The Toxicologist - Society of Toxicology

tokine products during carcinogenesis. Taken together, these results reveal that
IKKα is essential for embryonic skin development and plays a critical role in maintaining
skin homeostasis and preventing skin SCCs through regulating skin cell differentiation,
proliferation, and inflammation pathways.
1783 MODELING THE INFLAMMATORY TO
IMMUNOSUPPRESSIVE SWITCH DURING
PREMALIGNANT PROGRESSION.
A. Glick and A. Gunderson. Veterinary and Biomedical Sciences, Penn State
University, University Park, PA. Sponsor: L. Mordasky Markell.
Immunosuppression within the developing tumor microenvironment frequently
occurs under conditions of acute or chronic inflammation. Myeloid derived suppressor
cells (MDSC), a heterogeneous population of immature myeloid cells (Gr-
1+/CD11b+) that are greatly expanded in response to tumor derived factors, play a
significant role in generating systemic and localized immunosuppression in both
human cancer patients and experimental mouse models. Here we have investigated
the role of MDSC formation in skin carcinogenesis using a a bitransgenic model in
which oncogenic human c-Ha-RasG12V is induced in the suprabasal layers of the
mouse epidermis with the doxycycline regulated Involucrin-tTA driver line.
Induction of RasG12V in bitransgenic mice caused rapid epidermal hyperplasia
and cutaneous inflammation as expected, which was largely composed of infiltrating
neutrophils that formed cytotoxic microabscesses in the suprabasal layers of the
epidermis. Antibody mediated depletion of neutrophils concurrent with transgene
activation ablated neutrophil infiltration, reduced microabscesses and caused an increase
in epidermal thickening. Ras-induced neutrophils were cytotoxic towards
neoplastic keratinocytes in vitro. On a Rag1 null background this cytotoxic inflammatory
response was suppressed, and restored by adoptive transfer of T cells but not
B cells. However, 2 weeks post-Ras, neutrophil microabscesses were replaced by a
diffuse single cell infiltration of myeloid cells, coincident with increased systemic
levels of Gr-1/CD11b cells that could suppress in vitro proliferation of CD4 and
CD8 T cells, decreased neutrophil cytotoxicity in vitro, and decreased cutaneous
IFNγ+ T cells. By 2 weeks the hyperplasic epidermis had progressed to focal SCC
and keratoacanthomatous-like lesions. Surprisingly markers of infiltrating MDSC
and tumor progression and invasion such as MMP9 were significantly reduced on a
Rag1 null background, indicating a requirement of the adaptive immune system for
generation of the MDSC response and tumor progression.
1784 DOES SEX MATTER IN THE DEVELOPMENT OF NON-
MELANOMA SKIN CANCER?
T. Oberyszyn 1 , N. J. Sullivan 1 , K. L. Tober 1 , M. A. Bill 2 , J. A. Riggenbach 1 , J.
S. Schick 1 and G. B. Lesinski 2 . 1 Pathology, The Ohio State University, Columbus,
OH and 2 Internal Medicine, The Ohio State University, Columbus, OH. Sponsor: L.
Mordasky Markell.
Ultraviolet light B (UVB) is a major environmental carcinogen that has been implicated
in the development of nonmelanoma skin cancers (NMSC). These skin tumors
are the most common form of cancer in humans, with over 1 million new
cases identified in the United States each year. In fact, more Americans will be diagnosed
with some form of skin cancer than all other cancers combined.
Epidemiological studies have shown that there are sex differences in the development
of NMSC, with men being three times as likely to develop squamous cell carcinomas
as women. This disparity has been attributed to lifestyle choices. However,
recent studies from our laboratory using the Skh-1 mouse model suggest that the
pathways by which UV exerts its damaging effects in male and female skin are not
the same. While male murine skin exhibited less UVB-induced inflammation compared
to female mice, they displayed higher levels of epidermal oxidative DNA
damage and lower total antioxidant capacity both prior to and 48 hours following a
single UV exposure. Long-term studies showed that when exposed to equal doses of
UVB, male Skh-1 mice developed tumors earlier, in greater number and with a
more advanced grade than female mice. One major factor thought to contribute to
inflammation-induced immune suppression and consequent carcinogenesis is a
heterogeneous population of myeloid cells, known as myeloid-derived suppressor
cells (MDSC). The Skh-1 model provides a unique opportunity to examine MDSC
expansion before and throughout tumor progression. We found that male mice exhibited
increased splenic MDSC expansion both following acute as well as chronic
UVB exposure. After adjusting for tumor burden, sex was an independent predictor
of elevated splenic MDSC expansion, with male tumor-bearing mice having 55%
higher splenic MDSC levels. While our model focuses on skin cancer, these findings
also have the potential to impact the development of therapeutics for other
types of inflammation-associated carcinomas.
1785 BIOMARKERS AS INDICATORS OF PHOTOTOXICITY:
DO THEY HAVE A ROLE AS PREDICTORS OF
PHOTOCARCINOGENESIS?
D. B. Learn 1 , P. D. Forbes 2 , C. P. Sambuco 1 , A. M. Hoberman 1 and S. R.
Eldridge 3 . 1 Charles River Laboratories Preclinical Services, Horsham, PA, 2 Toxarus,
Inc., Malvern, PA and 3 Charles River-Pathology Associates, Frederick, MD.
Solar UVR exposure causes well-recognized dose- and time-dependent cutaneous
DNA damage, rapid-onset erythema (vasodilation) and edema, persistent erythema
with inflammatory infiltrate, impaired cutaneous immune function, cell proliferation
and hyperplasia. Together, these effects may be considered a “perfect storm” of
pre-cancerous signals in skin. Because its delivery can be precisely controlled and
distributed, UVR exposure provides an ideal stimulus for modeling neoplastic precursors,
including identifying relevant inflammatory markers and exogenous agents
that influence these markers and thus the course of UVR photocarcinogenesis.
Laboratory and clinical studies show that the effectiveness of a given UVR dose can
be modified by many factors, with one example being the influence of pharmaceuticals
on experimental photocarcinogenesis. But can biomarkers predict this influence?
What constitutes an inflammatory or neoplastic biomarker? Which biological
precursors are necessary or sufficient for neoplastic development? Which markers, if
any, are predictive of neoplastic enhancement? Unresolved questions temper the
understandable urge to replace photocarcinogenesis testing with tests based on
measuring biomarker responses. In general, variables that influence inflammation
(during or after UVR exposure) tend to have corresponding influences on the rate
of photocarcinogenesis. However, the apparent relationship has its limits, may not
correlate with anticipated effects and in known cases (e.g., anthracene or porphyrin
phototoxicity), erythema is not associated with enhanced photocarcinogenesis,
connoting a “false positive”. Whether tumor enhancement can occur in the absence
of these markers (i.e., a “false negative”) is not established. Thus, alternative tests
based on biomarkers may function as effective screening tools but are not yet ready
to displace the more definitive photocarcinogenesis test for risk identification.
1786 NEW INSIGHTS INTO THE NRF2-KEAP1 PATHWAY
AND ITS IMPACT ON HUMAN DISEASE.
D. D. Zhang 1 and T. W. Kensler 2 . 1 University of Arizona, Tucson, AZ and
2 University of Pittsburgh, Pittsburgh, PA.
Damage mediated by reactive electrophilic intermediates can have a profound effect
on many cellular functions, and has been implicated in cancer, inflammation, neurodegenerative
diseases, cardiovascular diseases, and aging. Eukaryotic cells have
evolved anti-oxidant defense mechanisms to neutralize reactive oxygen species
(ROS) and maintain cellular redox homeostasis. Eukaryotic cells also express cofactors
and enzymes for trapping reactive electrophiles. A key adaptive response system
for protection against ROS and electrophilic intermediates is mediated by the transcription
factor Nrf2, through the antioxidant responsive element (ARE) sequences
in the promoter regions of dozens of cytoprotective genes. Basal levels of Nrf2 remain
relatively low, due to its negative regulation by Keap1, which targets Nrf2 for
ubiquitination and degradation. However, upon activation, cysteine residues of
Keap1 are modified, leading to conformational changes that impair ubiquitination
of Nrf2, thus allowing Nrf2 to translocate into the nucleus to activate the expression
of its downstream genes. The activation of the Nrf2 pathway is not only important
in protecting cells against the deleterious effects caused by carcinogens and
environmental toxicants, but, also, Nrf2 protects against drug-induced organ toxicity
and damage. Unfortunately, the dark-side of Nrf2 has been revealed indicating
that constitutive activation of Nrf2, due to mutations in either Nrf2 or Keap1, creates
an environment conducive to cancer cell growth and thus, contributes to
chemoresistance. Our knowledge on the Nrf2 pathway has progressed rapidly, and
new important insights into its complex regulation have emerged. Thus it is important
to highlight the novel mechanisms that activate the Nrf2 pathway, cross-talk
between Nrf2 with other essential cell signaling pathways to maintain cellular
homeostasis, the protective role of Nrf2 in human diseases, and paradoxically its
role as a hostage in cancer. In conclusion, we will explore the essential role of Nrf2
in disease and in a variety of biological processes that regulate the response to environmental
exposures.
1787 THE NRF2-KEAP1 STRESS RESPONSE PATHWAY:
MOLECULAR BASIS OF ADAPTIVE RESPONSES AND
PATHOGENESIS.
M. Yamamoto, H. Kurokawa, T. Suzuki, K. Taguchi and H. Motohashi.
Medical Biochemistry, Tohoku University Graduate School of Medicine, Sendai,
Japan. Sponsor: T. Kensler.
Our bodies must counteract insults originating from the environment.
Electrophiles and ROS transcriptionally activate the expression of detoxifying and
antioxidant genes through the antioxidant/electrophile responsive element
SOT 2011 ANNUAL MEETING 383