title: Pivotal roles of peptide transporter PEPT1 and ATP-binding cassette (ABC) transporter ABCG2 in 5-aminolevulinic acid (ALA)-based photocytotoxicity of gastric cancer cells in vitro.
abstract: BACKGROUND
  Recently, 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT) is being widely used in cancer therapy owing to the tumor-specific accumulation of photosensitizing protoporphyrin IX (PpIX) after the administration of ALA. In the present study, by focusing on genes involved in the porphyrin biosynthesis pathway, we aimed to explore biomarkers that are predictive for the efficacy of ALA-PDT.
  
  
  METHODS
  We used five lines of human gastric cancer cells to measure the ALA-based photocytotoxicity. ALA-induced production of PpIX in cancer cells was quantified by fluorescence spectrophotometry. To examine the potential involvement of PEPT1 and ABCG2 in the ALA-PDT sensitivity, stable cell lines overexpressing PEPT1 were established and ABCG2-specific siRNA used.
  
  
  RESULTS
  We observed that three cell lines were photosensitive, whereas the other two cell lines were resistant to ALA-based photocytotoxicity. The ALA-based photocytotoxicity was found to be well correlated with intracellular PpIX levels, which suggests that certain enzymes and/or transporters involved in ALA-induced PpIX production are critical determinants. We found that high expression of the peptide transporter PEPT1 (ALA influx transporter) and low expression of the ATP-binding cassette transporter ABCG2 (porphyrin efflux transporter) determined ALA-induced PpIX production and cellular photosensitivity in vitro.
  
  
  CONCLUSIONS
  PEPT1 and ABCG2 are key players in regulating intracellular PpIX levels and determining the efficacy of ALA-based photocytotoxicity against gastric cancer cells in vitro. Evaluation of the expression levels of PEPT1 and ABCG2 genes could be useful to predict the efficacy of ALA-PDT. Primers specific to those target genes are practical and useful biomarkers for predicting the photo-sensitivity to ALA-PDT.
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Hagiya
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Endo
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Yonemura
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Takahashi
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ishizuka
authors.forename: Fuminori
authors.initials: F
authors.lastname: Abe
authors.forename: Tohru
authors.initials: T
authors.lastname: Tanaka
authors.forename: Ichiro
authors.initials: I
authors.lastname: Okura
authors.forename: Motowo
authors.initials: M
authors.lastname: Nakajima
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Shun-Ichiro
authors.initials: S
authors.lastname: Ogura
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000622:Aminolevulinic Acid / Q000008:administration & dosage*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D009363:Neoplasm Proteins / Q000378:metabolism*; D000074011:Peptide Transporter 1; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000008:administration & dosage*; D013274:Stomach Neoplasms; D027981:Symporters / Q000378:metabolism*
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D009363:Neoplasm Proteins; D000074011:Peptide Transporter 1; D017319:Photosensitizing Agents; C082186:SLC15A1 protein, human; D027981:Symporters; D000622:Aminolevulinic Acid