Download DNT Testing in the Name of Children`s Health: A Case for

Highlighting the Need for AOPs in Streamlining
Hazard Assessment Methods
(for cancer assessment)
Catherine Willett, PhD
Director, Regulatory Toxicology
Humane Society of the United States
2n McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
Outline
1. Rodent Cancer Bioassay: cost/benefit?
2. Advantages of mechanism based approaches
3. AOP approaches and activities at OECD
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
1. Rodent Cancer Bioassay: Cost
• Minimally 400 animals, 2 – 4 million USD and 3 years*
• Often performed in two species (drugs, food additives)
• Or rat bioassay plus shorter-term transgenic mouse
assays1
– ras H2 + p 53 +/- : use half the number of animals and for 6 months
– Reduced animal use mitigated by need for creation and
maintenance of multiple lines
– Only improves identification if both used (geno and non-genotoxic)
 no animal savings, minimal cost savings
*Thomas RS, Pluta L, Yang L, Halsey TA. Toxicol Sci 2007. 97(1):55-64.
1Alden
et al. Veterinary Pathology. 2011. 48(3):772-784.
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
1. Rodent Cancer Bioassay: Benefit?
• Drugs (review of 533)
– False positives: 80%
– False negatives: 27%
– Sensitivity: 73%
• 12 out of 44 chemicals with human concern not seen in either rodent
species
“When tested repeatedly, most molecules….had conflicting test results.”
Alden et al. Veterinary Pathology. 2011. 48(3):772-784
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
1. Rodent Cancer Bioassay: Benefit?
Other chemicals (e.g. NTP studies)
– 82% of 500 studies resulted in noncommittal classifications*
– Only 57% of chemicals tested multiple time give consistent results
– 22% of all chemicals tested test positive1
•
Largely due to findings at MTD and irrespective of biological plausibility
•
Nevertheless results in classification as “possible human carcinogen”
– Positive correlation?
•
9/10 known human carcinogens have tested positive either rats or mice in NTP studies
•
All known human carcinogens have tested positive in some rodent assay, with the possible
exception of arsenic
“This result says more about the persistence of toxicologists than about the
ability of a standard (rodent) protocol to predict human carcinogenicity.”1
* Wasted Money Wasted Lives. People for the Ethical treatment of Animals. 2006.
http://www.mediapeta.com/peta/pdf/Wasted-money-PDF.pdf
1 Ennerver and Lave. Reg. Toxicol. Pharma. 2003. 38: 52-57
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
1. Rodent Cancer Bioassay: Cost / benefit
400 animals
2 – 4 million USD
3 years
2
False Positives: 80%
False Negatives: 27%
or
82% noncommittal classifications
Too high
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
2. Advantages of mechanistic approaches
1. Refine design and interpretation of animal studies
2. Demonstrate human relevance (or not)
3. Improve predictivity for both human health and other
target species
4. Design assessment strategies that are not
dependent on animal testing
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
2. Early adoption of mechanistic approaches
DNA reactive vs non-DNA reactive
– Mouse transgenic lines
– 3Rs value highly debatable
– Chemical alerts for DNA reactivity
– Used to flag chemicals
– Genotoxicity battery
– Currently used to exclude chemicals
– In vitro tests have high false positive rates
– in vivo tests are insensitive
– Battery misses non-DNA reactive chemicals
– Cell transformation assays
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
2. Early adoption of mechanistic approaches
Human Relevance Frameworks
- Characterize MoA of each class of carcinogens
- Determine which rodent MoA is possible relevant to humans
- Built using case studies
Timeline stolen from V. Dellarco:
•
EPA & IPCS 1999-2001. Conceptual Framework for Evaluating a Mode of Action for
Chemical Carcinogenesis.
•
ILSI 2003. Framework for human relevance analysis of information on carcinogenic modes
of action.
•
ILSI 2005. Extends Framework to non-cancer outcomes & life stage information.
•
IPCS 2006 & 2008 Adopts Human Relevance Framework: Boobis, et al. IPCS framework
for analyzing the relevance of a non-cancer mode of action for humans. Crit Rev Toxicol.
2008;38(2):87-96.
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
Proposals to improve efficiency of rodent-based
assessment
Short-term screening tests*
– Step 1: 90-day “screen”
• E.g. hepatocarcinogenicity: hepatocellular necrosis, hypertrophy, cytomegaly,
increased liver weight
– Step 2: mechanistic screens (most 90-days)
•
•
•
•
•
•
•
•
•
Histopathology
Serum enzymes
Acyl Co-A oxidase
CYP induction
CAR, PSR, AHR binding
ER binding (or histologic evaluation of endocrine-sensitive organs)
Iron staining
Reversibility
Metabolic activation
*Cohen, S.M. Toxicol. Pathol. 2010. 38(3):487-501.
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
Proposals to improve efficiency of rodent-based
assessment
Testing strategy to rule out carcinogens*
– Negative genotoxicity in standard battery
– Negative hormonal perturbation in chronic studies
• effects on endocrine-related tissues, hormone levels
– Lack of histopathologic risk factors in 6 month rat study
• neoplasia in any tissue
– Negative in 6 month transgenic mouse
• Both genotox and non-genotox models required?
– Positives go into a standard rat bioassay
*Sistare et al. Toxicol. Path. 2011.39: 716-744.
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
2. Molecular approaches
Gene expression profiling following 13 week exposure*
– Predict lung tumors in B6C3F1 female mice
– Overall accuracy 77.5% in predicting mouse lung tumors
– 25 chemicals sufficient to develop predictive model
• (could create predictive models for 8 organs using 200 chemicals)
– Gene profiles placed into biologic process categories1
• Used to calculate BMD values for liver or lung
• Some transcriptional and tumor incident BMD values correlate well
 transcriptional BMD values could potentially be used as
points of departure for cancer as well as non-cancer risk
assessment
* Thomas, R.S. et al. Toxicol. Sci. 2009. 112(2): 311-321.
1 Thomas, R.S. et al. Toxicol. Sci. 2011. 120 (1): 194-205.
Could the predictive capacity of ‘omics be improved by AOPs?
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
3. Adverse Outcome Pathway Approaches
Adverse Outcome Pathway: a chemical and biological description of what
occurs when a substance interacts with a living organism and results in
an adverse reaction – a biological map from the initiating event through
the resulting adverse outcome that describes both mechanism and
mode of action.
From: Ankley et al. Environ.Toxicol.Chem. 2010. 29 (3): 730–741.
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
3. Adverse Outcome Pathway Approaches
AOPs can be useful for:
Near-term:
– Developing chemical categories and structure activity relationships
– Increasing certainty of interpretation of both existing and new information
– Developing integrated testing strategies that maximize useful information
gained from minimal testing
Longer-term:
– Identifying key events for which non-animal tests can be developed, thereby
facilitating mechanism-based, non-animal chemical assessment
– Creating predictive toxicological assessments with low uncertainty and high
human relevance
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
3. AOP activities at OECD: expert consultation on the
ER decision framework in Feb 2009
ER-mediated Reproductive Impairment
QSAR
focus
area
In vitro Assay
focus area
In vivo
CELLULAR
Response
MOLECULAR
Target
Chemicals
Receptor
Binding
TISSUE/ORGAN
Liver
Liver Cells
Altered
Protein
Expression
Altered
proteins
Vitellogenin
Ova-testis;
Sexreversed;
Fecundity
ER
Binding
Gonad
INDIVIDUAL
Sex
reversal;
Altered
behavior;
POPULATION
Skewed
Sex
Ratios;
Yr Class
Repro.
Toxicity Pathway
P. Schmieder, McKim conference 2008.
Adverse Outcome Pathway
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
3. AOP activities at OECD
2010 Workshop on using mechanistic information in forming
chemical categories near-term recommendations:
1) Develop AOPs for well-established effects (e.g., skin sensitization) as well as
several longer term health and ecotoxicological endpoints.
3) Establish, populate and maintain an accessible, electronic repository e.g.
Effectopedia.
4) Develop a strategic plan including:
–
an information template for developing and assessing AOPs
–
guiding principles for assessing completeness and acceptance of an AOP
–
a format for attaining mutual acceptance of an AOP.
5) Harmonize terminology associated with AOPs.
6) Integrate AOPs in the OECD QSAR Toolbox.
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
3. AOP activities at OECD: Sensitization draft AOP
OECD 2011. (Draft) The Adverse Outcome Pathway for Skin Sensitisation Initiated by Covalent Binding to Proteins
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
3. AOP activities at OECD
Agreed at last Joint Meeting in June 2011 that AOPs were to
become the cornerstone for all future projects in the test
guidelines programme.
Under development:
•
A process for development and maintenance of AOPs
•
A Guidance Document for Developing and Assessing Completeness of
AOPs
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD
Thank you.
Catherine Willett, PhD
Director, Regulatory Toxicology,
Risk Assessment and Alternatives
[email protected]
t +01.240.599.6785
The Humane Society of the United States
2100 L Street NW Washington, DC 20037
humanesociety.org/animalsinlaboratories
2nd McKim Workshop on Reducing Data Redundancy in Cancer Assessment | 8 – 10 May 2012 | Baltimore, MD