Efficacy of compounds 10 and 11 in PDXs. (A) Schematic of mouse trial using compound 10–supplemented chow (0.05%). (B) Kinetics of peripheral blood (PB) human CD45⁺ cells measured by flow cytometry during treatment with compound 10 by chow (0.05%). (C) Compound 10 plasma concentrations during oral administration via chow (0.05%) in the morning compared with the afternoon, indicating variant drug levels based on feeding activity of the animals. (D) Assessment of compound 10 toxicity measured by mouse body weight during administration via oral gavage (twice daily) at 50 and 100 mg/kg. Treatment was discontinued between days 3 and 5 because of toxicity observed with the 100 mg/kg dosing. (E) Plasma concentrations of compound 10 (left) and compound 11 (right) after oral and intraperitoneal (IP) administration, respectively. This pharmacokinetic study was performed at 14 days of twice-daily treatment to reflect the drug levels in PB during ongoing administration. Both drugs were solubilized in Kolliphor HS 15 before administration. (F) Schematic of PDX mouse trial using 2 different patient-derived samples and 2 novel DOT1L inhibitors as indicated. Both PDX grafts have been used and published by our laboratory before: PDX 1 (ID:68552; Krivtsov et al⁵  in 2019) and PDX 2 (ID:17; Wang et al¹⁷  in 2017). (G-H) Kinetics of PB human CD45⁺ cells measured by flow cytometry during treatment with compound 10 (G) or compound 11 (H). Statistics were performed at the end point of the experiment (4 weeks on treatment), comparing treated and nontreated animals using unpaired t test. (I) Human CD45⁺ cells measured by flow cytometry in the bone marrow, spleen, and PB at the experimental end point (4 weeks on treatment; same animals as shown in Figure 1G-H) after compound 10 (top) or compound 11 (bottom) treatment. (J) Spleen weights (in mg) at the experimental end point after compound 10 (top) or compound 11 (bottom) treatment. (K) Blood cell counts in the PDX 1 cohort treated with compound 10 at the end point of the experiment. (L) CD11b surface expression on human CD45⁺ cells in the bone marrow of mice treated with compound 10 at the experimental end point. (M) Gene expression of MEIS1 and HOXA10 in PB leukemia cells of PDX 1 cohort mice treated with compound 10 at 14 days after initiation of treatment. Quantitative real-time polymerase chain reaction was performed using validated Taqman assays. (N) Western blot of H3K79me2 and total H3 as control in PDX cells from bone marrow of each of 2 representative mice (PDX 1) treated with compound 10 or vehicle. Statistics for all comparisons were performed using unpaired t test. *P < .05, **P < .01, ***P < .001, ****P < .0001. HB, hemoglobin; PBMC, peripheral blood mononuclear cell; PLT, platelet; sAML, secondary AML; WBC, white blood cell.