Hydrophobic Zn(II)-naphthalocyanines as photodynamic therapy agents for Lewis lung carcinoma

Abstract

Four Zn(II) 2,3-naphthalocyanines (unsubstituted ZnNc1, tetracetylamido substituted ZnNc2, tetramino substituted ZnNc3 and tetramethoxy substituted ZnNc4) incorporated into unilamellar liposomes of dipalmitoylphosphati-dylcholine have been injected intra-peritoneally (i.p.) (0.25-0.3 mg kg −1) to male C57/Black mice bearing a transplanted Lewis lung carcinoma. The pharmacokinetic investigations show that three of the four studied ZnNcs, 1, 2 and 4, are good tumor-localizers in Lewis lung carcinoma. The highest concentration is detected after ZnNc1 administration. The lowest tumor concentration as well as the lowest phototherapeutic effect were established with ZnNc3. In previous work it was shown that this ZnNc did not differ from the other three studied ZnNcs regarding the quantum yield of 1O 2-formation and the photoinduced electron transfer. Obviously not only the good photochemical properties but also the tumor drug uptake can be an important factor of effective PDT. The biodistribution investigations also show that 72 h after drug injection, the skin concentration of the studied ZnNcs returns to the original base line. Indeed, we can expect that the skin photosensitivity will last for no longer than three days after PDT. The established higher drug concentration in the tumor rather than in the liver tissue (20 h after injection) shows again the tumor targeting selectivity of the applied liposome-sensitiser delivered procedure. Evaluating the PDT effect as reflected in the dynamics of the mean tumor diameter, we obtained unambiguous data on the potential capacity of ZnNcs 1,2,4 as PDT-photosensitisers. The data obtained from the assessment of the cytotoxic effect of PDT on the basis of the degree of induced necrosis, gave an adequate characterization of the tumor tissue destruction. The results from the morphological analysis show the presence of direct photocytotoxic changes of neoplastic cell targets ie. membrane, mitochondria and rough endoplasmic reticulum, as well as delayed damage in the endothelial cells. The lack of haemorrhagic necrosis suggests a different mechanism of photonecrosis in comparison with the mechanism of photoinduced tumor necrosis after HpD photosensitization, where heavy haemorrhagic changes are observed. We consider that the observed different mechanism of tumor cell photodamage is not a unique property of the studied ZnNcs because similar changes have been observed from other authors after Zn-phthalocyanine photosensitization. We also suppose that the nature of the induced necrosis is different from that of the spontaneous one (untreated tumors), where there was no established endothelial cell damage. In conclusion we consider that ZnNc 1, 2 and 4 can be effective sensitizers for PDT of cancer owing to their selective targeting and slow clearance from tumor tissue, fast clearance from skin and pronounced phototherapeutic effect evaluated by a large number of parameters.