GX15-070 enhances niraparib efficacy in ovarian cancer by promoting a shift in Mcl1-mediated DNA repair pathway from HR to NHEJ

PARP inhibitor (PARPi) maintenance therapy significantly extends progression-free survival of patients with homologous recombination repair deficiency (HRD) or BRCA mutations in ovarian cancer. However, more than 50% of patients lack HRD, highlighting the need to expand PARPi use for homologous recombination -proficient patients. In this study, the efficacy of GX15-070 combined with niraparib in ovarian cancer was evaluated. Based on the core regulators of genome stability and homologous recombination (HR) repair pathway, a compound library was constructed. The effect of candidate drugs on niraparib sensitivity were measured using CCK-8 in ovarian cancer cell lines. Immunofluorescence and non-homologous end joining repair (NHEJ) assay were conducted to examine HR and NHEJ activity. Co-immunoprecipitation was used to investigate the interaction between Mcl1 and Ku70. BH3 domain deletion mutant of Mcl1 was generated to elucidate the structural basis of the interaction between Mcl1 and Ku70. Additionally, cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) mouse models were established to evaluate the efficacy of GX15-070 combined with niraparib in vivo. We constructed a compound library based on the core regulators of genomic stability and HR repair. Through high-throughput drug screening, GX15-070, a Mcl1 inhibitor, was identified as a synergist of niraparib, independent of BRCA status. Inhibition of Mcl1 expression significantly impaired HR activity and potentiated niraparib sensitivity. High expression of Mcl1 was associated with a wore prognosis in ovarian cancer patients treating PARPi maintenance therapy. Mechanistically, Mcl1 directly interacts with Ku70 protein via its BH3 domain, serving as a functional switch in selecting between HR and NHEJ. GX15-070 disrupts the interaction by displacing Ku70, promoting a shift in DNA repair pathways from HR to NHEJ. Furthermore, the synergistic efficacy of the combination treatment was further validated in CDX and PDX models. The study demonstrated that the combination of GX15-070 with niraparib might be a promising therapeutic strategy for ovarian cancer patients with limited PARPi response.