An integrin-targeting glutathione-activated zinc(II) phthalocyanine for dual targeted photodynamic therapy.

A zinc(II) phthalocyanine substituted with three 2,4-dinitrobenzenesulfonate (DNBS) groups and a cyclic arginine-glycine-aspartic acid (cRGDfK) moiety was prepared and characterized. With three strongly electron-withdrawing DNBS groups, this compound was fully quenched in terms of fluorescence emission and singlet oxygen generation in N,N-dimethylformamide and phosphate buffered saline due to the strong photoinduced electron transfer effect. In the presence of glutathione (GSH), which is the most abundant intracellular thiol particularly in tumor cells, the DNBS moieties were cleaved, thereby restoring these photoactivities and making the conjugate as a GSH-activated photosensitizer. Being a well-known integrin antagonist, the cyclic RGD peptide sequence could enhance the localization of the conjugate in integrin-upregulated tumor cells. As shown by confocal laser scanning microscopy and flow cytometry, the intracellular fluorescence intensity of the conjugate was significantly higher in the integrin-positive A549 and MDA-MB-231 cells than in the integrin-negative MCF-7 and HEK293 cells. The photocytotoxicity of the conjugate against MDA-MB-231 cells was also higher than that toward MCF-7 cells. The results suggest that this dual-functional photosensitizer is a promising candidate for targeted photodynamic therapy.