Selective killing of mixed lineage leukemia cells by a potent small-molecule DOT1L inhibitor

Abstract

Mislocated enzymatic activity of DOT1L has been proposed as a driver of leukemogenesis in mixed lineage leukemia (MLL). The characterization of EPZ004777, a potent, selective inhibitor of DOT1L is reported. Treatment of MLL cells with the compound selectively inhibits H3K79 methylation and blocks expression of leukemogenic genes. Exposure of leukemic cells to EPZ004777 results in selective killing of those cells bearing the MLL gene translocation, with little effect on non-MLL-translocated cells. Finally, in vivo administration of EPZ004777 leads to extension of survival in a mouse MLL xenograft model. These results provide compelling support for DOT1L inhibition as a basis for targeted therapeutics against MLL.

Figure 1. Biochemical Characterization of EPZ004777 Inhibition of DOT1L

(A) Chemical structure of EPZ004777. (B) Inhibition of recombinant human DOT1L by EPZ004777. Each data point represents the mean of two replicates at each specified concentration of compound. The data are fit to a standard Langmuir isotherm equation for inhibition (Copeland, 2005). (C) Plot of IC₅₀ values of EPZ004777 as a function of SAM concentration relative to the K_m of S-adenosylmethionine (SAM) ([SAM]/K_m). These values display a linear relationship as expected for SAM-competitive inhibition with a K_i of 0.3 ± 0.03 nM (± error represents standard error of the mean [SEM]). (D) Plot of IC₅₀ values for EPZ004777 against a panel of human HMT enzymes.

Figure 2. EPZ004777 Inhibits Cellular H3K79 Methylation and MLL Fusion Target Gene Expression

(A) Upper panel: immunoblot analysis of H3K79me2 levels in MV4-11 (MLL-AF4), MOLM-13 (MLL-AF9), and Jurkat human leukemia cell lines following 4 days of treatment with EPZ004777 at indicated concentrations. Lower panel: time course of depletion of cellular H3K79me2 levels in MV4-11 cells treated with 3 μM EPZ004777. (B) Immunoblot analysis of histones extracted from MV4-11 cells treated with 10 μM EPZ004777 with a panel of methyl-lysine and methyl-arginine residue specific antibodies. (C) Quantitative real-time PCR analysis of HOXA9 and MEIS1 mRNA levels in MV4-11 and MOLM-13 cells following 6 day incubation with EPZ004777. Relative mRNA expression levels are plotted as a percentage of those in vehicle-treated control cells. (D) Time course of HOXA9, MEIS1 and TBP mRNA expression in MV4-11 and MOLM-13 cells over 8 days of incubation with 3 μM EPZ004777 as measured by quantitative real-time PCR. Relative mRNA expression levels are plotted as a percentage of those at day 0. Error bars: standard deviation (SD).

Figure 3. EPZ004777 Selectively Inhibits Proliferation of MLL-Rearranged Cell Lines and MLL-AF9-Transformed Murine Hematopoietic Cells

(A) Growth of MV4-11 (MLL-AF4), MOLM-13 (MLL-AF9), and Jurkat (non-MLL-rearranged) cells during several days incubation with 3 μM EPZ004777. Viable cells were counted every 3 to 4 days in the presence of EPZ004777 (+) or DMSO vehicle control (−) and results plotted on a logarithmic scale. See also Figure S1. Error bars represent standard deviation. (B) Effect of EPZ004777 on the proliferation of leukemia cell lines bearing MLL-AF4, MLL-AF9, and MLL-ENL fusions, or cell lines lacking an MLL rearrangement. Cell lines were maintained in the presence of increasing concentrations of EPZ004777 up to 50 μM. Viable cells counts were used to derive IC₅₀ values after 14 days of treatment for all cell lines apart from THP-1 cells, which were treated for 18 days. Fifty percent inhibition of growth was not achieved in HL60, Jurkat and U937 cells even at the highest EPZ004777 concentration and so IC₅₀ values are given as >50 μM. (C) Effect of EPZ004777 on the proliferation of primary murine hematopoietic progenitors transformed by retroviral expression of MLL-AF9, or coexpression of HoxA9 and Meis1a. Retrovirally transformed cells were maintained in the presence of increasing concentrations of EPZ004777 up to 30 μM for 10 days, then plated in 96-well plates for MTT assay at day 12. Following the MTT assay, plate ODs were read at 570 nM and plotted on the y axis. Results from two independent transductions are shown for each retroviral construct. Error bars represent standard deviation. (D) Inhibition of cellular H3K79me2 levels in MLL-AF9 or Hoxa9-Meis1a transformed hematopoietic progenitors following 10 days of treatment with the indicated concentrations of EPZ004777 as measured by immunoblot analysis of extracted histones with an anti-H3K79me2 antibody.

Figure 4. EPZ004777 Causes Apoptosis and Differentiation in MLL-Rearranged Cell Lines

(A and B) MV4-11 (A) and MOLM-13 (B) cells were treated with 3 μM EPZ004777 for up to 10 days and analyzed by flow cytometry every 2 days for DNA content, and Annexin V staining. See also Figure S2. (C) MOLM-13 cells were incubated in the presence of 3 μM EPZ004777 for 12 days and analyzed by flow cytometry for cell surface expression of CD14. Similar results were obtained in two independent experiments. (D) Gene Set Enrichment Analysis (GSEA) (Subramanian et al., 2005) of genes upregulated by EPZ004777 treatment of MOLM-13 cells as compared with members of the KEGG hematopoietic cell lineage gene set. The heat map shows genes comprising the leading edge of the GSEA plot. Red indicates high expression; blue indicates low expression.

Figure 5. Effect of EPZ004777 Treatment on MLL-Rearranged Gene Expression

(A) Gene expression changes following treatment of MV4-11 cells with EPZ004777 for 2, 4, or 6 days and MOLM-13 cells for 6 days. Two-group comparison expression data were collapsed to unique gene symbols. Changes in gene expression were filtered by log2 change > 1 or < −1 and by false discovery rate q values < 0.15. (B) GSEA of genes downregulated by EPZ004777 treatment of MOLM-13 cells as compared with genes overexpressed in MLL-rearranged human acute leukemias (Ross et al., 2004). The heat map shows genes comprising the leading edge of the GSEA plot. Red indicates high expression; blue indicates low expression. (C) GSEA of genes downregulated by EPZ004777 treatment of MOLM-13 cells as compared with genes bound by MLL-AF9 in MLL-AF9-transformed murine hematopoietic progenitors (see Experimental Procedures and Bernt et al., 2011 [this issue of Cancer Cell]). The heat map shows genes comprising the leading edge of the GSEA plot. (D) GSEA of genes downregulated by EPZ004777 treatment of MV4-11 cells as compared with genes bound by MLL-AF4 in human SEM cells (Guenther et al., 2008). The heat map shows genes comprising the leading edge of the GSEA plot. (E) GSEA of genes downregulated by EPZ004777 treatment of MOLM-13 cells as compared with genes downregulated following genetic knockout of Dot1l in a murine MLL-AF9 leukemia model (see Experimental Procedures and Bernt et al., 2011 [this issue of Cancer Cell]). The heat map shows genes comprising the leading edge of the GSEA plot.

Figure 6. In Vivo Activity of EPZ004777

(A) H3K79me2 levels were evaluated by immunoblot in subcutaneous MV4-11 tumors derived from untreated animals or animals implanted with pumps containing a 50 mg/ml solution of EPZ004777 for a period of 6 days. (B) EPZ004777 extends survival of NSG mice after intravenous injection of MV4-11 cells. MV4-11 cells were injected into the tail vein of NSG mice, and animals were implanted with pumps containing vehicle or 50, 100, or 150 mg/ml EPZ004777. Pumps were exchanged once to give a total of 14 days of exposure as indicated. See also Figure S3A. (C) Complete blood count analysis in C57BL/6 mice treated for 14 days with EPZ004777 or vehicle control. WBC, white blood cell count; NE, neutrophils; LY, lymphocytes; MO, monocytes; Hb, Hemoglobin; Plt, platelets; K/μl, thousands per microliter; M/μl, millions per microliter. N = 5 mice per group, *p < 0.01, all others not significant (p > 0.05). (D) Effect of 14 days of EPZ004777 treatment on colony formation of hematopoietic progenitors. Five mice per group, all differences not significant (p > 0.05). Error bars represent standard error of the mean. See also Figures S3B–S3D.