KSQ-4279

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

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

RO7623066 (KSQ-4279) reported an acceptable safety profile during a phase I dose escalation study, with anemia being the most common side effect, and demonstrated robust pharmacokinetic, pharmacodynamic, and clinical activity. Other USP1 inhibitors, including SIM0501, XL309-101, and HSK39775, are currently in early clinical development. In this review, we provide an overview of the molecular function of USP1 and its importance as a therapeutic target in oncology, before focusing on the current state of preclinical and clinical development of USP1 inhibitors.

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.

These findings indicate that USP1 inhibitors represent a promising therapeutic strategy for overcoming PARP inhibitor resistance in patients with BRCA-mutant/HR-deficient tumors and support continued testing in clinical trials. Significance: KSQ-4279 is a potent and selective inhibitor of USP1 that induces regression of PARP inhibitor-resistant tumors when dosed in combination with PARP inhibitors, addressing an unmet clinical need for BRCA-mutant tumors.

Inhibitor binding drives a substantial increase in thermal stability of USP1, which may be mediated through the inhibitors filling a hydrophobic tunnel-like pocket in USP1. Our results contribute to the understanding of the mechanism of action of USP1 inhibitors at the molecular level.

P1, N=250, Recruiting, Hoffmann-La Roche | N=140 --> 250