Bortezomib

Bortezomib is an antineoplastic medicine belonging to the proteasome inhibitor class and is used primarily in the treatment of multiple myeloma and mantle cell lymphoma. It is a reversible inhibitor of the 26S proteasome, a cellular protein-degradation system responsible for breaking down ubiquitinated proteins. By interfering with proteasome function, bortezomib causes accumulation of regulatory proteins and disrupts several signaling pathways involved in cell survival, proliferation, and apoptosis. This activity can make malignant plasma cells and other susceptible cancer cells less able to survive. Bortezomib is administered by injection, either intravenously or subcutaneously; it must not be administered by any other route. The recommended starting dose in current U.S. prescribing information is 1.3 mg/m², although the schedule and dose may be modified according to the disease setting, treatment combination, response, and toxicity. Bortezomib is clinically important because it was the first proteasome inhibitor to reach clinical use and established proteasome inhibition as an effective therapeutic approach in hematologic malignancies.

Bortezomib was developed from research into the ubiquitin-proteasome system and was initially known as PS-341. Early clinical development included phase I and phase II studies in hematologic malignancies, particularly multiple myeloma, followed by pivotal studies supporting regulatory approval. The U.S. FDA granted accelerated approval for multiple myeloma on May 13, 2003, for patients who had received at least two prior therapies and had progressive disease; subsequent approvals expanded its use, including multiple myeloma after at least one prior therapy in 2005 and first-line multiple myeloma therapy in 2008. FDA approval for mantle cell lymphoma was granted in 2006 and later expanded. In the European Union, Velcade containing bortezomib received marketing authorisation on April 26, 2004, with subsequent regulatory updates covering multiple myeloma and mantle cell lymphoma. Key clinical development programs included phase II studies in relapsed or refractory multiple myeloma and later randomized studies that supported broader use in earlier treatment settings.

Bortezomib is approved for the treatment of adult patients with multiple myeloma and mantle cell lymphoma. In multiple myeloma, it may be used as part of combination treatment or, in appropriate settings, as a single agent, depending on disease status and the treatment regimen. Approved combinations include regimens incorporating agents such as melphalan and prednisone, dexamethasone, or other established multiple-myeloma therapies. In mantle cell lymphoma, bortezomib may be used in combination regimens, including treatment incorporating rituximab, cyclophosphamide, doxorubicin, and prednisone in previously untreated patients who are not suitable for hematopoietic stem-cell transplantation. Specific approved combinations and treatment settings can differ between regulatory jurisdictions and should be confirmed against the applicable prescribing information.

Bortezomib is administered only by intravenous or subcutaneous injection. The standard starting dose is 1.3 mg/m², but the treatment schedule varies according to the indication and combination regimen. For some multiple myeloma and mantle cell lymphoma regimens, administration occurs twice weekly during defined treatment weeks followed by a rest period; less dose-intensive or once-weekly schedules may be used in selected circumstances, including extended treatment or when toxicity requires modification. Previously untreated multiple myeloma may be treated with bortezomib in combination with melphalan and prednisone over defined treatment cycles, while selected mantle cell lymphoma regimens use bortezomib with other chemotherapy and immunotherapy. At least 72 hours should generally separate consecutive doses in the labeled regimens. Dose interruption or reduction may be required for peripheral neuropathy, hematologic toxicity, hepatic impairment, or other clinically significant adverse effects. Treatment duration depends on the disease, regimen, response, and tolerability.

Common adverse effects associated with bortezomib include nausea, diarrhea, constipation, vomiting, fatigue, reduced appetite, fever, rash, anemia, thrombocytopenia, neutropenia, leukopenia, lymphopenia, neuralgia, and peripheral neuropathy. Peripheral sensory neuropathy can cause numbness, tingling, burning, or pain and is an important toxicity because it may require dose reduction, a less intensive schedule, treatment interruption, or discontinuation. Gastrointestinal symptoms and blood-count abnormalities may also require supportive treatment or temporary treatment modification. The frequency and severity of adverse effects vary according to the treatment regimen, disease, previous therapies, and individual patient factors.

Important serious risks include severe peripheral neuropathy, hypotension, cardiac toxicity including worsening or development of heart failure, pulmonary toxicity, posterior reversible encephalopathy syndrome, significant gastrointestinal toxicity, thrombocytopenia and neutropenia, tumor lysis syndrome, hepatic toxicity, and thrombotic microangiopathy. Patients with pre-existing severe neuropathy require careful risk-benefit assessment. New neurological, respiratory, cardiac, bleeding, or severe gastrointestinal symptoms should be assessed promptly. Liver abnormalities may require interruption of therapy, while suspected thrombotic microangiopathy requires discontinuation and urgent evaluation. Bortezomib can also cause embryo-fetal toxicity, so reproductive-risk counselling and appropriate contraception are important during treatment. Intrathecal administration is contraindicated and can be fatal.

Before treatment, clinicians generally assess blood counts, renal and hepatic function, hydration status, neurological symptoms, infection risk, and relevant cardiac history according to the treatment regimen and patient characteristics. Patients with diabetes may require closer glucose monitoring because bortezomib-based treatment can affect glycemic control, particularly when combined with corticosteroids. Patients with hepatic impairment may require a lower starting dose. Strong CYP3A4 inhibitors can increase bortezomib exposure and warrant close monitoring, while strong CYP3A4 inducers should generally be avoided. Unlike many orally administered small-molecule medicines, bortezomib has a relatively limited classic interaction profile, but concomitant medicines can still affect toxicity and treatment safety. Vaccination and infection-prevention decisions should be individualized, particularly in patients receiving multi-agent immunosuppressive therapy.

Confirm the intended route, concentration, dose, body-surface-area calculation, and treatment schedule before every administration because intravenous and subcutaneous preparations have different final concentrations. Assess baseline and ongoing complete blood counts, renal and hepatic parameters, neurological symptoms, blood pressure, hydration, and clinically relevant cardiac or pulmonary risk. Ask specifically about numbness, tingling, burning pain, weakness, dizziness, bowel symptoms, and signs of infection rather than relying only on spontaneous reporting. Subcutaneous administration may be considered for patients with pre-existing or higher risk of peripheral neuropathy. Dose interruption or reduction should follow the applicable prescribing information when clinically significant toxicity develops. Pharmacists and nursing teams should also verify that bortezomib is never administered intrathecally and that preparation, handling, storage, and administration follow the product-specific instructions.