Phase 1, Multicenter, Open-Label, Combination Study (NPI-0052-107; NCT02103335) of Pomalidomide (POM), Marizomib (MRZ, NPI-0052), and Low-Dose Dexamethasone (LD-DEX) in Patients with Relapsed and Refractory Multiple Myeloma

Introduction: MRZ is a novel, irreversible, proteasome inhibitor (PI) under clinical development for the treatment of relapsed and refractory multiple myeloma (RRMM).  MRZ potently inhibits the 3 proteolytic activities of the 20S proteasome with specificity and activity distinct from that of bortezomib (BZ) and carfilzomib (CFZ).  The combination of MRZ and POM has demonstrated promising synergy in in vitro and in vivo models of MM.

Methods: As of July 22, 2015, 22 of 36 planned patients (pts) were enrolled with 14 pts in the 3+3 dose-escalation stage and 8 pts into the Recommended Phase 2 Dose (RP2D) stage.  All pts received ≥2 prior therapies that must have included both lenalidomide (LEN) and BZ, and have been refractory to their last therapy.  Intravenous MRZ (0.3 to 0.5 mg/m²) was administered over 120 minutes on Days (D) 1, 4, 8, and 11; POM (3 or 4 mg) once daily on D1 through 21; and Lo-DEX (5 or 10 mg) once daily on D1, 2, 4, 5, 8, 9, 11, 12, 15, 16, 22, and 23 of every 28-D cycle.  Safety, pharmacokinetics (PK), cytogenetics, proteasome inhibition, and clinical response were assessed.

Results: Pts were 68% male, median (range) age 62 yrs (31 – 76), and with a median of 5 (2 - 15) prior lines of therapy.  All pts received prior BZ and LEN; 41% and 55% had also received prior CFZ and thalidomide (THAL), respectively.  There were no DLTs during dose-escalation and the most common (>10% incidence) adverse events (AEs) related to any study treatment in the 22  pts included fatigue (41%), neutropenia (41%), anemia (27%), thrombocytopenia (23%), nausea (18%), diarrhea, dyspnea, insomnia, edema peripheral, and white blood cell count decreased (14%).  The grade 3 AEs related to any study treatment in more than one pt included neutropenia (27%) and anemia (9%), pneumonia (9%), and thrombocytopenia (9%).  The only grade 4 AE related to any study treatment was neutropenia in one pt.  Tumor lysis syndrome (grade 2) related to study treatment was observed in 1 pt; 2 pts had grade 1 peripheral neuropathy (1 considered related to POM alone and 1 related to possibly MRZ and POM); 2 pts came off study and subsequently died from progressive disease (61 and 102 days after last dose); and 1 pt died suddenly during Cycle 1 due to cardiopulmonary arrest, considered possibly related to POM.  Since no DLTs were observed the maximum tolerated dose was not exceeded, the highest dose cohort studied, MRZ 0.5 mg/m², POM 4 mg, and Lo-DEX 10 mg, was determined to be the RP2D.  All 17 pts with pre and post dose measurements demonstrated a rapid decrease in their myeloma proteins by C2D1.  Preliminary IMWG response assessments provided for the 14 pts with response data through C3D1 included 9 (64%) with partial response (PR); 2 (14%) with minimal response (MR); and 3 (21%) with stable disease (SD).  The overall response rate (PR) was 64% and the clinical benefit rate (MR + PR) was 79%.  Subset analyses of these 14 pts included high risk cytogenetics (17p deletion and/or 4:14 chromosome translocation) and prior CFZ treatment.  In the high risk cytogenetics there were 4/5 PRs and 1/5 MR.  Of the 7 pts with prior CFZ treatment there were 5 with PR and 2 with SD, and all 4 pts who had CFZ in their last regimen achieved PR.  There was ~100% inhibition of the chymotrypsin-like subunit as early as C1D11, with robust inhibition of the trypsin-like and caspase-like subunits evolving over time in whole blood assays.  MRZ, POM, and Lo-DEX PK are in process and will be presented.

Conclusions: MRZ in combination with POM and Lo-DEX was generally well tolerated and demonstrated promising activity in heavily pre-treated pts with RRMM including those with high risk cytogenetics and who were refractory to prior treatment with CFZ.  The trial will enroll up to 22 pts at the RP2D (36 pts total) to provide additional safety and efficacy data.