Carfilzomib covalently [13] irreversibly binds to and inhibits the chymotrypsin-like activity of the 20S proteasome, an enzyme that degrades unwanted cellular proteins. Carfilzomib displays minimal interactions with non-proteasomal targets, thereby improving safety profiles over bortezomib.[13] Inhibition of proteasome-mediated proteolysis results in a build-up of polyubiquitinated proteins, which may cause cell cycle arrest, apoptosis, and inhibition of tumor growth.[2]