Abstract 3803: Development of genetic and chemical tools for understanding the recruitment of DOT1L in MLL-fusion driven leukemia and normal hematopoiesis

Abstract

Abstract Leukemias harboring rearrangements of mixed-lineage leukemia gene (MLL1) are associated with poor clinical outcomes, and new therapeutic approaches are needed. Rearrangements of the MLL1 gene generate fusion oncoproteins which drive the high expression of the clustered homeobox (HOX) genes and induce leukemic transformation. Genome wide histone methylation studies have revealed that the abnormal expression of MLL1 fusion target genes is associated with high levels of histone H3 lysine 79 (H3K79) methylation. Recruitment of DOT1L (disruptor of telomeric silencing 1-like), a unique histone methyltransferase that catalyzes methylation of H3K79, proved to be essential for the transforming activity of multiple MLL fusion proteins. To gain insights into the unique functions of DOT1L in MLL-driven leukemia, we elucidated the mechanisms of DOT1L recruitment to the MLL fusion partners. The binding site was mapped to a short segment of 10 amino acids in DOT1L and peptides derived from this region disrupted the interaction between DOT1L and MLL-AF9. DOT1L mutants lacking these 10 residues did not support transformation by MLL-AF9. This discovery has established a foundation for disease-specific therapies that target chromatin modifications in highly malignant leukemias. Applying high throughput screening approach several different chemical classes of small molecules that disrupt the protein-protein interactions between DOT1L and oncogenic MLL-fusion proteins were identified and validated. To evaluate if the AF9-binding domain of DOT1L is critical for its functions in normal hematopoietic stem cells as opposed to leukemias driven by MLL fusion proteins, genetic tools were developed to functionally investigate the importance of the DOT1L AF9-binding domain in MLL-AF9-driven leukemia and its role in the physiological functions of DOT1L in normal hematopoiesis. Our findings demonstrate that pharmacological inhibition of the DOT1L complex through disrupting the AF9-DOT1L interactions may provide therapeutic benefits in an array of malignancies with abnormal HOXA gene expression. Citation Format: Sierrah Grigsby, Jennifer Chase, James Ropa, Justin Serio, Chenxi Shen, Martha Larsen, Preston Donover, Melvin Reichman, Andrew Muntean, Ivan Maillard, Zaneta Nikolovska-Coleska. Development of genetic and chemical tools for understanding the recruitment of DOT1L in MLL-fusion driven leukemia and normal hematopoiesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3803.