Background: Patients with refractory multiple myeloma (MM) have limited treatment options and an extremely poor prognosis. A recent study of patients who were refractory to bortezomib and were relapsed following, refractory to or ineligible to receive an immunomodulatory drug (IMiD, thalidomide or lenalidomide) demonstrated a median event-free survival of only 5 months (Kumar S et al, Leukemia, 2011). Panobinostat is an oral pan-deacetylase inhibitor (pan-DACi) that increases acetylation of proteins involved in multiple oncogenic pathways. Preclinical studies have demonstrated synergistic anti-myeloma activity of the combination of panobinostat and bortezomib through dual inhibition of the aggresome and proteasome pathways.In a phase I study (B2207) of patients with relapsed or relapsed/refractory MM treated with panobinostat + bortezomib, clinical responses (≥ minimal response [MR]) were observed in 65% of patients, including in patients with bortezomib-refractory disease.PANORAMA 2 seeks to expand upon these preliminary results and seeks to determine whether panobinostat can sensitize resistant patients to a bortezomib-containing therapeutic regimen.
Methods: PANORAMA 2 is a single arm, phase II study of panobinostat + bortezomib + dexamethasone in patients with bortezomib-refractory MM. Patients with relapsed and bortezomib-refractory MM (≥ 2 prior lines of therapy including an IMiD and who had progressed on or within 60 days of the last bortezomib-based therapy) are treated in 2 phases. Treatment phase 1 consists of 8 three-week cycles of oral panobinostat (20 mg days 1, 3, 5, 8, 10, 12) + intravenous bortezomib (1.3 mg/m2 days 1, 4, 8, 11) + oral dexamethasone (20 mg on day of and after bortezomib). Patients demonstrating clinical benefit (≥ stable disease) can proceed to treatment phase 2, consisting of 4 six-week cycles of panobinostat (20 mg TIW 2 weeks on 1 week off, and repeat) + bortezomib (1.3 mg/m2 days 1, 8, 22, 29) + dexamethasone (20 mg on day of and after bortezomib). The primary endpoint is overall response (≥ partial response [PR]), as defined by the European Group of Blood and Marrow Transplantation 1998 criteria, in the first 8 cycles of treatment phase 1. A Simon 2-stage design is used to test the primary endpoint where ≥ 4 responses (≥ PR) in 24 patients are needed in stage 1 in order to proceed to stage 2, where ≥ 9 responses in all patients (N = 47) are required to reject the null hypothesis (overall response rate ≤ 10%).
Results: A sufficient number of responses ≥ PR were observed in stage 1 to allow for enrollment to continue to stage 2. As of 15 July 2011, 53 patients with bortezomib-refractory MM were enrolled. Safety and demographic data were available for 48 patients. The median age was 61 (41-88) years. Patients were heavily pretreated, with a median of 4 (2-14) prior regimens, and most patients (69%) received prior autologous stem cell transplant. Efficacy data were available for 44 patients. At the time of this analysis, 9 patients achieved ≥ PR (2 near CR [nCR] and 7 PR) as best overall response, and an additional 7 patients achieved an MR. Responders exhibited a long duration on therapy, and, to date, 8 patients have proceeded to treatment phase 2. The 2 patients with nCR have received ≥ 10 cycles of treatment (duration of therapy 190 and 253 days). Four patients who achieved PR have received ≥ 9 cycles (duration of therapy 155-225 days). Updated response data will be presented.
Common adverse events (AEs) of any grade included, fatigue (52%), diarrhea (41%), thrombocytopenia (38%), nausea (38%), and anemia (21%). Gastrointestinal AEs were generally mild, with a relatively low incidence of grade 3/4 events. Grade 3/4 AEs were generally hematologic in nature, with grade 3/4 thrombocytopenia, anemia, and neutropenia reported in 38%, 12%, and 10% of patients, respectively. Other common nonhematologic grade 3/4 AEs included fatigue (10%) and pneumonia (10%). Of note, to date, a relatively low rate of peripheral neuropathy (17%) has been observed. No grade 3/4 peripheral neuropathy has been observed.
Conclusions: The combination of panobinostat and bortezomib is a promising treatment for patients with bortezomib-refractory MM. These data, along with forthcoming data from the phase III study of panobinostat/placebo + bortezomib + dexamethasone in patients with relapsed MM (PANORAMA 1), will further define the potential role of panobinostat in the treatment of patients with MM.