Guided by USP1-UAF1 structural insights, we optimized the KSQ-4279 scaffold and identified 1,3-dihydro-2H-imidazo[4,5-c]pyridin-2-one as a scaffold-hopping core for proof-of-concept exploration...In vitro assays and in vivo xenograft studies demonstrated synergistic antitumor activity between compound 57 and Olaparib, resulting in DNA damage and significantly enhanced tumor growth inhibition compared with Olaparib monotherapy. Transcriptomic analysis and Western blot results further supported enhanced suppression of tumor survival pathways. Collectively, this work establishes compound 57 as a scaffold-hopping, proof-of-concept USP1 inhibitor and provides in vivo validation for USP1-PARP inhibitor combination therapy in TNBC.

In addition, a novel class of potent tetrahydroisoquinoline USP1 inhibitors was identified, and the representative compound 14a possessed superior enzymatic and cellular activity compared with the clinical candidate KSQ-4279, with potent in vivo anti-DLBCL efficacy and good druggability. Collectively, this study provides a valuable fluoroprobe, FP assay platform, and lead compounds targeting USP1 for further structural optimization and antitumor mechanism studies.

P1, N=13, Terminated, Jiangsu Simcere Pharmaceutical Co., Ltd. | N=176 --> 13 | Trial completion date: Dec 2027 --> Sep 2025 | Recruiting --> Terminated | Trial primary completion date: Jun 2026 --> Sep 2025; Company development strategy change

P1, N=116, Completed, Hoffmann-La Roche | Active, not recruiting --> Completed | N=250 --> 116

P1, N=40, Not yet recruiting, Chia Tai Tianqing Pharmaceutical Group Co., Ltd.

Supported by its favorable pharmacokinetic properties, compound 43 exhibited significant in vivo anticancer efficacy in an MDA-MB-436 xenograft model, achieving superior tumor growth inhibition both as monotherapy and in combination with Olaparib compared to KSQ-4279. Collectively, compound 43 emerges as a promising preclinical candidate with translational potential for BRCA-mutated breast cancer.

Besides, at the effective reversal concentrations, KSQ-4279 neither altered expression and localization of ABCB1/ABCG2/ABCC1, nor affected USP1's potential downstream AKT or ERK1/2 signaling. This is the first study to investigate the combination of USP1 inhibitor (KSQ-4279) with traditional chemotherapeutic drugs in reversing MDR, which surprisingly hinted ABCB1, ABCG2, and ABCC1 as the new targets of KSQ-4279, and advocated this promising combination therapy in clinical refractory MDR cancers.

P1, N=250, Active, not recruiting, Hoffmann-La Roche | Recruiting --> Active, not recruiting | Trial completion date: Jun 2026 --> Nov 2025

This inhibitory effect translates into in vitro cellular viability defects in a BRCA1-mutant breast cancer cell line, as well as an in vivo pharmacodynamic (PD) response and tumor growth suppression in a mouse xenograft efficacy model. Additionally, we report an X-ray co-crystal structure of TNG-6132 (18) bound in the USP1-UAF1 complex, a result that furthered our understanding of the role played by key elements of the pharmacophore of this chemotype as well as its mechanism of inhibition of USP1.

SJB2-043 exerts a suppressive effect on A549 cell proliferation, migration, and epithelial-mesenchymal transition while enhancing apoptosis. These cellular effects appear to be mediated through the inhibition of the MAPK, Wnt/β-catenin, and PI3K/AKT/mTOR signaling cascades, in addition to modulation of the cell cycle.

P1, N=250, Recruiting, Hoffmann-La Roche | Trial completion date: Jun 2027 --> Jun 2026 | Trial primary completion date: Jun 2026 --> Aug 2025

Herein, we utilized ring-opening and cyclization strategies based on KSQ-4279 to design a novel series of USP1 inhibitors featuring a morpholine scaffold...Importantly, it enhanced the sensitivity of olaparib-resistant cells to olaparib and showed a synergetic effect with andrographolide in BRCA-proficient cancer cells...In the MDA-MB-436 xenograft model, 38-P2 displayed significant, dose-dependent antitumor efficacy. Overall, these findings indicate that 38-P2 is a promising lead compound for further drug development.