Bortezomib

Mechanism

Bortezomib is a reversible inhibitor of the 26S proteasome, the large multi-catalytic protease complex responsible for degrading ubiquitinated proteins in the cytoplasm and nucleus. It specifically targets the chymotrypsin-like activity of the 20S proteasome core (β5 subunit) by forming a tetrahedral intermediate with the N-terminal threonine hydroxyl group via its boronic acid moiety.

Proteasome inhibition leads to:

1. Accumulation of pro-apoptotic proteins (e.g., Bax, p53, Noxa) and cyclin-dependent kinase inhibitors (e.g., p21, p27), triggering cell cycle arrest and apoptosis.
2. Stabilisation of IκB, preventing its degradation and thereby blocking NF-κB nuclear translocation — a key transcription factor for survival, inflammation, and drug resistance in myeloma cells.
3. Accumulation of misfolded proteins (particularly immunoglobulins in plasma cells), inducing endoplasmic reticulum stress and the unfolded protein response (UPR). Malignant plasma cells, which produce large quantities of immunoglobulins, are particularly vulnerable to proteotoxic stress, making them selectively sensitive to proteasome inhibition.
4. Inhibition of angiogenesis and cell adhesion to bone marrow stroma.

Malignant plasma cells are preferentially sensitive because of their high protein synthesis load; proteasome inhibition overwhelms their protein quality-control machinery, leading to terminal UPR and apoptosis.

Evidence base

APEX Trial (Relapsed Myeloma)

In the Phase III APEX trial, bortezomib significantly improved time to progression (6.2 vs 3.5 months) and 1-year survival (80% vs 66%) compared with dexamethasone in relapsed multiple myeloma (Richardson et al., NEJM, 2005).

VISTA Trial (Newly Diagnosed, Transplant-Ineligible)

Adding bortezomib to melphalan-prednisone (VMP) significantly improved complete response rate (30% vs 4%), progression-free survival, and overall survival in newly diagnosed patients ineligible for stem cell transplant (San Miguel et al., NEJM, 2008).

PINNACLE Trial (Mantle Cell Lymphoma)

In relapsed/refractory mantle cell lymphoma, bortezomib achieved a 33% overall response rate with a 6-month duration of response, leading to its approval for this indication (Fisher et al., JCO, 2006).

Subcutaneous Administration

The SC formulation was shown to be non-inferior to IV bortezomib for efficacy, with a significantly lower rate of grade ≥2 peripheral neuropathy (38% vs 53%) in the MMY-3021 trial (Moreau et al., Lancet Oncol, 2011), establishing SC as the preferred route.

Mechanism-Related Research

Ongoing research explores proteasome inhibition in solid tumours, autoimmune disease (e.g., antibody-mediated rejection, SLE), and as a tool for understanding ubiquitin-proteasome system biology.

Protocols

Multiple Myeloma — VRd (Standard Frontline)

• Bortezomib 1.3 mg/m² SC on Days 1, 4, 8, 11 of each 21-day cycle, with lenalidomide (Days 1–14) and dexamethasone.
• Typically 6–8 induction cycles.

VMP (Transplant-Ineligible)

• Bortezomib 1.3 mg/m² SC on Days 1, 4, 8, 11, 22, 25, 29, 32 of each 42-day cycle (4 cycles), then Days 1, 8, 22, 29 (5 cycles), with melphalan and prednisone.

Mantle Cell Lymphoma

• 1.3 mg/m² SC on Days 1, 4, 8, 11 of each 21-day cycle, up to 17 cycles.

Dose Modifications

• Grade ≥2 peripheral neuropathy: reduce to 1.0 mg/m², then 0.7 mg/m².
• Hepatic impairment (moderate): reduce to 0.7 mg/m².
• Thrombocytopenia <25,000/µL: hold dose.

All dosing reflects the licensed UK SmPC and NICE-approved protocols. This is a POM; administration occurs under specialist haematology/oncology supervision. This profile is for research and educational purposes only.

UK legal status

Bortezomib is a prescription-only medicine (POM) in the UK under the Human Medicines Regulations 2012. It is licensed for multiple myeloma (newly diagnosed and relapsed) and mantle cell lymphoma (relapsed). NICE recommends bortezomib for newly diagnosed myeloma in combination regimens (TA228, TA317) and for relapsed myeloma (TA129). The licensed product (Velcade) and generics hold UK marketing authorisations regulated by the MHRA. Supply without a valid prescription is unlawful. It is not classified as a controlled substance under the Misuse of Drugs Act 1971.

Vendor notes

As a licensed POM, bortezomib is supplied through hospital oncology pharmacies upon prescription. It is not available from research peptide vendors. Peptide Data does not list vendors for this compound.