CB-839 reduces IL-6/IL-10 secretion and impairs STAT3 activation. (A) ABC DLBCL cell lines were treated with solvent, 500 nM CB-839 and/or 5 ng/mL recombinant human IL-6 and IL-10, as indicated, and the phosphorylation of STAT3 was assessed by immunoblot analysis. Tubulin served as loading control. (B) ABC DLBCL cell lines were treated with solvent or 500 nM CB-839 for 48 hours. Secreted IL-6 and IL-10 were quantified by ELISA and normalized to the solvent control. (C) The ABC DLBCL cell lines HBL-1 and U2932 were treated with solvent, 500 nM CB-839 and/or 5 ng/mL recombinant human IL-6 and IL-10, as indicated. Cell numbers were determined daily and normalized to the solvent control. (D-E) HBL-1 and U2932 cells expressing an inducible control vector or the hyperactive mutant STAT3C-FLAG were treated with 1 μg/mL doxycycline to induce cDNA expression for 24 hours. Cells were then treated with solvent or 500 nM CB-839. Cell numbers were quantified at the indicated times and normalized to the respective solvent controls. Error bars correspond to the mean ± SD. Data are representative of 3 for panels B-C or 2 for panels A,D-E independent experiments. Statistical significance was calculated using the Student t test (unpaired, 2-tailed) to compare the solvent with the CB-839–treated samples. cDNA, complementary DNA.