The Toxicologist - Society of Toxicology

1334 AFFECT OF GENETIC VARIATION ON DRUG
METABOLISM AND TOXICITIES IN INBRED MOUSE
STRAINS.
M. Pletcher. Investigative Toxicology, Pfizer Global Research & Development,
Groton, CT.
Panels of inbred strains of mice have been shown to encompass a genetic and phenotypic
diversity that approximates that found in the human population. This variability
across mouse strains extends to the response observed after treatment with
pharmaceuticals, both in terms of efficacy and toxicity. Use of the antidepressant
fluoxetine revealed strain-dependant differences that reflected the clinical variability
associated with selective serotonin reuptake inhibitors. Likewise, the idiosyncratic
nature of acetaminophen-induced liver injury has also been accurately reproduced
in the inbred mouse strains. Underlying the variability of drug response and injury
are significant differences in the abilities of each of the strains to metabolize and
detoxify the compounds they are exposed to. A characterization of hundreds of
small molecules and metabolites in the blood and liver of 35 inbred strains revealed
significant strain-specific differences. Furthermore, by combining whole genome
transcriptional data from 33 strains of inbred mice with a detailed haplotype map
of those same strains, a strain-specific variation in the expression of an entire cluster
of phase II metabolic enzymes, the glutathione S-transferase mu family of genes,
was uncovered. The cataloged variation within the human glutathione S-transferase
mu orthologs has been associated with increased susceptibility to drug-induced
liver injury. If preclinical models are to predict outcomes in humans they must
properly replicate those susceptibilities and predispositions found in the human
population starting at the genetic level. This early work suggests that the inbred
mouse diversity panel could provide such a resource.
1337 IT’S NOT YOUR FATHER’S ARYL HYDROCARBON
RECEPTOR: NEW BIOLOGICAL ROLES FOR A
MISUNDERSTOOD RECEPTOR.
R. S. Thomas 1 and C. Rowlands 2 . 1 The Hamner Institutes for Health Sciences,
Research Triangle Park, NC and 2 The Dow Chemical Company, Midland, MI.
The aryl hydrocarbon receptor (AhR) has been traditionally associated with regulating
responses to a variety of environmental chemicals. However, the AhR has
been highly conserved throughout evolution and there is a growing body of evidence
that the receptor modulates critical aspects of cellular function that are independent
of its response to xenobiotics. The modulation of cell responses are highly
context specific resulting in growth promotion in certain cell types and growth arrest
and differentiation in other cells. Endogenous chemicals have been identified
in animals with AhR agonist activity indicating they are endogenous ligands for this
receptor. These results suggest that the AhR should be viewed in the same light as
other cellular receptors (e.g., ER, AR, and PPAR) with a physiological role that can
be disrupted by xenobiotic chemicals rather than a receptor that evolved primarily
as a xenobiotic sensor. Thefore, we will address new research on the biological roles
for the AhR in cell growth, death, and differentiation and the potential human
health risks and therapeutic benefits associated with exposure to exogenous AhR
ligands. Molecular aspects of AhR signaling are conserved across other nuclear receptor
pathways and therefore the issues discussed may have relevance to the
modes-of-action for xenobiotics mediated by other nuclear receptors. This session
will be of interest to investigators and regulators wanting to understand the latest
research on the underlying biological roles for this remarkable pleiotropic receptor.
1335 GENETIC VARIATION IN MICE: MODELING DISEASE,
PHARMACOGENETICS, AND BASIC BIOLOGY.
T. Wiltshire. Pharmacotherapy and Experimental Therapeutics, University of North
Carolina at Chapel Hill, Chapel Hill, NC. Sponsor: J. French.
Pharmacogenetics is the study of relationships between genetic variation and interindividual
differences with respect to drug response and aims to elucidate the genomic
determinants of drug disposition and effect. The etiology of this inter-individual
variation is multifactorial, but is due in part to host genetic variations. We
have used a model mouse population that has incorporated broad genetic variation
from across the mouse genome to identify and validate genetic components of the
responses to drugs and toxicants. We have developed a platform of both in-vitro
and in-vivo assays from these genetically well defined mouse strains which will enable
us to assess primarily effects of toxicity, but also efficacy of current and novel
agents in drug therapies. We have also developed high content imaging screens of
drug activity at a cellular level using primary cells from exactly the same mouse lines
and so generate an overlapping and interwoven analysis of whole organism phenotypes
with potential cellular mechanisms. In addition, gene expression phenotypes
have been used for genome-wide association analyses, an analysis referred to as expression
QTL (eQTL) mapping. We will present evidence that these patterns were
enriched for previously characterized relationships between known upstream transcriptional
regulators and their downstream target genes. Moreover, we use this
strategy to identify both novel regulators and novel members of known pathways.
These analysis approaches will be broadly applicable to other eQTL data sets in
pharmacology and toxicology.
1338 THE ROLE OF THE ARYL HYDROCARBON RECEPTOR
IN MAMMARY DIFFERENTIATION AND DISEASE.
J. M. Hall 1, 2 , M. A. Barhoover 1 , D. P. McDonnell 3 , W. F. Greenlee 1 and R. S.
Thomas 1 . 1 The Hamner Institutes for Health Sciences, Research Triangle Park, NC,
2
Department of Pharmaceutical Sciences, Campbell University, Buies Creek, NC and
3
Department of Pharmacology and Cancer Biology, Duke University, Durham, NC.
Breast cancer is currently the most prevalent malignancy among women in industrialized
countries. As a disease, breast cancer has a relatively high recurrence rate
with a poor survival for aggressive metastatic disease. Similar to the nuclear hormone
receptors, ligand activation of the AHR has identified context- and tissuespecific
effects including tumor promotion in certain tissues and decreased tumor
incidence in other tissues. In mammary tissue, both rodent studies and human epidemiological
investigations have shown significant decreases in tumor incidence.
We have examined the effect of the AHR activation in the metastatic process across
all the major breast cancer subtypes (ER+/-, PR+/-, and HER2+/-) and have found
that the receptor inhibits multiple aspects of the metastatic process in all subtypes.
Treatment with AhR agonists inhibited cell invasiveness in the Boyden chamber
assay and colony formation in soft agar. Knockdown of the AhR using siRNA duplexes
demonstrated that the inhibition of invasiveness was receptor-dependent and
that endogenous receptor activity was protective. Additional studies linked the inhibition
of the metastatic processes to the ability of AhR agonists to promote differentiation
of breast cancer cells. These results suggest that selective AHR modulators
may provide significant therapeutic advantages over current targeted breast
cancer therapies that are subtype-specific.
1336 MOUSE MODEL OF THE HUMAN OPULATION
(MMHP) FOR SYSTEMS BIOLOGY AND TOXICOLOGY.
D. W. Threadgill. Genetics, North Carolina State University, Raleigh, NC.
New population-level models are beginning to support a more advanced understanding
of how an exposure to chemicals differs among individuals and the identity
of the genetic factors that determine exposure sensitivity. Using various population-level
mouse models containing genetic diversity equal or greater than in the
human population, we will present data showing that genetic variation has a significant
impact on the molecular and phenotypic measures, which adds an important
dimension to toxicology. Specifically, we proposed and validated a strategy using a
Mouse Model of the Human Population (MMHP) to identify genetic polymorphisms
and novel mechanisms contributing to xenobiotic-induced liver injury
using acetaminophen and ethanol as model hepatotoxicants. To identify the genetic
causes of acetaminophen-related liver injury, we employed whole-genome haplotype
association analysis in the MMHP and discovered that polymorphisms in
Ly86, Cd44, Cd59a, and Capn8 are candidate genes. We then confirmed that variation
in the orthologous genes is associated with susceptibility to acetaminophen in
humans. These studies support the idea that a genetically diverse MMHP can be
useful as a model to understand and predict adverse toxicity in humans.
1339 DIRECT REGULATION OF ARYL HYDROCARBON
RECEPTOR FUNCTION BY SELECTIVE ESTROGEN
RECEPTOR MODULATORS (SERMS).
D. P. McDonnell. Department of Pharmacology and Cancer Biology, Duke
University, Durham, NC. Sponsor: R. Thomas.
Selective Estrogen Receptor Modulators (SERMs) have been used extensively for
the treatment and prevention of breast cancer and other diseases dependent on estrogen
receptor (ER) signaling. These compounds exhibit selective agonist/antagonist
activities in tissues through their ability to induce different conformational
changes in ER and recruit functionally distinct transcriptional coregulators. Recent
observations have suggested that SERMs interact with targets other than ER. Due
to alterations in traditional AHR-regulated genes by SERMS, we hypothesized that
the AHR plays a role in SERM pharmacology. In these studies, we demonstrate that
the AHR is activated directly by SERMs and that the ability of the active metabolite
of tamoxifen, 4-hydroxytamoxifen to suppress osteoclast differentiation in vitro
is largely dependent on AHR. These findings suggest that the role for the AHR
needs to be taken into account in the pharmacological actions of SERMs.
SOT 2010 ANNUAL MEETING 285