Let-7e Suppresses DNA Damage Repair and Sensitizes Ovarian Cancer to Cisplatin through Targeting PARP1

Increased DNA damage repair is one of the mechanisms implicated in cisplatin resistance. Our previous study indicated that the deregulation of let-7e promoted cisplatin resistance and that let-7e could suppress DNA double-strand break repair in ovarian cancer. In this study, we further characterized the role of let-7e in DNA damage repair and cisplatin resistance in ovarian cancer, and investigated the underlying mechanisms. The alkaline and neutral comet assay indicated that let-7e impeded both DNA single- and double-strand break repairs through downregulating its target gene PARP1. In vitro and in vivo experiments provided evidence that the let-7e-PARP1-DNA repair axis was involved in the modulation of cisplatin sensitivity in ovarian cancer. Contrary to let-7e, PARP1 was overexpressed in cisplatin-resistant ovarian cancer tissues, and patients with high PARP1 expression exhibited poor progression-free survival (PFS) and overall survival (OS). Multivariate logistic and Cox regression analyses showed that let-7e and FIGO stage were independent prognostic factors for PFS and OS, whereas let-7e and PARP1 were able to independently predict chemotherapy response. Taken together, our results indicated that low expression of let-7e promoted DNA single- and double-strand break repairs and subsequently contributed to cisplatin resistance by relieving the suppression on PARP1 in ovarian cancer.