Polθ-IN-9 is an orally active Polθ polymerase inhibitor (IC50 = 9.6 nM, Kd = 47.5 nM). Polθ-IN-9 shows remarkable selectivity with no inhibitory activity against other human DNA polymerases, including Pol α, Pol ε, Pol γ, Pol λ, and Pol μ. Polθ-IN-9 exhibits strong antiproliferative activity in DLD1 BRCA2 KO cells (IC50 = 2.9 μM), and high sensitivity to MDA-MB-436 cells (IC50 = 4.9 μM). Polθ-IN-9 increases DNA damage accumulation, induces γH2AX levels, and inhibits tumor growth in combination with Olaparib, in the MDA-MB-436 xenograft model. Polθ-IN-9 can be used for the research of homologous recombination (HR)-deficient cancers such as breast cancer.
