Fig. 3 and Table 1 depict that the IC50 values markedly decreased with the addition

of SG to epirubicin and paclitaxel. The IC50 value of epirubicin in the HeLa cells was 1.05 μg/mL, which decreased to 0.15 μg/mL with the addition of 80 μg/mL SG. This result indicates that a subtoxic concentration of SG significantly increases the cytotoxic efficacy of epirubicin. SG exhibited similar Protein Tyrosine Kinase inhibitor potentiating activities on paclitaxel in all three cancer cell lines. To examine whether the role of SG in the cytotoxic effect of epirubicin and paclitaxel was caused by the enhanced apoptosis, we assessed the resulting apoptosis in the HeLa cells after separate treatments with epirubicin and paclitaxel alone and after the treatment with the combination of SG and the two drugs. The stage of apoptosis was determined through annexin-V analysis. As shown in Fig. 4A and C, the percentage of apoptotic cells was considerably higher in the cotreated cells than in the epirubicin- and paclitaxel-treated cells. To determine the activation Antidiabetic Compound Library of caspase in the cells, we detected the PARP cleavage through immunoblotting analysis.

Fig. 4B and D show that PARP was cleaved to yield an 85-kD fragment in the drug-treated cells and that the amount of the cleaved 85-kD fragment was more significant in the co-treated cells than in the epirubicin- and paclitaxel-treated Rho cells. On the basis of these results, we suggest that SG enhances the anticancer activities of epirubicin and paclitaxel through caspase-associated apoptosis. To elucidate the initiation event of apoptosis, we inspected the activation kinetics of the two initiator caspases, namely, caspase-8 and -9, and the effector caspases, caspase-3/-7. As shown in Fig. 5,

the activities of caspase-9 and -3/-7 greatly increased in the cotreated cells than in the epirubicin- and paclitaxel-treated cells. By contrast, the activity of caspase-8 did not show any change in all cells. We then determined the cleavage of caspase-9 and -8. Specifically, we examined the proteolytic activation of these caspases through immunoblotting analysis. Apparent cleavage was observed in caspase-9 but not in caspase-8. The amounts of the active form of the cleaved caspase-9 were higher in the cotreated cells than in the epirubicin- and paclitaxel-treated cells. The data suggest that epirubicin and paclitaxel-induced apoptosis might be potentiated by SG via the intrinsic apoptosis pathway in HeLa cells. The release of mitochondrial cytochrome c is the crucial event in caspase-9 activation [40]. The family members of the Bcl-2 family, namely, Bax and Bak, serve as an essential gateway for the release of cytochrome c [5] and [41]. Fig.