Chemical exhaustion of RPA in cancer treatment

Replication protein A (RPA) plays essential roles in DNA replication, repair, recombination and the DNA-damage response (DDR). We have developed second generation RPA inhibitors (RPAis) that block the RPA-DNA interaction. These DNA-binding inhibitors (DBis) can elicit a state of cellular RPA exhaustion resulting in single agent in vitro anticancer activity across a broad spectrum of cancers and in vivo activity in two non-small cell lung cancer models. The cellular response to RPAi treatment suggests a threshold exists before RPA inhibition induces cell death. Chemical RPA exhaustion potentiates the anticancer activity of other DDR inhibitors as well as traditional DNA damaging cancer therapeutics. Consistent with the chemical RPA exhaustion model, we demonstrate that the effects of RPAi on replication fork dynamics and DNA damage signaling are similar to other known DDR inhibitors. In accordance with the RPA threshold model, 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. These data demonstrate a unique mechanism of action of RPAis eliciting a state of RPA exhaustion that impacts the DDR and may provide an effective therapeutic option for difficult to treat lung cancers. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=130 SRC="FIGDIR/small/404640v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@d662e4org.highwire.dtl.DTLVardef@f68b11org.highwire.dtl.DTLVardef@241c0corg.highwire.dtl.DTLVardef@ad7398_HPS_FORMAT_FIGEXP M_FIG C_FIG