Synergistic effect of photodynamic therapy with hypericin in combination with hyperthermia on loss of clonogenicity...

Hypericin is a natural photosensitizer produced in plants of the genus Hypericum. The compound exhibits a potent phototoxicity both in vitro and in vivo. In the present study we investigated the effect of hypericin-mediated PDT on hyperthermia (43 degrees C) in RIF-1 cell line. Our results demonstrated a synergistic effect on loss of cell clonogenicity when PDT exposure was followed immediately by hyperthermia. This synergistic effect was diminished by introducing an interval (at 37 degrees C) between the two treatments. Furthermore, it was found that combining PDT treatment with hyperthermia could significantly enhance the cell death by necrosis as indicated by morphological examination and significant loss of membrane integrity. Our data suggest that the common cell membrane damage by both PDT and hyperthermia is likely to be responsible for this synergistic effect.