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Dexpramipexole as an oral steroid-sparing agent in hypereosinophilic syndromes

Sandhya R. Panch, Michael E. Bozik, Thomas Brown, Michelle Makiya, Calman Prussin, Donald G. Archibald, Gregory T. Hebrank, Mary Sullivan, Xiaoping Sun, Lauren Wetzler, JeanAnne Ware, Michael P. Fay, Cynthia E. Dunbar, Steven I. Dworetzky, Paneez Khoury, Irina Maric and Amy D. Klion

Key Points

  • GC-sparing treatment alternatives are a critical need for patients with HESs.

  • The orally bioactive drug dexpramipexole demonstrated clinical efficacy with an excellent safety profile in a subset of patients with HESs.

Publisher's Note: There is a Blood Commentary on this article in this issue.

Abstract

Hypereosinophilic syndromes (HESs) are a heterogeneous group of disorders characterized by peripheral eosinophilia and eosinophil-related end organ damage. Whereas most patients respond to glucocorticoid (GC) therapy, high doses are often necessary, and side effects are common. Dexpramipexole (KNS-760704), an orally bioavailable synthetic aminobenzothiazole, showed an excellent safety profile and was coincidentally noted to significantly decrease absolute eosinophil counts (AECs) in a phase 3 trial for amyotrophic lateral sclerosis. This proof-of-concept study was designed to evaluate dexpramipexole (150 mg orally twice daily) as a GC-sparing agent in HESs. Dual primary end points were (1) the proportion of subjects with ≥50% decrease in the minimum effective GC dose (MED) to maintain AEC <1000/μL and control clinical symptoms, and (2) the MED after 12 weeks of dexpramipexole (MEDD) as a percentage of the MED at week 0. Out of 10 subjects, 40% (95% confidence interval [CI], 12%, 74%) achieved a ≥50% reduction in MED, and the MEDD/MED ratio was significantly <100% (median, 66%; 95% CI, 6%, 98%; P = .03). All adverse events were self-limited, and none led to drug discontinuation. Affected tissue biopsy samples in 2 subjects showed normalization of pathology and depletion of eosinophils on dexpramipexole. Bone marrow biopsy samples after 12 weeks of dexpramipexole showed selective absence of mature eosinophils in responders. Dexpramipexole appears promising as a GC-sparing agent without apparent toxicity in a subset of subjects with GC-responsive HESs. Although the exact mechanism of action is unknown, preliminary data suggest that dexpramipexole may affect eosinophil maturation in the bone marrow. This study was registered at www.clinicaltrials.gov as #NCT02101138.

  • Submitted February 22, 2018.
  • Accepted May 2, 2018.
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