A Phase II, Single-Center, Open-Label Study of Oral Panobinostat in Combination with Lenalidomide and Weekly Dexamethasone in Patients with Multiple Myeloma

Background: Treatment options for patients with multiple myeloma (MM) refractory (ref) to immunomodulatory drugs and proteasome inhibitors are urgently needed. A promising strategy is the use of epigenetic agents such as the pan histone deacetylase inhibitor (HDACi) panobinostat (pan) to modulate the acetylation of histones and proteins involved in oncogenesis. Pre-clinical studies with pan demonstrate synergy against MM cells when combined with dexamethasone (dex), lenalidomide (len), and bortezomib (btz) (Ocio EM et al. Haematologica 2010). Interim data from the phase 3 PANORMA 1 study of 768 patients randomized to receive IV btz and dex with either pan or placebo revealed a 3.9 month increase in PFS with pan along with an increase in CR rates. However, this was accompanied by 25% grade 3/ 4 diarrhea versus 8% in the placebo arm.

The safety and preliminary efficacy of the pan-len-dex triplet regimen was assessed in a phase 1b study of relapsed (rel) or rel/ref MM patients (Mateos et al, ASCO 2010) but was complicated by high dose dex toxicities. The maximum tolerated dose of pan and dex in that study are the doses selected for this phase 2 study. However we investigated a modified schedule (table 1) of this triplet regimen. Here, pan is given thrice weekly only every other week (instead of weekly) and dex is given weekly (instead of three 4 day pulses).

Patients and Methods: Inclusion criteria were patients with rel or rel/ref MM, measurable disease, adequate performance status, organ function, and hematologic parameters. Patients previously treated with a HDACI or currently receiving medications with a risk of prolonging the QTc interval were excluded.

The primary objective was to evaluate the best overall response rate (ORR). Secondary objectives were to evaluate safety, response duration, and overall and progression-free survival. Each drug was administered at the doses and schedule shown in Table 1.

Results: Overall, 13 evaluable patients with progressive disease (PD) at screening have been enrolled, including 9 len-refractory (2 also pomalidomide refractory) and 4 len sensitive with a median of 4 and 3 lines of prior therapy respectively (range 1–10). High-risk molecular findings were present in 9 patients, including 6 with gain of 1q21 by FISH and 3 with del p53. Three of the patients with gain of 1q21 also had t (4;14).

Of the 13 patients, there have been 3 very good partial responses (VGPR), 2 partial responses (PR), 3 minimal responses (MR), 4 stable diseases (SD), and 1 PD, for an ORR of 38% and clinical benefit rate (CBR i.e. MR or greater) of 61 %. With a median follow up of 4.5 months the median progression free survival and duration of response have not been reached. Of the 9 patients who were len refractory, there were 2 VGPR, 2 MRs, 4 SD, and 1 PD for a 22% ORR and 44% CBR. Notably, 3 len refractory patients remain on treatment for 11, 16, and 16 months including 2 with gain of 1q21 that have attained VGPRs.

Grade 3/4 toxicities (regardless of drug attribution) were primarily hematologic, with neutropenia, thrombocytopenia, lymphopenia, and anemia noted in 7, 4, 1, and 1 patients respectively. Grade 3/4 nonhematologic AEs included infections in 4 (with 1 one occurring while neutropenic), and 1 patient with each of the following: pulmonary embolus, neck pain, QTc prolongation, and weight loss 1. Dose modifications for neutropenia were required in 4 patients for len and in 2 patients for pan. 1 additional patient required pan dose reduction for asymptomatic T wave inversions. Nausea was noted in 2 patients and diarrhea in 3 with 2 additional patients experiencing both – however these were transient, Grade 1/2, and did not require dose modifications. Importantly, no patients discontinued therapy for toxicity.

Conclusions: In rel/ref MM patients, pan in combination with len and dex demonstrates durable responses, even in len-refractory patients with high-risk molecular findings, indicating the essential role of pan in attaining a response. These results suggest that pan modulates expression of genes to restore sensitivity to len, In notable contrast to the PANORMA 1 results, this completely oral regimen is well tolerated with no Grade 3/4 GI toxicities and primarily expected hematologic toxicities. Updated results, including correlative studies, will be presented at the annual meeting.