Oprozomib (PR-047) is an orally bioavailable derivative of carfilzomib, with similar biological activity, i.e. inhibition of the chymotrypsin-like activity of the proteasome. It 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. Oprozomib (PR-047) is being investigated for the treatment of hematologic malignancies, specifically, multiple myeloma, with Phase I/II trial ongoing.