Cocrystallization of multi-kinase inhibitor pazopanib with fenamic acids: improving dissolution and inhibiting cell migration

Abstract

A multi-kinase inhibitor, pazopanib (PAZ) is cocrystallized with cyclooxygenase (COX) inhibitor fenamic acids to investigate the dissolution rate and inhibition of cell migration in VEGF-triggered HUVEC cells to test the efficacy of stoichiometric drug–drug combinations. Crystallization experiments at the sub-milligram level in an acetonitrile–methanol mixture yielded two drug–drug salt forms of PAZ with flufenamic acid (FFA) and niflumic acid (NFA) as PAZ⁺·FFA⁻·ACN (an acetonitrile solvate named as form I) and PAZ⁺·NFA⁻. Structures of the crystal forms were characterized by single crystal X-ray diffraction (SC-XRD) method. Crystal structures revealed that the presence of a 2-aminopyrimidine group in PAZ is a strong partner for the carboxyl group in all solid forms, forming an acid⋯pyrimidine heterosynthon with COX inhibitor fenamic acids. To perform dissolution experiments and cell line analysis, the scale-up of both salt forms were done in the acetonitrile–methanol mixture through crystallization, which showed a polymorphic transformation in the case of PAZ⁺·FFA⁻·ACN (an acetonitrile solvate named form II). The thermodynamic stability of PAZ⁺·FFA⁻·ACN (form II) and PAZ⁺·NFA⁻ were analysed using slurry experiment under ambient conditions in pH 1.2 (0.1 N HCl) buffer medium and the residual solid phase was characterized by powder XRD, which showed that PAZ⁺·FFA⁻·ACN (form II) was a metastable solid form while PAZ⁺·NFA⁻ was a stable solid form. The dissolution experiments at gastric pH 1.2 showed that the rate of dissolution of PAZ⁺·FFA⁻·ACN was 10 times higher than PAZ⁺·NFA⁻. The cell migration assay suggested that PAZ⁺·FFA⁻·ACN inhibited ∼25% and PAZ⁺·NFA⁻ inhibited ∼20% migration of HUVEC cells compared to PAZ alone. These investigations suggested that the drug–drug salts PAZ⁺·FFA⁻ and PAZ⁺·NFA⁻ would be potential combo drug candidates for clinical trials.