A Phase 2a, Open-Label, Dose-Finding Study To Determine The Safety and Tolerability Of Sotatercept (ACE-011) In Adults With Beta (β)-Thalassemia: Interim Results

Beta (β)-thalassemia is characterized by ineffective erythropoiesis leading to anemia, bone marrow erythroid hyperplasia, iron overload, and organ failure. Sotatercept (ACE-011) is a novel and first-in-class activin type IIA receptor (ActRIIA) fusion protein that increases the release of mature erythrocytes into circulation by acting mainly on late-stage erythropoiesis (Carrancio S, et al. Blood. 2012;120:abstract 372). Clinical data in healthy volunteers have shown that treatment with sotatercept results in increased red blood cell (RBC) parameters, including hemoglobin level (Ruckle J, et al. J Bone Miner Res. 2009;24:744-52). RAP-011, a murine ortholog of sotatercept, was efficacious in a mouse model of β-thalassemia intermedia, reducing ineffective erythropoiesis as well as significantly improving anemia and decreasing bilirubin levels, supporting the clinical development of sotatercept (Dussiot M et al. Blood 2012;120:abstract 247).

This is an ongoing phase 2a, multicenter, open-label, dose-finding study to determine a safe and active dose level of sotatercept in adult patients with RBC-transfusion dependent (TD) β-thalassemia major or patients with β-thalassemia intermedia who are either TD or non-transfusion dependent (NTD). The dose levels of sotatercept studied to date are 0.1, 0.3, and 0.5 mg/kg, given subcutaneously once every 3 weeks. Safety is assessed according to NCI-CTC grading. Efficacy is assessed by hemoglobin increase from baseline and/or reduction in transfusion burden. Secondary endpoints include assessment of biomarkers for erythropoiesis, hemolysis, iron metabolism, and bone metabolism, as well as in vitro dyserythropoiesis. Dose escalation to higher dose levels is planned contingent on data review and favorable safety profile as determined by the Steering Committee.

Patient demographics. A total of 25 patients have been enrolled as of July 26, 2013; 8 in the 0.1 mg/kg cohort, 9 in the 0.3 mg/kg cohort, and 8 in the 0.5 mg/kg cohort. Treatment and analysis for the 0.5 mg/kg cohort is underway and will be updated and presented. In the 0.1 and 0.3 mg/kg cohorts, 3 (18%) patients had β-thalassemia major and 14 (82%) had β-thalassemia intermedia (12 of whom were NTD and 2 of whom were TD). Of the 12 NTD β-thalassemia intermedia patients, 6 were treated at the 0.1 mg/kg dose level and 6 at the 0.3 mg/kg dose level. Median baseline hemoglobin for these NTD patients was 8.6 g/dL (range 5.8 to 10.7 g/dL). Median number of sotatercept doses administered was 4 (range 2 to 7) in the 0.1 mg/kg cohort and 8 (range 3 to 9) in the 0.3 mg/kg cohort; 13/17 (76%) patients remained on treatment.

Safety.Sotatercept was generally well tolerated. There were no dose-limiting toxicities reported. Two serious adverse events were reported in the 0.1 mg/kg cohort: a grade 2 phlebitis in an NTD patient with a history of high D-dimer at baseline, and a worsening grade 3 bone pain in a TD β-thalassemia major patient with a history of osteoporosis; both were considered possibly study drug-related.

Hemoglobin levels/transfusion requirements. Among NTD patients, preliminary data showed that 1 (17%) patient in the 0.1 mg/kg cohort and all 6 (100%) patients in the 0.3 mg/kg cohort had at least a 1 g/dL increase in hemoglobin level from baseline; among these, 1 patient treated with sotatercept 0.3 mg/kg showed a 2 g/dL hemoglobin level increase from baseline as well as a decrease in total bilirubin level from 2.7 × upper limit of normal (ULN) at baseline to 1.8 × ULN. No other relevant decrease in total bilirubin level was reported at the lower dose levels (0.1 mg/kg or 0.3 mg/kg).

Three TD patients were still receiving treatment (2 β-thalassemia intermedia and 1 β-thalassemia major). There had been no appreciable reduction in transfusion burden in the 0.1 and 0.3 mg/kg cohorts to date; however further follow up is warranted and an update will be presented.

Based on these preliminary data, sotatercept administered subcutaneously every 3 weeks may improve anemia via a novel mechanism of action with a favorable safety profile, thereby addressing a significant unmet medical need for patients with NTD β-thalassemia intermedia. The current data suggest a dose-dependent response that supports further evaluation of the exposure–effect relationship of sotatercept in patients with NTD β-thalassemia intermedia.

The first, second, and last authors contributed equally to this abstract.

Cappellini:Genzyme: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau. Off Label Use: Sotatercept is an investigational agent that is being assessed for efficacy and safety in beta-thalassemia. Porter:Novartis: Consultancy, Research Funding; Shire: Consultancy; Celgene: Honoraria. Forni:Celgene: Research Funding; Shire: Research Funding; Novartis Pharma: Research Funding. Laadem:Celgene Corp.: Employment, Equity Ownership. Galacteros:Celgene: Consultancy. Miteva:Celgene Corp.: Employment. Sung:Celgene Corp.: Employment, Equity Ownership. Chopra:Celgene Corp.: Employment, Equity Ownership. Klesczewski:Celgene Corp.: Employment. Attie:Acceleron Pharma: Employment. Hermine:Celgene Corporation: Consultancy, Research Funding.