Validation of a UPLC-MS/MS Method for Quantifying Intracellular Olaparib Levels in Resistant Ovarian Cancer Cells

Background: Ovarian cancer remains one of the leading causes of cancer-related mortality among women and constitutes a major unmet medical need. A common treatment-limiting factor for ovarian cancer patients is resistance to Poly(ADP-ribose) polymerase (PARP) inhibitors such as olaparib. Resistance mechanisms include restoration of functional homologous recombination repair, replication fork protection, PARP1 mutations, and increased drug efflux or metabolism. Understanding these cellular and molecular mechanisms is essential for developing more effective therapeutic strategies and improving patient outcomes. Methods: In this study, patient-derived ovarian cancer cells (OC12) in which resistance to olaparib was induced by exposing the cells to increasing concentrations of the drug over multiple treatment cycles were investigated. To compare intracellular olaparib levels in sensitive and resistant cell lines, a UPLC-MS/MS method to quantify olaparib in the range of 1-300 ng/mL was developed. Results: The method was validated for selectivity, calibration curve performance, carryover, dilution integrity, precision, accuracy, matrix effect, and recovery in accordance with ICH M10 guidelines for bioanalytical method validation. Our findings revealed no significant difference in olaparib levels between resistant and sensitive OC12 cells, excluding the involvement of efflux transporters or enhanced metabolism of olaparib in the resistant OC12 ovarian cancer cells. Conclusions: These results shift the future focus toward pharmacodynamic factors as key drivers of olaparib resistance in OC12 cells. Taken together, the developed UPLC-MS/MS analytical method can be successfully applied to quantify intracellular olaparib levels and investigate the potential contribution of drug efflux mechanisms or increased metabolic activity in cells resistant to olaparib treatment.