Lead compound profiling for small molecule inhibitors of the REV1-CT/RIR Translesion synthesis Protein-Protein interaction.

Translesion synthesis (TLS) is a cellular mechanism through which actively replicating cells recruit specialized, low-fidelity DNA polymerases to damaged DNA to allow for replication past these lesions. REV1 is one of these TLS DNA polymerases that functions primarily as a scaffolding protein to organize the TLS heteroprotein complex and ensure replication occurs in the presence of DNA lesions. The C-Terminal domain of REV1 (REV1-CT) forms many protein-protein interactions (PPIs) with other TLS polymerases, making it essential for TLS function and a promising drug target for anti-cancer drug development. We utilized several lead identification strategies to identify various small molecules capable of disrupting the PPI between REV1-CT and the REV1 Interacting Regions (RIR) present in several other TLS polymerases. These lead compounds were profiled in several in vitro potency and PK assays to identify two scaffolds (1 and 6) as the most promising for further development. Both 1 and 6 synergized with cisplatin in a REV1-dependent fashion and demonstrated promising in vivo PK and toxicity profiles.

SARS-CoV-2 hijacks host cell genome instability pathways.

The repertoire of coronavirus disease 2019 (COVID-19)-mediated adverse health outcomes has continued to expand in infected patients, including the susceptibility to developing long-COVID; however, the molecular underpinnings at the cellular level are poorly defined. In this study, we report that SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection triggers host cell genome instability by modulating the expression of molecules of DNA repair and mutagenic translesion synthesis. Further, SARS-CoV-2 infection causes genetic alterations, such as increased mutagenesis, telomere dysregulation, and elevated microsatellite instability (MSI). The MSI phenotype was coupled to reduced MLH1, MSH6, and MSH2 in infected cells. Strikingly, pre-treatment of cells with the REV1-targeting translesion DNA synthesis inhibitor, JH-RE-06, suppresses SARS-CoV-2 proliferation and dramatically represses the SARS-CoV-2-dependent genome instability. Mechanistically, JH-RE-06 treatment induces autophagy, which we hypothesize limits SARS-CoV-2 proliferation and, therefore, the hijacking of host-cell genome instability pathways. These results have implications for understanding the pathobiological consequences of COVID-19.

REV1 Inhibition Enhances Radioresistance and Autophagy.

Cancer therapy resistance is a persistent clinical challenge. Recently, inhibition of the mutagenic translesion synthesis (TLS) protein REV1 was shown to enhance tumor cell response to chemotherapy by triggering senescence hallmarks. These observations suggest REV1's important role in determining cancer cell response to chemotherapy. Whether REV1 inhibition would similarly sensitize cancer cells to radiation treatment is unknown. This study reports a lack of radiosensitization in response to REV1 inhibition by small molecule inhibitors in ionizing radiation-exposed cancer cells. Instead, REV1 inhibition unexpectedly triggers autophagy, which is a known biomarker of radioresistance. We report a possible role of the REV1 TLS protein in determining cancer treatment outcomes depending upon the type of DNA damage inflicted. Furthermore, we discover that REV1 inhibition directly triggers autophagy, an uncharacterized REV1 phenotype, with a significant bearing on cancer treatment regimens.