AR-42 inhibits the proliferation of malignant mast cells via cell-cycle arrest and apoptosis. (A) P815 (top panel), C2 (middle panel), and BR (bottom panel) cells were treated with increasing concentrations of AR-42 for 24 hours. The cell proliferation rate was assessed by BrdU incorporation and the median inhibitory concentration was then calculated for each cell line. Three independent experiments were performed, and 1 representative result is presented. (B) P815, C2, and BR cells were treated with 0.5μM AR-42 for 24 hours. Cells were then evaluated for effects on cell cycle using propidium iodide (PI) staining and flow cytometry. Three independent experiments were performed, and 1 representative result is presented. (C) P815, C2, and BR cells (10 × 10⁶) were treated with increasing concentrations of AR-42 and 1μM 17-AAG for 24 hours. Apoptosis was assessed by annexin V/PI staining and flow cytometry. Three independent experiments were performed and their data were calculated (*P < .05). (D) P815, C2, and BR cells were incubated with various concentrations of AR-42 and 17-AAG for 24 hours and caspases-3/7 activation was assessed (*P < .05). Experiments were performed in triplicate and repeated 3 times. (E) P815, C2, and BR cells were treated with various concentrations of AR-42 or 1μM 17-AAG for 24 hours. Effects on the expression of Bcl-2, Bcl-xL, and PARP were determined by Western blot analysis.