Synergistic effect of photodynamic therapy with hypericin in combination with hyperthermia on loss of clonogenicity of RIF-1 cells

Hypericin is a natural photosensitizer produced in plants of the genus Hype ricum. The compound exhibits a potent phototoxicity both in vitro and in vi vo. In the present study we investigated the effect of hypericin-mediated P DT on hyperthermia (43 degreesC) in RIF-1 cell line. Our results demonstrat ed a synergistic effect on loss of cell clonogenicity when PDT exposure was followed immediately by 'hyperthermia. This synergistic effect was diminis hed by introducing an interval (at 37 degreesC) between the two treatments. Furthermore, it was found that combining PDT treatment with hyperthermia c ould significantly enhance the cell death by necrosis as indicated by morph ological examination and significant loss of membrane integrity. Our data s uggest that the common cell membrane damage by both PDT and hyperthermia is likely to be responsible for this synergistic effect.