PHOTODYNAMICALLY INDUCED CYTOTOXICITY OF HYPERICIN DYE ON HUMAN FIBROBLAST CELL-LINE MRC5

The possible application of hypericin (hyp) in the photodynamic therap y (PDT) of cancer was investigated using the human fibroblast cell lin e MRC5. In aerobic conditions, at pH 7.4, irradiation of MRCS cells wa s carried out with different doses of visible light and different dose s of hyp. A low concentration of hyp (5x10(-9) M) was highly toxic to MRC5 cells, producing 15% survival for an irradiation period of 40 min . In the dark, no cytotoxicity was observed in the range 10(-9)-10(-7) M hyp. The mechanism of cell killing by hyp was also examined. Signif icant inhibition of MRCS killing was observed on addition of 1,4-diaza bicyclo[2,2,2]octane (DABCO) or histidine, known quenchers of type II mechanisms. In addition, the photodynamic effect of hyp was enhanced b y deuterium oxide. The addition of desferrioxamine, catalase or supero xide dismutase (SOD), known scavenging agents of the type I mechanism, had a significant inhibitory effect on the rate of photodynamic actio n of hyp. The experimental results suggest that hyp has considerable p otential for use as a sensitizer in the PDT of cancer.