Abstract
Resistance to PARP inhibitors (PARPi) remains a major clinical challenge in ovarian cancer (OC), emphasizing the need for novel strategies to enhance therapeutic efficiency. Our previous work revealed that the antimalarial drug quinacrine (QC) can be repurposed to induce cell death in OC by promoting lysosomal release of active cathepsin L (CTSL). Building on these outcomes, we investigated whether QC-activated CTSL influences DNA damage and homologous recombination (HR) repair in OC cells. Our experimental evidence shows that QC-activated CTSL downregulates key DNA repair proteins RAD51 and 53BP1, leading to impaired HR repair and increased DNA damage. Importantly, genetic knockdown of CTSL significantly reduced QC-induced DNA damage, confirming the CTSL plays a direct functional role in this process. We also found out that the response of combined QC and PARPi differs in models. CTSL was translocated to the nucleus (nCTSL) in responsive patient-derived ascitic (PDA) and patient-derived xenograft (PDX) spheroids. Contrarily, non-responsive models did not have nuclear CTSL. Mechanically, QC could not suppress CRM1/XPO1 nuclear export receptor in non-responsive cells, leading to continued export of CTSL from the nucleus. To address this, we have used the CRM1 inhibitor KPT-8602, which restored nuclear retention of CTSL. This led to enhanced therapeutic synergy with PARPi and overcame resistance in QC-treated PDA 3D-spheroids. Consistent with these findings, QC reduced tumor burden in both the cell-derived OVCAR-5 xenograft and PDX-PH070 models that showed QC-induced nCTSL, but not in the non-responsive PDX-PH095 model. However, in additional non-responsive PDX models (PH747 and PH081), treatment with QC and KPT-8602 substantially reduced tumor burden. Collectively, our results confirm a critical role for nuclear CTSL in QC-induced DNA damage and identify nCTSL as a possible predictive biomarker of therapeutic response. These results suggest that combining QC with PARPi or CRM1 inhibitors represents a promising strategy to overcome PARPi resistance in OC.