A phase 2 study of the lsd1 inhibitor img- 7289 (bomedemstat) for the treatment of essential thrombocythemia (et).

Background: For patients with essential thrombocythaemia (ET) intolerant of or resistant to hydroxyurea (HU), interferon or anagrelide, there is a need for therapies with distinct MOAs that reduce thromboses, improve the patient experience and potentially offer distinct clinical benefits. Lysine-specific demethylase-1 (LSD1) is a histone H3K4 demethylase critical for the self-renewal potential of malignant myeloid cells and the differentiation of myeloid progenitors, e.g., LSD1 licenses progenitors to mature into megakaryocytes, a cell central to the pathogenesis of ET. IMG-7289 (bomedemstat) is an orally active LSD1 inhibitor that reduced peripheral cell counts, splenomegaly, inflammatory cytokines, and mutant cell burdens in mouse models of MPNs (Jutzi et al. 2018). In an ongoing study of IMG-7289 for the treatment of myelofibrosis (MF) (NCT03136185), symptoms, platelets, neutrophils, mutant allele burdens and inflammatory cytokines were favorably impacted (Pettit et al. 2020). Aim(s): IMG-7289-CTP-201 is an ongoing, multi-national, open-label, 24-week Phase 2b study of bomedemstat taken once daily in patients with ET who are resistant to or intolerant of at least one standard of care treatment (NCT04254978). Key objectives are safety and reduction in the platelet count to <=400k/muL in the absence of thromboembolic events. Dosing is individually tailored targeting a platelet count between 200- 400k/muL. All patients were started at a dose of 0.6mg/kg/d and titrated as needed to the target platelet count range. Method(s): At the censoring date (16 Feb 2021), 10 patients had enrolled. All patients remain on study. The median duration of treatment is 85 days (6-141). Median age, 66 years (55-84), 20% males. 60% were deemed resistant to or intolerant of HU (by ELN criteria), 20% to anagrelide and 10% to interferon or busulfan. 40% had received at least one additional previous treatment. After a 14- to 28-day washout of prior ET treatment, the mean platelet and WBC co