Current advances in non-proteasome inhibitor-based approaches to the treatment of relapsed/refractory multiple myeloma.

In the past decade, immunomodulatory drugs have been approved by the US Food and Drug Administration for the treatment of multiple myeloma (MM)-and a number of emerging agents that target the cellular pathways or proteins involved in the pathophysiology of MM are currently in development. Lenalidomide (Revlimid) and pomalidomide induce apoptosis and sensitize MM cells while demonstrating superior efficacy and better tolerability than thalidomide (Thalomid). Several novel classes of drugs, including the histone deacetylase (HDAC) inhibitors, heat shock protein (HSP) inhibitors, and monoclonal antibodies have been shown to have activity in myeloma in early-stage clinical trials. HDAC inhibitors, including vorinostat (Zolinza), panobinostat, and romidepsin (Istodax) are thought to affect multiple pathways involved in MM and correct the deregulation of genes involved in apoptosis and cell cycle arrest, thus potentially sensitizing MM cells to apoptosis. HSP inhibitors (eg, tanespimycin) decrease MM proliferation and suppress the long-term replicative potential of MM cells; they may also sensitize MM cells to other anticancer agents. The humanized monoclonal antibody elotuzumab induces antibody-dependent cell cytotoxicity-mediated apoptosis. It is likely that in the near future the treatment armamentarium for MM will undergo significant expansion as some of these additional target pathways become validated.