title: Dose-dependent cytotoxic effects of menthol on human malignant melanoma A-375 cells: correlation with TRPM8 transcript expression.
abstract: BACKGROUND
  Transient receptor potential melastatin 8 (TRPM8), a principle membrane receptor involved in calcium ion influx and cell signal transduction, has been found to be up-regulated in some cancer types, including melanomas. Efficiency of menthol, an agonist of TRPM8, in killing melanoma cancer cells has been reported previously, but the mechanisms remain unclear. We here determined whether in vitro cytotoxic effects of menthol on A-375 human malignant melanoma cells might be related to TRPM8 transcript expression.
  
  
  METHODS
  The PrestoBlue® cell viability assay was used to assess the in vitro cytotoxic effect of menthol after 24h of treatment. RT-PCR was used to quantify TRPM8 transcript expression levels in normal and menthol- treated cells. Cell morphology was observed under inverted phase contrast light microscopy.
  
  
  RESULTS
  TRPM8 transcript expression was found at low levels in A-375 cells and down-regulated in a potentially dose-dependent manner by menthol. Menthol exerted in vitro cytotoxic effects on A-375 cells with an IC50 value of 11.8 μM, which was at least as effective as 5-fluorouracil (IC50=120 μM), a commonly applied chemotherapeutic drug. Menthol showed no dose-dependent cytotoxicity on HeLa cells, a TRPM8 non-expressing cell line.
  
  
  CONCLUSIONS
  The cytotoxic effects on A-375 cells caused by menthol might be related to reduction of the TRPM8 transcript level. This suggests that menthol might activate TRPM8 to increase cytosolic Ca2+ levels, which leads to cytosolic Ca2+ imbalance and triggers cell death.
authors.affiliation: Department of Biology, Faculty of Science, 2Department of Anatomy, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand E-mail : chanpen.c@chula.ac.th.
authors.forename: Teeratas
authors.initials: T
authors.lastname: Kijpornyongpan
authors.forename: Amornpun
authors.initials: A
authors.lastname: Sereemaspun
authors.forename: Chanpen
authors.initials: C
authors.lastname: Chanchao
mesh_terms: D000982:Antipruritics / Q000009:adverse effects / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation; D015870:Gene Expression / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D008545:Melanoma / Q000188:drug therapy*; D008610:Menthol / Q000009:adverse effects / Q000494:pharmacology*; D050053:TRPM Cation Channels / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000982:Antipruritics; D050053:TRPM Cation Channels; C425966:TRPM8 protein, human; D008610:Menthol; D002118:Calcium