Selinexor, Pomalidomide, and Dexamethasone (SPd) in Patients with Relapsed or Refractory Multiple Myeloma

Introduction: The nuclear export protein exportin 1 (XPO1) is overexpressed in a wide variety of cancers including multiple myeloma (MM) and associated with poor prognosis. Selinexor is a first-in-class Selective Inhibitor of Nuclear Export (SINE) compound that selectively binds and inactivates XPO1, therefore forces the nuclear retention and re-activation of cell cycle regulators such as p53, FOXO, IkB, and Rb. Selinexor in combination with low dose dexamethasone (Sel-dex) was recently approved based on data from the STORM study, wherein Sel-dex induced an overall response rate (ORR) of 26.2% in patients with penta-exposed, triple-class refractory multiple myeloma. Pomalidomide/dexamethasone achieved an ORR of 31% and progression-free survival (PFS) rate of < 4 months in patients refractory to prior bortezomib and lenalidomide. We conducted the STOMP study to assess the efficacy and safety of the combination of selinexor, pomalidomide and dexamethasone (SPd) in patients with relapsed/refractory multiple myeloma.Methods: STOMP is a multicenter, open-label, phase 1/2b, dose escalation study with an expansion phase. Patients with relapsed/refractory multiple myeloma who received prior therapies including lenalidomide and a proteasome inhibitor were eligible for enrollment. Oral selinexor was evaluated in 2 different dosing schedules: once-weekly (QW, 60 or 80 mg) or twice-weekly (BIW, 60 or 80 mg), with escalating doses of pomalidomide 2, 3 or 4 mg PO (days 1-21), and low dose dexamethasone 20 mg BIW or 40 mg QW. The primary objectives of the study were to determine the maximum tolerated dose (MTD), the recommended phase 2 dose (RP2D), and to assess the safety, tolerability, and preliminary efficacy of the combination of SPd in patients with relapsed/refractory multiple myeloma.Results: As of July 01 2019, 48 patients (26 male and 22 female) were enrolled. The median age was 64 years (range:43-83 years). Patients received a median of 4 (range: 2-13) prior treatment regimens. Forty patients (83%) received prior autologous stem cell transplantation (one patient received prior autologous and allogenic stem cell transplantation). The phase 1 dose escalation enrollment is now complete. Across all cohorts, eight dose limiting toxicities (DLTs) were observed (Table 1). Common hematologic treatment related adverse events (TRAE) included (Grades 1/2, Grades ≥3): neutropenia (8%, 54%), thrombocytopenia (21%, 33%), anemia (17%, 29%) and leukopenia (13%, 15%). Common non-hematologic TRAE included: nausea (56%, 0%), fatigue (40%, 10%), decreased appetite (46%, 0%), weight decreased (33%, 0%), diarrhea (27%, 0%), vomiting (21%, 2%). Lower rates of ≥ Grade 3 thrombocytopenia (27% vs 44%) and anemia (20% vs 44%) were observed in QW dosing vs BIW dosing. Out of 48 patients, 44 were evaluable for response (27 patients lenalidomide refractory/pom naive, 4 patients lenalidomide treated/pom naïve, 13 patients refractory to pomalidomide and lenalidomide, and 19 patients refractory to lenalidomide and bortezomib). Among patients who were pomalidomide naive (N=31), the ORR was 58% (7 very good partial responses and 11 partial responses) and the median PFS was 12.2 months. Among patients refractory to lenalidomide/pomalidomide (N=13) the ORR was 31% (4 partial responses) and the median PFS was 4.2 months.Conclusions: The all oral SPd combination is durable and active with an ORR of 58% in patients with disease that is lenalidomide refractory and pomalidomide naïve compared to previously published data of 31% ORR for pomalidomide/dexamethasone in a similar patient population. The median PFS on SPd of 12.2 months in pomalidomide naïve patients is longer than that observed with pomalidomide/dexamethasone (<4 months). No unexpected adverse events were noted. Selinexor QW demonstrated a manageable side effects with ≤2% Grade 3/4 nausea, vomiting, diarrhea, weight decreased and decreased appetite suggesting that the side effects of selinexor are a function of the dose and schedule. This observed activity and manageable side effect profile with QW selinexor in combination with pom/dex supports further studies.

Duke Scholars

Author Cristina Gasparetto Medicine, Hematologic Malignancies and Cellular Therapy