Pharmacological and shRNA-mediated inhibition of STAT3 in TEL-AML1 leukemic cells blocks proliferation and induces apoptosis. (A-B) Proliferation of leukemic cell lines as measured by MTS assay after 96 hours culture with the indicated concentrations of the STAT3 inhibitor, S3I-301 (A), and STAT5 inhibitor (STAT5in) (B). Results are normalized to the proliferation of dimethylsulfoxide (DMSO)-treated cells. (C) Percentage of apoptotic Annexin V⁺PI^- cells 24 hours after DMSO or S3I-301 treatment. (D) Percentage of cells in the S-phase of the cell-cycle 24 hours after DMSO or S3I-201 exposure. Cells were pulsed with 10 µM 5-ethynyl-2´-deoxyuridine (Edu) for 1 hour. (E) Percentage of apoptotic Annexin V⁺PI^- 6 days after transduction with control scramble or 2 different STAT3 (shSTAT3) shRNA. (F) Percentage of cells in the S-phase of the cell-cycle 6 days after transduction with control scramble or 2 different STAT3 (shSTAT3) shRNA. Cells were pulsed with 10 µM 5-ethynyl-2´-deoxyuridine (Edu) for 1 hour. All data are representative of 3 independent experiments and show mean ± standard deviation of triplicate measurements. *P < .05, **P < .01, ***P < .005 compared with control (Student’s unpaired t test).