Optimization of a Series of Novel 1H-Pyrrolo[3,2-c]pyridine-Based USP1 Inhibitors with Potent In Vivo Antitumor Activity.

USP1, a deubiquitinating enzyme critical for DNA damage repair, represents a promising therapeutic target for cancers. In this study, we employed scaffold hopping to design and synthesize a series of 1H-pyrrolo[3,2-c]pyridine-based USP1 inhibitors. Among these, the lead compound 38a displayed robust enzymatic and cellular potencies. 38a dose-dependently induced Ub-PCNA accumulation, triggered cell cycle arrest, and potently suppressed cell viability. Additionally, 38a synergized with olaparib in MDA-MB-463 cells. Uniquely, 38a effectively induced c-MYC downregulation. In vivo studies confirmed 38a's favorable oral bioavailability. In the MDA-MB-436 xenograft model, the combination of 38a with olaparib exerted potent antitumor efficacy, with a tumor inhibition rate of 80.7%, and the antitumor activity of 38a stemmed from USP1 inhibition. Furthermore, in the DLBCL PDX model with high c-MYC expression, 38a demonstrated efficacy comparable to standard first-line therapies. Preliminary safety evaluation confirmed the safety profile of 38a. Taken together, 38a is a highly promising antitumor lead compound with great translational potential.