Bortezomib in combination with other therapies for the treatment of multiple myeloma.

The ubiquitin proteasome pathway is the major mechanism used by eukaryotic cells for degradation of proteins. Bortezomib, a highly potent and specific inhibitor of the proteasome, has been demonstrated to have activity against multiple myeloma as a single agent in phase I and II clinical trials. Modulation of proteasome function with agents such as bortezomib may also have a significant role in combination chemotherapy, however, by impacting upon mechanisms that overcome chemoresistance and support chemosensitization. Proteasome inhibition seems to be able to overcome Bcl-2-mediated suppression of apoptosis, P-glycoprotein-mediated multidrug resistance, and inducible resistance through nuclear factor kappa B. Preclinical studies with bortezomib and other agents have provided evidence of sensitization to several classes of chemotherapeutics that are used against multiple myeloma. Preliminary reports from phase I trials using bortezomib in combination with some of these standard cytotoxics have not found any pharmacologic interactions, and toxicities were not significantly increased with these regimens. Moreover, they have shown promising results, with documented major responses in patients who have previously progressed on the standard cytotoxic alone, and also high overall response rates. These findings are consistent with the possibility that bortezomib can act clinically as a chemosensitizing agent, and strongly support further studies of these regimens.