title: Synergistic and Antagonistic Mutation Responses of Human MCL-5 Cells to Mixtures of Benzo[a]pyrene and 2-Amino-1-Methyl-6-Phenylimidazo[4,5-b]pyridine: Dose-Related Variation in the Joint Effects of Common Dietary Carcinogens.
abstract: BACKGROUND
  Chemical carcinogens such as benzo[a]pyrene (BaP) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) may contribute to the etiology of human diet-associated cancer. Individually, these compounds are genotoxic, but the consequences of exposure to mixtures of these chemicals have not been systematically examined.
  
  
  OBJECTIVE
  We determined the mutagenic response to mixtures of BaP and PhIP at concentrations relevant to human exposure (micromolar to subnanomolar).
  
  
  METHODS
  Human MCL-5 cells (metabolically competent) were exposed to BaP or PhIP individually or in mixtures. Mutagenicity was assessed at the thymidine kinase (TK) locus, CYP1A activity was determined by ethoxyresorufin-O-deethylase (EROD) activity and qRT-PCR, and cell cycle was measured by flow cytometry.
  
  
  RESULTS
  Mixtures of BaP and PhIP produced dose responses different from those of the individual chemicals; we observed remarkably increased mutant frequency (MF) at lower concentrations of the mixtures (not mutagenic individually), and decreased MF at higher concentrations of the mixtures, than the calculated predicted additive MF of the individual chemicals. EROD activity and CYP1A1 mRNA levels were correlated with TK MF, supporting involvement of the CYP1A family in mutation. Moreover, a cell cycle G2/M phase block was observed at high-dose combinations, consistent with DNA damage sensing and repair.
  
  
  CONCLUSIONS
  Mixtures of these genotoxic chemicals produced mutation responses that differed from those expected for the additive effects of the individual chemicals. The increase in MF for certain combinations of chemicals at low concentrations that were not genotoxic for the individual chemicals, as well as the nonmonotonic dose response, may be important for understanding the mutagenic potential of food and the etiology of diet-associated cancers.
  
  
  BACKGROUND
  David R, Ebbels T, Gooderham N. 2016. Synergistic and antagonistic mutation responses of human MCL-5 cells to mixtures of benzo[a]pyrene and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine: dose-related variation in the joint effects of common dietary carcinogens. Environ Health Perspect 124:88-96; http://dx.doi.org/10.1289/ehp.1409557.
authors.affiliation: Computational and Systems Medicine, Imperial College London, London, United Kingdom.
authors.forename: Rhiannon
authors.initials: R
authors.lastname: David
authors.forename: Timothy
authors.initials: T
authors.lastname: Ebbels
authors.forename: Nigel
authors.initials: N
authors.lastname: Gooderham
mesh_terms: D001564:Benzo(a)pyrene / Q000633:toxicity*; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D004249:DNA Damage / Q000187:drug effects / Q000235:genetics; D006801:Humans; D007093:Imidazoles / Q000633:toxicity*; D009154:Mutation / Q000187:drug effects / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D002273:Carcinogens; D007093:Imidazoles; D012333:RNA, Messenger; D001564:Benzo(a)pyrene; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine; D019363:Cytochrome P-450 CYP1A1