Abstract

Cancer is a devastating disease, with over 17 million new cases and 9.5 million deaths in 2018 alone. Due to population growth and aging, projected annual cancer cases and death will reach 27.5 million and 16.3 million by 2040, respectively, highlighting the urgent need for more effective cancer therapeutics. DNA-damaging agents are often the first line of defense against rapidly dividing cancer cells. However, intrinsic and acquired drug resistance and induction of secondary malignancies can limit the success of chemotherapy. Tumor cells can become chemoresistant by up-regulating a mutagenic DNA-repair process called translesion DNA synthesis (TLS). Thus, targeting TLS is an attractive avenue for improving chemotherapeutics. However, development of small molecules with high specificity and in vivo efficacy for mutagenic TLS has been challenging. TLS is orchestrated by Rev1 polymerase, which recruits the extender polymerase (Pol ζ) to bypass the DNA lesion We report the discovery and characterization of an inhibitor of TLS, which disrupts the protein-protein interaction between Rev1 polymerase and Rev7, a subunit of Pol ζ. Our X-ray crystallographic structural analysis of the Rev1 and the inhibitor (JH-RE-06) complex reveals that the inhibitor blocks Rev7 binding by inducing Rev1 dimerization and unexpectedly converting a "featureless" interface to a deep binding pocket. This surprising observation is confirmed by in vitro crosslinking. Cell-killing assays show that JH-RE-06 enhances sensitivity of a variety of cancer cell lines to different chemotherapeutic agents; furthermore, co-administration of JH-RE-06 with cisplatin significantly suppresses melanoma growth in mice and prolongs the survival time of tumor-bearing mice, highlighting the therapeutic potential of translesion synthesis inhibitors as novel adjuvant therapeutics to enhance the outcome of currently available chemotherapy.