Eltanexor (KPT-8602), a Second-Generation Selective Inhibitor of Nuclear Export (SINE) Compound, in Patients with Higher-Risk Myelodysplastic Syndrome

Background: Overexpression of exportin 1 (XPO1) in malignant cells increases the nuclear export/inactivation of tumor suppressor proteins (e.g. p53, IκB), and promotes the translation of eIF4E-bound mRNAs coding oncoproteins (e.g. c-MYC, BCL-2, AR). Selinexor plus low dose dexamethasone (Sel-dex) was recently approved in the United States 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. Eltanexor (elta), a second-generation SINE compound, has demonstrated reduced brain penetration and improved tolerability compared to selinexor in non-clinical animal models, and preliminary anti-tumor activity in clinical trials of hematologic and solid tumor malignancies. The primary objective of this study was to assess the safety, tolerability and anti-tumor activity of elta in patients (pts) with higher risk (HR)-Myelodysplastic Syndrome (MDS).

Methods: This is part of a Phase 1/2 study (NCT02649790) to determine the safety, tolerability and anti-tumor activity of elta in advance malignancies. This trial planned to evaluate single agent activity of elta in an expansion cohort of 20 pts with HR-MDS (intermediate-2 [Int-2] or high-risk by the International Prognostic Scoring System [IPSS]). Other key eligibility criteria included: age ≥18, ECOG ≥1, adequate organ function, and documented evidence of progressive disease as defined by the 2006 International Working Group (IWG) Response Criteria for MDS, which includes hypomethylating agent (HMA) failure. The dose levels evaluated in the MDS cohort were 10 and 20 mg elta taken orally once daily for 5 consecutive days per week in a 28-day cycle. A key efficacy endpoint is overall response rate (ORR) which includes complete response (CR), partial response (PR), marrow CR (mCR), and hematologic improvement (HI) using the 2006 IWG Response Criteria for MDS.

Results: Twenty pts (median age 77 years-old; range 62-89; 55% male) were enrolled as of 15 July 2018 (n=15 at 20 mg and n=5 at 10 mg). All pts were refractory to HMA with a median of 2 prior therapies (range 1 - 5) and 90% high risk via IPSS (11 pts high, 7 pts Int-2, 2 pts Int-1 [IPSS-R high]). Fourteen of 20 pts were evaluable for response, 2 are pending disease reassessment and 4 were not evaluable (NE). Preliminary efficacy demonstrated best responses of 4 mCR (29%) and 6 stable disease (SD; 43%) and 4 progressive disease (PD; 29%). The disease control rate (mCR + SD) was 71%. The median time on treatment for all pts was 69 days (range 5+ - 379) with a median time on study of 115 days (range 5+ - 400). The most frequent (≥3 pts) treatment-related adverse events (TRAEs) any grade (Gr) included nausea (53%), decreased appetite (33%), diarrhea (27%), thrombocytopenia, anemia, neutropenia, vomiting and dysgeusia (20% each). The most frequent Gr≥3 TRAEs included thrombocytopenia and anemia which are expected in this immune compromised patient population. All AEs were reversible and manageable by supportive care and dose modification. The 4 pts NE for response were pts who discontinued from treatment before having the first disease response reassessment due to: Gr3 diarrhea related to eltanexor, Gr5 sepsis not related per investigator, Gr3 pneumonia not related, and withdrawal by pt.

Conclusion: Oral eltanexor demonstrated preliminary anti-tumor activity as a single agent in elderly pts with HMA-refractory HR-MDS, including mCRs or disease stabilization, and a manageable tolerability profile. Further evaluation of efficacy and safety in HR-MDS is on-going.

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