Counterion Tuning of Near-Infrared Organic Salts Dictates Phototoxicity to Inhibit Tumor Growth

Counterion influence on near-infrared-II heptamethine cyanine salts for photothermal therapy

Photothermal therapy (PTT) has attracted extensive attention in cancer treatment. Heptamethine cyanine dyes with near-infrared (NIR) absorption performance have been investigated for PTT. However, they are often accompanied by poor photostability, suboptimal photothermal conversion and limited therapeutic efficacy. The photophysical properties of fluorescent organic salts can be tuned through counterion pairing. However, whether the counterion can influence the photostability and photothermal properties of heptamethine cyanine salts has not been clarified. In this work, we investigated the effects of eleven counter anions on the physical and photothermal properties of NIR-II heptamethine cyanine salts with the same heptamethine cyanine cation. The anions have great impacts on the physiochemical properties of dyes in solution including aggregation, photostability and photothermal conversion efficiency. The physical tuning enables the control over the cytotoxicity and phototoxicity of the dyes. The selected salts have been demonstrated to significantly suppress 4T1 breast tumor growth with low toxicity. The findings that the counterion has great effects on the photothermal properties of cationic NIR-II heptamethine cyanine dyes will provide a reference for the preparation of improved photothermal agents through counterion pairing with possible translation to humans.

Synthesis of Near-Infrared-Absorbing Anionic Heptamethine Cyanine Dyes with Trifluoromethyl Groups

A novel anionic heptamethine cyanine (HMC) dye with two trifluoromethyl groups that selectively absorb near-infrared light is synthesized. When contrasted with previously studied anionic HMC dyes with substituents such as methyl, phenyl, and pentafluorophenyl groups, the trifluoromethylated dye displays a red-shifted maximum absorption wavelength (for instance, 948 nm in CH₂Cl₂) along with enhanced photostability. Furthermore, HMC dyes with broad absorption in the near-infrared region are synthesized by combining a trifluoromethylated anionic HMC dye with a cationic HMC dye as a counterion.