Lysosomal sequestration of PARP inhibitors drives heterogeneous accumulation in ovarian cancer to increase efficacy [RNA-seq]

PARP inhibitors have had a transformative impact in the treatment of high-grade serous ovarian cancer (HGSOC), but resistance remains a clinical hurdle. Increased expression of ABC drug efflux transporters has been identified as a resistance mechanism in patients but whether intracellular concentrations of these drugs is heterogeneous within tumours remains unclear. We developed a patient-derived explant multi-modal imaging pipeline which demonstrated significant cell-intrinsic heterogeneity of PARP inhibitor accumulation, both between patients and within tumours. Spatial transcriptomics revealed enrichment of apoptotic signatures in high-drug compared to low-drug regions, as well as metabolic and ECM-related differences. While some cases demonstrated a clear anticorrelation of PARP inhibitor levels with MDR1(ABCB1), this was not universal. Rucaparib, an intrinsically fluorescent PARP inhibitor accumulates heterogeneously at the single cell-level in established cell lines, and omics approaches revealed that this is driven by lysosomal sequestration, a pattern also observed in patient samples. Perturbation of lysosomal content altered intracellular levels of rucaparib and niraparib and impacted efficacy suggesting that lysosomes act as a drug reservoir to improve drug response.