Abstract 1380: Towards peptidomimetics to target DOT1L recruitment in MLL-AF9 leukemia

Abstract

Abstract Leukemias harboring rearrangements of mixed-lineage leukemia gene (MLL1) are associated with poor clinical outcomes, and new therapeutic approaches are needed. Rearrangement of the MLL1 gene generates 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. We have mapped the binding site to a short segment of 10 amino acids in DOT1L and shown that DOT1L mutants lacking these residues did not support transformation by MLL-AF9. We hypothesized that by targeting the AF9-DOT1L protein-protein interactions (PPIs), we would selectively kill MLL-AF9 cells without effecting DOT1L role in normal hematopoiesis. Using established DOT1Lf/f MLL-AF9 with reintroduced WT-DOT1L, DOT1L missing 10aa AF9-binding domain (D10), DOT1L with a point mutation in the AF9-binding domain (I867A) and enzymatically inactive DOT1L (RCR), we were able to demonstrate that by disrupting the AF9-DOT1L PPIs, although we can inhibit leukemogenesis similarly to enzymatic inhibition, this interaction is not essential for normal hematopoiesis. Based on our initial studies to map the DOT1L interaction site and in conjunction with utilizing reported NMR structures of the AF9-DOT1L complex, we investigated the nature of the interactions and the minimum length of the peptide. Using different natural and unnatural amino acids, we successfully designed a 7mer peptide with KD of 10 nM and 25 nM against AF9 and ENL, respectively, showing similar potency as the originally identified and validated 10mer peptide. These results lay the groundwork for further optimization of the 7mer peptide towards developing DOT1L peptidomimetics with improved potency and cellular activity, to further validate the PPIs between DOT1L and MLL-fusion proteins as a potential therapeutic target for MLL rearranged leukemia. Citation Format: Sierrah Marie Grigsby, Jennifer Chase, Bridget Waas, Ann Friedman, Lei Du, Aihong Yao, James Ropa, Justin Serio, Andrew Muntean, Ivan Maillard, Haying Sun, Zaneta Nikolovska-Coleska. Towards peptidomimetics to target DOT1L recruitment in MLL-AF9 leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1380.