Discovery, Synthesis, and Biological Evaluation of 1,3,4,5-Tetrahydro-6 H -pyrano[4,3- c ]isoquinolin-6-one Derivatives as Novel and Highly Selective PARP1 Inhibitors

Developing highly selective PARP1 inhibitors is a promising strategy to improve the therapeutic window compared with dual PARP1/2 inhibitors. Through structure-guided design and optimization, we developed (R)-A17, a novel, highly selective PARP1 inhibitor featuring a unique tricyclic scaffold. It demonstrates nanomolar enzymatic potency (PARP1 IC50 = 2.4 nM), exceptional 65.8-fold selectivity over PARP2, and robust antiproliferative activity in BRCA-deficient cells. (R)-A17 exhibits favorable pharmacokinetic properties with complete oral bioavailability (F = 100%) in mice. Mechanistically, it selectively inhibits PARP1-mediated PARylation and induces DNA damage and G2/M phase arrest. In vivo, oral administration of (R)-A17 produced dose-dependent antitumor efficacy in BRCA mutant xenograft models, achieving tumor growth inhibition values of 57.8, 86.3, and 91.3% at doses of 0.3, 1, and 3 mg/kg, respectively, while also synergizing effectively with liposomal irinotecan in an HCT116 xenograft model. These results establish (R)-A17 as a promising candidate and validate the design strategy for the next-generation PARP1-targeted therapy.