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Photodynamic therapy (PDT), a new treatment modality for localized cancers involving the selective interaction of visible light with photosensitizers, such as hematoporphyrin derivatives (HpD) or dihematoporphyrin ether/ester (DHE) (Photofrin II). Photodynamic therapy of malignant tumors includes biological, photochemical and photophysical processes. These processes involve: (i) absorption of photosensitizing agent; (ii) selective retention of photosensitizer in tumors and (iii) irradiation of sensitized tumor by laser irradiation. This paper provides a review of photosensitizers, photochemistry, subcellular targets, side effects and lasers involved in photodynamic therapy. In addition, gradual increase in knowledge related to in vivo and in vitro mechanisms of action of PDT, as well as some clinical applications of photodynamic therapy are presented.

Experiments were performed on five batches of Wistar inbred rats with Walker-256 carcinoma receiving sole (PDT, MAK) or combined therapy (PDT + MAK-A; PDT + MAK-B); the control batch (HBSS) consisted of animals with untreated tumors. The results were as follows: a) the sole treatment (PDT, MAK) gave survival rates between 37.7 and 47.5%, b) the "combined" therapy in five doses increased significantly (70.8%) the survival rate of tumor bearing rate as well as the rate of complete regression (82.1%). The cell-mediated immunity test and histopathological as well as the electron microscopy observations were in full agreement with the results above. Summing up, these results demonstrate that "combined" photodynamic therapy with intra- and peritumoral MAK infusion stimulated cell-mediated antitumoral activity, increased survival rates and reduces incidence of Walker-256 carcinoma in rat model.

The purpose of this study was to evaluate by electron microscopy the tumoral fine structure changes induced by photodynamic therapy (PDT) in diabetic animals. Walker -256 carcinosarcoma harvested from animals with/without diabetes mellitus exposed to PDT (Photofrin II/5 mg/kg and 24 hrs later He-Ne laser irradiation/632.8 nm; 10 mW) and examined by electron microscopy showed different degrees of lesions in the nucleus and cytoplasmic fine structure. The ultrastructural changes induced by PDT in animals with diabetes mellitus bearing carcinosarcoma are characterized by: lysis of chromatin situated on the central zone of nucleus; swelling and vacuolization of mitochondria; formation of phagosome--like structures; myelin figures; degenerescence and disappearance of cytoplasmic organelles. Summing up, the data presented in this work demonstrate that the exposure to three doses of PDT produces changes in tumoral fine structure, increases survival rate and reduces incidence of carcinosarcoma in rats with diabetes mellitus.

Photodynamic therapy (PDT) is a promising local treatment modality based on the selective accumulation of a photosensitizer in malignant tissues and the subsequent irradiation with laser light. Photodynamic therapy of malignant tumors includes biological, photochemical and photophysical processes. These processes involve: (a) absorption of photosensitizing agent; (b) selective retention of the photosensitizer in tumors and (c) irradiation of sensitized tumor by laser radiation. This report provides a review of photosensitizers, photochemistry, subcellular targets, side effects and laser involved in photodynamic therapy. In addition, gradual increase in knowledge related to in vitro and in vivo mechanisms of action of PDT, as well as some clinical applications of photodynamic therapy are presented.

HeLa S3 tumoral cells were used as an experimental model for studying the association of photodynamic therapy (PDT) and antitumoral agents. Tumoral monolayer cultures were incubated 18 hours at 37 degrees C with Photofrin II, trypsinized and suspended in Eagle medium supplemented with 10% FCS and then treated with antitumoral agents 90 minutes before He-Ne laser exposure. The tumoral cells were exposed to antitumoral agents in the following concentrations (equivalent to ED70): adriamycin (0.0297 micrograms); mitomycin C (0.0199 micrograms); 5-FU (0.4937 micrograms) and vinblastine (0.0109 micrograms) per 10(5) cells. Macromolecular syntheses (DNA, RNA and proteins) were investigated by use of radioactive precursors: 3H-thymidine, 3H-uridine and 3H-leucine, as expressed in percent referring to Photofrin II-pretreated controls; they were exposed to He-Ne laser but not treated with antitumoral agents. All experiments were followed for 72 hours incubation at 37 degrees C. The conclusions of the results of PDT associated with antitumoral agents sustain the following aspects: a) the antitumoral agents activity (adriamycin, mitomycin C, 5-FU, vinblastine) was more noticeable when applied 90 minutes before He-Ne laser irradiation; b) inhibition of radioactive precursors uptake in DNA, RNA and proteins was accompanied by suppression of in vitro tumoral cells development and c) PDT association with antitumoral agents could manifest at least three positive effects upon animals; 1) PDT potentiating effects with antitumoral agents; 2) suppressing effects on tumoral macromolecular synthesis; 3) antitumoral agents cytotoxic elimination (due to the low doses used).