Effects of ectopic Meis1 expression in murine Npm1^mut Flt3-ITD⁺ leukemias. (A) Relative mRNA expression of Meis1, Hoxa9, and Flt3 in murine Npm1^CA/+Flt3^ITD/+ cells ectopically expressing Meis1 or both Meis1 and Hoxa9, normalized to cells with just endogenous Meis1 and Hoxa9 expression. (B) Dose-response curves from cell viability assays after 11 days of MI-503 treatment comparing Npm1^CA/+Flt3^ITD/+ cells vs Npm1^CA/+Flt3^ITD/+ cells overexpressing Meis1 or Meis1-Hoxa9. Dashed lines indicate the shift of IC₅₀ values. (C) Dose-response curves from cell viability assays after combinatorial treatment with MI-503 (MI, 6 days) and ponatinib (Po; 72 hours) comparing Npm1^CA/+Flt3^ITD/+ cells vs Npm1^CA/+Flt3^ITD/+ cells overexpressing Meis1 or Meis1-Hoxa9. Dashed lines indicate the shift of IC₅₀ values. Cells with ectopic Meis1 and Hoxa9 expression in panels A-C were each obtained from 2 different clones after retroviral transduction. Shown are the average results of 3 different experiments with clone #1, all performed in triplicate. Error bars, standard deviation.