Knockdown or inhibition of HDAC6 augments loss of clonogenic survival due to treatment with 17-AAG. (A) K562-transfected with control/siHDAC6 construct for 24 hours followed by treatment with indicated doses of 17-AAG for 24 hours and colonies were counted on day 10. Values plotted are means of 3 experiments plus or minus SD. P values were determined by Student t test. (B) K562-transfected with control/siHDAC6 construct for 48 hours, stained with anti-HDAC6 and anti–Ki-67 antibodies, and imaged using confocal immunofluorescent microscope using a 63×/1.2 W correction objective. (C) K562 cells were treated with indicated doses of tubacin with or without 17-AAG for 48 hours, and the loss of survival was assessed by trypan blue exclusion test. Error bars represent SD.