Wang T, Li Y et al (2019) DHA inhibits proliferation and induces ferroptosis of leukemia cells through autophagy depend- ent degradation of ferritin. Free Radical Biol Med 131:356–369
64. Efferth T (2017) From ancient herb to modern drug: Artemisia annua and artemisinin for cancer therapy. Semin Cancer Biol 46:65–83
65. Yoshida GJ (2017) Therapeutic strategies of drug repositioning targeting autophagy to induce cancer cell death: from patho- physiology to treatment. J Hematol Oncol 10:67
66. Guan X, Guan Y (2020) Artemisinin induces selective and potent anticancer effects in drug resistant breast cancer cells by inducing cellular apoptosis and autophagy and G2/M cell cycle arrest. J BUON 25:1330–1336
67. Wang L, Li J, Shi X et al (2019) Antimalarial dihydroartemisinin triggers autophagy within HeLa cells of human cervical can- cer through Bcl-2 phosphorylation at Ser70. Phytomedicine 52:147–156
68. Kabeya Y, Mizushima N, Ueno T et al (2000) LC3, a mamma- lian homologue of yeast Apg8p, is localized in autophagosome membranes after processing. EMBO J 19:5720–5728
69. Zhou X, Chen Y, Wang F et al (2020) Artesunate induces autophagy dependent apoptosis through upregulating ROS and activating AMPK-mTOR-ULK1 axis in human bladder cancer cells. Chemico-Biol Interact 331:109273
70. Ganguli A, Choudhury D, Datta S, Bhattacharya S, Chakrabarti G (2014) Inhibition of autophagy by chloroquine potentiates synergistically anti-cancer property of artemisinin by promot- ing ROS dependent apoptosis. Biochimie 107 Pt B:338–349.
71. Feng X, Li L, Jiang H, Jiang K, Jin Y, Zheng J (2014) Dihydroar- temisinin potentiates the anticancer effect of cisplatin via mTOR inhibition in cisplatin-resistant ovarian cancer cells: involvement of apoptosis and autophagy. Biochem Biophys Res Commun 444:376–381
72. Hu W, Chen SS, Zhang JL, Lou XE, Zhou HJ (2014) Dihydroar- temisinin induces autophagy by suppressing NF-κB activation. Cancer Lett 343:239–248
73. Chen SS, Hu W, Wang Z, Lou XE, Zhou HJ (2015) p8 attenu- ates the apoptosis induced by dihydroartemisinin in cancer cells through promoting autophagy. Cancer Biol Ther 16:770–779
74. Du XX, Li YJ, Wu CL et al (2013) Initiation of apoptosis, cell cycle arrest and autophagy of esophageal cancer cells by dihy- droartemisinin. Biomed Pharmacother 67:417–424
75. Jia G, Kong R, Ma ZB et al (2014) The activation of c-Jun NH2-terminal kinase is required for dihydroartemisinin-induced autophagy in pancreatic cancer cells. J Exp Clin Cancer Res 33:8
76. Shi X, Wang L, Ren L et al (2019) Dihydroartemisinin, an anti- malarial drug, induces absent in melanoma 2 inflammasome activation and autophagy in human hepatocellular carcinoma HepG2215 cells. Phytother Res: PTR 33:1413–1425
77. Zou J, Ma Q, Sun R et al (2019) Dihydroartemisinin inhibits HepG2.2.15 proliferation by inducing cellular senescence and autophagy. BMB Rep 52:520–524
78. Zhang ZS, Wang J, Shen YB et al (2015) Dihydroartemisinin increases temozolomide efficacy in glioma cells by inducing autophagy. Oncol Lett 10:379–383

79. Lemke D, Pledl HW, Zorn M et al (2016) Slowing down glio- blastoma progression in mice by running or the anti-malarial drug dihydroartemisinin? Induction of oxidative stress in murine glioblastoma therapy. Oncotarget 7:56713–56725
80. Shi X, Wang L, Li X et al (2017) Dihydroartemisinin induces autophagy-dependent death in human tongue squamous cell carcinoma cells through DNA double-strand break-mediated oxidative stress. Oncotarget 8:45981–45993
81. Liu X, Wu J, Fan M et al (2018) Novel dihydroartemisinin derivative DHA-37 induces autophagic cell death through upregulation of HMGB1 in A549 cells. Cell Death Dis 9:1048
82. Liu J, Ren Y, Hou Y et al (2019) Dihydroartemisinin induces endothelial cell autophagy through suppression of the Akt/ mTOR pathway. J Cancer 10:6057–6064
83. Hwang DR, Wu YS, Chang CW et al (2006) Synthesis and anti-viral activity of a series of sesquiterpene lactones and ana- logues in the subgenomic HCV replicon system. Bioorg Med Chem 14:83–91
84. Knight DW (1995) Feverfew: chemistry and biological activity. Nat Prod Rep 12:271–276
85. Woynarowski JM, Konopa J (1981) Inhibition of DNA biosyn- thesis in HeLa cells by cytotoxic and antitumor sesquiterpene lactones. Mol Pharmacol 19:97–102
86. Ghantous A, Sinjab A, Herceg Z, Darwiche N (2013) Par- thenolide: from plant shoots to cancer roots. Drug Discovery Today 18:894–905
87. Guzman ML, Rossi RM, Neelakantan S et al (2007) An orally bioavailable parthenolide analog selectively eradicates acute myelogenous leukemia stem and progenitor cells. Blood 110:4427–4435
88. Zhang S, Ong CN, Shen HM (2004) Critical roles of intracel- lular thiols and calcium in parthenolide-induced apoptosis in human colorectal cancer cells. Cancer Lett 208:143–153
89. D’Anneo A, Carlisi D, Lauricella M et al (2013) Parthenolide induces caspase-independent and AIF-mediated cell death in human osteosarcoma and melanoma cells. J Cell Physiol 228:952–967
90. Liu JW, Cai MX, Xin Y et al (2010) Parthenolide induces proliferation inhibition and apoptosis of pancreatic cancer cells in vitro. J Exp Clin Cancer Res 29:108
91. Sun Y, St Clair DK, Xu Y, Crooks PA, St Clair WH (2010) A NADPH oxidase-dependent redox signaling pathway medi- ates the selective radiosensitization effect of parthenolide in prostate cancer cells. Can Res 70:2880–2890
92. Jeyamohan S, Moorthy RK, Kannan MK, Arockiam AJ (2016) Parthenolide induces apoptosis and autophagy through the sup- pression of PI3K/Akt signaling pathway in cervical cancer. Biotech Lett 38:1251–1260
93. Li C, Zhou Y, Cai Y et al (2019) Parthenolide inhibits the proliferation of MDA-T32 papillary thyroid carcinoma cells in vitro and in mouse tumor xenografts and activates autophagy and apoptosis by downregulation of the mammalian target of rapamycin (mTOR)/PI3K/AKT signaling pathway. Med Sci Monitor 25:5054–5061
94. Liu D, Han Y, Liu L et al (2021) Parthenolide inhibits the tumor characteristics of renal cell carcinoma. Int J Oncol 58:100–110
95. Kreuger MR, Grootjans S, Biavatti MW, Vandenabeele P, D’Herde K (2012) Sesquiterpene lactones as drugs with multi- ple targets in cancer treatment: focus on parthenolide. Anticancer Drugs 23:883–896
96. Zhang S, Ong CN, Shen HM (2004) Involvement of proapoptotic Bcl-2 family members in parthenolide-induced mitochondrial dysfunction and apoptosis. Cancer Lett 211:175–188
97. Wu LM, Liao XZ, Zhang Y et al (2020) Parthenolide aug- ments the chemosensitivity of non-small-cell lung cancer to

cisplatin via the PI3K/AKT signaling pathway. Front Cell Dev Biol 8:610097
98. Yang C, Yang QO, Kong QJ, Yuan W, Ou Yang YP (2016) Par- thenolide induces reactive oxygen species-mediated autophagic cell death in human osteosarcoma cells. Cell Physiol Biochem 40:146–154
99. D’Anneo A, Carlisi D, Lauricella M et al (2013) Parthenolide generates reactive oxygen species and autophagy in MDA- MB231 cells. A soluble parthenolide analogue inhibits tumour growth and metastasis in a xenograft model of breast cancer. Cell Death Dis 4:e891
100. Liu W, Wang X, Sun J, Yang Y, Li W, Song J (2017) Parthe- nolide suppresses pancreatic cell growth by autophagy-medi- ated apoptosis. Onco Targets Ther 10:453–461
101. Lu C, Wang W, Jia Y, Liu X, Tong Z, Li B (2014) Inhibition of AMPK/autophagy potentiates parthenolide-induced apoptosis in human breast cancer cells. J Cell Biochem 115:1458–1466
102. Sun J, Zhang C, Bao YL et al (2014) Parthenolide-induced apoptosis, autophagy and suppression of proliferation in HepG2 cells. Asian Pac J Cancer Prevent 15:4897–4902
103. Han Y, Yang J, Sun Y, Fan S, Lu Y, Li L (2021) Parthenolide induces autophagy and apoptosis of breast cancer cells associ- ated with the PI3K/AKT/mTOR pathway.
104. Pozarowski P, Halicka DH, Darzynkiewicz Z (2003) Cell cycle effects and caspase-dependent and independent death of HL-60 and Jurkat cells treated with the inhibitor of NF-kappaB par- thenolide. Cell Cycle (Georgetown, Tex) 2:377–383
105. Zhou W-S, Xu X-X (1994) Total synthesis of the antimalarial sesquiterpene peroxide qinghaosu and yingzhaosu A. Acc Chem Res 27:211–216
106. Lan B, Wan YJ, Pan S et al (2015) Parthenolide induces autophagy via the depletion of 4E-BP1. Biochem Biophys Res Commun 456:434–439
107. Zhou GB, Kang H, Wang L et al (2007) Oridonin, a diter- penoid extracted from medicinal herbs, targets AML1-ETO fusion protein and shows potent antitumor activity with low adverse effects on t(8;21) leukemia in vitro and in vivo. Blood 109:3441–3450
108. Yao Z, Xie F, Li M et al (2017) Oridonin induces autophagy via inhibition of glucose metabolism in p53-mutated colorectal cancer cells. Cell Death Dis 8:e2633
109. Shi M, Lu XJ, Zhang J et al (2016) Oridonin, a novel lysine acetyltransferases inhibitor, inhibits proliferation and induces apoptosis in gastric cancer cells through p53- and caspase- 3-mediated mechanisms. Oncotarget 7:22623–22631
110. Ikezoe T, Yang Y, Bandobashi K et al (2005) Oridonin, a dit- erpenoid purified from Rabdosia rubescens, inhibits the prolif- eration of cells from lymphoid malignancies in association with blockade of the NF-kappa B signal pathways. Mol Cancer Ther 4:578–586
111. Huang H, Weng H, Dong B, Zhao P, Zhou H, Qu L (2017) Ori- donin triggers chaperon-mediated proteasomal degradation of BCR-ABL in Leukemia. Sci Rep 7:41525
112. Li Y, Wang Y, Wang S, Gao Y, Zhang X, Lu C (2015) Oridonin phosphate-induced autophagy effectively enhances cell apoptosis of human breast cancer cells. Med Oncol 32:365
113. Gao FH, Liu F, Wei W et al (2012) Oridonin induces apoptosis and senescence by increasing hydrogen peroxide and glutathione depletion in colorectal cancer cells. Int J Mol Med 29:649–655
114. Bao R, Shu Y, Wu X et al (2014) Oridonin induces apoptosis and cell cycle arrest of gallbladder cancer cells via the mitochondrial pathway. BMC Cancer 14:217
115. Dong X, Liu F, Li M (2016) Inhibition of nuclear factor κB transcription activity drives a synergistic effect of cisplatin and oridonin on HepG2 human hepatocellular carcinoma cells. Anti- cancer Drugs 27:286–299

116. Patravale VB, Date AA, Kulkarni RM (2004) Nanosuspen- sions: a promising drug delivery strategy. J Pharm Pharmacol 56:827–840
117. Duan C, Gao J, Zhang D et al (2011) Galactose-decorated pH- responsive nanogels for hepatoma-targeted delivery of oridonin. Biomacromol 12:4335–4343
118. Qi X, Zhang D, Xu X et al (2012) Oridonin nanosuspension was more effective than free oridonin on G2/M cell cycle arrest and apoptosis in the human pancreatic cancer PANC-1 cell line. Int J Nanomed 7:1793–1804
119. Rabinow BE (2004) Nanosuspensions in drug delivery. Nat Rev Drug Discovery 3:785–796
120. Zhao Y, Xiao W, Peng W et al (2021) Oridonin-loaded nano- particles inhibit breast cancer progression through regulation of ROS-related Nrf2 signaling pathway. Front Bioeng Biotechnol 9:600579
121. Jin H, Tan X, Liu X, Ding Y (2011) Downregulation of AP-1 gene expression is an initial event in the oridonin-mediated inhi- bition of colorectal cancer: studies in vitro and in vivo. J Gastro- enterol Hepatol 26:706–715
122. Abdullah NA, Md Hashim NF, Ammar A, Muhamad Zakuan N (2021) An insight into the anti-angiogenic and anti-metastatic effects of oridonin: current knowledge and future potential. Mol- ecules 26
123. Zhang J, Wang N, Zhou Y et al (2021) Oridonin induces ferrop- tosis by inhibiting gamma-glutamyl cycle in TE1 cells. Phytother Res 35:494–503
124. Zhou J, Li Y, Shi X et al (2021) Oridonin inhibits tumor angio- genesis and induces vessel normalization in experimental colon cancer. J Cancer 12:3257–3264
125. Liu W, Huang G, Yang Y, Gao R, Zhang S, Kou B (2021) Ori- donin inhibits epithelial-mesenchymal transition of human nasopharyngeal carcinoma cells by negatively regulating AKT/ STAT3 signaling pathway. Int J Med Sci 18:81–87
126. Zhang CL, Wu LJ, Tashiro S, Onodera S, Ikejima T (2004) Oridonin induces a caspase-independent but mitochondria- and MAPK-dependent cell death in the murine fibrosarcoma cell line L929. Biol Pharm Bull 27:1527–1531
127. Zhang X, Chen LX, Ouyang L, Cheng Y, Liu B (2012) Plant natural compounds: targeting pathways of autophagy as anti- cancer therapeutic agents. Cell Prolif 45:466–476
128. Forouzanfar F, Mousavi SH (2020) Targeting autophagic path- ways by plant natural compounds in cancer treatment. Curr Drug Targets
129. Wang Y, Ding L, Wang X et al (2012) Pterostilbene simulta- neously induces apoptosis, cell cycle arrest and cyto-protective autophagy in breast cancer cells. Am J Transl Res 4:44–51
130. Liu Y, Liu JH, Chai K, Tashiro S, Onodera S, Ikejima T (2013) Inhibition of c-Met promoted apoptosis, autophagy and loss of the mitochondrial transmembrane potential in oridonin-induced A549 lung cancer cells. J Pharm Pharmacol 65:1622–1642
131. Li X, Li X, Wang J, Ye Z, Li JC (2012) Oridonin up-regulates expression of P21 and induces autophagy and apoptosis in human prostate cancer cells. Int J Biol Sci 8:901–912
132. Cheng B, Jin J, Liu D et al (2021) Oridonin interferes with sim- ple steatosis of liver cells by regulating autophagy. Tissue Cell 72:101532
133. Zhang LD, Liu Z, Liu H et al (2016) Oridonin enhances the anticancer activity of NVP-BEZ235 against neuroblastoma cells in vitro and in vivo through autophagy. Int J Oncol 49:657–665
134. Tiwari RV, Parajuli P, Sylvester PW (2015) Synergistic antican- cer effects of combined γ-tocotrienol and oridonin treatment is associated with the induction of autophagy. Mol Cell Biochem 408:123–137
135. Cao S, Huang Y, Zhang Q et al (2019) Molecular mechanisms of apoptosis and autophagy elicited by combined treatment with

oridonin and cetuximab in laryngeal squamous cell carcinoma. Apoptosis 24:33–45
136. Yang H, Gao Y, Fan X, Liu X, Peng L, Ci X (2019) Oridonin sensitizes cisplatin-induced apoptosis via AMPK/Akt/mTOR- dependent autophagosome accumulation in A549 cells. Front Oncol 9:769
137. Zhao Y, Xia H (2019) Oridonin elevates sensitivity of ovarian carcinoma cells to cisplatin via suppressing cisplatin-mediated autophagy. Life Sci 233:116709
138. Zeng R, Chen Y, Zhao S, Cui GH (2012) Autophagy counteracts apoptosis in human multiple myeloma cells exposed to oridonin in vitro via regulating intracellular ROS and SIRT1. Acta Phar- macol Sin 33:91–100
139. Zang L, Xu Q, Ye Y et al (2012) Autophagy enhanced phago- cytosis of apoptotic cells by oridonin-treated human histocytic lymphoma U937 cells. Arch Biochem Biophys 518:31–41
140. Chen SR, Dai Y, Zhao J, Lin L, Wang Y, Wang Y (2018) A mechanistic overview of triptolide and celastrol, natural products from tripterygium wilfordii hook F. Front Pharmacol 9:104
141. Bai S, Hu Z, Yang Y et al (2016) Anti-inflammatory and neuro- protective effects of triptolide via the NF-κB signaling pathway in a Rat MCAO model. Anat Rec (Hoboken) 299:256–266
142. Li R, Lu K, Wang Y et al (2017) Triptolide attenuates pressure overload-induced myocardial remodeling in mice via the inhibi- tion of NLRP3 inflammasome expression. Biochem Biophys Res Commun 485:69–75
143. Wang X, Zhang L, Duan W et al (2014) Anti-inflammatory effects of triptolide by inhibiting the NF-κB signalling pathway in LPS-induced acute lung injury in a murine model. Mol Med Rep 10:447–452
144. Yuan XP, He XS, Wang CX, Liu LS, Fu Q (2011) Triptolide attenuates renal interstitial fibrosis in rats with unilateral ureteral obstruction. Nephrology (Carlton) 16:200–210
145. Zhang Z, Qu X, Ni Y et al (2013) Triptolide protects rat heart against pressure overload-induced cardiac fibrosis. Int J Cardiol 168:2498–2505
146. Yang S, Zhang M, Chen C et al (2015) Triptolide mitigates radi- ation-induced pulmonary fibrosis. Radiat Res 184:509–517
147. Kong X, Zhang Y, Liu C et al (2013) Anti-angiogenic effect of triptolide in rheumatoid arthritis by targeting angiogenic cascade. PloS One 8:e77513
148. Li Z, Zheng C (1982) Observation on treatment of systemic lupus erythematosus with extract of Tripterygium wilfordii Hook. Xin Zhong Yi 12:22–24
149. Leuenroth SJ, Okuhara D, Shotwell JD et al (2007) Triptolide is a traditional Chinese medicine-derived inhibitor of polycystic kidney disease. Proc Natl Acad Sci USA 104:4389–4394
150. Wei YM, Wang YH, Xue HQ, Luan ZH, Liu BW, Ren JH (2019) Triptolide, a potential autophagy modulator. Chin J Integr Med 25:233–240
151. Tong L, Zhao Q, Datan E et al (2021) Triptolide: reflections on two decades of research and prospects for the future. Nat Prod Rep 38:843–860
152. Huang W, He T, Chai C et al (2012) Triptolide inhibits the pro- liferation of prostate cancer cells and down-regulates SUMO- specific protease 1 expression. PloS One 7:e37693
153. Ding X, Zhou X, Jiang B, Zhao Q, Zhou G (2015) Triptolide suppresses proliferation, hypoxia-inducible factor-1α and c-Myc expression in pancreatic cancer cells. Mol Med Rep 12:4508–4513
154. Zhang C, He XJ, Li L, Lu C, Lu AP (2017) Effect of the natural product triptolide on pancreatic cancer: a systematic review of preclinical studies. Front Pharmacol 8:490
155. Wang C, Liu B, Xu X et al (2016) Toward targeted therapy in chemotherapy-resistant pancreatic cancer with a smart triptolide nanomedicine. Oncotarget 7:8360–8372

156. Gao H, Zhang Y, Dong L et al (2018) Triptolide induces autophagy and apoptosis through ERK activation in human breast cancer MCF-7 cells. Exp Ther Med 15:3413–3419
157. Li X, Lu Q, Xie W, Wang Y, Wang G (2018) Anti-tumor effects of triptolide on angiogenesis and cell apoptosis in osteosarcoma cells by inducing autophagy via repressing Wnt/β-Catenin signaling. Biochem Biophys Res Commun 496:443–449
158. Chan SF, Chen YY, Lin JJ et al (2017) Triptolide induced cell death through apoptosis and autophagy in murine leuke- mia WEHI-3 cells in vitro and promoting immune responses in WEHI-3 generated leukemia mice in vivo. Environ Toxicol 32:550–568
159. Deng QD, Lei XP, Zhong YH et al (2021) Triptolide suppresses the growth and metastasis of non-small cell lung cancer by inhib- iting β-catenin-mediated epithelial-mesenchymal transition. Acta Pharmacologica Sinica
160. Zhao F, Huang W, Zhang Z et al (2016) Triptolide induces protective autophagy through activation of the CaMKKβ- AMPK signaling pathway in prostate cancer cells. Oncotarget 7:5366–5382
161. Jiang X, Cao G, Gao G, Wang W, Zhao J, Gao C (2021) Trip- tolide decreases tumor-associated macrophages infiltration and M2 polarization to remodel colon cancer immune microenvi- ronment via inhibiting tumor-derived CXCL12. J Cell Physiol 236:193–204
162. Carneiro BA, El-Deiry WS (2020) Targeting apoptosis in cancer therapy. Nat Rev Clin Oncol 17:395–417
163. Dai H, Jiang Y, Luo Y, Bie P, Chen Z (2019) Triptolide enhances TRAIL sensitivity of pancreatic cancer cells by acti- vating autophagy via downregulation of PUM1. Phytomedicine 62:152953
164. Mujumdar N, Mackenzie TN, Dudeja V et al (2010) Triptolide induces cell death in pancreatic cancer cells by apoptotic and autophagic pathways. Gastroenterology 139:598–608
165. Qin G, Li P, Xue Z (2018) Triptolide induces protective autophagy and apoptosis in human cervical cancer cells by down- regulating Akt/mTOR activation. Oncol Lett 16:3929–3934
166. Zhong Y, Le F, Cheng J et al (2021) Triptolide inhibits JAK2/ STAT3 signaling and induces lethal autophagy through ROS gen- eration in cisplatin-resistant SKOV3/DDP ovarian cancer cells. Oncol Rep 45
167. Krosch TC, Sangwan V, Banerjee S et al (2013) Triptolide-medi- ated cell death in neuroblastoma occurs by both apoptosis and autophagy pathways and results in inhibition of nuclear factor- kappa B activity. Am J Surg 205:387–396
168. Law BY, Wang M, Ma DL et al (2010) Alisol B, a novel inhibi- tor of the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase pump, induces autophagy, endoplasmic reticulum stress, and apoptosis. Mol Cancer Ther 9:718–730
169. Zhao Y, Li ETS, Wang M (2017) Alisol B 23-acetate induces autophagic-dependent apoptosis in human colon cancer cells via ROS generation and JNK activation. Oncotarget 8:70239–70249
170. Huang YT, Huang DM, Chueh SC, Teng CM, Guh JH (2006) Alisol B acetate, a triterpene from Alismatis rhizoma, induces Bax nuclear translocation and apoptosis in human hormone- resistant prostate cancer PC-3 cells. Cancer Lett 231:270–278
171. Xu YH, Zhao LJ, Li Y (2009) Alisol B acetate induces apopto- sis of SGC7901 cells via mitochondrial and phosphatidylino- sitol 3-kinases/Akt signaling pathways. World J Gastroenterol 15:2870–2877
172. Lou C, Xu X, Chen Y, Zhao H (2019) Alisol A suppresses pro- liferation, migration, and invasion in human breast cancer MDA- MB-231 cells. Molecules 24
173. Shi Y, Wang M, Wang P et al (2020) Alisol A is potentially therapeutic in human breast cancer cells. Oncol Rep

174. Kwon MJ, Kim JN, Lee MJ, Kim WK, Nam JH, Kim BJ (2021) Apoptotic effects of alisol B 23-acetate on gastric cancer cells. Mol Med Rep 23
175. Zhang LL, Xu YL, Tang ZH et al (2016) Effects of alisol B 23-acetate on ovarian cancer cells: G1 phase cell cycle arrest, apoptosis, migration and invasion inhibition. Phytomedicine 23:800–809
176. Pan G, Li T, Zeng Q, Wang X, Zhu Y (2016) Alisol F 24 Acetate enhances chemosensitivity and apoptosis of MCF-7/DOX cells by inhibiting P-glycoprotein-mediated drug efflux. Molecules 21.
177. Wang C, Zhang JX, Shen XL, Wan CK, Tse AK, Fong WF (2004) Reversal of P-glycoprotein-mediated multidrug resist- ance by Alisol B 23-acetate. Biochem Pharmacol 68:843–855
178. Akl MR, Elsayed HE, Ebrahim HY, Haggag EG, Kamal AM, El Sayed KA (2014) 3-O-[N-(p-fluorobenzenesulfonyl)-carbamoyl]- oleanolic acid, a semisynthetic analog of oleanolic acid, induces apoptosis in breast cancer cells. Eur J Pharmacol 740:209–217
179. Ng YP, Chen Y, Hu Y, Ip FC, Ip NY (2013) Olean-12-eno[2,3- c] [1,2,5]oxadiazol-28-oic acid (OEOA) induces G1 cell cycle arrest and differentiation in human leukemia cell lines. PloS one 8:e63580
180. Cheng Y, Qiu F, Ye YC et al (2009) Autophagy inhibits reactive oxygen species-mediated apoptosis via activating p38-nuclear factor-kappa B survival pathways in oridonin-treated murine fibrosarcoma L929 cells. FEBS J 276:1291–1306
181. Fulda S (2008) Betulinic acid for cancer treatment and preven- tion. Int J Mol Sci 9:1096–1107
182. Potze L, Mullauer FB, Colak S, Kessler JH, Medema JP (2014) Betulinic acid-induced mitochondria-dependent cell death is counterbalanced by an autophagic salvage response. Cell Death Dis 5:e1169
183. Zhang DM, Xu HG, Wang L et al (2015) Betulinic acid and its derivatives as potential antitumor agents. Med Res Rev 35:1127–1155
184. Lee SY, Kim HH, Park SU (2015) Recent studies on betulinic acid and its biological and pharmacological activity. EXCLI J 14:199–203
185. Gheorgheosu D, Duicu O, Dehelean C, Soica C, Muntean D (2014) Betulinic acid as a potent and complex antitumor phytochemical: a minireview. Anticancer Agents Med Chem 14:936–945
186. Liu W, Li S, Qu Z et al (2019) Betulinic acid induces autophagy- mediated apoptosis through suppression of the PI3K/AKT/ mTOR signaling pathway and inhibits hepatocellular carcinoma. Am J Transl Res 11:6952–6964
187. Xu T, Pang Q, Zhou D et al (2014) Proteomic investigation into betulinic acid-induced apoptosis of human cervical cancer HeLa cells. PloS One 9:e105768
188. Schmidt ML, Kuzmanoff KL, Ling-Indeck L, Pezzuto JM (1997) Betulinic acid induces apoptosis in human neuroblastoma cell lines. Eur J Cancer 33:2007–2010
189. Seo J, Jung J, Jang DS, Kim J, Kim JH (2017) Induction of cell death by betulinic acid through induction of apoptosis and inhibi- tion of autophagic flux in Microglia BV-2 cells. Biomol Therap 25:618–624
190. Park C, Jeong J-W, Han MH et al (2021) The anti-cancer effect of betulinic acid in u937 human leukemia cells is mediated through ROS-dependent cell cycle arrest and apoptosis. Animal Cells Sys 1–9
191. Kim SY, Hwangbo H, Kim MY et al (2021) Betulinic acid restricts human bladder cancer cell proliferation in vitro by inducing caspase-dependent cell death and cell cycle arrest, and decreasing metastatic potential. Molecules 26
192. Kutkowska J, Strzadala L, Rapak A (2021) Hypoxia increases the apoptotic response to betulinic acid and betulin in human non-small cell lung cancer cells. Chem-Biol Interact 333:109320

193. Yang LJ, Chen Y, He J et al (2012) Betulinic acid inhibits autophagic flux and induces apoptosis in human multiple mye- loma cells in vitro. Acta Pharmacol Sin 33:1542–1548
194. Chen F, Zhong Z, Tan HY et al (2020) Suppression of lncRNA MALAT1 by betulinic acid inhibits hepatocellular carcinoma progression by targeting IAPs via miR-22-3p. Clin Transl Med 10:e190
195. Gonzalez P, Mader I, Tchoghandjian A et al (2012) Impairment of lysosomal integrity by B10, a glycosylated derivative of betu- linic acid, leads to lysosomal cell death and converts autophagy into a detrimental process. Cell Death Differ 19:1337–1346
196. Wang S, Wang K, Zhang C et al (2017) Overaccumulation of p53-mediated autophagy protects against betulinic acid-induced apoptotic cell death in colorectal cancer cells. Cell Death Dis 8:e3087
197. Wu BY, Parks LM (1953) Oleanolic acid from cranberries. J Am Pharmac Assoc Am Pharmac Assoc 42:602–603
198. He X, Liu RH (2007) Triterpenoids isolated from apple peels have potent antiproliferative activity and may be partially responsible for apple’s anticancer activity. J Agric Food Chem 55:4366–4370
199. Vioque E, Maza M (1963) On triterpenic acids from olive and olive pomace oils. Grasas Aceites 14:9–11
200. Sánchez-Quesada C, López-Biedma A, Gaforio JJ (2015) Oleanolic acid, a compound present in grapes and olives, pro- tects against genotoxicity in human mammary epithelial cells. Molecules 20:13670–13688
201. Sánchez-Quesada C, López-Biedma A, Warleta F, Campos M, Beltrán G, Gaforio JJ (2013) Bioactive properties of the main triterpenes found in olives, virgin olive oil, and leaves of Olea europaea. J Agric Food Chem 61:12173–12182
202. Ismaili H, Tortora S, Sosa S et al (2001) Topical anti-inflam- matory activity of Thymus willdenowii. J Pharm Pharmacol 53:1645–1652
203. Pollier J, Goossens A (2012) Oleanolic acid. Phytochemistry 77:10–15
204. Yoshikawa M, Matsuda H (2000) Antidiabetogenic activity of oleanolic acid glycosides from medicinal foodstuffs. BioFactors 13:231–237
205. Kashiwada Y, Nagao T, Hashimoto A et al (2000) Anti-AIDS agents 38. Anti-HIV activity of 3-O-acyl ursolic acid derivatives. J Nat Prod 63:1619–1622
206. Yim TK, Wu WK, Pak WF, Ko KM (2001) Hepatoprotec- tive action of an oleanolic acid-enriched extract of Ligustrum lucidum fruits is mediated through an enhancement on hepatic glutathione regeneration capacity in mice. Phytotherapy Res 15:589–592
207. Liu J (1995) Pharmacology of oleanolic acid and ursolic acid. J Ethnopharmacol 49:57–68
208. Rodriguez-Rodriguez R (2015) Oleanolic acid and related triter- penoids from olives on vascular function: molecular mechanisms and therapeutic perspectives. Curr Med Chem 22:1414–1425
209. Sheng H, Sun H (2011) Synthesis, biology and clinical signifi- cance of pentacyclic triterpenes: a multi-target approach to pre- vention and treatment of metabolic and vascular diseases. Nat Prod Rep 28:543–593
210. Wang X, Bai H, Zhang X et al (2013) Inhibitory effect of oleanolic acid on hepatocellular carcinoma via ERK-p53-me- diated cell cycle arrest and mitochondrial-dependent apoptosis. Carcinogenesis 34:1323–1330
211. Lúcio KA, Rocha Gda G, Monção-Ribeiro LC, Fernandes J, Tak- iya CM, Gattass CR (2011) Oleanolic acid initiates apoptosis in non-small cell lung cancer cell lines and reduces metastasis of a B16F10 melanoma model in vivo. PloS one 6:e28596
212. Pratheeshkumar P, Kuttan G (2011) Oleanolic acid induces apoptosis by modulating p53, Bax, Bcl-2 and caspase-3 gene

expression and regulates the activation of transcription factors and cytokine profile in B16F. J Environ Pathol Toxicol Oncol 30:21–31
213. Zhou R, Zhang Z, Zhao L et al (2011) Inhibition of mTOR signaling by oleanolic acid contributes to its anti-tumor activ- ity in osteosarcoma cells. J Orthop Res 29:846–852
214. Chu R, Zhao X, Griffin C et al (2010) Selective concomitant inhibition of mTORC1 and mTORC2 activity in estrogen receptor negative breast cancer cells by BN107 and oleanolic acid. Int J Cancer 127:1209–1219
215. Furtado RA, Rodrigues EP, Araújo FR et al (2008) Ursolic acid and oleanolic acid suppress preneoplastic lesions induced by 1,2-dimethylhydrazine in rat colon. Toxicol Pathol 36:576–580
216. Ovesná Z, Kozics K, Slamenová D (2006) Protective effects of ursolic acid and oleanolic acid in leukemic cells. Mutat Res 600:131–137
217. Mu DW, Guo HQ, Zhou GB, Li JY, Su B (2015) Oleanolic acid suppresses the proliferation of human bladder cancer by Akt/mTOR/S6K and ERK1/2 signaling. Int J Clin Exp Pathol 8:13864–13870
218. Zhu YY, Huang HY, Wu YL (2015) Anticancer and apoptotic activities of oleanolic acid are mediated through cell cycle arrest and disruption of mitochondrial membrane potential in HepG2 human hepatocellular carcinoma cells. Mol Med Rep 12:5012–5018
219. Laszczyk MN (2009) Pentacyclic triterpenes of the lupane, oleanane and ursane group as tools in cancer therapy. Planta Med 75:1549–1560
220. Feng L, Jia XB, Jiang J et al (2010) Combination of active components enhances the efficacy of Prunella in prevention and treatment of lung cancer. Molecules (Basel, Switzerland) 15:7893–7906
221. Nishino H, Nishino A, Takayasu J et al (1988) Inhibition of the tumor-promoting action of 12-O-tetradecanoylphorbol- 13-acetate by some oleanane-type triterpenoid compounds. Can Res 48:5210–5215
222. Ishida M, Okubo T, Koshimizu K et al (1990) Topical prepara- tions containing ursolic acid and/or oleanolic acid for preven- tion of skin cancer. Chem Abstract 12173y.
223. Janakiram NB, Indranie C, Malisetty SV, Jagan P, Steele VE, Rao CV (2008) Chemoprevention of colon carcinogenesis by oleanolic acid and its analog in male F344 rats and modulation of COX-2 and apoptosis in human colon HT-29 cancer cells. Pharm Res 25:2151–2157
224. Gao X, Deeb D, Liu Y et al (2011) Prevention of prostate cancer with oleanane synthetic triterpenoid CDDO-me in the TRAMP mouse model of prostate cancer. Cancers 3:3353–3369
225. Tran K, Risingsong R, Royce D, Williams CR, Sporn MB, Liby K (2012) The synthetic triterpenoid CDDO-methyl ester delays estrogen receptor-negative mammary carcinogenesis in polyoma middle T mice. Cancer Prev Res 5:726–734
226. Liby K, Risingsong R, Royce DB et al (2009) Triterpenoids CDDO-methyl ester or CDDO-ethyl amide and rexinoids LG100268 or NRX194204 for prevention and treatment of lung cancer in mice. Cancer Prev Res 2:1050–1058
227. Liby K, Black CC, Royce DB et al (2008) The rexinoid LG100268 and the synthetic triterpenoid CDDO-methyl amide are more potent than erlotinib for prevention of mouse lung car- cinogenesis. Mol Cancer Ther 7:1251–1257
228. Xiaofei J, Mingqing S, Miao S et al (2021) Oleanolic acid inhib- its cervical cancer Hela cell proliferation through modulation of the ACSL4 ferroptosis signaling pathway. Biochem Biophys Res Commun 545:81–88
229. Chen X, Zhang Y, Zhang S, Wang A, Du Q, Wang Z (2021) Oleanolic acid inhibits osteosarcoma cell proliferation and

invasion by suppressing the SOX9/Wnt1 signaling pathway. Exp Ther Med 21:443
230. Shyu MH, Kao TC, Yen GC (2010) Oleanolic acid and ursolic acid induce apoptosis in HuH7 human hepatocellular carcinoma cells through a mitochondrial-dependent pathway and downregu- lation of XIAP. J Agric Food Chem 58:6110–6118
231. Chakravarti B, Maurya R, Siddiqui JA et al (2012) In vitro anti- breast cancer activity of ethanolic extract of Wrightia tomentosa: role of pro-apoptotic effects of oleanolic acid and urosolic acid. J Ethnopharmacol 142:72–79
232. Lu X, Li Y, Yang W et al (2021) Inhibition of NF-κB is required for oleanolic acid to downregulate PD-L1 by promoting DNA demethylation in gastric cancer cells. J Biochem Mol Toxicol 35:e22621
233. Zhang XK, Wang QW, Xu YJ, Sun HM, Wang L, Zhang LX (2021) Co-delivery of cisplatin and oleanolic acid by silica nan- oparticles-enhanced apoptosis and reverse multidrug resistance in lung cancer. Kaohsiung J Med Sci
234. Lisiak N, Paszel-Jaworska A, Bednarczyk-Cwynar B, Zaprutko L, Kaczmarek M, Rybczyńska M (2014) Methyl 3-hydroxyimino- 11-oxoolean-12-en-28-oate (HIMOXOL), a synthetic oleanolic acid derivative, induces both apoptosis and autophagy in MDA- MB-231 breast cancer cells. Chem Biol Interact 208:47–57
235. Fan J-P, Lai X-H, Zhang X-H et al (2021) Synthesis and evalu- ation of the cancer cell growth inhibitory activity of the ionic derivatives of oleanolic acid and ursolic acid with improved solubility. J Mol Liquids 332:115837
236. Liu J, Zheng L, Zhong J, Wu N, Liu G, Lin X (2014) Oleanolic acid induces protective autophagy in cancer cells through the JNK and mTOR pathways. Oncol Rep 32:567–572
237. Castrejón-Jiménez NS, Leyva-Paredes K, Baltierra-Uribe SL et al (2019) Ursolic and oleanolic acids induce mitophagy in A549 human lung cancer cells. Molecules 24
238. Nie H, Wang Y, Qin Y, Gong XG (2016) Oleanolic acid induces autophagic death in human gastric cancer cells in vitro and in vivo. Cell Biol Int 40:770–778
239. Shi Y, Song Q, Hu D, Zhuang X, Yu S, Teng D (2016) Oleanolic acid induced autophagic cell death in hepatocellular carcinoma cells via PI3K/Akt/mTOR and ROS-dependent pathway. Korean J Physiol Pharmacol 20:237–243
240. Zhou W, Zeng X, Wu X (2020) Effect of oleanolic acid on apop- tosis and autophagy of SMMC-7721 hepatoma cells. Med Sci Monitor 26:e921606
241. Liu J, Zheng L, Ma L et al (2014) Oleanolic acid inhibits prolif- eration and invasiveness of Kras-transformed cells via autophagy. J Nutr Biochem 25:1154–1160
242. Hosny S, Sahyon H, Youssef M, Negm A (2020) Oleanolic acid suppressed DMBA-induced liver carcinogenesis through induc- tion of mitochondrial-mediated apoptosis and autophagy. Nutr Cancer 1–15
243. Chen Y, McMillan-Ward E, Kong J, Israels SJ, Gibson SB (2008) Oxidative stress induces autophagic cell death independent of apoptosis in transformed and cancer cells. Cell Death Differ 15:171–182
244. Scherz-Shouval R, Elazar Z (2007) ROS, mitochondria and the regulation of autophagy. Trends Cell Biol 17:422–427
245. Ueda S, Masutani H, Nakamura H, Tanaka T, Ueno M, Yodoi J (2002) Redox control of cell death. Antioxidants Redox Signal 4:405–414
246. Song Y, Zhang P, Sun Y et al (2017) AMPK activation-dependent autophagy compromises oleanolic acid-induced cytotoxicity in human bladder cancer cells. Oncotarget 8:67942–67954
247. Macleod KF (2020) Mitophagy and mitochondrial dysfunction in cancer. Ann Rev Cancer Biol 4:41–60
248. Ahn KS, Noh EJ, Zhao HL, Jung SH, Kang SS, Kim YS (2005) Inhibition of inducible nitric oxide synthase and

cyclooxygenase II by Platycodon grandiflorum saponins via suppression of nuclear factor-kappaB activation in RAW 264.7 cells. Life Sci 76:2315–2328
249. Kim YP, Lee EB, Kim SY et al (2001) Inhibition of prosta- glandin E2 production by platycodin D isolated from the root of Platycodon grandiflorum. Planta Med 67:362–364
250. Choi SS, Han EJ, Lee TH et al (2002) Antinociceptive mecha- nisms of platycodin D administered intracerebroventricularly in the mouse. Planta Med 68:794–798
251. Lee H, Kang R, Kim YS, Chung SI, Yoon Y (2010) Platyco- din D inhibits adipogenesis of 3T3-L1 cells by modulating Kruppel-like factor 2 and peroxisome proliferator-activated receptor gamma. Phytother Res 24(Suppl 2):S161-167
252. Lee H, Bae S, Kim YS, Yoon Y (2011) WNT/β-catenin path- way mediates the anti-adipogenic effect of platycodin D, a natural compound found in Platycodon grandiflorum. Life Sci 89:388–394
253. Wu J, Yang G, Zhu W et al (2012) Anti-atherosclerotic activity of platycodin D derived from roots of Platycodon grandiflorum in human endothelial cells. Biol Pharm Bull 35:1216–1221
254. Xie Y, Deng W, Sun H, Li D (2008) Platycodin D2 is a poten- tial less hemolytic saponin adjuvant eliciting Th1 and Th2 immune responses. Int Immunopharmacol 8:1143–1150
255. Choi JH, Yoo KY, Park OK et al (2009) Platycodin D and 2’’-O-acetyl-polygalacin D2 isolated from Platycodon gran- diflorum protect ischemia/reperfusion injury in the gerbil hip- pocampus. Brain Res 1279:197–208
256. Kim MO, Moon DO, Choi YH, Lee JD, Kim ND, Kim GY (2008) Platycodin D induces mitotic arrest in vitro, leading to endoreduplication, inhibition of proliferation and apoptosis in leukemia cells. Int J Cancer 122:2674–2681
257. Kim MO, Moon DO, Choi YH et al (2008) Platycodin D induces apoptosis and decreases telomerase activity in human leukemia cells. Cancer Lett 261:98–107
258. Lee SK, Park KK, Kim Y-S, Ha Y-W, Chung WY (2008) P24. The effect of platycodin D on tumor-induced osteolysis in breast cancer bone metastasis. Cancer Treat Rev 34:22
259. Tang ZH, Li T, Gao HW et al (2014) Platycodin D from Plat- ycodonis Radix enhances the anti-proliferative effects of doxo- rubicin on breast cancer MCF-7 and MDA-MB-231 cells. Chin Med 9:16
260. Ahn KS, Hahn BS, Kwack K, Lee EB, Kim YS (2006) Platycodin D-induced apoptosis through nuclear factor-kappaB activation in immortalized keratinocytes. Eur J Pharmacol 537:1–11
261. Chun J, Joo EJ, Kang M, Kim YS (2013) Platycodin D induces anoikis and caspase-mediated apoptosis via p38 MAPK in AGS human gastric cancer cells. J Cell Biochem 114:456–470
262. Dai Q, Chen Z, Ge YQ et al (2012) Mechanism of platycodin D-induced apoptosis in A549 human lung cancer cells. Zhong- guo Zhong yao za zhi = Zhongguo zhongyao zazhi = China J Chin Mater Med 37:2626–2629
263. Li T, Xu WS, Wu GS, Chen XP, Wang YT, Lu JJ (2014) Plat- ycodin D induces apoptosis, and inhibits adhesion, migration and invasion in HepG2 hepatocellular carcinoma cells. Asian Pac J Cancer Prevent 15:1745–1749
264. Chen D, Chen T, Guo Y, Wang C, Dong L, Lu C (2021) Suppres- sive effect of platycodin D on bladder cancer through microRNA- 129–5p-mediated PABPC1/PI3K/AKT axis inactivation. Braz J Med Biol Res 54:e10222
265. Chun J, Kim YS (2013) Platycodin D inhibits migration, inva- sion, and growth of MDA-MB-231 human breast cancer cells via suppression of EGFR-mediated Akt and MAPK pathways. Chem Biol Interact 205:212–221
266. Wu D, Zhang W, Chen Y, Ma H, Wang M (2019) Platycodin D inhibits proliferation, migration and induces chemosensi- tization through inactivation of the NF-κB and JAK2/STAT3

pathways in multiple myeloma cells. Clin Exp Pharmacol Physiol 46:1194–1200
267. Hsu WC, Ramesh S, Shibu MA et al (2021) Platycodin D reverses histone deacetylase inhibitor resistance in hepatocel- lular carcinoma cells by repressing ERK1/2-mediated cofilin-1 phosphorylation. Phytomedicine 82:153442
268. Menon MB, Kotlyarov A, Gaestel M (2011) SB202190-induced cell type-specific vacuole formation and defective autophagy do not depend on p38 MAP kinase inhibition. PloS One 6:e23054
269. Zeng CC, Zhang C, Yao JH et al (2016) Platycodin D induced apoptosis and autophagy in PC-12 cells through mitochondrial dysfunction pathway. Spectrochim Acta Part A Mol Biomol Spectrosc 168:199–205
270. Li T, Tang ZH, Xu WS et al (2015) Platycodin D triggers autophagy through activation of extracellular signal-regulated kinase in hepatocellular carcinoma HepG2 cells. Eur J Pharmacol 749:81–88
271. Zhao R, Chen M, Jiang Z et al (2015) Platycodin-D induced autophagy in non-small cell lung cancer cells via PI3K/Akt/ mTOR and MAPK signaling pathways. J Cancer 6:623–631
272. Jeon D, Kim SW, Kim HS (2019) Platycodin D, a bioactive component of Platycodon grandiflorum, induces cancer cell death associated with extreme vacuolation. Animal Cells Syst 23:118–127
273. Dai Q, Ge YQ (2018) Inhibitory effect and mechanism of plat- ycodin D combined with imatinib on K562/R. Zhongguo Zhong yao za zhi = Zhongguo zhongyao zazhi= China J Chin Mater Med 43:385–389
274. Li T, Xu XH, Tang ZH et al (2015) Platycodin D induces apop- tosis and triggers ERK- and JNK-mediated autophagy in human hepatocellular carcinoma BEL-7402 cells. Acta Pharmacol Sin 36:1503–1513
275. Yu L, McPhee CK, Zheng L et al (2010) Termination of autophagy and reformation of lysosomes regulated by mTOR. Nature 465:942–946
276. Davis RJ (2000) Signal transduction by the JNK group of MAP kinases. Springer, Inflammatory Processes, pp 13–21
277. Bennett BL, Sasaki DT, Murray BW et al (2001) SP600125, an anthrapyrazolone inhibitor of Jun N-terminal kinase. Proc Natl Acad Sci USA 98:13681–13686
278. Duncia JV, Santella JB 3rd, Higley CA et al (1998) MEK inhibi- tors: the chemistry and biological activity of U0126, its analogs, and cyclization products. Bioorg Med Chem Lett 8:2839–2844
279. Lee SJ, Choi YJ, Kim HI et al (2021) Platycodin D inhibits autophagy and increases glioblastoma cell death via LDLR upregulation. Mol Oncol
280. López-Hortas L, Pérez-Larrán P, González-Muñoz MJ, Falqué E, Domínguez H (2018) Recent developments on the extraction and application of ursolic acid. A review. Food Res Int 103:130–149
281. Zhang D-M, Tang PM-K, Chan JY-W et al (2007) Anti-prolifer- ative effect of ursolic acid on multidrug resistant hepatoma cells R-HepG2 by apoptosis induction. Cancer Biol Ther 6:1377–1385
282. Zheng QY, Jin FS, Yao C, Zhang T, Zhang GH, Ai X (2012) Ursolic acid-induced AMP-activated protein kinase (AMPK) activation contributes to growth inhibition and apoptosis in human bladder cancer T24 cells. Biochem Biophys Res Com- mun 419:741–747
283. Li J, Liang X, Yang X (2012) Ursolic acid inhibits growth and induces apoptosis in gemcitabine-resistant human pancreatic cancer via the JNK and PI3K/Akt/NF-κB pathways. Oncol Rep 28:501–510
284. Baricevic D, Sosa S, Della Loggia R et al (2001) Topical anti- inflammatory activity of Salvia officinalis L. leaves: the rele- vance of ursolic acid. J Ethnopharmacol 75:125–132
285. Lee JY, Choi JK, Jeong NH et al (2017) Anti-inflammatory effects of ursolic acid-3-acetate on human synovial fibroblasts

and a murine model of rheumatoid arthritis. Int Immunophar- macol 49:118–125
286. Tu J, Sun HX, Ye YP (2008) Immunomodulatory and antitumor activity of triterpenoid fractions from the rhizomes of Astilbe chinensis. J Ethnopharmacol 119:266–271
287. Lewinska A, Adamczyk-Grochala J, Kwasniewicz E, Dere- gowska A, Wnuk M (2017) Ursolic acid-mediated changes in glycolytic pathway promote cytotoxic autophagy and apopto- sis in phenotypically different breast cancer cells. Apoptosis 22:800–815
288. Conway GE, Zizyte D, Mondala JRM et al (2021) Ursolic acid inhibits collective cell migration and promotes JNK-dependent lysosomal associated cell death in glioblastoma multiforme cells. Pharmaceuticals 14
289. Lee YH, Wang E, Kumar N, Glickman RD (2014) Ursolic acid differentially modulates apoptosis in skin melanoma and retinal pigment epithelial cells exposed to UV-VIS broadband radiation. Apoptosis 19:816–828
290. Pironi AM, de Araújo PR, Fernandes MA, Salgado HRN, Cho- rilli M (2018) Characteristics, biological properties and ana- lytical methods of ursolic acid: a review. Crit Rev Anal Chem 48:86–93
291. Bailly C (2020) Anticancer properties of Prunus mume extracts (Chinese plum, Japanese apricot). J Ethnopharmacol 246:112215
292. Chen X, Krakauer T, Oppenheim JJ, Howard OM (2004) Yin zi huang, an injectable multicomponent chinese herbal medicine, is a potent inhibitor of T-cell activation. J Alternat Comp Med 10:519–526
293. Kang DY, Sp N, Lee JM, Jang KJ (2021) Antitumor effects of ursolic acid through mediating the inhibition of STAT3/PD-L1 signaling in non-small cell lung cancer cells. Biomedicines 9
294. Mandal S, Gamit N, Varier L, Dharmarajan A, Warrier S (2021) Inhibition of breast cancer stem-like cells by a triterpenoid, urso- lic acid, via activation of Wnt antagonist, sFRP4 and suppression of miRNA-499a-5p. Life Sci 265:118854
295. Deng S, Shanmugam MK, Kumar AP, Yap CT, Sethi G, Bish- ayee A (2019) Targeting autophagy using natural compounds for cancer prevention and therapy. Cancer 125:1228–1246
296. Luo J, Hu YL, Wang H (2017) Ursolic acid inhibits breast can- cer growth by inhibiting proliferation, inducing autophagy and apoptosis, and suppressing inflammatory responses via the PI3K/ AKT and NF-κB signaling pathways in vitro. Exp Ther Med 14:3623–3631

297. Leng S, Hao Y, Du D et al (2013) Ursolic acid promotes cancer cell death by inducing Atg5-dependent autophagy. Int J Cancer 133:2781–2790
298. Zhao C, Yin S, Dong Y et al (2013) Autophagy-dependent EIF2AK3 activation compromises ursolic acid-induced apoptosis through upregulation of MCL1 in MCF-7 human breast cancer cells. Autophagy 9:196–207
299. Wu CC, Huang YF, Hsieh CP, Chueh PJ, Chen YL (2016) Com- bined use of zoledronic acid augments ursolic acid-induced apop- tosis in human osteosarcoma cells through enhanced oxidative stress and autophagy. Molecules 21
300. Shin SW, Kim SY, Park JW (2012) Autophagy inhibition enhances ursolic acid-induced apoptosis in PC3 cells. Biochem Biophys Acta 1823:451–457
301. Cao C, Wang W, Lu L et al (2018) Inactivation of Beclin-1-de- pendent autophagy promotes ursolic acid-induced apoptosis in hypertrophic scar fibroblasts. Exp Dermatol 27:58–63
302. Jung J, Seo J, Kim J, Kim JH (2018) Ursolic acid causes cell death in PC-12 cells by inducing apoptosis and impairing autophagy. Anticancer Res 38:847–853
303. Lin CW, Chin HK, Lee SL et al (2019) Ursolic acid induces apoptosis and autophagy in oral cancer cells. Environ Toxicol 34:983–991
304. Lin JH, Chen SY, Lu CC, Lin JA, Yen GC (2020) Ursolic acid promotes apoptosis, autophagy, and chemosensitivity in gemcit- abine-resistant human pancreatic cancer cells. Phytother Res
305. Hanahan D, Weinberg RA (2011) Hallmarks of cancer: the next generation. Cell 144:646–674
306. Zhang YH, Wu YL, Tashiro S, Onodera S, Ikejima T (2011) Reactive oxygen species contribute to oridonin-induced apopto- sis and autophagy in human cervical carcinoma HeLa cells. Acta Pharmacol Sin 32:1266–1275
307. Shi Y, Wang M, Wang P et al (2020) Alisol A is potentially thera- peutic in human breast cancer cells. Oncol Rep 44:1266–1274
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