JH-RE-06

Chemotherapy with cisplatin becomes limiting due to toxicity and secondary malignancies. In principle, therapeutics could be improved by targeting translesion synthesis (TLS) polymerases (Pols) that promote replication through intrastrand cross-links, the major cisplatin-induced DNA adduct. However, to specifically target malignancies with minimal adverse effects on normal cells, a good understanding of TLS mechanisms in normal versus cancer cells is paramount. We show that in normal cells, TLS through cisplatin intrastrand cross-links is promoted by Polη- or Polι-dependent pathways, both of which require Rev1 as a scaffolding component. In contrast, cancer cells require Rev1-Polζ. Our findings that a recently identified Rev1 inhibitor, JH-RE-06, purported to specifically disrupt Rev1 interaction with Polζ to block TLS through cisplatin adducts in cancer cells, abrogates Rev1's ability to function with Y family Pols as well, implying that by inactivating Rev1-dependent TLS in normal cells, this inhibitor will exacerbate the toxicity and tumorigenicity of chemotherapeutics with cisplatin.

REV1/POLζ-dependent mutagenic translesion synthesis (TLS) promotes cell survival after DNA damage but is responsible for most of the resulting mutations. A novel inhibitor of this pathway, JH-RE-06, promotes cisplatin efficacy in cancer cells and mouse xenograft models, but the mechanism underlying this combinatorial effect is not known. We report that, unexpectedly, in two different mouse xenograft models and four human and mouse cell lines we examined in vitro cisplatin/JH-RE-06 treatment does not increase apoptosis. Rather, it increases hallmarks of senescence such as senescence-associated β-galactosidase, increased p21 expression, micronuclei formation, reduced Lamin B1, and increased expression of the immune regulators IL6 and IL8 followed by cell death. Moreover, although p-γ-H2AX foci formation was elevated and ATR expression was low in single agent cisplatin-treated cells, the opposite was true in cells treated with cisplatin/JH-RE-06. These observations suggest that targeting REV1 with JH-RE-06 profoundly affects the nature of the persistent genomic damage after cisplatin treatment and also the resulting physiological responses. These data highlight the potential of REV1/POLζ inhibitors to alter the biological response to DNA-damaging chemotherapy and enhance the efficacy of chemotherapy.