3173 – HUMAN MODELS OF PEDIATRIC CBFA2T3-GLIS2 ACUTE MEGAKARYOBLASTIC LEUKEMIA CONTRIBUTE TO UNCOVER THERAPEUTIC VULNERABILITIES

Abstract

Acute megakaryoblastic leukemia (AMKL) is a poor prognostic subtype of AML afflicting children mostly under 3 years of age. Chromosomal translocations generating chimeric fusion genes are considered critical transforming events and are present in a high proportion of cases. Among them, the CBFA2T3-GLIS2 (CG2) fusion is associated with a high risk of relapse and accounts for ∼15% of pediatric AMKL cases. Using overexpression of CG2 in human cord blood CD34+ stem /progenitor cells (hHSPC) followed by xenotransplantation in immunodeficient mice, we are reporting the generation of multiple synthetic AMKL models that phenocopy the human disease in term of immunophenotype, morphology and gene expression. CG2 models revealed a stable genomic landscape with few copy number anomalies and lack of recurrent cooperating mutations. Leveraging from local and published transcriptomic datasets of CG2 AMKL samples (14 patients, 10 models), non-CG2 pediatric AMKL (n=66), NUP98-KDM5A synthetic models (n=5) and normal hHSPC (n=4), we have determined a robust gene expression signature defining CG2 AMKL. Gene set enrichment analysis of CG2 AMKL expression profile identified the JAK2-STAT5 axis as a potential pathway that is upregulated in CG2 leukemia, confirmed by downstream STAT5 phosphorylation in CG2 cells. Cell surface proteomic analysis by LC-MS identified multiple membrane proteins upstream of JAK-STAT signaling in CG2 model leukemia compared to normal hHSPC. Single-agent dose-response curves conducted with multiple FDA-approved drugs targeting JAK2 showed specific grow inhibition of CG2 AMKL models compared to normal hHSPC and non-AMKL cell line. Progress in leukemia research is hampered by the paucity of patient samples and the generated AMKL models pave the way toward a better understanding of leukemogenesis and development of targeted therapy. Acute megakaryoblastic leukemia (AMKL) is a poor prognostic subtype of AML afflicting children mostly under 3 years of age. Chromosomal translocations generating chimeric fusion genes are considered critical transforming events and are present in a high proportion of cases. Among them, the CBFA2T3-GLIS2 (CG2) fusion is associated with a high risk of relapse and accounts for ∼15% of pediatric AMKL cases. Using overexpression of CG2 in human cord blood CD34+ stem /progenitor cells (hHSPC) followed by xenotransplantation in immunodeficient mice, we are reporting the generation of multiple synthetic AMKL models that phenocopy the human disease in term of immunophenotype, morphology and gene expression. CG2 models revealed a stable genomic landscape with few copy number anomalies and lack of recurrent cooperating mutations. Leveraging from local and published transcriptomic datasets of CG2 AMKL samples (14 patients, 10 models), non-CG2 pediatric AMKL (n=66), NUP98-KDM5A synthetic models (n=5) and normal hHSPC (n=4), we have determined a robust gene expression signature defining CG2 AMKL. Gene set enrichment analysis of CG2 AMKL expression profile identified the JAK2-STAT5 axis as a potential pathway that is upregulated in CG2 leukemia, confirmed by downstream STAT5 phosphorylation in CG2 cells. Cell surface proteomic analysis by LC-MS identified multiple membrane proteins upstream of JAK-STAT signaling in CG2 model leukemia compared to normal hHSPC. Single-agent dose-response curves conducted with multiple FDA-approved drugs targeting JAK2 showed specific grow inhibition of CG2 AMKL models compared to normal hHSPC and non-AMKL cell line. Progress in leukemia research is hampered by the paucity of patient samples and the generated AMKL models pave the way toward a better understanding of leukemogenesis and development of targeted therapy.