Dicyanomethylene Substituted Benzothiazole Squaraines: The Efficiency of Photodynamic Therapy In Vitro and In Vivo

The lack of ideal photosensitizers limits the clinical application of photodynamic therapy (PDT). Here we report the PDT efficiency of dicyanomethylene substituted benzothiazole squaraine derivatives. This class of squaraine derivatives possess strong absorption and long excitation and emission wavelengths (ex/em, 685/720 nm). They show negligible dark toxicity, but can generate singlet oxygen under irradiation resulting in the apoptosis and necrosis of cells (phototoxicity). Changing the side chains of these compounds greatly influences their albumin-binding rate, cellular uptake and their phototoxicity. One of the squaraine derivatives with two methyl butyrate side chains shows high PDT efficiency in a mouse subcutaneous xenograft model under the irradiation of a 690 nm laser. These results show the great potential of dicyanomethylene substituted benzothiazole squaraines to be the leading compound of near-infrared photosensitizers in PDT.