title: Cisplatin-induced expression of Gb3 enables verotoxin-1 treatment of cisplatin resistance in malignant pleural mesothelioma cells.
abstract: BACKGROUND
  A major problem with cisplatin treatment is the development of acquired-drug resistance of the tumour cells. Verotoxin-1 (VT-1) exerts its cytotoxicity by targeting the membrane glycolipid globotriasosylceramide (Gb3), a molecule associated with drug resistance. Cisplatin- and VT-1-induced apoptosis involves mitogen-activated protein kinase (MAPK) activation, and deactivation of MAPKs is associated with cisplatin resistance. This study aimed to investigate whether a sub-toxic concentration of VT-1 could enhance cisplatin-induced apoptosis and overcome acquired-cisplatin resistance in cultured cancer cell lines.
  
  
  METHODS
  P31 and H1299 cells with corresponding cisplatin-resistant sub-lines (P31res/H1299res) were incubated with VT-1 and/or cisplatin followed by determination of Gb3 expression, cell viability, apoptosis, and signalling pathways.
  
  
  RESULTS
  Cells from the resistant sub-lines had elevated Gb3 expression compared with the parental cell lines, and cisplatin further increased Gb3 expression, whereas VT-1 reduced the percentage of Gb3-expressing cells. Combination of cisplatin and sub-toxic concentrations of VT-1 led to a super-additive increase of cytotoxicity and TUNEL staining, especially in the cisplatin-resistant sub-lines. Blockade of Gb3 synthesis by a Gb3 synthesis inhibitor not only led to eradicated TUNEL staining of P31 cells, but also sensitised P31res cells to the induction of apoptosis by cisplatin alone. Cisplatin- and VT-1-induced apoptosis involved the MAPK pathways with increased C-Jun N-terminal kinase and MAPK kinase-3 and -6 phosphorylation.
  
  
  CONCLUSIONS
  We show the presence of Gb3 in acquired-cisplatin resistance in P31res and H1299res cells. Cisplatin up-regulated Gb3 expression in all cells and thus sensitised the cells to VT-1-induced cytotoxicity. A strong super-additive effect of combined cisplatin and a sub-toxic concentration of VT-1 in cisplatin-resistant malignant pleural mesothelioma cells were observed, indicating a new potential clinical-treatment approach.
authors.affiliation: Department of Medical Biosciences, Clinical Chemistry, Umeå University, Umeå S-901 85, Sweden.
authors.forename: D
authors.initials: D
authors.lastname: Johansson
authors.forename: C
authors.initials: C
authors.lastname: Andersson
authors.forename: J
authors.initials: J
authors.lastname: Moharer
authors.forename: A
authors.initials: A
authors.lastname: Johansson
authors.forename: P
authors.initials: P
authors.lastname: Behnam-Motlagh
mesh_terms: D015295:Antigens, Tumor-Associated, Carbohydrate / Q000096:biosynthesis*; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D006801:Humans; D008654:Mesothelioma / Q000188:drug therapy* / Q000378:metabolism; D010997:Pleural Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D022622:Shiga Toxin 1 / Q000627:therapeutic use*
chemical_list: D015295:Antigens, Tumor-Associated, Carbohydrate; D000970:Antineoplastic Agents; C472766:Gb3 antigen; D022622:Shiga Toxin 1; D002945:Cisplatin