Revealing Eltrombopag's promotion of human megakaryopoiesis through AKT/ERK-dependent pathway activation

Eltrombopag is a small non-peptide thrombopoietin mimetic that has been approved for increasing platelet count not only in immune thrombocytopenia and HCV-related thrombocytopenia, but also in aplastic anemia. Moreover, this drug is under investigation for increasing platelet count in myelodysplastic syndromes. Despite current clinical practice, the mechanisms governing Eltrombopag's impact on human hematopoiesis are largely unknown in part due to the impossibility of using traditional in vivo models. To investigate Eltrombopag's impact on megakaryocyte functions, we employed our established in vitro model for studying hematopoietic stem cell differentiation combined with our latest 3D silk-based bone marrow tissue model. Results demonstrated that Eltrombopag favors human megakaryocyte differentiation and platelet production in a dose-dependent manner. These effects are accompanied by increased phosphorylation of AKT and ERK1/2 signaling molecules, which have been proven to be crucial in regulating physiologic thrombopoiesis. These data further clarify the different mechanisms of action of Eltrombopag when compared to Romiplostim, which we have shown induces proliferation of immature megakaryocytes rather than platelet production, due to unbalanced activation of AKT and ERK1/2 signaling molecules. In conclusion, our research clarifies the underlying mechanisms that govern the action of Eltrombopag on megakaryocyte functions and its relevance in clinical practice.