Quantification of olaparib in human liver microsomes using an ultra-fast UPLC-MS/MS quantitative approach: in vitro and in silico metabolic stability assessment

Olaparib (Lynparza®) is a highly selective poly(ADP-ribose) polymerase (PARP) inhibitor used in the advanced treatment of ovarian, breast, and prostate cancers. An effective, environmentally friendly, rapid, and reliable UPLC-MS/MS method was established to quantify OLA in human liver microsomes (HLMs) and was used to evaluate the in vitro metabolic stability of OLA. The UPLC-MS/MS method was validated in accordance with the US-FDA bioanalytical method validation standards. The current UPLC-MS/MS method showed a high degree of greenness, as evidenced by a ComplexMoGAPI value of 66.0 and an AGREEprep tool value of 0.63. The StarDrop software package (WhichP450 and DEREK modules) was used to assess metabolic lability and characterize in silico alerts regarding the OLA chemical structure. The current UPLC-MS/MS method showed a linearity range of 1 to 4000 ng mL^-1, ultra-fast separation in 1 min, and exhibited precision and accuracy unaffected by HLMs. Chromatographic separation of OLA and dasatinib (internal standard) was performed using a reversed-phase Eclipse Plus 1.8 µm C8 column (50 mm × 2.1 mm), with the mobile phase consisting of 0.1% HCOOH in water (pH 3.2) at 60% and 0.1% HCOOH in ACN (40%). The intra- and inter-day evaluations of the accuracy and precision of the UPLC-MS/MS approach ranged from 0.79% to 11.67% and -0.86% to 10.33%, respectively. The in vitro half-life (t_1/2) of OLA was 43.7 min, and its intrinsic clearance (Cl_int) was 18.55 mL min^-1 kg^-1, confirming the low metabolic clearance (high metabolic stability). In silico studies suggest that minor structural modifications of the phthalazin-1-one (52%) and piperazine (24%) moieties during drug design may improve the safety profile and metabolic stability of new derivatives compared with OLA; however, experimental confirmation is needed.