title: PDT induced bystander effect on human xenografted colorectal tumors as evidenced by sodium MRI.
abstract: BACKGROUND
  Previous in vivo studies on photodynamic therapy (PDT)-treated, high cellular density tumors showed evidences of a bystander effect accompanying the therapy, cellular death continuing beyond the limits of the photochemical reactions in time and space. This process is generated by the initially damaged cells on the light pathway. The aim of this study was to determine if the bystander effect may be induced as well in colorectal xenografted tumors (less compact structure) and if the cellular signaling depends primarily on cellular proximity or not.
  
  
  METHODS
  The photosensitizer was a glycoconjugated, meso substituted porphyrin derivative synthesized at Institut Curie. The longitudinal follow-up of the tumors was carried out by (23)Na/(1)H MRI, ideal imaging modality for mapping the extracellular compartment. Two regimens were followed in order to target either blood vessels alone or blood vessels and cancer cells simultaneously.
  
  
  RESULTS
  The antivascular PDT did not succeed to arrest the tumors growth at the end of the follow-up. For double targeting PDT, we managed to stop the tumoral evolution. Sodium MRI evidenced a bystander effect.
  
  
  CONCLUSIONS
  The results obtained showed that the bystander effect is more difficult to induce for the type of colorectal tumors used in this work. It needs a double treatment, 4 days apart, in order to be promoted.
authors.affiliation: Institut Curie, Bât.112, Centre Universitaire, F 91405 Orsay Cedex, France. florent.poyer@curie.u-psud.fr
authors.forename: Florent
authors.initials: F
authors.lastname: Poyer
authors.forename: Carole D
authors.initials: CD
authors.lastname: Thomas
authors.forename: Guillaume
authors.initials: G
authors.lastname: Garcia
authors.forename: Alain
authors.initials: A
authors.lastname: Croisy
authors.forename: Danièle
authors.initials: D
authors.lastname: Carrez
authors.forename: Philippe
authors.initials: P
authors.lastname: Maillard
authors.forename: Mihaela
authors.initials: M
authors.lastname: Lupu
authors.forename: Joël
authors.initials: J
authors.lastname: Mispelter
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D024201:Bystander Effect / Q000187:drug effects*; D002452:Cell Count; D015179:Colorectal Neoplasms / Q000188:drug therapy*; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D051379:Mice; D008819:Mice, Nude; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011166:Porphyrins / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D017319:Photosensitizing Agents; D011166:Porphyrins