Introduction: Vorinostat (VOR), an oral inhibitor of histone deacetylase (HDAC) class I and class II proteins, affects pathways regulating cell proliferation and apoptosis in a diverse array of tumor types. Phase 1/2 trials in multiple myeloma (MM) have indicated clinical activity of vorinostat, as both a single agent and in combination with bortezomib (BTZ) and immunomodulatory drugs (IMiDs).
Materials and methods: The present study (MK-0683 PN095) was an open-label, single-arm phase 2b trial of VOR plus BTZ in BTZ-refractory patients (defined as < 25% response on therapy, or progression during or < 60 days after completion of therapy) and patients considered to be refractory, intolerant, or ineligible for IMiD-based therapy regimens. Eligible patients were aged ≥ 18 years, had measurable secretory MM, had received ≥ 2 prior anti-myeloma regimens, and relapsed or progressed following prior systemic therapy. Patients received 21-day cycles of BTZ (1.3 mg/m2 intravenously [IV]; days 1, 4, 8, and 11) plus oral VOR 400 mg/d on days 1 to 14. If patient had no change as the best response after 4 cycles of treatment or progressive disease after 2 cycles of treatment, oral dexamethasone 20 mg on the day of and day after each dose of BTZ could be added to the treatment regimen. Patients were treated until disease progression, unacceptable toxicities, or withdrawal from the study. The primary endpoint was overall response rate (ORR; ≥ partial response). Secondary and exploratory endpoints included clinical benefit response (ORR + minimal response), overall survival (OS), time to progression (TTP), progression-free survival (PFS), and safety. Responses and progression were determined according to the International Myeloma Working Group criteria and the European Bone and Marrow Transplantation Group criteria. All efficacy data will be confirmed by an Independent Adjudication Committee.
Results: Between January 2009 and October 2010, 143 patients were enrolled from 41 centers in 12 countries across Asia-Pacific, Europe, and North America. Median duration of MM for the entire study population was 4.6 years, including 31% whose disease had progressed on or within 60 days of last therapy and 66% whose disease had achieved < 25% response to the regimen immediately preceding study entry. The study population was heavily pretreated, having received a median of 4 prior lines of therapy (range 2–17, ≥ 4 prior regimens: 69%). Prior anti-myeloma agents included 100% BTZ (median 2 prior regimens containing BTZ), 100% IMiDs (thalidomide [85%], lenalidomide [71%], or pomalidomide [4%]), and 74% stem cell transplant. As of July 2011, 142 of the enrolled patients received study medication, with a median exposure of 4 cycles (mean 6.2 cycles; range 1–26 cycles). The most common treatment-emergent adverse events regardless of relationship to study drug were predominantly hematologic and gastrointestinal disorders. Of interest, peripheral neuropathy was infrequent and grade ≥ 3 PN occurred in 2 patients (1.6%). The final efficacy evaluation of the IAC will occur in September 2011.
Conclusions: Final data for all primary and secondary endpoints, including response assessment and time-to-event data for PFS/TTP, OS, and duration of response will be available at the annual ASH meeting.