McKim Conference on Predictive Toxicology The Inn of Lake Superior Duluth, Minnesota September 25-27, 2007 Toxicity Pathways as an Organizing Concept Gilman Veith

Molecular Initiating Events Chemical Speciation and Metabolism Measurable System Effects Adverse Outcomes Parent Chemical Conceptual Framework Rather than developing statistical models of complex endpoints, key molecular initiating events become the “well-defined” endpoints for QSAR.

Molecular Initiating Events Speciation and Metabolism Measurable System Effects Adverse Outcomes Parent Chemical IQF Framework for QSAR 1. Identify Plausible Molecular Initiating Events 2. Design Database for Abiotic Binding Affinity/Rates 3. Explore Linkages in Pathways to Downstream Effects 4. Develop QSARs to Predict Initiating Event from Structure QSAR SystemsBiology Chemistry/Biochemistry

Major Pathway for Reactive Toxicants To Fish Michael Addition Schiff base Formation S N 2 Acylation Irreversible Protein Modification MechanismsMolecular Initiating Events Exposed Surface “Irritation” Necrosis of the Gill Epithelium In vivo Endpoints Pathogenesis Organ Pathology Death

Primary Pathways for Reactive Toxicity from Soft Electrophiles Systemic Responses Skin Liver Lung Michael Addition Schiff base Formation S N 2 Acylation Irreversible Protein Modification (Rates) Immunogenic Mechanisms Molecular Initiating Events Exposed Surface Irritation Systemic Immune Responses Necrosis Skin Lung/Gills GI Tract In vivo Endpoints Yes No

Mortality Systemic Toxicity Disease Cancer Developmental Impairment Terato Prenatal Deficits Reproductive Fitness Viable Offspring Fertility Molecular Interactions Biochemical Responses Cellular Responses Tissue/Organ Function Chemical Inventories C 2 Cl 3 Cl C C 2 Cl 3 Cl C C 2 Cl 3 Cl C ClCl ClCl ClCl ClCl OH A Hypothesis-Driven Paradigm Existing data; In silico and In vitro Prioritization; Screening Adverse Outcomes Efficient, Confirmatoru Tests if Needed

Mortality Systemic Toxicity Disease Cancer Reproductive Fitness Viable Offspring Fertility Developmental Impairment Terato Prenatal Deficits Current Paradigm Risk Managers Focus on Potential Adverse Outcomes Current toxicology testing paradigm generates In Vivo animal data for all possible outcomes to determine which are relevant BATTERY of Animal Testing

Chemical 2-D Structure/ Properties Chemical 3-D Structure/ Properties Receptor/Ligand Interaction -Gene Activation -Protein Production -Gonad Development -Altered Hormone Levels Impaired Reproduction Linkage Across Levels of Biological Organization Molecular Cellular Organ Individual Example: Receptor-Mediated Pathways

Appropriate Dose Metric Response Endpoint Subcellular Cell Tissue Chronic Whole Organism Acute Whole Organism