GLPG0259 free base is poorly soluble in aqueous media, and its solubility decreases with increasing pH (<0.01 mg/mL at pH 7). Two approaches were developed in parallel to overcome this low solubility and to improve compound bioavailability after dosing in a solid dosage form. The first approach was a salt screening, AZD5363 which resulted in the selection of the fumarate salt for further formulation development work. The water solubility of
the GLPG0259 fumarate salt, as compared with that of the free base, was increased to 1.9–2.7 mg/mL. The impact of the improvement in solubility was confirmed in a comparative bioavailability study in fasted dogs. In that study, GLPG0259 fumarate salt (suspension in 20% [w/v] hydroxypropyl-ß–cyclodextrin, pH 3, or as crystalline powder in capsule form) resulted in plasma exposure similar to that of GLPG0259 free base in suspension in 20% acidified hydroxypropyl-ß–cyclodextrin, but 4-fold higher plasma exposure than that of GLPG0259 free-base crystalline powder in capsule form (data not shown). In humans, administration of GLPG0259 fumarate salt as a crystalline powder in capsule form leads to 50% lower bioavailability than that of GLPG0259 free base
given as a solution in 40% (w/v) hydroxypropyl-ß–cyclodextrin, pH 3 (study 3). The lower performance of the fumarate capsule in humans than in dogs is explained by the higher percentage of hydroxypropyl-ß–cyclodextrin (40% versus 20%) in the liquid formulation, which enhances GLPG0259 free-base solubility. Bafilomycin A1 mouse Concomitant food intake with the solid
dosage form Sitaxentan prevents this decrease in bioavailability by increasing the solubility further. The second approach was the improvement of GLPG0259 solubility by physical modifications of the drug substance – in particular, the development of solid dispersion formulations with GLPG0259 free base in an amorphous form homogenously dispersed in a polymer matrix. The free-base solid dispersion as a powder or pellets filled into capsules was tested in fasted dogs, and both solid dispersion formulations showed GLPG0259 plasma exposure similar to that of the fumarate salt as a crystalline powder in capsule form. Similar results were obtained in humans (study 4). In the Biopharmaceutical Classification System, drugs are classified according to measurements of solubility and permeability. Regarding GLPG0259, it is a poorly soluble compound, with solubility that decreases with increased pH. The absorption of GLPG0259 was not measured in vivo in humans (there are no data after intravenous dosing), but its permeability assessed using the well established in vitro system, based on the human adenocarcinoma cell line Caco-2, was good, with an apparent permeability coefficient (Papp) of 12.4 10-6 cm/s and limited efflux (Papp B2A/Papp A2B = 2).