Inhibiting Rev1-mediated translesion DNA synthesis for cancer therapy - Project Summary/Abstract Prostate cancer is a leading cause of cancer death in American men. The National Cancer Institute estimated that there would be ~268,490 new cases of prostate cancer and ~34,500 deaths from prostate cancer within the United States for 2022. Despite the development of second-generation hormonal therapies (e.g., enzalutamide) and targeted poly(ADP-ribose) polymerase (PARP) inhibitors (e.g., olaparib), the mortality of prostate cancer remains high as intrinsic and acquired drug resistance is common to all these agents, and many patients develop incurable metastatic castration-resistant prostate cancer (mCRPC) within 2–3 years. Accumulating evidence and our preliminary data show that mCRPC cells deficient in homologous recombination repair (HRR) activities due to genetic mutations of DNA repair genes, such as BRCA1/2, or due to the enzalutamide treatment-induced BRCAness state are particularly vulnerable to disruption of DNA-damage tolerance pathways, such as the mutagenic translesion DNA synthesis (TLS). TLS is a fundamental cellular defense mechanism that enables DNA replication across lesion sites under replication stress in order to promote cell survival at the cost of replication fidelity. The eukaryotic Y-family polymerase Rev1 is an essential scaffolding protein in TLS, and the interaction between its C-terminal domain (CTD) with translesion polymerase z is absolutely required for function. Aided by our structural elucidation of the Rev1-bridged translesionsome complex in TLS, we have identified the first-in- class in vivo active small molecule inhibitor, JH-RE-06, that disrupts TLS by directly binding to the Rev1 CTD to block the Rev1 interaction with the Rev7 component of polymerase z. JH-RE-06 suppresses spontaneous and treatment-induced mutagenesis in cells and sensitizes cancer cells to a variety of DNA-damaging agents both in vitro and in a murine xenograft tumor model. Recently, we have shown that mCRPC cells in the BRCAness state are particularly vulnerable to JH-RE-06 inhibition. The goal of this proposal is to further characterize JH- RE-06 and derivatives in prostate cancer cells, optimize their potency, safety, and other pharmacological properties, and demonstrate their effectiveness in treating mCRPC and suppressing acquired drug resistance in murine tumor models. The successful execution of the proposal will profoundly alter the existing paradigm of lethal prostate cancer treatment by providing effective means to overcome intrinsic and acquired drug resistance, thus improving the outcomes for patients with lethal prostate cancer.
