Evolving approaches to AOP development: observations from MOA frameworks to systems biology

Transcription

1 Evolving approaches to AOP development: observations from MOA frameworks to systems biology Molecular ini'a'ng event Intermediary steps Adverse Outcome Catherine WilleI, PhD Director, Regulatory Tes'ng Risk Assessment and Alterna'ves The Humane Society of the United States

2 Outline Mode of Action frameworks AOP concept in ecotoxicity OECD skin sensitisation project Estrogen receptor-mediated effects Thyroid hormone pathway Pathways of Toxicity

3 Early Application of Mode-of-Action Human Relevance Frameworks - Characterize MoA of each class of carcinogens - Determine which rodent MoA is possibly relevant to humans - Built using case studies Meek et al A Framework for human relevance analysis of information on carcinogenic modes of action. Crit. Rev. Toxicol. 33 (6):

4 Early Application of Mode-of-Action Carcinogenicity DNA-reactive (genotoxic) vs non-dna reactive Simple test battery for DNA reactive chemicals allows negatives to be set aside Current exploration of incorporation of non-dna reactive tests (e.g. Syrian Hamster Embryo assay) Use of mouse transgenic lines modest increase in predictivity of 2 species rodent assessment but high cost in terms of 3Rs Until non-animal assessments can achieve confidence necessary to use both positive and negatives for RA

5 The Adverse Outcome Pathway Concept A conceptual construct that portrays existing knowledge of linkages between a direct molecular initiating event and an adverse outcome at a level of biological organization relevant to risk assessment From: Ankley et al. Environ.Toxicol.Chem (3):

6 Example from aquatic toxicity: narcosis Non- specific, results from hydrophobic interac'ons with cell membranes In fish leads to decreased respiratory rate, metabolic rate, and low blood O2 leading to death Acute aqua'c tox can be adequately predicted from the octanol/water par''on coefficient Many missing intermediate steps but useful non the less since approx. 60% organic compounds work via this mechanism

7 ER- mediated reproduc've impairment Developed from: an understanding of the MIE plus a need for a strategy for measuring endocrine- mediated effects. Includes use of biomarker (vitellogenin) that is (in the case of females) or is not (in the case of males) directly linked to the adverse outcome

8 OECD sensi'za'on project QSAR In vitro In vivo Chemical Properties Electrophilic substance or precursor Molecular Initiating Event Covalent interaction with cell protein OECD The Adverse Outcome Pathway for Skin Sensitisation Initiated by Covalent Binding to Proteins Cellular Response Organ Response Organism Response Dendritic cells (DCs) Induction of inflammatory cytokines and surface molecules Mobilization of DCs Keratinocyte s Activation of inflammatory cytokines Induction cyto-protective gene pathways Lymph node Histocompatibility complexes presentation by DCs Activation of T cells Expansion of activated T-cells Skin (epidermis) Inflammation upon challenge with allergen Sensi'sa'on ITS Aeby et al. (2010). Toxicol In Vitro 24, Bauch et al. (2011). Toxicol In Vitro 25, European Union, 7 th Framework Programme Sens- it- iv: hip:// it- iv.eu Lambrechts et al. (2010). Tox Sci 116(1), Jaworska et al. (2011). ALTEX 28, McKim et al. Cutan Ocul Toxicol Apr 12. [Epub ahead of print] OECD,

9 AOP Examples: carcinogenicity Parent Chemical Direct DNA Binding Indirect DNA Damage Nongenotoxic Mechanisms Individual Ini'a'ng Events/ Structural Alerts Grouping Data for Interac'on Categories Ac'vated Metabolites No Evidence Of Cancer Poten'al Structural Evidence of Cancer Poten'al Category with Data for Cancer Poten'al Modified from: Veith, McKim Conference summary, 2010

10 Thyroid hormone pathway(s) Crooon, K. US EPA. Presented at DC area SOT, May 2012.

11 Thyroid hormone pathway Crooon, K. US EPA. Presented at DC area SOT, May 2012.

12 Center for Alternatives to Animal Testing: ToP project 2012 Workshop: Workshop on the Concept and Tools for Pathways of Toxicity, Oct 10 12, Baltimore Pathways of toxicity = NRC report toxicity pathways From MIE to cell or tissue level Traditional toxicology and AOP projects (Kegg, Hamner): Biological pathways derived from detailed animal experimentation Detailed analysis of chemical effects Bioinformatics (GeneGo, Reactome) omics information à associative fingerprints Not necessarily explained by pathways or linked to underlying biology Project will likely involve a combination of these approaches

13 OECD AOP Project 2010 Workshop on using mechanistic information in forming chemical categories near-term recommendations: Develop AOPs for well- established effects (e.g., skin sensi'za'on) And several longer term health and ecotoxicological endpoints Establish, populate and maintain an accessible, electronic repository e.g. Effectopedia Develop a strategic plan including: an informa'on template for developing and assessing AOPs guiding principles for assessing completeness and acceptance of an AOP a format for aiaining mutual acceptance of an AOP Harmonize terminology associated with AOPs Integrate AOPs in the OECD QSAR Toolbox

14 OECD AOP Project Extended Advisory Group on Molecular Screening and Toxicogenomics, June 2012 In process: Mitochondrial toxicity OECD Cell proliferation/differentiation OECD Fish reproductive toxicity US EPA Thyroid hormone pathways US EPA PPARα OEDC, Hamner Cancer epigenetics S.Korea Proposed Germ cell mutagenicity Canada Neurotoxicity and inflammation Switzerland Liver Steatosis and Fibrosis JRC AhR BIAC Aquatic toxicity: UK and Japan Mutagenic MOA: US PPARa/CAR: US Embryonic vascular development: US Narcosis -? Acetylcholinesterase -?

15 OECD AOP Project Response matrix Guidance Integration of AOPs into all Test Guideline Programme projects Template for building Criteria for evaluating

16 Conclusions AOPs can be built in a number of different ways Using information from a wide range of biological organization For a number of different decision-making purposes Likely best approach: combine Exiting biological knowledge from humans and other animals Bioinformatics approaches and fingerprint biomarkers

17 Conclusions Essential elements Well-defined MOE and AO (for specific use) Description, including context Diagram (may include some context) Documented QC of data, linkages (well curated, objective criteria) Consistent definitions, terms, formats Quantitative dimension to linkages needed for use in RA Integrated databases and knowledge bases ACToR and MetaPath: EPA all available chemical toxicity data on over 500,000 environmental chemicals searchable by chemical name and structure Kegg pathway database: collection of manually drawn pathway maps representing current knowledge on the molecular interaction and reaction networks Effectopedia: open knowledge aggregation and collaboration tool that provides a means of describing adverse outcome pathways in an encyclopedic manner.

18 ArLculaLng the Vision: Communica'ng the purpose and goals of TT21C ImplementaLon: facilita'ng scien'fic and technical approaches to accomplishing the vision globally Lobbying/Funding: in the US and interna'onally

19 Thank You Catherine Willett, PhD Director, Regulatory Testing Risk Assessment and Alternatives Humane Society of the United States Coordinator, Human Toxicology Project Consortium