Pre-clinical evaluation of bortezomib, doxorubicin, dexamethasone, and lenalidomide in multiple myeloma (MM)

19513 Background: Treatment with bortezomib combinations have shown to improve efficacy in MM. In clinical studies, among the most active are 3-drug combinations of bortezomib, liposomal doxorubicin and dexamethasone (VDD), with 93% patients achieving at least 50% disease reduction (PR), and lenalidomide, bortezomib, Dexamethasone (RVD) with 89% PR rate. However, > 90% reduction of the disease (VGPR) associated with longer survival was seen in only 63% and 35% patients, respectively. In this study, we evaluated whether combining 4- drugs (VDDR) can further improve elimination of myeloma cells. In addition to cytotoxicity, we investigated the effects of bortezomib combinations on Noxa and c-myc as markers of activity of bortezomib combinations. Methods: MM cell lines MM1.S, NCI H929 and RPMI 8226 were treated with combinations of bortezomib (Vel), doxorubicin (Dox), dexamethasone (Dex) and lenalidomide (Rev) and cytotoxicity was measured by MTT assays. Noxa and c-myc induction, and caspase-3,-8 and -9 activation were evaluated by immunoblotting after treatment with drugs in MM cells and normal PBMCs. Results: VDDR showed 2–4 fold higher cytotoxicity than Vel/Dox, Vel/Dex and Vel/Rev, and comparable toxicity to VDD in NCI H929 cells. In cells sensitive to Rev (MM1.S), VDDR showed higher cytotoxicity than VDD. Vel selectively increased Noxa levels in MM cell lines but not in normal PBMCs. In studies to date, the combination of VDD resulted in higher levels and faster kinetics of Noxa induction than Vel alone and leads to more potent caspase activation observed within 16hrs of treatment. Neither Dox nor Dex had any effect on Noxa levels. Noxa induction correlated with higher c-myc levels upon Vel treatment in RPMI 8226 cells. Knocking down c-myc with shRNA resulted in partial loss of Noxa suggesting that c-myc is required for Noxa induction. Conclusions: VDDR shows higher efficacy in preclinical models providing a rationale for a phase I/II clinical trial in newly diagnosed MM to be activated in the MMRC. Based on the preliminary results, tumor specific Noxa induction can be used as a biomarker for pre-clinical evaluation of the efficacy of Velcade-based regimens in myeloma. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Celgene, Millennium Celgene, Millennium