RTx-161 (RTx161) is a potent, selective, allosteric DNA Polymerase θ (Polθ) inhibitor with IC50 of 4.1 nM, exhibits preferential killing of HR-deficient cells.
RTx-161 shows higher potency than recently published Polθ-pol inhibitors ART558 (11.4 nM IC50) and RP6685 (6.9 nM IC50) using the identical assay.
RTx-161 shows selective killing of BRCA2-null HCT116 and DLD1 cells, with little to no effect in BRCA2-WT cells.
RTx-161 also induceds selective killing of mouse embryonic fibroblasts (MEFs) harboring a Brca1 mutation (Brca1cc/cc).
RTx-161 shows concentration dependent inhibition of Polθ-pol MMEJ activity in vitro, selectively causes DNA damage in BRCA2-null DLD1 cells, induces PARP cleavage and apoptosis.
RTx-161 exhibits strong synergistic activity with Olaparib in BRCA2-null HCT116 cells, essentially overcomes cellular resistance to Olaparib.
RTx-161 exclusively inhibits closed Polθ-pol:DNA/DNA complexes, selectively inhibits Polθ-pol in the closed state.