- Bortezomib (PS-341, Velcade ), a proteasome inhibitor, has been reported to have several putative mechanisms of action and it is likely that its toxicity is mediated by affecting more than one pathway or target. Bortezomib is reported to inhibit the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappaB) pathway and regulate NF-kappaB-dependent expression of several other inhibitors of apoptosis.