Exposure of U937 cells to 17-AAG and UCN-01. (A) U937 cells were exposed for 30 hours to 400 nM 17-AAG (AAG) in the presence or absence of the designated concentration of UCN-01 (UCN). At the end of the incubation interval, the percentage of apoptotic cells was determined by examining Wright-Giemsa–stained cytospin preparations as described in “Materials and methods.” For each determination, at least 10 randomly selected fields containing more than 500 cells were evaluated. (B) U937 cells were exposed to 75 nM UCN-01 for 30 hours in the presence or absence of the designated concentration of 17-AAG, after which the percentage of apoptotic cells was determined as described. For both panels, values represent the means ± SD for 3 separate experiments performed in triplicate.