title: Enhancing the antitumoral effect of hypericin-mediated photodynamic therapy by hyperthermia.
abstract: OBJECTIVE
  In the previous study, we have found a synergistic effect on the RIF-1 tumor cell killing when hypericin-mediated photodynamic therapy (PDT) was combined with hyperthermia. The purpose of the present study was to investigate the antitumoral effect of hypericin-PDT in combination with hyperthermia in the RIF-1 mouse tumor model.
  
  
  METHODS
  Tumor response to PDT in combination with hyperthermia was compared to the response to PDT or hyperthermia alone. To explore the possible mechanism involved in the interaction of PDT and hyperthermia, we determined the tumor cell survival by in vivo/in vitro cell survival assay and analyzed the functional blood vessels by Hoechst 33342 staining. The mode of cell death was examined by TUNEL assay.
  
  
  RESULTS
  Enhanced tumor response was obtained by PDT immediately followed by hyperthermia. Tumor cell survival assay revealed that indirect vascular effect contributed greatly to the overall tumor cell death induced by PDT with hypericin, whereas direct tumor cytotoxicity played a major role in hyperthermia-induced tumor cell killing. Combining PDT with hyperthermia brought about a synergistic interaction on direct tumor cell killing. Even though PDT or hyperthermia alone induced severe blood vessel shutdown and the combined treatments led to significant potentiation of the vascular damage as examined by Hoechst staining, the gain in tumor cell death as a result of this secondary vascular effect was limited after the combined treatments. Following the cellular damage by PDT in combination with hyperthermia, tumor cells were triggered to undergo apoptosis.
  
  
  CONCLUSIONS
  Our study demonstrated the possibility of using hyperthermia to potentiate the antitumoral effect of hypericin-mediated PDT.
authors.affiliation: Laboratorium voor Farmaceutische Biologie en Fytofarmacologie, Faculteit Farmaceutische Wetenschappen, K. U. Leuven, 3000 Leuven, Belgium.
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.forename: Tania
authors.initials: T
authors.lastname: Roskams
authors.forename: Peter A M
authors.initials: PA
authors.lastname: de Witte
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000097:blood / Q000627:therapeutic use*; D017209:Apoptosis; D001562:Benzimidazoles; D003131:Combined Modality Therapy; D004195:Disease Models, Animal; D005260:Female; D006979:Hyperthermia, Induced; D020287:In Situ Nick-End Labeling; D051379:Mice; D008809:Mice, Inbred C3H; D009374:Neoplasms, Experimental / Q000097:blood / Q000628:therapy*; D010569:Perylene / Q000097:blood / Q000627:therapeutic use*; D010778:Photochemotherapy; D013194:Staining and Labeling / Q000379:methods; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000473:pathology
chemical_list: D000970:Antineoplastic Agents; D001562:Benzimidazoles; C447680:hoechst 32258; D010569:Perylene