Beside the metabolic substrates such as folate and glucose, some clinical drugs and preclinical small molecules can also be used for tumor‐seeking dyes development.[40] For example, the combination of a small‐molecule compound such as pharmacophore acetazolamide (15, Figure 4),[41] crizotinib (16, Figure 4),[42] indomethacin,[43] histone deacetylase 6 inhibitor[44] and a fluorophore maintains the tumor‐seeking ability. This evidence concerns the gene HDAC6 and neoplasm.