Activity of HH/GLI inhibitors in induced pluripotent stem cells model of pediatric acute myeloid leukemia with CBFA2T3-GLIS2 fusion gene

CBFA2T3-GLIS2 is a fusion gene identified in 7-8% of pediatric acute myeloid leukemia with poor outcome. This fusion gene drives a peculiar expression pattern and leads to overexpression of some of Hedgehog related genes. GLI similar protein 2 (GLIS2) is closely related to the GLI family, the final effectors of classic Hedgehog pathway. These observations lend compelling weight to the application of GLI inhibitors in the treatment of AML with the aberration CBFA2T3-GLIS2. GANT61 is an inhibitor of GLI proteins. The exposure to the GANT61 resulted in higher sensitivity of cell lines and primary AML cells carrying CBFA2T3-GLIS2 than the AML cells without GLIS2 fusion as well as in promoting apoptosis and downregulation of GLIS2 specific signature genes. Moreover, ChIP analysis revealed direct regulation by GLIS2 chimeric protein of DNMT1 and DNMT3B, two genes implicated in important epigenetic functions. Furthermore, considering the limitations of cell lines model we set up a model based on induced pluripotent stem cells (iPSC) derived from healthy donor engineered to express CBFA2T3-GLIS2 fusion gene. We demonstrated that CBFA2T3-GLIS2 and other targets of fusion gene were expressed in hematopoietic cells derived from iPSC differentiation. The CD43+ hematopoietic cells were composed of a higher percentage of CD41+CD42+ megakaryocytic cells. Importantly, we observed strong differentiation alterations, including a lower expression of CD61 on CBFA2T3-GLIS2 megakaryocytes compared to controls and a progressive accumulation of an abnormal CD41lowCD42low population never detected in control conditions. Finally, clonogenic assays in methylcellulose indicated that CBFA2T3-GLIS2 enhances serial replating activity for several weeks. Moreover treatment with GANT61 affected proliferation of CBFA2T3-GLIS2 hematopoietic cells derived from iPSC differentiation. Taken together, our findings indicate that the GLI inhibitor GANT61 may be used to specifically target the CBFA2T3-GLIS2 fusion in pediatric AML.