Selective aggregation of zinc phthalocyanines in the skin

In photodynamic therapy it is important to avoid undesirable side effects caused by photodynamic reactions with accumulated photosensitizers, especially in the skin. Although phthalocyanine monomers can serve as photosensitizers, aggregated phthalocyanines are inactive. In this study the aggregations of five zinc phthalocyanines (MSPc, TSPc, TX-101A, TX-105A and TX-106A) in the skin and in the tumor are compared. Every phthalocyanine was more dissociated in the tumor than in the skin. In particular, TX-101A and TX-106A remained in monomeric form in the tumor but were aggregated in the skin. The aggregation effects of phthalocyanines in organic solvents and biological materials were also investigated. These phthalocyanines were aggregated in water and ethanol and also by the addition of bovine serum albumin and ghosts of red cells. On the other hand, they were dissociated in propanol and also by the addition of low-density lipoprotein. It was found that the dissociation of these phthalocyanines depended strongly on the polarity of the solvents and on the biological microenvironment.