title: Thermal sensitisation by lonidamine of human melanoma cells grown at low extracellular pH.
abstract: OBJECTIVE
  This study tested the ability of lonidamine (LND), a clinically applicable inhibitor of monocarboxylate transporters (MCT), to thermally sensitise human melanoma cells cultured at a tumour-like extracellular pH (pHe) 6.7.
  
  
  METHODS
  Human melanoma DB-1 cells cultured at pHe 6.7 and pHe 7.3 were exposed to 150 µM LND for 3 h, beginning 1 h prior to heating at 42 °C (2 h). Intracellular pH (pHi) was determined using 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) and whole spectrum analysis. Levels of heat shock proteins (HSPs) were determined by immunoblot analysis. Cell survival was determined by colony formation.
  
  
  RESULTS
  Treatment with LND at pHe 6.7 reduced pHi to 6.30 ± 0.21, reduced thermal induction of HSPs, and sensitised cells growing at pHe 6.7 to 42 °C. When LND was combined with an acute acidification from pHe 6.7 to pHe 6.5, pHi was reduced to 6.09 ± 0.26, and additional sensitisation was observed. LND had negligible effects on cells cultured at pH 7.3.
  
  
  CONCLUSIONS
  The results show that LND can reduce pHi in human melanoma cells cultured at a tumour-like low pHe so that the 42 °C induction of HSPs are abrogated and the cells are sensitised to thermal therapy. Cells cultured at a normal tissue-like pHe 7.3 were not sensitised to 42 °C by LND. These findings support the strategy that human melanoma cells growing in an acidic environment can be sensitised to thermal therapy in vivo by exposure to an MCT inhibitor such as LND.
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University , Philadelphia, Pennsylvania , USA and.
authors.forename: Ronald Allen
authors.initials: RA
authors.lastname: Coss
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Storck
authors.forename: Tiffany C
authors.initials: TC
authors.lastname: Wells
authors.forename: Kari A
authors.initials: KA
authors.lastname: Kulp
authors.forename: Miriam
authors.initials: M
authors.lastname: Wahl
authors.forename: Dennis B
authors.initials: DB
authors.lastname: Leeper
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D055551:HSP27 Heat-Shock Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007191:Indazoles / Q000494:pharmacology*; D008545:Melanoma; D018832:Molecular Chaperones; D027501:Monocarboxylic Acid Transporters / Q000037:antagonists & inhibitors; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: D055551:HSP27 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D007191:Indazoles; D018832:Molecular Chaperones; D027501:Monocarboxylic Acid Transporters; D011838:Radiation-Sensitizing Agents; C016371:lonidamine