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

Background

There are an increasing number of multiple myeloma (MM) patients (pts) refractory to currently available drugs, including the proteasome inhibitors bortezomib and carfilzomib (CFZ), necessitating development of novel therapeutics. Pre-clinical evaluation of selinexor (SEL), an orally available Selective Inhibitor of Nuclear Export (SINE) compound, demonstrated synergistic myeloma cell death with CFZ and mechanistic rationale for overcoming resistance to CFZ (Rosebeck et al., 2016), providing support for this phase 1 trial.

Aims

The primary objectives were to assess the maximum tolerated dose (MTD) of a SEL, CFZ and dexamethasone (DEX) combination and to obtain preliminary efficacy data for this novel regimen in RRMM pts.

Methods

Pts with RRMM who progressed after at least two prior treatment regimens of myeloma therapy were eligible for enrollment. Dose escalation followed the 3+3 design with pts receiving 30 mg/m² - 40 mg/m² SEL PO on days (D) 1, 3, 8, 10, 15, 17; 20 mg/m² - 56 mg/m² CFZ IV on D 1, 2, 8, 9, 15, 16, and DEX PO (20mg cycles 1-4/ 10mg cycles 5⁺) in 28-day cycles (C) in up to 5 dose levels. An expansion cohort has enrolled additional pts to a total of 12 CFZ-refractory pts treated at the recommended Phase 2 dose (RP2D). Dose Limiting Toxicities (DLTs) were evaluated through C2D1. Responses were assessed by IMWG criteria plus near complete response (nCR).

Results

As of July 1^st, 2016, the study has completed dose escalation and enrolled a total of 18 pts; 5 at dose level 1 (30 mg/m² SEL, 20/27 mg/m² CFZ, 20/10 mg DEX), 3 at dose level 2a (30 mg/m² SEL, 20/36 mg/m² CFZ, 20/10 mg DEX), and a total of 10 (7 in dose escalation, 3 in cohort expansion) at dose level 2b (60mg flat dose SEL, 20/27 mg/m² CFZ and 20/10 DEX). Pts age ranged between 55 to 74 years with a median of 63.5 years; and had a median of 4 prior treatment regimens (range 2-10). Sixteen pts were evaluable for response, all refractory to their last line of therapy. All 16 response evaluable pts were refractory to CFZ, of which 11 were refractory to CFZ combinations as their last line of therapy, including 8 to a KPd combination of CFZ, pomalidomide, and DEX. Fifteen pts were evaluable for DLT and 3 of 18 pts required replacement for DLT evaluation (1 had DEX reduced not due to DLT; 2 did not receive all scheduled C1 doses). In the dose escalation phase, there was one DLT of cardiac amyloidosis (CA) in a pt with history of prior congestive heart failure and CA at baseline. While the maximum tolerated dose (MTD) has not been reached, the RP2D was identified at dose level 2b based on tolerability. Grade 3/4 adverse events (AEs) included: thrombocytopenia (67%), neutropenia (33%), anemia (17%), fatigue (17%), and infections (11%). The most common all grade AEs included: gastrointestinal disorders (78%), thrombocytopenia (73%), fatigue (72%), anemia (47%), dyspnea (33%), and elevated liver and pancreatic enzymes (28%). There were 2 (11%) serious AEs, 1 upper respiratory infection and 1 lower gastrointestinal bleeding. All adverse events were manageable with concomitant medications. Response rates for all evaluable pts were 75% ≥MR (12 of 16), 63% ≥PR, and 25% ≥VGPR. Response rates in CFZ-refractory pts at last line of treatment were 73%, 64%, and 18% respectively. Responses occurred rapidly; after C1 with 75% ≥MR. As of the data cutoff date, 15 pts progressed (between 1 and 14 months on study) and 3 pts remained on treatment (1 - 4 months).

Conclusions

The combination of SEL, CFZ, and DEX demonstrates encouraging activity and safety in heavily pretreated, mostly CFZ-refractory myeloma. In addition, with 64% PR or better for pts progressing on CFZ, these results provide early clinical evidence that selinexor has the ability to overcome CFZ resistance, warranting further investigation of this regimen in RRMM.