NSC 632839 is a nonselective inhibitor of isopeptidases with IC50 values of 45 μM, 37μM, and 9.8μM, respectively for USP2, USP7, and SENP2 [1].

NSC 632839 is reported to have activity against the purified isopeptidases. It inhibits not only DUB (USP2, USP7) but also deSUMOylase (SENP2). It is also shown to inhibit cleavage of an Ub mimetic (z-LRGG-AMC) by transformed fibroblast lysates. However, NSC 632839 has no inhibition to the reporter enzyme PLA2, suggesting the inhibition is selective for isopeptidases [1].

NSC 632839 prevents removal of ubiquitin chains from polyubiquitinated proteins, inhibiting ubiquitin-dependent, proteasome-mediated degradation. It activates apoptosis in an apoptosome-independent manner [2, 3].

References:
[1] Nicholson B, Leach CA, Goldenberg SJ, Francis DM, Kodrasov MP, Tian X, Shanks J, Sterner DE, Bernal A, Mattern MR, Wilkinson KD, Butt TR. Characterization of ubiquitin and ubiquitin-like-protein isopeptidase activities. Protein Sci. 2008 Jun;17(6):1035-43.
[2] Gupta-Saraf P, Miller CL. HIF-1α downregulation and apoptosis in hypoxic prostate tumor cells infected with oncolytic mammalian orthoreovirus. Oncotarget. 2014 Jan 30;5(2):561-74.
[3] Eldridge AG, O'Brien T. Therapeutic strategies within the ubiquitin proteasome system. Cell Death Differ. 2010 Jan;17(1):4-13.