B-AP15 (NSC-687852)(NSC-687852) is a selective inhibitor of the deubiquitinating enzymes Usp14 and UCHL5 of the 26S proteasome. It blocks the deubiquitinating activity of the 26S proteasome.

UCHL5:2.1 μM

In mice with HCT-116 colon carcinoma xenografts, B-AP15 (5 mg/kg) significantly delayed tumor onset. Additionally, in severely immunodeficient mice bearing squamous cell carcinoma xenografts, B-AP15 (5 mg/kg) demonstrated notable antitumor activity.

As a UPS (Ubiquitin-Proteasome System) inhibitor, B-AP15 induces cell death by triggering the cathepsin-D-dependent lysosomal apoptotic pathway. Compared to peripheral blood mononuclear cells or immortalized epithelial cells (hTERT-RPE1), B-AP15 exhibits greater cytotoxicity towards HCT-116 cells. It dose-dependently accumulates the UbG76V-YFP receptor (IC50: 0.8 μM), indicating impaired proteasomal degradation. When applied to human colon cancer HCT-116 cells, B-AP15 (1 μM) rapidly accumulates polyubiquitinated proteins. At a concentration of 1 μM, B-AP15 inhibits the release of IL-1β induced by ATP from lipopolysaccharide-induced peritoneal macrophages. In THP-1 cells, 1 μM B-AP15 reduces the level of cell death induced by nigericin and significantly decreases the formation of ASC specks in lipopolysaccharide-induced THP-1 cells treated with nigericin. Additionally, B-AP15 (1 μM) causes a G2/M phase cell cycle arrest and accumulation of cell cycle inhibitors in HCT-116 cells. At 2.2 μM, B-AP15 dose-dependently increases the levels of the cyclin-dependent kinase inhibitors CDKN1A and CDKN1B, and the tumor suppressor gene TP53, without affecting the levels of ornithine decarboxylase 1.

For deubiquitinase inhibition assays, 19S regulatory particle (5 nM), 26S (5 nM) UCH-L1 (5 nM), UCH-L3 (0.3 nM), USP2CD (5 nM) USP7CD (5 nM) USP8CD (5 nM) or BAP1 (5 nM) is incubated with DMSO or b-AP15 and monitored the cleavage of ubiquitin-AMC (1,000 nM) using a Wallac VICTOR Multilabel counter or a Tecan Infinite M1000 equipped with 380 nm excitation and 460 nm emission filters[1].

b-AP15 is dissolved in DMSO and stored, and then diluted with appropriate medium before use[2]. Cell viability is monitored by either the fluorometric microculture cytotoxicity assay or the MTT assay. For the MTT assay, cells are seeded into 96-well flat-bottomed plates overnight and exposed to drugs, using DMSO as the control. At the end of incubations, 10 μl of a stock solution of 5 mg/mL MTT is added into each well, and the plates are incubated 4 hours at 37°C. Formazan crystals are dissolved with 100 μL 10% SDS/10 mM HCl solution overnight at 37°C. Absorbance is measured using an enzyme-linked immunosorbent assay (ELISA) plate reader at 590 nm[2].