title: Etretinate enhances the susceptibility of human skin squamous cell carcinoma cells to 5-aminolaevulic acid-based photodynamic therapy.
abstract: BACKGROUND
  Photodynamic therapy (PDT) with 5-aminolaevulinic acid (5-ALA) is a noninvasive and effective treatment for superficial skin cancers. Etretinate, a derivate of vitamin A, with the chemical formula ethyl(2E,4E,6E,8E)-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-2,4,6,8-nona-tetraenoate, has been reported to have antitumour effects and to regulate the proliferation and differentiation of skin cancers.
  
  
  OBJECTIVE
  In order to develop more efficient PDT, we investigated whether etretinate enhanced the cytotoxic action of ALA-based PDT against human squamous cell carcinoma cell line, HSC-5.
  
  
  METHODS
  The in vitro cytotoxicity was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptotic cells were detected by double-staining with fluorescent annexin V and propidium iodide. Intracellular protoporphyrin IX (PpIX) converted from exogenous ALA was measured by a fluorescence meter.
  
  
  RESULTS
  HSC-5 cells pretreated with a nontoxic concentration of etretinate became more susceptible to the cytotoxic action of ALA-based PDT. Etretinate-pretreated cells underwent apoptosis in response to ALA-based PDT. Etretinate pretreatment resulted in enhanced accumulation of ALA-dependent intracellular PpIX.
  
  
  CONCLUSIONS
  The results suggest that etretinate enhances the susceptibility of HSC-5 cells to ALA-based PDT via the intracellular increase of ALA-dependent PpIX. Etretinate might be useful for improvement of ALA-based PDT.
authors.affiliation: Department of Dermatology, Aichi Medical University School of Medicine, Nagakute, Aich, Japan. natsuko@aichi-med-u.ac.jp
authors.forename: N
authors.initials: N
authors.lastname: Ishida
authors.forename: D
authors.initials: D
authors.lastname: Watanabe
authors.forename: Y
authors.initials: Y
authors.lastname: Akita
authors.forename: A
authors.initials: A
authors.lastname: Nakano
authors.forename: N
authors.initials: N
authors.lastname: Yamashita
authors.forename: T
authors.initials: T
authors.lastname: Kuhara
authors.forename: T
authors.initials: T
authors.lastname: Yanagishita
authors.forename: T
authors.initials: T
authors.lastname: Takeo
authors.forename: Y
authors.initials: Y
authors.lastname: Tamada
authors.forename: Y
authors.initials: Y
authors.lastname: Matsumoto
mesh_terms: D000622:Aminolevulinic Acid / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D016923:Cell Death / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004341:Drug Evaluation; D004357:Drug Synergism; D005050:Etretinate / Q000494:pharmacology*; D006801:Humans; D007641:Keratolytic Agents / Q000494:pharmacology*; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology; D011524:Protoporphyrins / Q000378:metabolism; D012878:Skin Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D014407:Tumor Cells, Cultured
chemical_list: D007641:Keratolytic Agents; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D005050:Etretinate; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX