HSP90 inhibition impairs the growth of mutant KRAS-dependent colon tumors on chicken CAM. (a) Tumor formation on chicken CAM of KRAS WT (Caco-2) and mutant KRAS-dependent (HCT-116) colon cancer cell lines treated with 5 µM 17-AAG or 1 µM PU-H71 or vehicle for 48 h. Representative photographs of tumors (cells were deposited within a 5-mm silicon ring to allow drug administration) and tumor areas (error bars represent mean ± SEM of four to six tumors) are shown. Bar, 1.5 mm. (b and c) IHC analysis of CAM tumors shown in a. STK33 protein expression (b) and TUNEL staining (c) of Caco-2 and HCT-116 tumors. Representative photographs of tissue sections and the proportion of TUNEL-positive cells (error bars represent mean ± SEM of four microscopic fields with 600 cells) are shown. NS, not significant. Insets in c show details of the corresponding photographs. Bar: 125 µm; inset, 25 µm.