Dose-Dependent Cytotoxic Effects of Menthol on Human Malignant Melanoma A-375 Cells: Correlation with TRPM8 Transcript Expression

Abstract

<b>Background:</b> Transient receptor potential melastatin 8 (TRPM8), a principle membrane receptor involved incalcium ion influx and cell signal transduction, has been found to be up-regulated in some cancer types, includingmelanomas. Efficiency of menthol, an agonist of TRPM8, in killing melanoma cancer cells has been reportedpreviously, but the mechanisms remain unclear. We here determined whether in vitro cytotoxic effects of mentholon A-375 human malignant melanoma cells might be related to TRPM8 transcript expression. Materials and<br/><b>Methods</b>: The PrestoBlue® cell viability assay was used to assess the in vitro cytotoxic effect of menthol after24h of treatment. RT-PCR was used to quantify TRPM8 transcript expression levels in normal and mentholtreatedcells. Cell morphology was observed under inverted phase contrast light microscopy. <br/><b>Results</b>: TRPM8transcript expression was found at low levels in A-375 cells and down-regulated in a potentially dose-dependentmanner by menthol. Menthol exerted in vitro cytotoxic effects on A-375 cells with an IC50 value of 11.8 μM, whichwas at least as effective as 5-fluorouracil (IC50=120 μM), a commonly applied chemotherapeutic drug. Mentholshowed no dose-dependent cytotoxicity on HeLa cells, a TRPM8 non-expressing cell line. <br/><b>Conclusions</b>: Thecytotoxic 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.