Photodynamic therapy (PDT) is the method of photosensitized tumor treatment. It is based on the photosensitizer (PS) selective accumulation in tumors, its subsequent activation under the light influence and oxygen active form formation that results in tumor destruction. Photodynamic action of some new water-soluble porphyrins was investigated in our laboratory. Dose-dependent effect of these porphyrins was shown on PC-12 murine pheochromocytoma cell line. The results revealed that the efficiency of the investigated porphyrins decreased in the following way: TOEPyP (meso-tetra-(4-N-oxyethylpyridyl)porphyrin) > Zn-TOEPyP > Ag-TOEPyP. It was shown that TOEPyP possessed nearly the same photodynamic activity (LD50) as well-known photosensitizer chlorin e6. These porphyrins have also demonstrated quite high photodynamic activity in vivo. The results were obtained in the experiments on white mice with engrafted C-180 (Croker's sarcoma). Antitumor activity of these porphyrins in the dark was 30-40%, whereas photodynamic activity was 45-60%.
Influence of hypericin and synthetic (see manuscript for formula) on haemolysis of human erythrocytes was investigated. It was shown that both hypericin and synthetic
porphyrins (TOEPyP and Zn-TOEPyP) did not cause haemolysis in the dark (24 hrs incubation), whereas Ag-TOEPyP
leaded to haemolysis already after 40 min incubation, i.e. was cytotoxic. Hypericin (25 μM -125 μM) possessed
haemolytic activity upon light exposure (visible spectrum, 30 mW/cm2, 5 min and more). Total haemolysis of
erythrocytes was observed at 15 min exposure to light at all the investigated concentrations of hypericin. Dose-dependent
haemolytic effect of TOEPyP and Zn-TOEPyP depending on light exposure time was also investigated. TOEPyP
demonstrated considerably higher haemolytic activity compared to Zn-TOEPyP. Ag-TOEPyP demonstrated the weakest
photodynamic activity. The effect of ascorbic acid on porphyrin-induced haemolysis was also revealed. Ascorbic acid at
the concentration of 0.15 μM and above significantly increased haemolysis induced by hypericin, whereas at
concentration of 0.75 μM and less it appeared to possess protective property. TOEPyP and Zn-TOEPyP did not
demonstrate photodynamic properties in the presence of ascorbic acid (3.75 μM and more). The ascorbic acid at the
concentrations below 3.75 μM did not have any influence on erythrocyte haemolysis induced by TOEPyP, while it
increased haemolytic effect of Zn-TOEPyP. Thus, the full inhibition of photohaemolysis induced by (see manuscript for formula) by singlet oxygen quenchers - ascorbic acid and tryptophan - was shown. This testifies to the fact, that the
photohaemolysis induced by these porphyrins is caused by Type II reactions.
The necessity of researches of antitumor efficiency of new photosensitizers (PS) is explained by the opportunity of their application in photodynamic therapy of tumors. PS, selectively accumulated in cancer cells and activated by the light, generate the active oxygen species that cause apoptosis. Earlier, it was shown that PS chlorin e6 (0.3-0.5 μg/ml) induces rat embryo fibroblast-like cell apoptosis. In present work antitumor activity of the new photosensitizers, water-soluble cationic porphyrins and their metal complexes, is investigated. The dose-dependent destruction of cancer cells was shown on PC-12 (pheochromocytoma, rat adrenal gland) and Jurkat (human lymphoma) cell lines. Meso-tetra-[4-N-(2 `- oxyethyl) pyridyl] porphyrin (TOEPyP) and chlorin e6 possessed the same toxicity at LD50 dose on PC-12 cell line, whereas phototoxicity of TOEPyP was 3 times less compared to chlorin e<sub>6</sub>(LD<sub>50</sub>=0.2 and 0.075 μg/ml accordingly). The results have shown weak photosensitizing effect of Zn-and Ag-derivatives of TOEPyP on PC-12 cell line. TOEPyP and Zn-TOEPyP (0.1 - 50 μg/ml) were non-toxic for Jurkat cell line, whereas Ag-TOEPyP was toxic at 10 μg/ml (LD<sub>90</sub>). TOEPyP and chlorin e<sub>6 </sub>have shown phototoxic effect in the same dose range (LD<sub>50</sub>=0.5 and 0.3 μg/ml accordingly). The investigation of toxic and phototoxic effects of the new porphyrins revealed significantly different sensitivity of various cell lines to PSs.