Eprenetapopt in combination with carboplatin in high-grade ovarian and triple negative breast cancer cell lines with acquired resistance to olaparib.

High-grade serous ovarian cancer (HGSOC) and triple-negative breast cancer (TNBC) frequently exhibit mutations in DNA damage response (DDR) genes, as BRCA1, BRCA2 and TP53, which are associated with chemotherapy sensitivity. Olaparib, a PARP inhibitor, provides the greatest clinical benefit as maintenance therapy in HGSOC-particularly in tumors with BRCA1/2 mutations or broader homologous recombination deficiency (HRD)-whereas benefit in HRD-negative disease is limited. Eprenetapopt (APR-246) restores wild-type p53 function in tumor cells with TP53 mutations. This study investigates the potential of combining eprenetapopt with carboplatin to overcome resistance to the PARP inhibitor (PARPi) olaparib in HGSOC and TNBC cell lines. As preclinical models, human ovarian cancer cell lines (HGSOC) (PEO1, Kuramochi) and a triple-negative breast cancer cell line (MDA-MB-231) were utilized as parental lines to generate their respective olaparib-resistant cell lines (PEO1R, Kuramochi-R, MDA-MB-231-R) by exposing the cells to increasing doses of olaparib. Cell viability, apoptosis and cell cycle progression, were assessed using MTT assays and Annexin V assay and propidium iodide staining, respectively. The Chou-Talalay method was used to calculate the combination index (CI) for drug synergism. Olaparib-resistance was confirmed in both HGSOC and TNBC cell lines, as they exhibited significantly higher IC50 values compared to their respective parental lines. Moreover, the olaparib-resistant cells exhibited cross-resistance to carboplatin. Remarkably, the combination of eprenetapopt with carboplatin showed a synergistic effect in both parental and resistant cell lines, reducing tumor cell viability and demonstrating synergistic interaction compared with single agents. Combinatorial treatment also significantly increased apoptotic cell population in parental HGSOC and TNBC cell lines as well as in MDA-MB-231-R olaparib-resistant cells. Cell cycle analysis revealed that carboplatin mainly induced a significant increase in S or G2/M phase accumulation and a reduction in G1-phase cells, with eprenetapopt having a minimal additional impact. Combining eprenetapopt with carboplatin shows promising preclinical efficacy by enhancing cytotoxicity in olaparib-resistant models and demonstrating synergistic interaction; these data support the combination as a potential strategy to mitigate PARPi resistance and carboplatin cross-resistance in TP53 mutant HGSOC and TNBC cell lines. Although further studies are needed to elucidate the molecular mechanisms underlying the synergistic effect, here we point out the combination of eprenetapopt and carboplatin as a potential therapeutic strategy to address olaparib resistance in HGSOC and TNBC patients.