title: Multidrug-resistant hela cells overexpressing MRP1 exhibit sensitivity to cell killing by hyperthermia: interactions with etoposide.
abstract: OBJECTIVE
  Multidrug resistance (MDR) remains one of the primary obstacles in cancer chemotherapy and often involves overexpression of drug efflux transporters such as P-glycoprotein and multidrug resistance protein 1 (MRP1). Regional hyperthermia is undergoing clinical investigation in combination with chemotherapy or radiotherapy. This study evaluates whether hyperthermia can reverse MDR mediated by MRP1 in human cervical adenocarcinoma (HeLa) cells.
  
  
  METHODS
  Cytotoxicity of hyperthermia and/or etoposide was evaluated using sulforhodamine-B in HeLa cells overexpressing MRP1 and their drug-sensitive counterparts. Glutathione, glutathione peroxidase (GPx), and glutathione S-transferase (GST) were quantified by spectrophotometry. GST isoenzymes were quantified by immunodetection. Caspase activation was evaluated by fluorometry and chromatin condensation by fluorescence microscopy using Hoechst 33258. Necrosis was determined using propidium iodide.
  
  
  RESULTS
  The major finding is that HeLa and HeLaMRP cells are both sensitive to cytotoxicity of hyperthermia (41-45 degrees C). Hyperthermia induced activation of caspase 3 and chromatin condensation. Although total levels of cell killing were similar, there was a switch from apoptotic to necrotic cell death in MDR cells. This could be explained by decreased glutathione and GPx in MDR cells. MDR cells also contained very low levels of GST and were resistant to etoposide-induced apoptosis. Hyperthermia caused a modest increase in etoposide-induced apoptosis in HeLa and HeLaMRP cells, which required appropriate heat-drug scheduling.
  
  
  CONCLUSIONS
  Hyperthermia could be useful in eliminating MDR cells that overexpress MRP1.
authors.affiliation: Département de Chimie et de Biochimie, Université du Québec à Montréal, Succursale Centre Ville, Montréal, Québec, Canada.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Souslova
authors.forename: Diana A
authors.initials: DA
authors.lastname: Averill-Bates
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000972:Antineoplastic Agents, Phytogenic / Q000627:therapeutic use*; D017209:Apoptosis / Q000502:physiology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003131:Combined Modality Therapy; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005047:Etoposide / Q000627:therapeutic use*; D005978:Glutathione / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006979:Hyperthermia, Induced; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D053148:Caspase 3; D020169:Caspases; D005047:Etoposide; D005978:Glutathione; D005979:Glutathione Peroxidase; D005982:Glutathione Transferase; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C505407:CASP3 protein, human