Abstract SY02-01: Targeting the histone methyltransferase DOT1L in MLL-rearranged leukemia

Abstract

Abstract Protein methyltransferases (PMTs) are enzymes that catalyze the addition of methyl groups to the lysine and arginine residues of proteins, including histones. Recent evidence shows that PMTs are misregulated in a variety of cancers and thus may serve as therapeutic targets. A subset of acute leukemias have reciprocal translocations at 11q23 involving the PMT gene mixed lineage leukemia (MLL). MLL translocations occur in approximately 5% of adult acute lymphocytic leukemias (ALL) and 5 to 10% of adult acute myeloid leukemias (AML) including therapy-related leukemias. Multiple studies have demonstrated that patients with leukemias bearing the MLL translocation have a poor prognosis and are in need of new therapies. Translocations of the MLL gene result in the loss of the catalytic domain of the protein. The most common translocation partners, AF4, AF9 and ENL, recruit another PMT, DOT1L that methylates histone H3K79. Recruitment of DOT1L to the MLL fusion protein results in increased H3K79 methylation at MLL fusion protein target genes and elevated expression of the MLL target genes resulting in leukemogenesis. Mistargeted DOT1L enzymatic activity has therefore been proposed to be required for the development and maintenance of leukemias bearing the MLL translocation. To evaluate the potential of DOT1L as a therapeutic target in MLL- rearranged leukemia, we designed and characterized the DOT1L inhibitor EPZ004777, a small molecule with sub-nanomolar affinity for this enzyme and >1000 fold selectivity against other PMTs. EPZ004777 selectively inhibits intracellular histone H3K79 methylation in a concentration and time dependent manner. Significant changes in genes expression were observed in MLL-rearranged cell lines following the decrease in histone H3K79 methylation. Gene set enrichment analysis (GSEA) of genes downregulated following EPZ004777 treatment demonstrated strong enrichment for genes overexpressed in MLL-rearranged human acute leukemias as compared with MLL-germline acute leukemias. Phenotypically, EPZ004777 inhibits proliferation and induces apoptosis in human MLL-rearranged leukemia cell lines, with little effect on non-MLL-translocated cells. In vivo administration of EPZ004777 leads to extension of survival in a mouse MLL xenograft model. These studies provide compelling validation for the development of DOT1L inhibitors as targeted therapeutics for MLL-rearranged leukemia. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr SY02-01. doi:1538-7445.AM2012-SY02-01