title: Insulin induces drug resistance in melanoma through activation of the PI3K/Akt pathway.
abstract: BACKGROUND
  There is currently no curative treatment for melanoma once the disease spreads beyond the original site. Although activation of the PI3K/Akt pathway resulting from genetic mutations and epigenetic deregulation of its major regulators is known to cause resistance of melanoma to therapeutic agents, including the conventional chemotherapeutic drug dacarbazine and the Food and Drug Administration-approved mutant BRAF inhibitors vemurafenib and dabrafenib, the role of extracellular stimuli of the pathway, such as insulin, in drug resistance of melanoma remains less understood.
  
  
  OBJECTIVE
  To investigate the effect of insulin on the response of melanoma cells to dacarbazine, and in particular, the effect of insulin on the response of melanoma cells carrying the BRAF(V600E) mutation to mutant BRAF inhibitors. An additional aim was to define the role of the PI3K/Akt pathway in the insulin-triggered drug resistance.
  
  
  METHODS
  The effect of insulin on cytotoxicity induced by dacarbazine or the mutant BRAF inhibitor PLX4720 was tested by pre-incubation of melanoma cells with insulin. Cytotoxicity was determined by the MTS assay. The role of the PI3K/Akt pathway in the insulin-triggered drug resistance was examined using the PI3K inhibitor LY294002 and the PI3K and mammalian target of rapamycin dual inhibitor BEZ-235. Activation of the PI3K/Akt pathway was monitored by Western blot analysis of phosphorylated levels of Akt.
  
  
  RESULTS
  Recombinant insulin attenuated dacarbazine-induced cytotoxicity in both wild-type BRAF and BRAF(V600E) melanoma cells, whereas it also reduced killing of BRAF(V600E) melanoma cells by PLX4720. Nevertheless, the protective effect of insulin was abolished by the PI3K and mTOR dual inhibitor BEZ-235 or the PI3K inhibitor LY294002.
  
  
  CONCLUSIONS
  Insulin attenuates the therapeutic efficacy of dacarbazine and PLX4720 in melanoma cells, which is mediated by activation of the PI3K/Akt pathway and can be overcome by PI3K inhibitors.
authors.affiliation: School of Medicine and Public Health, The University of Newcastle, Newcastle, NSW, Australia.
authors.forename: Mengna
authors.initials: M
authors.lastname: Chi
authors.affiliation: School of Medicine and Public Health, The University of Newcastle, Newcastle, NSW, Australia.
authors.forename: Yan
authors.initials: Y
authors.lastname: Ye
authors.affiliation: School of Medicine and Public Health, The University of Newcastle, Newcastle, NSW, Australia.
authors.forename: Xu Dong
authors.initials: XD
authors.lastname: Zhang
authors.affiliation: School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia ; Faculty of Science, Medicine and Health, The University of Wollongong, Wollongong, NSW, Australia.
authors.forename: Jiezhong
authors.initials: J
authors.lastname: Chen
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003606:Dacarbazine / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D008545:Melanoma / Q000188:drug therapy*; D051379:Mice; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: D007211:Indoles; D007328:Insulin; C528407:PLX 4720; D013449:Sulfonamides; D003606:Dacarbazine; D019869:Phosphatidylinositol 3-Kinases; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D051057:Proto-Oncogene Proteins c-akt
keywords: BRAF inhibitors; DTIC; PI3K/Akt; drug resistance; insulin; melanoma