A Phase 1/2 Trial of Pomalidomide, Dexamethasone and Pegylated Liposomal Doxorubicin for Patients with Relapsed/Refractory Multiple Myeloma

Background

Immunomodulatory drugs (IMiD), such as thalidomide and lenalidomide (LEN) and its newest derivative pomalidomide (POM), have shown great promise for the treatment of multiple myeloma (MM) patients (pts). POM has in vitro anti-MM potency and has shown efficacy for the treatment of relapsed/refractory (RR) MM pts. POM with dexamethasone (DEX) induces responses even for MM pts who are refractory to bortezomib (BORT) and LEN (Richardson et al, 2012). Pegylated liposomal doxorubicin (PLD) with BORT is FDA-approved for the treatment of MM pts who have received one prior therapy not containing BORT. The combination of PLD and LEN or thalidomide has shown efficacy for both RR and frontline MM pts (Offidani et al, 2006; 2007). We have also demonstrated that both the efficacy and tolerability of LEN in combination with DEX, PLD and BORT (DVD-R) may be improved by changing the doses and schedules of these drugs (Berenson et al, 2012). Based on these results, we hypothesized that the combination of POM, DEX and PLD would be effective for the treatment of RRMM pts. Thus, we conducted the first study investigating the safety and efficacy of POM in combination with intravenous (IV) DEX and PLD as a phase 1/2 trial using a modified dose, schedule and longer 28-day cycles for pts with RRMM.

Methods

The phase 1 portion enrolled MM pts w/ progressive disease whereas those enrolled in phase 2 also had to be refractory to LEN (single-agent or in combination), as demonstrated by progressive disease while receiving their last LEN-containing regimen or relapsed within 8 weeks of their last dose of this IMiD. Pts who have previously received POM treatment were ineligible. In the phase 1 portion, POM was administered at 2, 3 or 4 mg daily in three cohorts on days 1-21 of a 28-day cycle and DEX (40 mg) and PLD (5 mg/m²) were fixed and given intravenously on days 1, 4, 8, and 11.

Results

As of June 20^th, 2014, 48 pts were enrolled in the trial and a total of 47 pts had received study drug. Pts had received a median of 4 prior treatments (range 1-18), with a median of 2 prior IMiD-containing regimens (range, 0-8). Fifty-three percent of the pts had received a prior PLD-containing regimen and 21% had received a prior IMiD and PLD combination treatment. Among all enrolled pts, 40 pts discontinued treatment and seven remain active. Pts completed a median of 3 cycles (range: 1-8), with a median follow-up time of 5.4 months (range: 0-22).

During the phase 1 portion of the trial, the maximum tolerated dose (MTD) of POM was established at 4 mg. Enrollment of pts into the phase 2 portion of the trial began at the MTD. However, neutropenia ≥ grade 3 was observed at this dose in 10/17 (58.8%) phase 2 pts; and, as a result, the protocol was amended so that the MTD was lowered to 3 mg for all pts subsequently enrolled.

Among the 36 pts enrolled in phase 2, 78% percent were refractory to LEN and steroids with or without other agents and 47% had previously received PLD. A median of 2 cycles (range, 1 to 8) were administered among the pts enrolled in phase 2. Thirty-five pts were evaluable for response as one pt was active but had not yet had any post-baseline disease assessments. Among all pts enrolled in phase 2, the overall response rate (ORR) and clinical benefit rate (CBR) were 29% and 49%, respectively, with 6 pts (17%) showing stable disease and 12 pts (34%) demonstrating progressive disease. For all pts enrolled in phase 2, the median follow-up time was 4.7 months (range 0-12) and the median PFS was 5.3 months.

ORR and CBR for pts in the phase 2 were higher among pts receiving POM at 3 mg (32% and 58%, respectively) than among pts receiving POM at 4 mg (25% and 37%, respectively). Pts receiving the 4 mg dose of POM experienced more toxicities resulting in discontinuations, which likely explains the lower ORR and CBR observed among pts receiving this POM dose.

Common ≥ grade 3 adverse events observed throughout the trial were neutropenia (21 pts; 44.7%), lymphopenia (10 pts; 21.3%), and hyponatremia (4 pts; 8.5%). One pt died of grade 5 sepsis.

Conclusions

This phase 1/2 trial is the first evaluating POM with PLD and DEX and demonstrates that the combination of POM at 3 mg, PLD and DEX using a modified 28-day cycle schedule is safe and effective for the treatment of MM pts refractory to LEN.