An orally bioavailable proteasome inhibitor with potential antineoplastic activity. Oprozomib inhibits the activity of the proteasome, thereby blocking the targeted proteolysis normally performed by the proteasome; this may result in an accumulation of unwanted or misfolded proteins. Disruption of various cell signaling pathways may follow, eventually leading to the induction of apoptosis and inhibition of tumor growth. Proteasomes are large protease complexes that degrade unneeded or damaged proteins that have been ubiquitinated.