Exposure of human leukemia cell lines to 17-AAG and UCN-01. Human leukemia cell lines were exposed to 17-AAG with or without UCN-01 for 24 or 48 hours, after which the extent of apoptosis was determined by morphologic analysis of Wright-Giemsa–stained cytospin preparations as described in “Materials and methods.” (A) NB4 promyelocytic leukemia cells were exposed to 50 nM UCN-01 with or without 300 nM 17-AAG for 24 hours; (B) Jurkat lymphoblastic leukemia cells were exposed to 75 nM UCN-01 with or without 1.5 μM 17-AAG for 48 hours. In each case, values represent the means ± SD for 3 separate experiments performed in triplicate.