The long-term goal of the research being conducted in our laboratory is personalized therapeutics - the safe and effective treatment of an individual’s disease using the right dose of the right medicine tailored specifically for that patient. Unfortunately, many drugs used today are characterized by high interindividual variability in therapeutic response and adverse effects necessitating a trial and error approach using escalating doses and different classes of drugs to achieve a successful outcome. Our research involves identifying significant causes of this variability, particularly those resulting from differences in the genetic makeup of an individual (i.e. pharmacogenomics). The ultimate outcome of this work will be the development of rational drug treatment algorithms based on a patient’s genotype, predictive biomarkers, demographics, disease state, as well as other coadministered drugs.
Drug glucuronidation enzymology and pharmacogenomics
The UDP-glucuronosyltransferases (UGTs) are an underappreciated and understudied superfamily of drug metabolizing enzymes that metabolize and inactivate drugs by conjugation with glucuronic acid (i.e. glucuronidation). UGTs are second only to the cytochromes P450 (CYPs) in terms of the number of clinically important drugs that are substrates for these enzymes. Primary pharmaceutical substrates for the UGTs that have been extensively studied in our lab include acetaminophen (Tylenol), azidothymidine (AZT), morphine, mycophenolic acid, oxazepam, and lorazepam. Published and ongoing studies involve establishing the responsible UGT isoforms for each of these (and other) drugs, as well as identifying genetic variants that predict increased or decreased rates of drug glucuronidation in a patient.
Fig. 1. Variability in glucuronidation of probes specific for UGT1A1, 1A4, 1A6, 1A9, 2B7 and 2B15 measured in the same bank of human liver microsomes. Also shown are activities for midazolam 1’-hydroxylation and chlorzoxazone 6-hydroxylation, as probes for CYP3A and CYP2E1. Data for each activity are given relative to the mean activity for all livers. Also shown are the coefficients of variation (CV%) for each activity. [Court MH. Interindividual variability in hepatic drug glucuronidation: studies into the role of age, sex, enzyme inducers, and genetic polymorphism using the human liver bank as a model system. Drug Metab Rev. 2010;42(1):202-17.]
Acetaminophen-induced acute liver failure
Acetaminophen is one of the most commonly used drugs in the world, but is also the leading cause of acute liver failure in the United States and Europe. While many cases result from intentional overdose (i.e. suicide attempts), as many cases are the result of therapeutic use of this drug for chronic pain relief. We are currently conducting studies using cell and tissue-based model systems, human volunteers, and DNA collected from patients that developed acetaminophen-induced acute liver failure, to identify genotypes predictive of altered acetaminophen metabolism and increased risk for developing liver injury. Such genotypes would be used to identify individuals that should avoid or perhaps minimize the use of acetaminophen.
Fig. 2. Etiology of acute liver failure in the United States as determined by the Acute Liver Failure Study Group multicenter trial (courtesy Will Lee, UTSW, 2009). Almost half of the cases are the result of acetaminophen ingestion, and of those approximately half were taking acetaminophen for therapeutic purposes.
HIV drug pharmacogenomics and TB drug interactions
Antiretroviral drug combination therapies have had a substantial impact on reducing the morbidity and mortality associated with HIV infection. However, certain highly effective antiretroviral drugs, such as efavirenz, demonstrate high interindividual variability in blood levels resulting in either adverse neurological effects (high levels) or potential virologic failure (low levels). Research in our laboratory and others have established that polymorphisms in the gene encoding CYP2B6 are largely responsible for high variability in efavirenz metabolism. In collaboration with researchers at Brown University, University of North Carolina, and the University of Ghana, we are identifying genetic variants in CYP2B6 and other genes that are predictive of slow as well as fast metabolism of efavirenz using DNA samples from a cohort of HIV-infected Ghanaians. We are also exploring the molecular basis for variable drug-drug interactions between efavirenz and the drugs used to treat tuberculosis (TB), a common comorbid infection in HIV-infected patients. The ultimate goal is to develop rational therapeutic protocols based on patient genotype and coadministered drugs.
Fig. 3. Scatter plot showing the relationship between log10 pharmacogenetic-predicted efavirenz mid-dose plasma concentrations (y-axis) and log10 observed concentration (x-axis) in 94 HIV-infected patients. Log10 efavirenz mid-dose plasma concentrations predictions for each subject were made based on their genotype carrier status (CYP2B6 c.516TT, CYP2A6*9 or *17 and/or UGT2B7*1a as indicated by arrows) using the pharmacogenetic algorithm derived by multiple linear regression analysis. [Kwara A, Lartey M, Sagoe KW, Kenu E, Court MH. CYP2B6, CYP2A6 and UGT2B7 genetic polymorphisms are predictors of efavirenz mid-dose concentration in HIV-infected patients. AIDS. 2009 Oct 23;23(16):2101-6.]
Substantial differences in drug metabolism capacity also exist between different breeds of dog and between different species of animal. These phenomena are important to investigate for comparative purposes (especially humans versus laboratory animals) as well as for improving the health and welfare of our companion animals. Several projects are investigating why Greyhound dogs metabolize certain anesthetic agents more slowly compared with other dog breeds, and why cats have a poor capacity to metabolize certain drugs by glucuronidation.
Fig. 4. Phylogram showing the established evolutionary relationships between species in the suborder Feloidea in relation to the appearance of disruptive mutations within the UGT1A6 gene. All Felidae share 5 mutations that likely originated between 11 and 35 million years ago resulting in UGT1A6 pseudogenization. mya - estimated times of divergence in millions of years ago. [Shrestha B, Reed JM, Starks PT, Kaufman GE, Goldstone JV, Roelke ME, O'Brien SJ, Koepfli KP, Frank LG, Court MH. Evolution of a major drug metabolizing enzyme defect in the domestic cat and other felidae: phylogenetic timing and the role of hypercarnivory. PLoS One. 2011 Mar 28;6(3):e18046.]
Comparative and Molecular Pharmacogenomics Laboratory
Department of Veterinary Clinical Sciences,
Washington State University College of Veterinary Medicine
100 Grimes Way, Pullman, WA 99163, USA.
Phone: 509-335-0817; Fax: 509-335-0880
Comments or problems please send email to: firstname.lastname@example.org
Last update: 10 October, 2012
Comparative and Molecular Pharmacogenomics
IMPORTANT - This laboratory has recently relocated to Washington State University in Pullman, WA.