Cytotoxicity assay (MTT) for HT-29 colon cancer cells post-treatment with free Dox, and with non-targeted (NT) and CA IX targeted- (T), unloaded and Dox-loaded Au NPs, bearing either amide (AM) or hydrazone (HZN) groups, under normoxic and hypoxic conditions. Note that CA IX targeted, HZN-bearing Au nanoplatform THZN enhanced the toxicity of doxorubicin under hypoxic conditions as compared with the non-targeted nanoplatform NTHZN (P < 0.001) and it also reversed the hypoxia-induced chemoresistance, observed for the free doxorubicin