ERCC1-XPF deficiency is a predictor of olaparib induced synthetic lethality and platinum sensitivity in epithelial ovarian cancers.

PARP inhibitor maintenance therapy in platinum sensitive sporadic ovarian cancers improves progression free survival. However, biomarker for synthetic lethality in platinum sensitive sporadic disease is yet to be defined. ERCC1-XPF heterodimer is a key player in nucleotide excision repair (NER) involved in the repair of platinum induced DNA damage. In the current study, we tested whether ERCC1-XPF deficiency would predict synthetic lethality to the PARP inhibitor Olaparib and platinum sensitivity in ovarian cancers. ERCC1, XPF and PARP1 protein expression was evaluated in tumors from a cohort of 331 patients treated at Nottingham University Hospitals and correlated to clinicopathological features and survival. Pre-clinically, ERCC1 and XPF was depleted in A2780 (platinum sensitive) and A2780cis (platinum resistant) ovarian cancer cell lines and tested for platinum sensitivity as well as for Olaparib induced synthetic lethality. Low ERCC1 was significantly associated with improved progression free survival (PFS) in patients with ovarian cancers in univariate (p = 0.001) and multivariate (p = 0.002) analysis. In addition, low ERCC1/low XPF (p = 0.003) or low ERCC1/low PARP1 (p = 0.0001) tumors was also linked to better PFS compared to high ERCC1/high XPF or high ERCC1/high PARP1 tumors. Pre-clinically, ERCC1 or XPF depletion not only increased platinum sensitivity but also increased toxicity to Olaparib therapy. Increased sensitivity was associated with DNA double strand breaks (DSBs) accumulation, cell cycle arrest and increased apoptosis. The data provide evidence that low ERCC1 is not only a predictor of platinum sensitivity but is also a promising biomarker for Olaparib induced synthetic lethality in ovarian cancers.