Discovery and optimization of 1H-pyrazolo[3,4-d]pyrimidine-3-carboxamide derivatives as USP1 inhibitors for BRCA1-mutant cancer treatment.

Ubiquitin-specific protease 1 (USP1) plays a critical role in deubiquitinating key protein complexes involved in the DNA damage response (DDR). Inhibition of USP1 has been shown to induce synthetic lethality in BRCA1-mutant cancers, making it an attractive anticancer therapeutic target. In this study, a series of 1H-pyrazolo[3,4-d]pyrimidine-3-carboxamide derivatives were designed and synthesized as novel inhibitors of USP1. The resulting compounds exhibited nanomolar-level inhibitory activity against USP1 and potently inhibited the proliferation of the BRCA1-mutant MDA-MB-436 cells. Among them, compound 18 exhibited an IC50 value of 8.1 nM against MDA-MB-436 and demonstrated superior selectivity for BRCA1-mutant cells over BRCA1-wild-type cells. Western blot analysis revealed that compound 18 significantly increased DNA damage accumulation of BRCA1-mutant cells. In vivo pharmacokinetic studies were conducted to determine the oral exposure of compound 18. Moreover, molecular docking and dynamics studies were performed to elucidate the detailed binding mechanism of compound 18 with USP1. Taken together, this study presents a promising class of 1H-pyrazolo[3,4-d]pyrimidine-3-carboxamide derivatives as novel USP1 inhibitors with significant therapeutic potential for the treatment of BRCA1-mutant cancers.