Faculty: Denis M. Grant, PhD

Denis M. Grant, PhDDenis M. Grant, PhD
Professor

General Research Areas: Drug Metabolism and Pharmacogenetics, Carcinogenesis
Molecular Pharmacogenetics and the Study of Aromatic Amine Metabolism, Toxicity and Cancer

Our general interest is in studying the molecular causes and the toxic consequences of variation in the activities of drug-metabolizing enzymes. The potential consequences of this variation include differences in the risk for drug side effects as well as for cancers associated with exposure to environmental chemicals. Methods of study used in the laboratory include pharmacokinetic, biochemical, molecular biological, genetic and analytical techniques on humans, human tissues, genetically modified animal models, cultured cells, cloned genes and expressed gene products to analyze drug disposition, gene structure, gene regulation, enzyme function and toxic endpoints. One class of chemicals of particular interest to us is the aromatic amines, many of which are used not only as therapeutic agents but also in various chemical manufacturing processes. Aromatic amines are also found in some cooked foods and in the environment as by-products of combustion processes, including cigarette smoke. Epidemiological and animal studies have linked aromatic amine exposure to cancers of the bladder, colon and other tissues. The cancers are thought to be caused, however, only after these agents have been "metabolically activated" into DNA-damaging, electrophilic mutagens by drug-metabolizing enzymes. Two classes of enzymes that may be important for affecting the conversion of aromatic amines into toxic metabolites are the arylamine N-acetyltransferases (NATs) and the cytochromes P450 (CYPs). Many of these enzymes are genetically polymorphic in human populations, possibly accounting for some of the differences in risk for acute chemical-induced toxicity or for cancer between individuals. However, since a major weakness of epidemiological studies of risk for toxic effects such as cancer is in obtaining accurate estimates of chemical exposure in humans, it is very important to develop more accurate testing systems to predict the ability of such chemicals to produce acute toxicity and cancer, and to determine the role of enzymes such as the NATs in these processes.

While animal models have been the 'gold standard' for predicting the toxic potential of chemicals, species differences often make it difficult to extrapolate the risk to humans. Thus one of our main current research goals is to develop improved animal models to better predict the toxicity of aromatic amines, and to understand how differences in NAT enzyme function affect both aromatic amine disposition and toxic risk. To do this, we have used genetic manipulation technologies and cross-breeding approaches to develop strains of mice that lack their own NAT and/or CYP enzymes, or in which they have been replaced with their human counterparts in a tissue-selective fashion that mimics patterns of enzyme activity in humans. Comparing both short-term and long-term measures of toxicity of aromatic amines between normal and genetically altered strains should allow us to better determine the importance of the human NATs, CYPs and other related enzymes in turning aromatic amines into products that cause cellular toxicity and/or cancers in man.

Selected Publications:

Wang S, Bott D, Tung A, Sugamori KS, Grant DM. Relative contributions of CYP1A2 and CYP2E1 to the bioactivation and clearance of 4-aminobiphenyl in adult mice.  Drug Metab Dispos 43(7): 916-921 (2015).

Wang S, Sugamori KS, Tung A, McPherson JP, Grant DM.  N-hydroxylation of 4-aminobiphenyl by CYP2E1 produces oxidative stress in a mouse model of chemically-induced liver cancer. Toxicol Sci 144(2): 393-405 (2015).

Metushi I, Cai P, Vega L, Grant DM, Uetrecht J.  Paradoxical attenuation of autoimmune hepatitis by oral isoniazid in wild-type and N-acetyltransferase-deficient mice. Drug Metab Dispos 42(6): 963-73 (2014).

Witham KL, Butcher NJ, Sugamori KS, Brenneman D, Grant DM, Minchin RF.  5-Methyltetrahydrofolate and the S-adenosylmethionine cycle in C57BL/6J mouse tissues: gender differences and effects of arylamine N-acetyltransferase-1 deletion.  PLoS One 8: e77923 (2013).

Ogawa S, Surapisitchat J, Virtanen C, Ogawa M, Niapour M, Sugamori KS, Wang S, Tamblyn L, Guillemette C, Hoffmann E, Bin Z, Laposa RR, Tyndale RF, Grant DM, Keller G.  Three dimensional culture and cAMP signaling promote the maturation of human pluripotent stem cell-derived hepatocytes. Development 140: 3285-3296 (2013).

Grant DM.  Chemical carcinogenesis, in  The Basic Science of Oncology, 5th Edition, Tannock IF, Hill RP, Bristow RG, Harrington L (eds.), McGraw-Hill, New York, pp. 73-88 (2013).

Wang S, Sugamori KS, Brenneman D, Hsu I, Calce A, Grant DM.  Influence of arylamine N-acetyltransferase, sex and age on 4-aminobiphenyl-induced in vivo mutant frequencies and spectra in mouse liver.  Environ Mol Mutagen 53: 350-357 (2012).

Sugamori KS, Brenneman D, Sanchez O, Doll MA, Hein DW, Pierce WM, Grant DM. Reduced 4-aminobiphenyl-induced liver tumorigenicity but not DNA damage in arylamineN-acetyltransferase null mice.  Cancer Lett 318: 206-213 (2012).

Sugamori KS, Brenneman D, Grant DM. Liver-selective expression of human arylamine N-acetyltransferase NAT2 in transgenic mice. Drug Metab Dispos 39: 882-890 (2011).

Contact:

Department of Pharmacology and Toxicology
Room 4316, Medical Sciences Building 
1 King's College Circle 
Toronto, Ontario 
M5S 1A8 
Phone: 416-978-8191 
FAX: 416-978-6395 
Email:  denis.grant@utoronto.ca

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