Sotatercept Promotes Differentiation and Survival Of Erythroid Progenitors By Blocking Inhibitory Effects Of TGFβ Superfamily Members

• Published in: Blood 2013-11, Vol.122 (21), p.944-944
• Main Authors: Carrancio, Soraya, Markovics, Jennifer A., Wong, Piu, Heise, Carla, Daniel, Tom O., Chopra, Rajesh, Sung, Victoria
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V122.21.944.944

Erythropoiesis, the process of cell proliferation and differentiation that produces erythrocytes, is a tightly regulated process, but apart from early progenitor development and the EPO-dependent response, very little is known about other molecular signals which control cellular fate during RBC production. Members of the transforming growth factor beta (TGFβ) superfamily have been studied as potential regulators of erythropoiesis, iron regulation and globin expression. Sotatercept, an ActRIIA ligand trap, binds to and inhibits activin and other members of the TGFβ superfamily to induce a rapid increase in red cell number and hemoglobin in healthy volunteers. Pharmacological findings demonstrate that RAP-011, a murine ortholog of sotatercept, stimulates RBC parameters in mice through a mechanism distinct from EPO. We conducted the current study to evaluate if RAP-011 may stimulate expansion of a late-stage erythroblast population that is not normally expanded and/or may induce faster differentiation of erythroid precursors. In order to determine if RAP-011 promotes proliferation or differentiation during erythropoiesis, the number of cell divisions was quantified by CFSE staining. During in vitro erythroid differentiation, RAP-011 did not appear to alter the number of cell divisions; however, the percentage of cells that underwent the last division was higher in cultures treated with RAP-011, suggesting that the drug induced faster cellular maturation/differentiation. We also analyzed cell viability of GPA+ cells at the end of the differentiation process and observed that the percentage of apoptotic death was higher in control vs. RAP-011-treated cells. This suggests that RAP-011 may promote survival of late-stage precursors. To assess potential candidates which may mediate the erythropoietic effects of RAP-011, we selected three high affinity RAP-011 ligands, Activin A, Activin B and GDF-11, and proceeded to evaluate their effects on Smad signaling and on erythroid differentiation of human bone marrow progenitors. First, we observed that RAP-011 blocked ligand-induced Smad2/3 phosphorylation in the bone marrow-derived cells. Secondly, RAP-011 rescued activin A-induced inhibition of BFU-E colony formation. Finally, when mature CD36+ cells were differentiated in liquid media containing each of the three ligands, RAP-011 was able to reverse GDF-11- and Activin A-induced inhibition of of erythroid cell proliferation. GDF-11 and Activin A also significantly dec