Cell-permeable. A pan-specific ubiquitin isopeptidase inhibitor (IC₅₀ = 45, 37 and 9.8 µM for USP2, USP7 and SENP2 respectively). NSC-632839 does not affect proteasome proteolytic activity. Induces apoptosis via a Bcl-2-dependent but apoptosome-independent mitochondrial pathway.