Discovery of a potent and selective small-molecule inhibitor of ubiquitin-specific peptidase 15 (USP15) for the treatment of breast cancer.

Ubiquitin-specific protease 15 (USP15) plays a critical role in the pathogenesis of various malignancies, including breast cancer, by virtue of its specific deubiquitinating functions. However, small-molecule inhibitors targeting USP15 have not been reported to date. In the present study, we established a novel high-throughput screening (HTS) platform based on USP15, which led to the identification of a class of active compounds characterized by a 1-(azetidin-3-yl)-triazole scaffold. Following extensive structure-activity relationship (SAR) investigations and structural optimization, we identified TH-407a as a potent small-molecule inhibitor of USP15. Using TH-407a as a chemical probe, we investigated its mechanism of action and anticancer activity. Our findings demonstrate that TH-407a functions as a reversible, non-competitive inhibitor of USP15. It potently and dose-dependently suppressed the growth, proliferation, clonogenicity, and migratory capacity across a panel of breast cancer cell lines. TH-407a was shown to modulate p53 cancer-associated signaling pathways and reduce the stability of Poly (ADP-ribose) polymerase 1 (PARP1). In breast cancer xenograft mouse models, TH-407a exhibited potent anti-tumor activity. Collectively, these results highlight TH-407a as a promising candidate for the development of novel anticancer therapeutics.