Probing tricarbocyanine dyes for targeted delivery of anthracyclines

Heptamethine carbocyanine dyes possess bright fluorescence in the near IR range and affinity to cancer cells. Thus, these dyes could be utilized as fluorescent labels and vectors for drug delivery in their covalent conjugates with cytotoxic compounds. In this work we synthesized four drug-dye conjugates of tricarbocyanine dyes with anthracycline drug daunorubicin using a CuAAC reaction. Conjugates with hydrophobic dyes possess submicromolar cytotoxicity. Fluorescent imaging revealed significant accumulation of the conjugates in mitochondria, suggesting an enhancement of an additional mechanism of anthracycline cytotoxicity – generation of ROS. The hypothesis was supported by significant reduction of activity of the conjugates in presence of an antioxidant compound.