title: Selection of radioresistant tumor cells and presence of ALDH1 activity in vitro.
abstract: BACKGROUND
  Tumor resistance to radiotherapy has been hypothesized to be mediated by a tumor subpopulation, called cancer stem cells (CSCs). Based on the proposed function of CSCs in radioresistance, we explored the cancer stem cell properties of cells selected for radioresistance phenotype.
  
  
  METHODS
  A549 and SK-BR-3 cells were radioselected with four single doses of 4 or 3 Gy in intervals of 10-12 days and used for colony formation assay and γ-H2AX foci formation assay. Expression of putative stem cell markers, i.e. Sox2, Oct4, ALDH1, and CD133 were analyzed using Western blotting. A549 and SK-BR-3 cells sorted based on their ALDH1 activity were analyzed in clonogenic survival assays.
  
  
  RESULTS
  Radioselected A549 and SK-BR-3 cells (A549-R, SK-BR-3-R) showed increased radioresistance and A549-R cells presented enhanced repair of DNA-double strand breaks. PI3K inhibition significantly reduced radioresistance of A549-R cells. Cell line specific differences in the expression of the putative CSC markers Sox2 and Oct4 were observed when parental and radioselected cells were compared but could not be directly correlated to the radioresistant phenotype. However, enzyme activity of the putative stem cell marker ALDH1 showed a correlation to radioresistance.
  
  
  CONCLUSIONS
  Subpopulations of pooled radioresistant colonies, selected by various radiation exposures were analyzed for the presence of putative stem cell markers. Although the pattern of Sox2, Oct4, and CD133 expression was not generally associated with radioresistance, presence of ALDH1 seems to be indicative for subpopulations with increased radioresistance.
authors.affiliation: Division of Radiobiology and Molecular Environmental Research, University of Tuebingen, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Mihatsch
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Toulany
authors.forename: Petra M
authors.initials: PM
authors.lastname: Bareiss
authors.forename: Sabrina
authors.initials: S
authors.lastname: Grimm
authors.forename: Claudia
authors.initials: C
authors.lastname: Lengerke
authors.forename: Rainer
authors.initials: R
authors.lastname: Kehlbach
authors.forename: H Peter
authors.initials: HP
authors.lastname: Rodemann
mesh_terms: D000071916:AC133 Antigen; D000080924:Aldehyde Dehydrogenase 1 Family; D015703:Antigens, CD / Q000378:metabolism; D014408:Biomarkers, Tumor / Q000378:metabolism; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology / Q000532:radiotherapy*; D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology* / Q000473:pathology / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D002470:Cell Survival; D053960:DNA Breaks; D005260:Female; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism*; D008175:Lung Neoplasms / Q000201:enzymology* / Q000473:pathology / Q000532:radiotherapy*; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000528:radiation effects*; D050814:Octamer Transcription Factor-3 / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D010641:Phenotype; D011836:Radiation Tolerance; D050697:Retinal Dehydrogenase / Q000378:metabolism*; D055748:SOXB1 Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured; D059016:Tumor Microenvironment
chemical_list: D000071916:AC133 Antigen; D015703:Antigens, CD; D014408:Biomarkers, Tumor; D006023:Glycoproteins; D007527:Isoenzymes; D050814:Octamer Transcription Factor-3; C494173:POU5F1 protein, human; C000606023:PROM1 protein, human; D010455:Peptides; C527782:SOX2 protein, human; D055748:SOXB1 Transcription Factors; D000080924:Aldehyde Dehydrogenase 1 Family; C510223:ALDH1A1 protein, human; D050697:Retinal Dehydrogenase