In vitro activity: b-AP15 inhibits the activity of two 19S regulatory-particle-associated deubiquitinases, ubiquitin C-terminal hydrolase 5 (UCHL5) and ubiquitin-specific peptidase 14 (USP14), resulting in accumulation of polyubiquitin. b-AP15 results in a dose-dependent accumulation of the UbG76V-YFP reporter with IC50 of 0.8 μM, indicating impaired proteasome degradation. b-AP15 (1 μM) results in rapid accumulation of polyubiquitinated proteins in human colon carcinoma HCT-116 cells. b-AP15 (2.2 μM) increases the amounts of the cyclin-dependent kinases CDKN1A and CDKNIB and the tumor suppressor TP53 in a dose-dependent manner without altering the amounts of ornithine decarboxylase 1 (ODC1) in HCT-116 cells. b-AP15 (1 μM) results in G2/M phase cell-cycle arrest in HCT-116 cells, consistent with the accumulation of cell-cycle inhibitors. b-AP15 treatment increases the number of hypodiploid cells and is associated with increased amounts of apoptotic markers, including activated caspase-3, caspase-cleaved poly-ADP ribose polymerase (PARP) and cytokeratin-18 (CK18). b-AP15 is more toxic to HCT-116 cells as compared to immortalized epithelial cells (hTERT-RPE1) or peripheral blood mononuclear cells. b-AP15 inhibits deubiquitinating activity using a variety of substrates, including Ub-AMC, Ub-GFP22, ubiquitinated p53-binding protein homolog (HDM2), and K48- and K63-linked ubiquitin tetramer chains. b-AP15 is an inhibitor of the UPS that induced cell death via induction of the lysosomal apoptosis pathway in a cathepsin-D dependent manner. b-AP15 elicits characteristic UPS defects including the accumulation of ubiquitin conjugates and cell cycle inhibitors such as p21, p27 and the tumor suppressor p53. b-AP15 inhibits the deubiquitinase activity of both cysteine DUBs, with USP14 being slightly more sensitive than UCHL5. b-AP15 induces apoptosis in cells over-expressing the anti-apoptotic Bcl-2 protein and in cells lacking the p53 gene. b-AP15 (1 μM) inhibits ATP-induced IL-1β release from LPS-primed peritoneal macrophages. b-AP15 (1 μM) reduces the levels of cell death induced by nigericin treatment in THP-1 cells. b-AP15 (1 μM) significantly reduces the numbers of ASC specks formed after nigericin treatment in LPS-primed THP-1 cells.

Kinase Assay: For deubiquitinase inhibition assays, 19S regulatory particle (5 nM), 26S (5 nM) UCH-L1 (5 nM), UCH-L3 (0.3 nM), USP2_CD (5 nM) USP7_CD (5 nM) USP8_CD (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.

Cell Assay: NSC 687852 blocked deubiquitylating activity of USP14 and UCHL5 selectively without inhibiting proteasome activity. NSC 687852 decreased viability in multiple myeloma (MM) cell lines and patient MM cells, inhibited MM cell proliferation even in the presence of bone marrow stroma cells, and overcomed bortezomib resistance. Anti-MM activity of NSC 687852 was associated with growth arrest through downregulating CDC2, CDC25C, and cyclin B1, as well as induction of caspase-dependent apoptosis and activation of unfolded protein response.

Nat Med. 2011 Nov 6;17(12):1636-40; Int J Biochem Cell Biol. 2012 Nov;44(11):1729-38.