Efficacy to target in vivo patient-derived xenografts. (A) Diagram of treatment of T-ALL PDX mice with OTSSP167 (10 mg/kg) daily for 3 weeks. (B) Representative flow cytometric detection of human CD45 blasts at the end of each treatment week in T-ALL PDX01 (relapse) xenografts. (C) Monitoring human CD45 expansion in individual T-ALL PDX mice (PDX01) treated with vehicle or OTSSP167 (n= 10 per group). (D) Overall survival of mice from the experiment in C (n= 10 per group, P < .0001). (E) Human CD45 expansion in individual T-ALL PDX mice (PDX02, relapse) treated with vehicle or OTSSP167 (n= 5 per group) during a 3-week treatment. Leukemia cells were analyzed in the bone marrow 2 days after the end of treatment. (F) Monitoring human CD45 expansion in individual T-ALL PDX mice (PDX04) treated with vehicle or OTSSP167 (n= 4 vehicle, n=3 OTSSP167) during a 3-week treatment. Leukemia cells were analyzed in the bone marrow 2 days after the end of treatment. (G) Percentage of human CD45 in blood at the end of a 3-week treatment for the 3 T-ALL PDXs. (H) Immunoblot analysis of inhibition of MAP2K7 and NOTCH1 pathways in T-ALL PDX01 and PDX04 treated with vehicle or 100 nM OTSSP167 for 17 hours. ∗∗P < .01, ∗∗∗∗P < .0001 two-tailed Student t test was used in (D). Log-rank test was used in (D).