Study of vorinostat in combination with bortezomib in patients with relapsed or refractory multiple myeloma after at least 2 prior treatment regimens.

Histone deacetylases (HDAC) facilitate gene transcription by modulating the uncoiling of chromatin. HDAC function is dysregulated in hematologic and solid malignancies, and this dysregulation may result in over-expression of oncogenes. Thus, inhibition of HDACs may result in anti-cancer effects. HDAC inhibitors, like vorinostat, represent a new class of antitumor agents that have the ability to induce antiproliferative effects including cyto-differentiation, cell cycle growth arrest or apoptosis in various cancer cell lines. Several studies have investigated the in vitro antimyeloma activity of vorinostat in combination with bortezomib and have demonstrated that vorinostat may act synergistically with bortezomib to modulate tumor cell growth. Mitsiades et al have shown that vorinostat enhances the sensitivity of bortezomib. Pei et al found that exposure of human multiple myeloma cell lines & patient-derived multiple myeloma cells to bortezomib and vorinostat resulted in synergistic interactions as a result of: (1) Interruption of NF-kB & related signaling pathways (JNK, XIAP, Mcl-1, etc.) (2) Inhibition of Hsp90 (3) Induction of ER stress signal and (4) acetylation of Dynein/ disruption of aggresome function/formation, salvage for ubiquinated proteins. In addition a marked increase in mitochondrial injury, caspase activation, and apoptosis was also observed.

Bortezomib is indicated for the treatment of patients with multiple myeloma. Two Phase I dose-ranging studies of a regimen combining vorinostat and bortezomib among patients with relapsed as well as end-stage, refractory multiple myeloma have been conducted. These studies enrolled a total of 57 patients. In these studies, administration of vorinostat with standard doses of bortezomib resulted in responses in 20/45 (44%) evaluable patients (Weber et al 2007, Badros et al 2007). The purpose of the present study is to definitively evaluate the clinical activity of vorinostat in combination with bortezomib in patients with multiple myeloma