p38^MAPKlimits H₂O₂-induced proliferation. (A) p38^MAPK phosphorylation was induced in MV4-11 cells treated with 12.5 mU/mL GOX for 3 hours. (B) Demonstration of inhibitor efficacy. MV4-11 cells were pretreated with either vehicle control, UR13756, SB203580 (p38^MAPK inhibitors), or catalase before treatment with 1 mM H₂O₂. Phosphorylation of p38^MAPK and its downstream target MAPKAPK2 were then examined by Western blot. Phosphorylation of MAPKAPK2 causes a retardation of electrophoretic migration (arrows). (C) MV4-11 cells (n = 4) (i) or 3 primary AML blast samples (ii-iv) were incubated for 48 hours with GOX and either vehicle control or 50 nM UR13756. The chart shows MTS reagent absorbance at 492 nm as a percentage of untreated control absorbance, which was set at 100%. Significance of difference determined by one-way analysis of variance followed by Tukey’s honestly significant difference test. *P < .05.