Poly ADP-ribose polymerase inhibitors (PARPis) exhibit promising efficacy in patients with BRCA mutations or homologous repair deficiency (HRD) in ovarian cancer (OC). However, less than 40% of patients have HRD, it is vital to expand the indications for PARPis in BRCA-proficient patients. Ferroptosis suppressor protein 1 (FSP1) is a key protein in a newly identified ferroptosis-protective mechanism that occurs in parallel with the GPX4-mediated pathway and is associated with chemoresistance in several cancers. Herein, FSP1 is reported to be negatively correlated with the prognosis in OC patients. Combination therapy comprising olaparib and iFSP1 (a FSP1 inhibitor) strongly inhibited tumour proliferation in BRCA-proficient OC cell lines, patient-derived organoids (PDOs) and xenograft mouse models. Surprisingly, the synergistic killing effect could not be reversed by ferroptosis inhibitors, indicating that mechanisms other than ferroptosis were responsible for the synergistic lethality. In addition, cotreatment was shown to induce increased γH2A.X foci and to impair nonhomologous end joining (NHEJ) activity to a greater extent than did any single drug. Mass spectrometry and immunoprecipitation analyses revealed that FSP1 interacted with Ku70, a classical component recruited to and occupying the end of double-strand breaks (DSBs) in the NHEJ process. FSP1 inhibition decreased Ku70 PARylation, impaired subsequent DNA-PKcs recruitment to the Ku complex at DSB sites and was rescued by restoring PARylation. These findings unprecedentedly reveal a novel role of FSP1 in DNA damage repair and provide new insights into how to sensitize OC patients to PARPi treatment.

聚 ADP-核糖聚合酶抑制剂 (PARPis) 对卵巢癌 (OC) 中 BRCA 突变或同源修复缺陷 (HRD) 患者表现出良好的疗效。然而，只有不到 40% 的患者患有 HRD，因此扩大 PARPis 在 BRCA 熟练患者中的适应症至关重要。铁死亡抑制蛋白 1 (FSP1) 是新发现的铁死亡保护机制中的关键蛋白，该机制与 GPX4 介导的途径同时发生，并与多种癌症的化疗耐药相关。据报道，FSP1 与 OC 患者的预后呈负相关。奥拉帕尼和 iFSP1（一种 FSP1 抑制剂）联合治疗可强烈抑制 BRCA 丰富的 OC 细胞系、患者来源的类器官 (PDO) 和异种移植小鼠模型中的肿瘤增殖。令人惊讶的是，铁死亡抑制剂不能逆转协同杀伤作用，这表明铁死亡以外的机制是造成协同致死的原因。此外，与任何单一药物相比，联合治疗可诱导 γH2A.X 病灶增加，并更大程度地损害非同源末端连接 (NHEJ) 活性。质谱和免疫沉淀分析表明，FSP1 与 Ku70 相互作用，Ku70 是 NHEJ 过程中招募并占据双链断裂 (DSB) 末端的经典成分。FSP1 抑制降低了 Ku70 PARylation，损害了随后 DNA-PKcs 在 DSB 位点向 Ku 复合物的募集，并通过恢复 PARylation 来挽救。这些发现前所未有地揭示了 FSP1 在 DNA 损伤修复中的新作用，并为如何提高 OC 患者对 PARPi 治疗的敏感性提供了新的见解。