Gene Expression-Based Chemical Genomics Identifies Valproic Acid to Revert the Oncogenic Effect of GATA1s In Down Syndrome Megakaryoblastic Leukemia.

Abstract 3646

Children with Down syndrome (DS) are at high risk to develop acute megakaryoblastic leukemia (DS-AMKL) and the antecedent transient leukemia (DS-TL). Acquired mutations in the hematopoietic transcription factor GATA1, leading to expression of a shorter GATA1 variant (referred to as GATA1s) truncated at its N-terminus, are consistently present in the affected cells of children with DS-AMKL and DS-TL. Mechanistically, we recently found that in fetal megakaryocytic progenitor cells, GATA1 coordinates proliferation and differentiation by repressing E2F target genes through a direct interaction with E2F activators. Failure of this GATA1-E2F interaction in mutated GATA1s likely converges with overactive IGF signaling to promote cellular transformation.

The treatment of DS-AMKL is hampered by their sensitivity against current cytostatic agents, resulting in treatment-related mortality as the main cause of death. To develop novel targeted and less toxic treatment options for DS-AMKL and DS-TL, we conducted a gene expression-based chemical genomic screen. We connected a DS-AMKL gene expression signature (compared to non-DS-AMKL, i.e. GATA1s vs. GATA1) to a reference collection of gene-expression profiles from cultured human cells treated with bioactive small molecules (Connectivity Map). We discovered the histone deacetylase (HDAC) inhibitor valproic acid (VPA) reverses the DS-AMKL gene expression program.

Cell viability assays, cell cycle analyses, growths curves and colony-forming assays revealed exceptional sensitivity of DS-AMKL cell lines (CMK, CMY; IC50 1mM) and primary DS-AMKL and DS-TL blasts to VPA treatment compared to control cell lines K562 (IC50 4.75mM), M07 (IC50 6.75mM) and CD34+ hematopoietic stem and progenitor cells (IC50 4.75mM). VPA induces apoptosis (26.8% 7-AAD-)Annexin V+ and 38.8% 7-AAD+ CMK cells after 48h at 2mM VPA) and cell cycle arrest (50% reduction of CMK cells in S-phase at 2mM) via activation of the cell cycle inhibitor p21 and the proapoptotic genes BAX and BAK. Gene expression profiles indicated that VPA interferes with the oncogenic effects of GATA1s by globally repressing the deregulated E2F targets. The effects of VPA on leukemic growth in DS-AMKL could be attributed to its HDAC inhibitory function, as the global HDAC inhibitors SAHA and TSA induced a similar response.

Thus, by using a gene expression-based chemical genomic approach, we identified VPA as an efficient and well-tolerated treatment option for DS-AMKL and DS-TL by targeting GATA1s-mediated deregulation of the E2F transcription network.