title: Topographical study of O(6)-alkylguanine DNA alkyltransferase repair activity and N7-methylguanine levels in resected lung tissue.
abstract: BACKGROUND
  Tobacco specific nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are genotoxic alkylating agents found within cigarette smoke that induce lung adenocarcinomas in animal models. In humans, adenocarcinomas originate most frequently in the lung periphery. The aim of this study was to determine whether peripheral lung has increased susceptibility to the genotoxic effects of alkylating agents by comparing DNA alkylation damage (N7-methylguanine: N7-meG) and repair (O(6)-alkylguanine DNA alkyltransferase: MGMT) in peripheral relative to central lung tissue.
  
  
  METHODS
  Macroscopically normal lung tissue, resected from patients undergoing surgery for lung cancer, was sampled at equidistant points from central to peripheral lung along a bronchus. N7-meG levels were determined using an immunoslotblot technique and MGMT activity with a [32P]-labelled oligodeoxynucleotide cleavage assay.
  
  
  RESULTS
  A total of 20 subjects were recruited, 12 males and 8 females with a mean age of 68.7±5.8years. There were 14 former and 6 current smokers with a mean smoking exposure of 34.0±18.3packyears. N7-meG (mean 0.75±0.57/10(6)dG, n=65 samples from 14 patients) and MGMT repair (geometric mean 9.57±1.62fmol/μg DNA, n=79 samples from 16 patients) were detected in all samples assayed. MGMT activity increased towards the lung periphery (r=0.28, p=0.023; n=16) with a highly significant association in current (r=0.53, p=0.008; n=6) but not former smokers (r=0.13; p=0.41; n=10). No correlation was seen with N7-meG levels and lung position (r=-0.18; p=0.21; n=14). N7-meG levels were higher in current compared to former smokers reaching significance in two lung positions including peripheral lung (p=0.047).
  
  
  CONCLUSIONS
  The findings in this study do not support the hypothesis that peripheral tissue is more susceptible to the genotoxic effects of alkylating agents than central lung tissue. In addition exposure to cigarette smoke reduced the level of MGMT in central bronchial tissue possibly through increased alkylating agent exposure.
authors.affiliation: Cancer Research UK Carcinogenesis Group, Paterson Institute for Cancer Research, University of Manchester, Manchester M20 4BX, UK. philip.crosbie@manchester.ac.uk
authors.forename: Philip A J
authors.initials: PA
authors.lastname: Crosbie
authors.forename: Kathryn
authors.initials: K
authors.lastname: Harrison
authors.forename: Rajesh
authors.initials: R
authors.lastname: Shah
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Watson
authors.forename: Raymond
authors.initials: R
authors.lastname: Agius
authors.forename: Philip V
authors.initials: PV
authors.lastname: Barber
authors.forename: Geoffrey P
authors.initials: GP
authors.lastname: Margison
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Povey
mesh_terms: D000368:Aged; D018736:DNA Adducts / Q000378:metabolism; D005260:Female; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008168:Lung / Q000737:chemistry / Q000201:enzymology* / Q000601:surgery; D008175:Lung Neoplasms / Q000737:chemistry / Q000201:enzymology*; D008297:Male; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism*; D012907:Smoking
chemical_list: D018736:DNA Adducts; D006147:Guanine; C008450:7-methylguanine; D019853:O(6)-Methylguanine-DNA Methyltransferase