Rearrangement of the gene mixed-lineage leukemia (MLL) occurs in ~75% of infant and ~10% child/adult acute leukemias. Outcomes for MLL-rearranged leukemias are dismal, with fewer than 20% of infants <3 months of age expected to survive the disease. Intensified chemotherapy has led to increased toxicity without significantly improved survival, likely due to a small population of leukemic stem cells that are resistant to conventional chemotherapeutic agents. DOT1L, the only known histone 3-lysine 79 (H3K79) methyltransferase, is essential for the survival and proliferation of MLL-rearranged leukemia stem cells. A potent inhibitor of DOT1L, SYC-522, has been reported by our collaborator, Dr. Yongcheng Song [Yao, et al. (2011) J. Am. Chem. Soc.]. Treatment of MLL-rearranged leukemia cell lines with SYC-522 for 24 hours resulted in decreased H3K79 methylation at 3μM for MV4-11 and 10μM for THP-1 and MOLM13 cell lines. SYC-522 did not affect H3K4 methylation in MLL-rearranged or MLL-wild type leukemia cell lines. After 3-6 days of treatment with SYC-522 (3μM), the mRNA levels of two important genes regulated by DOT1L, HOXA9 and MEIS1, were decreased by more than 50% in MV4-11 cells. Additionally, CCND1 expression was decreased by 30~50%, but BCL2L1 expression was not changed. Exposure of MLL-rearranged leukemia cells to SYC-522 caused cell cycle arrest in G0/G1 phase and promoted differentiation, as assessed both morphologically and by increased CD14 expression. Furthermore, SYC-522 treatment decreased the number of myeloid colony forming units (CFUs) of primary MLL-rearranged AML samples by 50% (30μM), but decreased myeloid CFUs from normal bone marrow samples by only 20%. SYC-522 induced <10% apoptosis in MLL-rearranged AML cell lines at doses up to 10μM for up to 20 days. However, pretreatment with SYC-522 (3μM for 3 days) significantly increased the sensitivity of MLL-rearranged leukemia cells to chemotherapy drugs, such as etoposide and mitoxantrone. Treatment of MV4-11 cells with 10nM mitoxantrone caused 20% ± 5% apoptosis, which was increased to 40% ± 5% with 10nM mitoxantrone+ 3μM SYC-522 (n=3; p<0.05). Similar results were obtained for MV4-11 cells treated with etoposide with and without SYC-522 pretreatment, and for MOLM-13 cells treated with each chemotherapy agent. These results suggest that SYC-522-mediated inhibition of DOT1L activity sensitizes MLL-rearranged leukemia cells to DNA-damaging chemotherapy, and therefore the inhibition of DOT1L is likely to be a promising approach to improving therapies for MLL-rearranged leukemia.

Citation Format: Wei Liu, Wei Liu, Lisheng Deng, Yongcheng Song, Michele Redell, Michele Redell. The inhibitory effect of a novel DOT1L inhibitor in MLL-rearranged acute myeloid leukemia. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr B45.