Positively charged phthalocyanine-arginine conjugates as efficient photosensitizer for photodynamic therapy

Abstract

Positively charged drugs usually have enhanced water solubility, cellular uptake efficiency and anticancer activity. However, the common quaternized and protonated cationic photosensitizers both have some drawbacks such as needing potentially dangerous agents for preparation and easily being deprotonated in alkaline circumstance. Arginine is unique among the amino acids as its guanidine group has exceptionally high basicity in aqueous solution, which may make it positively charged in a wide range of pH. In this paper, two arginine substituted zinc phthalocyanines (ArgEZnPc and ArgZnPc) were reported. They can be positively charged in the range of pH 5–9. Moreover, the photobiological, photochemical properties, subcellular localization, and in vitro anticancer activities of the them were also carried out. The results show that ArgZnPc may be not a good photosensitizer because of its poor photobiological activities though it is positively charged in a wide range of pHs. This may be attributed to the formation of inner salts between guanidine and carboxyl groups of ArgZnPc, which weakens its photobiological and in vitro anticancer activity. While in contrast, ArgEZnPc shows preferential localization in the lysosomes of HeLa cells, exhibits high water solubility, excellent 1O2 and intracellular reactive oxygen species generation efficiency as well as high in vitro anticancer activity, making it a promising photosensitizer for photodynamic therapy.