Phase 3 study of the lysine-specific demethylase 1 (LSD1) inhibitor bomedemstat in patients with essential thrombocythemia (ET).

Abstract

TPS6596 Background: ET is a myeloproliferative neoplasm (MPN) driven by mutations in JAK2, CALR, and MPL that is characterized by thrombocytosis and megakaryocyte hyperplasia. Currently available treatments can prevent thrombotic complications but do not substantially alter the natural history of ET. LSD1 is an enzyme that regulates hematopoietic stem and progenitor cell proliferation and is overexpressed in MPNs. In a phase 2 study, the LSD1 inhibitor bomedemstat was generally well tolerated and improved symptoms, durably reduced platelet and white blood cell counts, and reduced mutation burden in patients with ET. Here, we describe the methods for a randomized, open-label, phase 3 study (NCT06079879) that has been designed to evaluate bomedemstat versus best available therapy in patients with ET who had an inadequate response to or were intolerant of hydroxyurea. Methods: Key eligibility criteria include age ≥18 years, a diagnosis of ET per World Health Organization 2016 diagnostic criteria, a bone marrow fibrosis score of grade 0 or 1, a platelet count of >450 x 109/L, and an absolute neutrophil count of ≥0.75 x 109/L. All patients must have a history of inadequate response to or intolerance of hydroxyurea per modified European LeukemiaNet (ELN) criteria. Patients will be randomly assigned 1:1 to bomedemstat 50 mg/day by mouth (starting dose) or investigator’s choice of best available therapy (anagrelide, busulfan, interferon alfa/pegylated interferon alpha, or ruxolitinib). Bomedemstat dose will be titrated to a target platelet count of ≥150 to ≤350 x 109/L. After 52 weeks, patients receiving best available therapy can cross over to bomedemstat at the investigator’s discretion and patients in the bomedemstat arm can continue on treatment (maximum of 156 weeks on study). Randomization will be stratified by hydroxyurea history (inadequate response vs intolerance) and MFSAF v4.0 baseline score (≥4 vs <4). Clinic visits will occur every 2 weeks until week 12 and monthly thereafter. Adverse events will be graded per NCI CTCAE v5.0 criteria and monitored for up to 30 days after last dose of study drug. The primary end point is durable clinicohematologic response rate per modified ELN criteria. Secondary end points are duration of clinicohematologic response, duration of hematologic remission, change from baseline in total symptom and fatigue score per MFSAF v4.0 criteria, change from baseline in total fatigue score per the PROMIS Fatigue SF-7a scale, incidence of thrombotic or major hemorrhagic events, transformation to post-ET myelofibrosis or myelodysplastic syndrome/acute myeloid leukemia, event-free survival, and safety. Exploratory end points include pharmacokinetics, the proportion of patients reporting stability or improvement versus decline on the MSAF v4.0 and PROMIS Fatigue SF-7a domains, and molecular biomarkers. Approximately 300 patients will be enrolled. Clinical trial information: NCT06079879 .