Discovery of TNG-6132, a potent, selective, and orally bioavailable USP1 inhibitor.

USP1 (ubiquitin-specific peptidase 1) is a deubiquitinating enzyme that has been identified as essential in BRCA1/2 mutant cells and implicated in the DNA damage response. Inhibition of USP1 by small molecule inhibitors disrupts DNA repair and replication and is being pursued as a potential anticancer therapeutic in BRCA1/2 mutant cancers. We report the discovery of an in vitro and in vivo USP1 inhibitor tool compound TNG-6132 (18), a reversible, allosteric inhibitor of USP1, which strongly inhibits USP1 enzymatic activity. 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.