title: Radiation- and chemoinduced multidrug resistance in colon carcinoma cells.
abstract: OBJECTIVE
  Radiation can induce multidrug resistance (MDR) and thus interfere with simultaneous or subsequent chemotherapy. In SW620 colon carcinoma cells, the interrelation of various biological endpoints of MDR was analyzed and the potential of fractionated irradiation and chemoselection to evoke MDR was compared.
  
  
  METHODS
  To induce/select an MDR phenotype, SW620 were exposed to either 27 Gy in 1.8-Gy daily fractions or to 50% inhibiting concentrations of doxorubicin or cisplatin, given over 6-15 weeks. Expression of genes involved in MDR, including glutathione metabolism, was determined by semiquantitative RT-PCR (reverse transcription-polymerase chain reaction). Efflux was analyzed by flow cytometry after staining with rhodamine-123 or 5-chloromethyl fluorescein diacetate. Apoptosis was monitored after pulse exposure to doxorubicin or cisplatin. Colony-forming assays were performed under continuous drug exposure.
  
  
  RESULTS
  A pronounced gene induction was found in MRP2 after cisplatin selection and up to 3 weeks after radiation. LRP was activated only shortly after radiation. Radiation enhanced rhodamine-123 efflux to a similar extent as short-term chemoselection but not as much as long-term drug exposure. Drug-induced apoptosis was slightly delayed in preirradiated cells. Clonogenic growth in the progeny of irradiated cells was less sensitive to cisplatin but not to doxorubicin.
  
  
  CONCLUSIONS
  Fractionated radiation can induce an MDR phenotype in SW620. However, long-term drug exposure establishes a more efficient selection. Various endpoints are not fully concordant regarding the extent of MDR. Posttranscriptional modifications, pleiotropic regulation, and alternative pathways may cause these discrepancies.
authors.affiliation: Department of Radiotherapy and Radiooncology, University of Ulm, Ulm, Germany. detlef.bartkowiak@uniklinik-ulm.de
authors.forename: Detlef
authors.initials: D
authors.lastname: Bartkowiak
authors.forename: Michael
authors.initials: M
authors.lastname: Stempfhuber
authors.forename: Thomas
authors.initials: T
authors.lastname: Wiegel
authors.forename: Dirk
authors.initials: D
authors.lastname: Bottke
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D016923:Cell Death / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects*; D002945:Cisplatin / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000235:genetics / Q000473:pathology*; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D004317:Doxorubicin / Q000494:pharmacology*; D018432:Drug Resistance, Multiple / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000528:radiation effects; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects; D014410:Tumor Stem Cell Assay
chemical_list: D000903:Antibiotics, Antineoplastic; D000970:Antineoplastic Agents; D002945:Cisplatin; D004317:Doxorubicin; D005978:Glutathione; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C000715087:ABCC2 protein, human