Phase I/Ib Trial of the Efficacy and Safety of Combination Therapy with Lenalidomide/Bortezomib/Dexamethasone (RVD) and Panobinostat in Transplant-Eligible Patients with Newly Diagnosed Multiple Myeloma

Background: Induction therapy prior to consolidation with autologous stem cell transplantation (ASCT) continues to improve with the use of proteasome inhibitors and imids and combination regimens such as RVD. Bortezomib-based induction therapy has improved overall response rates (ORR) prior to transplant, which has translated to improvements in ORR and progression free survival post ASCT. However, complete remission (CR) rates with RVD remain low (10-15%) after 4 cycles of induction therapy. Panobinostat, a histone deacetylase inhibitor, in combination with bortezomib/dexamethasone, has demonstrated a significant improvement in depth of response and progression free survival in patients (pts) with relapsed myeloma as seen in PANORMA I. Preclinical data demonstrate synergy between the combination of bortezomib and panobinostat. We undertook a phase I/Ib trial in pts with newly diagnosed myeloma (NDMM) of RVD + Panobinostat to establish the safety of the combination and goal of improving the depth of response with induction therapy prior to ASCT.

Methods: The primary objective was to determine the maximum tolerated dose (MTD) and safety/tolerability of RVD + panobinostat in NDMM. Secondary objectives were to determine efficacy as measured by the CR/nCR rate after 4 cycles, ORR, tolerability/toxicity, and progression free survival. Pts had to have NDMM with indication for therapy, candidates for ASCT with and had adequate organ function. Panobinostat was administered on days 1, 3, 5, 8, 10, 12; bortezomib 1.3 mg/m² was administered subcutaneously on days 1, 4, 8, 11; lenalidomide 25 mg on days 1-14; dexamethasone 20 mg on days 1, 2, 4, 5, 8, 9, 11, and 12 on a 21 day cycle. Dose-escalation of panobinostat used a standard 3+3 schema with dose-limiting toxicities (DLTs) assessed during cycle 1. Three dose levels were studied with Panobinostat escalated from 10 to 20 mg. Adverse events (AEs) were graded by NCI-CTCAE v4, while responses were assessed by the modified International Uniform Response Criteria.

Results: 22 pts were enrolled; 12 pts in the completed phase 1 dose escalation portion of the study and 10/20 in the ongoing dose expansion. The median age was 61 (range 53-79); ISS stage I 12; stage II 7/20; stage III in 3/20 pts.

No DLTs were observed in 3 pts dosed in cohort 1, with Panobinostat at 10 mg. In cohort 2, panobinostat was dosed at 15 mg, 2/6 pts encountered a DLT. One patient experienced Grade 4 (G4) thrombocytopenia, and the second patient had G3 diarrhea without supportive measures, for <12 hours and resolved with supportive measures. In cohort 1, 3 additional patients were enrolled and no DLTs were encountered in the remaining 3 pts. The final recommended dose was Panobinostat 10 mg in combination with RVD in NDMM.

Treatment emergent SAEs related to therapy observed in 5 pts with 2 incidences of G3 diarrhea; 2 pts with atrial fibrillation; and other events included G4 thrombocytopenia; G3 bacteremia, G3 cellulitis, G3 myocardial infarction (MI), G3 pulmonary emboli; G3 pneumonia.

Hematologic adverse events G3/4 included anemia 3/22; neutropenia 4/22; thrombocytopenia 7/22. G3/4 nonhematologic toxicities included ALT elevation (n=2); AST elevation (n=1); constipation (n=2); diarrhea (n=2); fatigue/muscle weakness (n=2); MI (n=1); pneumonia (n=3).

Among 18/22 pts who have completed 4 cycles of therapy and are evaluable for efficacy, the ORR (≥PR) was 100%: including nCR/CR in 5/18 (28%), VGPR in 5/18 (28%), PR in 8/18 (44%).

Conclusions: MTD has been established at level 1, with panobinostat 10 mg and full dose RVD in NDMM. The DLTs were diarrhea (irrespective of supportive care) and thrombocytopenia. This is the first experience with panobinostat and subcutaneous bortezomib and first experience in combination with RVD. The combination is well tolerated with limited toxicity and side effects can be managed with supportive care. The preliminary activity after 4 cycles of therapy demonstrated a high ORR of 100% and a promising depth of response with a nCR/CR of 27%. Enrollment in a dose expansion cohort is near completion and full data will be presented at ASH.