Bortezomib

Bortezomib (Velcade) is an FDA-approved first-in-class dipeptide boronic acid proteasome inhibitor used in the treatment of multiple myeloma and mantle cell lymphoma. Approved in 2003, it revolutionized myeloma treatment and remains a cornerstone of frontline and relapsed therapy regimens worldwide, typically used in combination with lenalidomide and dexamethasone.

Bortezomib is a dipeptide boronate that reversibly inhibits the chymotrypsin-like activity of the 26S proteasome. The boronic acid moiety forms a reversible covalent bond with the N-terminal threonine residue of the 20S proteasome beta5 subunit, blocking protein degradation. This causes accumulation of pro-apoptotic proteins normally targeted for proteasomal destruction, including IκB (which sequesters the NF-κB transcription factor). NF-κB inhibition is particularly relevant in myeloma, where constitutive NF-κB activity drives proliferation and survival. Additionally, bortezomib phosphorylates Bcl-2, upregulates the BH3-only protein NOXA, blocks p53 degradation, activates caspase cascades, generates reactive oxygen species, and inhibits tumor angiogenesis. The combined pro-apoptotic burden overwhelms the unfolded protein response in malignant plasma cells.

Bortezomib received accelerated FDA approval in May 2003 for relapsed/refractory multiple myeloma based on the SUMMIT Phase II trial, which showed a 35% response rate in heavily pretreated patients. Full approval followed in 2005 after APEX confirmed superiority over high-dose dexamethasone (38% vs. 18% response rate). The VISTA trial established bortezomib + melphalan + prednisone as a frontline standard. Approval for mantle cell lymphoma followed in 2006. Peripheral neuropathy remains the principal dose-limiting toxicity; subcutaneous administration reduces neuropathy incidence compared to intravenous delivery.