Phase 1 MMRC Trial of Selinexor, Carfilzomib (CFZ), and Dexamethasone (DEX) in Relapsed and Relapsed/Refractory Multiple Myeloma (RRMM)

Background

There is an increasing number of multiple myeloma patients (pts) refractory to currently available drugs, including the proteasome inhibitors bortezomib and Carfilzomib (CFZ), necessitating development of novel effective therapeutics. Pre-clinical evaluation of selinexor, a novel orally available selective inhibitor of nuclear export (SINE), in human myeloma cell lines (HMCL), primary plasma cells derived from myeloma patients, and HMCL tumor-bearing mice demonstrated synergistic myeloma cell death with CFZ (Rosebeck et al. ASH 2013) and the ability to overcome resistance to CFZ (Rosebeck et al. ASH 2014).

Aims

The primary objective is to assess the maximum tolerated dose (MTD) of selinexor and CFZ in combination with DEX in RRMM pts and to provide preliminary evaluation of efficacy of this novel triplet regimen.

Methods

Pts with RRMM, including CFZ-refractory pts, who have failed at least two prior treatment regimens of myeloma therapy, were eligible for enrollment. Dose escalation follows the 3+3 design with pts receiving 30 mg/m² – 40 mg/m² selinexor PO on days 1, 3, 8, 10, 15, 17; 20 mg/m² – 56 mg/m²CFZ given IV on days 1, 2, 8, 9, 15, 16, and DEX PO 20/10mg (cycles 1-4/cycles 5+) in 28-day cycles. At least 12 and up to 48 pts are planned for evaluation. Dose Limiting Toxicities (DLT) are measured for the Cycle 1 as well as Day 1 of Cycle 2. Dose modifications are allowed to manage toxicities. Response was assessed by IMWG criteria plus near complete response (nCR).

Results

As of July 1^st, 2015 the study has enrolled 8 pts, 5 pts were treated at dose level 1 (30 mg/m² selinexor, 20/27 mg/m² CFZ, 20/10 mg DEX) and 3 patients were treated at dose level 2a (30 mg/m² selinexor, 20/36 mg/m² CFZ, 20/10 mg DEX). Pts had median age of 65.5 (range 55-73) and a median of 5 prior treatment regimens (range 2-5).  Six pts were refractory to CFZ combinations at their last line of therapy, including 4 to CFZ, pomalidomide (POM), and DEX. Of the 2 remaining pts, 1 was refractory to high dose CFZ with DEX in prior line of therapy and both were refractory to last line of therapy. Six pts were DLT-evaluable and two pts required replacement for DLT evaluation (1 pt had DEX reduced in cycle 1 not due to DLT; 1 pt did not receive all scheduled cycle 1 doses due to progressive disease). There have been no DLTs and MTD is not yet established. Adverse events (AEs) were reversible and managed with concomitant therapy. G3/4 hematologic AEs include thrombocytopenia (75%), neutropenia (50%), leukopenia (37.5%), lymphopenia (25%), and anemia (25%). The most common G3/4 non-hematologic AEs included fatigue (25%) and upper respiratory tract infection (25%). The most common G1/2 AEs are fatigue (75%), dyspnea (62.5%), nausea (62.5%), anemia (50%), leukopenia (50%), and thrombocytopenia (50%). Response rates for all enrolled pts are 87.5% ≥MR, 75% ≥PR, 12.5% ≥VGPR. Responses occurred rapidly; after 1 cycle: 75% ≥MR, 63% ≥PR, 12.5% VGPR. As of the cut off date, 4 pts have progressed (after 1, 2, 4, and 4 months) and 4 pts remain on treatment (10+, 1+, 1+, and 1+ months); 1 pt did not respond and died due to progression of disease.

Conclusions

Although still very early, the combination of selinexor, CFZ, and DEX demonstrates encouraging activity with 75% PR or better and no unexpected toxicities in highly refractory MM pts, including those previously refractory to CFZ. Responses in pts refractory to very active CFZ combinations in the last line of therapy suggest that this regimen has the ability to overcome CFZ resistance.