Updated Efficacy of Eltanexor Monotherapy in Patients with Higher Risk Hypomethylating Myelodysplastic Syndrome Primary Refractory to Hypomethylating Agents

Background: Patients with higher-risk myelodysplastic syndrome (MDS) refractory to hypomethylating agents (HMAs) have limited therapeutic options and poor prognosis with a median overall survival (mOS) of 4-6 months. Lack of response to HMA therapy, advanced age at relapse, male sex, bone marrow blasts >5% and high risk disease classification by International Prognostic Scoring System (IPSS) confer worse outcomes. Eltanexor is a second-generation, oral, selective inhibitor of nuclear export (SINE) compound with markedly reduced brain penetration relative to selinexor in preclinical models. This is believed to result in attenuation of centrally mediated anorexia, weight loss, and nausea, allowing for more frequent dosing. Early results from a phase 1/2 study of eltanexor in patients with higher-risk HMA-refractory MDS demonstrated marrow complete responses (mCRs), hematologic improvement (HI) and stable disease (SD); side effects were primarily low-grade, dose-dependent, and reversible (Lee EHA 2021). Here we provide an update on baseline characteristics, blast reduction in mCR patients, extent of transfusion independence and additional subgroup analyses.

Methods: This phase 1/2 study (NCT02649790) evaluated oral eltanexor monotherapy in patients with high-risk or intermediate-2 by IPSS and 5%-19% myeloblasts. Of 20 patients enrolled, 15 patients were evaluable for efficacy and constitute the population studied in this analysis; 5 patients were non evaluable for efficacy due to trial discontinuation prior to response assessment. Two doses of eltanexor were evaluated: 10 mg (n=5) or 20 mg (n=10) each given qd 5 days per week.

Results: Amongst the 15 efficacy evaluable patients, there were 8 males, median age 76 years (range 62-89), 10.0% (range 7-18%) median bone marrow blasts at enrollment, and with a median of two prior regimens (range 1-4). All patients primary HMA-refractory MDS; 9 patients (60%) with high risk and 5 (33%) with intermediate-2 per IPSS, 1 with intermediate-1 per IPSS. Similarly, using the global MD Anderson Cancer Center risk prognosis model, 14 patients (93%) had intermediate-2 or high-risk MDS. The overall response rate (mCR+HI) was 53% including 47% mCRs. Additionally, 5 patients (33%) had SD. Median blast reduction in the 7 patients with mCR was 78.6% (range 55.6%, 85.7%). Four patients had hematologic improvement (HI) including 2 patients with tri-lineage HI. Of the 7 patients who achieved mCR, 4 had significant reduction in transfusion requirements with 3 of these patients achieving complete transfusion independence for 5-10 cycles. In the 10-mg cohort (n=5), all patients derived clinical benefit with 3 patients reaching mCR and 2 patients with SD. In the 20-mg cohort (n=10), 4 patients had mCR and 3 had SD. Median overall survival for all efficacy evaluable patients was 9.86 months. OS for patients who reached mCR (n=7) was significantly longer than for patients who did not reach mCR (n=8): median 11.86 vs 8.67 months (hazard ratio [HR]=0.27, p=0.05), and significantly longer than OS for patients with PD (n=3, mOS=3.15 months, HR=0.23, p=0.04). Notably, mCR was seen in the 3 patients treated with >2 prior therapies and/or with secondary MDS: 1 patient with secondary MDS and 4 prior therapies; 1 with secondary MDS and one prior therapy; and 1 with de novo MDS and 3 prior therapies).

Conclusions: Single-agent oral eltanexor was active in patients with higher-risk, primary HMA-refractory MDS including those with secondary MDS or with >2 lines of prior therapy. Patients with mCR had significantly longer mOS than patients without mCR and had median blast reduction of 78.6%. Further evaluation of eltanexor in MDS as a single agent and in combination with other agents is ongoing.