A phase I study of MEK inhibitor selumetinib in combination with azacitidine in patients with higher-risk chronic myeloid neoplasia

TPS7084 Background: Myelodysplastic syndrome (MDS), Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), and MDS/MPN overlap syndromes present significant clinical challenges for patients deemed transplant ineligible, and who are relapsed or refractory to conventional therapies. RAS-pathway activating mutations in myeloid malignancies are associated with a proliferative phenotype and contribute to disease progression. Cooperation between RAS-dependent signaling and epigenetic dysregulation provides the basis for rationally designed combination studies. Selumetinib (AZD6244) is a potent, selective, orally bioavailable, and non-ATP competitive small molecule inhibitor of MEK1/2, downstream of RAS. Methods: This is an investigator-initiated, Phase I, open-label dose-escalation study of selumetinib in combination with azacitidine for patients with higher risk MDS, MDS/MPNs, and myelofibrosis. The trial will enroll patients with high-risk myeloid neoplasms that meet disease-specific criteria for MDS or MPNs and who require treatment. This phase I study follows a 3+3 dose-escalation design, with three planned dose levels across two different cohorts (A and B). The dose of azacitidine 75 mg/m 2 will remain stable, with three planned selumetinib dose levels (50 mg, 75 mg, and 100mg, respectively) across the two cohorts. Azacitidine will be given on days 1-7 followed by selumetinib from days 7-21 of 28 day cycles. Cohort A includes subjects with MDS with relapsed/refractory disease requiring therapy and MDS/MPN overlap syndromes; Cohort B includes subjects with myelofibrosis refractory or intolerant to JAK inhibitor therapy or ineligible for ruxolitinib treatment given baseline cytopenias (thrombocytopenia < 50,000/uL, anemia < 9 g/dL, and/or red cell transfusion dependent). The trial has an enrollment goal of 18 to 24 subjects, and treatment will continue indefinitely if the patient continues to derive benefit. Dose escalation will proceed independently within both cohorts. Cohort A is nearing completion of enrollment and cohort B is actively enrolling. The primary objective is to determine the maximum tolerated dose of selumetinib in combination with azacitidine. Select secondary and exploratory objectives include describing the preliminary clinical response rates and observing relationships between the presence of RAS activating mutations, RAS pathway activation, and clinical response. Clinical trial information: NCT03326310 .