Phase 2 Study of the Combination of Daratumumab, Ixazomib, Pomalidomide, and Dexamethasone As Salvage Therapy in Relapsed/Refractory Multiple Myeloma: Stage I Results

Background: Triplet combination regimens have been widely accepted as the standard of care for the management of multiple myeloma (MM) due to improved outcomes as compared to doublet regimens. The combination of daratumumab, pomalidomide, and dexamethasone (DPd) has previously demonstrated deep and durable responses including high rates of minimal residual disease (MRD) negativity in patients with relapsed/refractory (R/R) MM. Quadruplet regimens may further improve these outcomes. We report preliminary findings from an ongoing phase 2 multi-center trial of the addition of ixazomib to DPd (DIPd) in patients with R/R MM.

Methods: We are conducting a prospective, multi-center, open-label, single-arm phase 2 study to determine the efficacy and safety of DIPd as salvage therapy in R/R MM. A Simon's optimal 2-stage design includes a safety run-in period at the beginning of Stage 1 where the first 6 patients are enrolled for toxicity assessment. If ≤1 patient experiences any DLT, the study continues to accrue more Stage 1 patients. Key secondary endpoints include progression-free survival (PFS), overall survival (OS) and MRD-negativity rates. Eligible patients may have received ≥1 and ≤3 prior lines of therapy, have had no prior exposure to daratumumab or ixazomib, are lenalidomide refractory, and may have not progressed on prior pomalidomide. The first six patients were treated in a safety run-in with daratumumab 16mg/kg IV weekly x 8 doses, biweekly x 8 doses, then monthly, pomalidomide 4mg orally daily on days 1-21 of a 28-day cycle, ixazomib 4mg orally daily on days 1,8,15 every 28 days, and dexamethasone 20-40mg weekly. Patients continued therapy until disease progression, intolerability or preference. Dose-limiting toxicities (DLT) were defined as grade 3-4 hematologic adverse events (AE) or any AE that required a dose modification of pomalidomide or ixazomib at the lowest dose levels on a dose de-escalation plan. An interim safety review is being performed after the enrollment and completion of the DLT observation period for the 14 planned patients in stage I. An interim efficacy analysis was also planned after all patients had completed 3 months of therapy. Minimal residual disease assessments are being performed by EuroFlow for patients in VGPR or suspected CR. Pharmacodynamic changes in patients' tumor microenvironments were established by custom panel mass cytometry to include T-cell memory and activated subpopulations, B-cell content, NK-cell subpopulations as well as MDSCs, Tregs and T-exhaustive markers, monocytes and dendritic cells.

Results: At the time of this analysis, all 14 patients have enrolled and started treatment as part of stage I of the trial. Patients had a median age of 61 (range 52-65) and median number of 1 prior line of therapy (range 1-3). All patients were refractory to lenalidomide and all were pomalidomide naïve. In the safety run-in, all 6 patients experienced ≥ grade 3 neutropenia, and per DSMB recommendation, the starting doses of pomalidomide and ixazomib were both reduced to 3mg for the subsequent 8 patients in stage 1. Common AEs included neutropenia, thrombocytopenia, and upper respiratory infection. Grade 3-4 AEs were predominantly hematologic, including neutropenia and thrombocytopenia. One patient had a grade 3 infusion-related reaction (IRR) with daratumumab administration. No DLTs have occurred. After median follow up of 4.1 months (range 1-22), all 14 patients were evaluable for efficacy. At the time of data analysis, the overall response rate to date is 85%, and the best responses include: 5 (36%) stringent complete response; 1 (7%) very good partial response; 5 (36%) partial responses; and 3 (21%) patients with stable disease. Six (42%) patients are off study treatment: 3 due to disease progression, 1 to undergo salvage autologous SCT, and 2 due to toxicity related to treatment (IRR and upper respiratory infection). MRD and pharmacodynamic data will be presented at ASH.

Conclusion: The quadruplet regimen DIPd in patients with R/R MM is a well-tolerated combination and has shown early safety and promising efficacy in the first 14 patients enrolled to stage 1 of the trial. A pre-planned interim efficacy analysis is ongoing prior to future enrollment in stage 2 at multiple sites within the University of California Hematologic Malignancies Consortium.