Replication protein A (RPA) plays essential roles in DNA replication, repair, recombination, and the DNA damage response (DDR). Retrospective analysis of
lung cancer patient data demonstrates high RPA expression as a negative prognostic
biomarker for overall survival in smoking-related
lung cancers. Similarly, relative expression of RPA is a predictive marker for response to
chemotherapy. These observations are consistent with the increase in RPA expression serving as an adaptive mechanism that allows tolerance of the genotoxic stress resulting from
carcinogen exposure. We have developed second-generation RPA inhibitors (RPAis) that block the RPA-
DNA interaction and optimized formulation for in vivo analyses. Data demonstrate that unlike first-generation RPAis, second-generation molecules show increased cellular permeability and induce cell death via apoptosis. Second-generation RPAis elicit single-agent in vitro anticancer activity across a broad spectrum of
cancers, and the cellular response suggests existence of a threshold before chemical RPA exhaustion induces cell death. Chemical RPA inhibition potentiates the anticancer activity of a series of DDR inhibitors and traditional
DNA-damaging
cancer therapeutics. Consistent with chemical RPA exhaustion, we demonstrate that the effects of RPAi on replication fork dynamics are similar to other known DDR inhibitors. An optimized formulation of RPAi NERx 329 was developed that resulted in single-
agent anticancer activity in two
non-small cell lung cancer models. These data demonstrate a unique mechanism of action of RPAis eliciting a state of chemical RPA exhaustion and suggest they will provide an effective therapeutic option for difficult-to-treat
lung cancers.