Drug Groups

approved; investigational

Description

Bortezomib (originally PS-341 and marketed as Velcade by Millennium Pharmaceuticals) is the first therapeutic proteasome inhibitor to be tested in humans. It is approved in the U.S. for treating relapsed multiple myeloma and mantle cell lymphoma. In multiple myeloma, complete clinical responses have been obtained in patients with otherwise refractory or rapidly advancing disease.

Indication

For treatment of multiple myeloma in patients who have not been successfully treated with at least two previous therapies.

Pharmacology

Bortezomib is a drug that inhibits the mammalian 26S proteasome. The ubiquitin-proteasome pathway plays an essential role in regulating the intracellular concentration of specific proteins, thereby maintaining homeostasis within cells. Inhibition of the 26S proteasome prevents this targeted proteolysis, which can affect multiple signaling cascades within the cell. This disruption of normal homeostatic mechanisms can lead to cell death. Experiments have demonstrated that bortezomib is cytotoxic to a variety of cancer cell types in vitro. Bortezomib causes a delay in tumor growth in vivo in nonclinical tumor models, including multiple myeloma. Tumor cells, that is, rapidly dividing cells, appear to be more sensitive to proteasome inhibition.

Toxicity

Cardiovascular safety pharmacology studies in monkeys show that lethal IV doses are associated with decreases in blood pressure, increases in heart rate, increases in contractility, and ultimately terminal hypotension. In monkeys, doses of 3.0 mg/m² and greater (approximately twice the recommended clinical dose) resulted in progressive hypotension starting at 1 hour and progressing to death by 12 to 14 hours following drug administration.

Affected Organisms

Biotransformation

In vitro studies with human liver microsomes and human cDNA-expressed cytochrome P450 isozymes indicate that bortezomib is primarily oxidatively metabolized via cytochrome P450 enzymes 3A4, 2C19, and 1A2, while bortezomib metabolism by CYP 2D6 and 2C9 enzymes is minor. The major metabolic pathway is deboronation to form 2 deboronated metabolites that subsequently undergo hydroxylation to several metabolites which are inactive as 26S proteasome inhibitors.

Half Life

The mean elimination half-life of bortezomib after first dose ranged from 9 to 15 hours at doses ranging from 1.45 to 2.00 mg/m2 in patients with advanced malignancies.

Protein Binding

83% over the concentration range of 100-1000 ng/ml.

Elimination

The pathways of elimination of bortezomib have not been characterized in humans.

Clearance

* 102 L/h [patients with multiple myeloma following the first dose for doses of 1 mg/m2]
* 112 L/h [patients with multiple myeloma following the first dose for doses of 1.3 mg/m2]
* 15 - 32 L/h [patients with multiple myeloma following subsequent doses for doses of 1 and 1.3 mg/m2]

References

External Links