Phase II Study of the ALK5 Inhibitor Galunisertib in Very Low-, Low-, and Intermediate-Risk Myelodysplastic Syndromes

Purpose: Overactivation of TGF-beta signaling is observed in myelodysplastic syndromes (MDS) and is associated with dysplastic hematopoietic differentiation. Galunisertib, a first-in-class oral inhibitor of the TGF-beta receptor type 1 kinase (ALK5) has shown effectiveness in preclinical models of MDS and acceptable toxicity in phase I studies of solid malignancies. Patients and Methods: A phase II multicenter study of galunisertib was conducted in patients with very low-, low-, or intermediate-risk MDS by the Revised International Prognostic Scoring System criteria with hemoglobin <= 10.0 g/dL. Patients received oral galunisertib 150 mg twice daily for 14 days on/14 days off. Results: Ten of 41 evaluable patients (24.4%; 95% confidence interval, 12.4-40.3) achieved hematologic improvement erythroid response by International Working Group (IWG) 2006 criteria. A total of 18 of 41 patients (43.9%) achieved erythroid response as per IWG 2000 criteria. Nine of 28 (32.1%) of transfusion-dependent patients had hematologic improvement. A total of 18 of 41 (44%) patients had a significant reduction in fatigue. Overall median duration of response was 90 days in all patients. Rigorous stem and progenitor flow cytometry showed that patients with an early stem cell differentiation block were more likely to respond to galunisertib. The most common treatment-emergent adverse events were grade 1 or 2 in 20 (49%) of 41 patients, including any-grade fatigue (8/41, 20%), diarrhea (7/41, 17%), pyrexia (5/41, 12%), and vomiting (5/41, 12%). Conclusions: In summary, galunisertib treatment has an acceptable safety profile and was associated with hematologic improvements in lower- and intermediate-risk MDS, with responses in heavily transfusion-dependent patients and in those with signs of an early stem cell differentiation block.