Introduction: Vorinostat (VOR), an oral inhibitor of histone deacetylase class I and class II proteins, regulates genes and proteins involved in tumor growth and survival. The synergistic effects of VOR and bortezomib (BTZ) have been shown in preclinical studies and were confirmed in independent phase 1 trials in patients with relapsed/refractory multiple myeloma (MM), producing objective response rates (ORRs) of up to 42% and overall clinical benefit of up to 90%.
Materials and methods: Eligible patients were aged ≥ 18 years, had measurable secretory MM, had received 1 to 3 prior systemic anti-myeloma regimens, and had an Eastern Cooperative Oncology Group status ≤ 2. Previous exposure to BTZ and the presence of extracellular plasmacytoma were allowed per protocol, but patients with prior resistance to BTZ were excluded. Patients were randomized 1:1 to receive 21-day cycles of BTZ (1.3 mg/m2 intravenously; days 1, 4, 8, and 11) in combination with oral VOR 400 mg/d, or matching placebo, on days 1 to 14. Additional use of corticosteroids for the treatment of MM was not allowed during the trial. Patients were treated until disease progression, unacceptable toxicities, or withdrawal from the study. The primary endpoint for this trial was progression-free survival (PFS; occurrence of 412 PFS events). Secondary and exploratory endpoints included ORR (≥ partial response), clinical benefit response (ORR + minimal response), overall survival, time to progression, patient-reported outcomes questionnaires (QLQ-C30, QLQ-MY20), and safety/tolerability of this novel drug combination. Responses and progression were determined according to the European Bone and Marrow Transplantation Group criteria and will be confirmed by an Independent Adjudication Committee.
Results: Between January 2009 and January 2011, 637 patients were enrolled from 174 centers in 33 countries across the globe making this trial one of the largest studies conducted in patients with relapsed/refractory myeloma. Median age of the study population was 62 years (range, 29–86 years). Of the enrolled patients, 59% were male and 56% were Caucasian. Patients had received a median of 2 prior regimens (range, 1–3). Prior anti-myeloma agents included BTZ (24%), thalidomide (56%), lenalidomide (13%), melphalan (56%), and stem cell transplantation (35%). As of July 2011, 635 patients had received study medication, with a median exposure of 7 cycles (mean: 7.6 cycles; range 1–30 cycles). Reported median exposure to BTZ monotherapy in previous phase 3 trials was approximately 5 cycles.
Conclusions: The study passed the protocol-specified futility analyses by the independent data monitoring committee in November 2010. Database lock is anticipated in November 2011, and top-line data on primary and secondary endpoints will be available at the meeting.