Project Summary Mutant forms of isocitrate dehydrogenase (IDH) have been identified in 20% of AML. The goal of this project is to better understand the effects of mutant IDH on chromatin, and to develop novel therapies for IDH-mutant AML. Mutant forms of IDH1/2 gain a neomorphic function, producing 2-hydroxyglutarate (2HG) instead of the normal metabolite αKG. 2HG inhibition of TET2, which mediates DNA hydroxymethylation, is a major mechanism of transformation by mutant IDH. However, 2HG also inhibits JmjC domain containing histone demethylases. Whether inhibition of JmjC demethylases and altered histone methylation contributes to leukemogenesis is currently not known. This project investigates the role of histone 3 lysine 79 methylation (H3K79me) in mutant-IDH mediated leukemogenesis. H3K79 methylation is increased in response to expression of mutant IDH, or exogenous exposure to 2HG, suggesting the existence of an H3K79 demethylase that is inhibited by 2HG. H3K79 is methylated by DOT1L. A contribution of aberrant H3K79 methylation to IDH–mutant leukemogenesis is highly relevant as a pharmacologic inhibitor of DOT1L is currently in clinical trials. This project will investigate whether DOT1L is required in IDH-mediated leukemogenesis using a murine leukemia model (SA1) as well as detailed analysis of changes in chromatin and gene expression in patient samples (SA2). Finally, the project aims to identify a demethylase for H3K79 (SA3).