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Biokinetics in vitro
S16
Abstracts / Toxicology Letters 205S (2011) S2–S18
not survive in immunocompetent animals. Finally, there are also features of cellular therapies that require some reflection in terms of GLP compliance. doi:10.1016/j.toxlet.2011.05.062 S12—Improving quantitative in vitro–in vivo extrapolations (QIVIVE) for risk assessment
S12-1 Quantitative in vitro–in vivo extrapolations: Essential issues
presentation describes why these differences may occur and how these differences may in part explain variations in concentrationeffect relationships between in vitro assays and between in vitro and in vivo assays. A chemical may bind to serum constituents, evaporate, bind to cell membranes and sorb to plastic. All these processes decrease the concentration of the chemical freely available for uptake into cells and binding to target sites. For a more accurate description of the intrinsic potency of a test chemical, the free concentration and the cell burden may be used instead. A number of measurement techniques and modelling approaches exist to determine the free and cell concentration of a chemical. doi:10.1016/j.toxlet.2011.05.065
H. Clewell The Hamner Institutes for Health Sciences, Research Triangle Park, USA The field of toxicology is currently undergoing a global paradigm shift to use of in vitro approaches for assessing the risks of chemicals and drugs, yielding results more rapidly and more mechanistically based than current approaches relying primarily on in vivo testing. However, reliance on in vitro data entails a number of new challenges associated with translating the in vitro results to corresponding in vivo exposures. Physiologically based pharmacokinetic (PBPK) models provide an effective framework for conducting quantitative in vitro to in vivo extrapolation (IVIVE). Their physiological structure facilitates the incorporation of in silico- and in vitro-derived chemical-specific parameters in order to predict in vivo absorption, distribution, metabolism and excretion. In particular, the combination of in silico and in vitro parameter estimation with PBPK modeling can be used to predict the in vivo exposure conditions that would produce chemical concentrations in the target tissue equivalent to the concentrations at which effects were observed with in vitro assays of tissue/organ toxicity. This presentation will describe the various elements of IVIVE and highlight key aspects of the process including: (1) characterization of free concentration, metabolism, and cellular uptake in the toxicity assay; (2) conversion of in vitro data to equivalent PBPK model inputs, and (3) potential complications associated with metabolite toxicity. Two examples of PBPK-based IVIVE will be described: a simple approach using whole hepatocyte clearance and plasma binding that is suitable for a high-throughput environment, and a more complicated approach for a case of metabolite toxicity. doi:10.1016/j.toxlet.2011.05.064
S12-2 Biokinetics in vitro N.I. Kramer ∗ , J. Hermens, B.J. Blaauboer Institute for Risk Assessment Sciences, Utrecht University, Utrecht, The Netherlands Determining the most appropriate dose metrics of a test chemical in an in vitro assay has generally been overlooked, but may be vital for in vitro-in vivo dose extrapolation in toxicological risk assessment. Generally, the nominal concentration is used to construct concentration-effect curves in in vitro assays and the nominal effect concentration is then compared to effect concentrations obtained in in vivo studies. However, the amount of a chemical reaching the cell in an in vitro assay may be different between cell assays and between in vitro and in vivo systems, even if the nominal or total concentration in the surrounding medium is the same. This
S12-3 Biotransformation: A bottleneck in in vitro toxicology S. Coecke Ecvam/ivmu/institute For Health And Consumer Protection, European Commission Joint Research Centre, Ispra, Italy In international meetings, including 2 workshops of the European Partnership for Alternative Approaches to Animal Testing (EPAA), experts from research, industry and regulatory bodies agreed that questions of absorption, distribution, metabolism and excretion (ADME) are pivotal to the issue of systemic toxicity. It is recommended that ADME methods and models become an integral part of any Integrated Testing Strategies (ITS), aiming at replacing the systemic toxicity endpoints. Furthermore, current European legislation for cosmetics (Directive 2003/15/EC) and chemicals (REACH Regulation 1907/2006/EC) emphasises the need for the development of alternative methods and integrated non-animal test strategies. For regulatory purposes there is a strong need for a reliable and relevant human metabolic competent source, modelling the process of xenobiotic biotransformation. The Institute IHCP-JRC of the European Commission organised under the auspices of ECVAM a stakeholder meeting in the field of Toxicokinetics and Metabolism in which the basis for the current multi-study validation trial for cytochrome P-450 (CYP) induction were established. The objective of this trial is the provision of a reliable humanmetabolic competent test system for use in ITS. In this validation study the test systems cryopreserved HepaRG® and cryopreserved human hepatocytes will be used. Five test facilities are involved including, the CRO’s Pharmacelsus and Kaly-Cell as the lead laboratories, the pharmaceutical companies Astra Zeneca and Janssens Pharmaceutica, and the European Commission JRC ECVAM In VitroMethods Unit and Systems Toxicology laboratories. The result of this validation trial will be the starting point for a novel in vitro platform for assessing biotransformation and toxicity. doi:10.1016/j.toxlet.2011.05.066
S12-4 Extrapolation of mechanisms of toxicity from in vitro to the in vivo situation W. Pfaller Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, Austria The interest in biomarkers and intracellular pathways started way back when structure function correlation became capable of attributing certain biochemical measures obtained from body fluids
Abstracts / Toxicology Letters 205S (2011) S2–S18
not survive in immunocompetent animals. Finally, there are also features of cellular therapies that require some reflection in terms of GLP compliance. doi:10.1016/j.toxlet.2011.05.062 S12—Improving quantitative in vitro–in vivo extrapolations (QIVIVE) for risk assessment
S12-1 Quantitative in vitro–in vivo extrapolations: Essential issues
presentation describes why these differences may occur and how these differences may in part explain variations in concentrationeffect relationships between in vitro assays and between in vitro and in vivo assays. A chemical may bind to serum constituents, evaporate, bind to cell membranes and sorb to plastic. All these processes decrease the concentration of the chemical freely available for uptake into cells and binding to target sites. For a more accurate description of the intrinsic potency of a test chemical, the free concentration and the cell burden may be used instead. A number of measurement techniques and modelling approaches exist to determine the free and cell concentration of a chemical. doi:10.1016/j.toxlet.2011.05.065
H. Clewell The Hamner Institutes for Health Sciences, Research Triangle Park, USA The field of toxicology is currently undergoing a global paradigm shift to use of in vitro approaches for assessing the risks of chemicals and drugs, yielding results more rapidly and more mechanistically based than current approaches relying primarily on in vivo testing. However, reliance on in vitro data entails a number of new challenges associated with translating the in vitro results to corresponding in vivo exposures. Physiologically based pharmacokinetic (PBPK) models provide an effective framework for conducting quantitative in vitro to in vivo extrapolation (IVIVE). Their physiological structure facilitates the incorporation of in silico- and in vitro-derived chemical-specific parameters in order to predict in vivo absorption, distribution, metabolism and excretion. In particular, the combination of in silico and in vitro parameter estimation with PBPK modeling can be used to predict the in vivo exposure conditions that would produce chemical concentrations in the target tissue equivalent to the concentrations at which effects were observed with in vitro assays of tissue/organ toxicity. This presentation will describe the various elements of IVIVE and highlight key aspects of the process including: (1) characterization of free concentration, metabolism, and cellular uptake in the toxicity assay; (2) conversion of in vitro data to equivalent PBPK model inputs, and (3) potential complications associated with metabolite toxicity. Two examples of PBPK-based IVIVE will be described: a simple approach using whole hepatocyte clearance and plasma binding that is suitable for a high-throughput environment, and a more complicated approach for a case of metabolite toxicity. doi:10.1016/j.toxlet.2011.05.064
S12-2 Biokinetics in vitro N.I. Kramer ∗ , J. Hermens, B.J. Blaauboer Institute for Risk Assessment Sciences, Utrecht University, Utrecht, The Netherlands Determining the most appropriate dose metrics of a test chemical in an in vitro assay has generally been overlooked, but may be vital for in vitro-in vivo dose extrapolation in toxicological risk assessment. Generally, the nominal concentration is used to construct concentration-effect curves in in vitro assays and the nominal effect concentration is then compared to effect concentrations obtained in in vivo studies. However, the amount of a chemical reaching the cell in an in vitro assay may be different between cell assays and between in vitro and in vivo systems, even if the nominal or total concentration in the surrounding medium is the same. This
S12-3 Biotransformation: A bottleneck in in vitro toxicology S. Coecke Ecvam/ivmu/institute For Health And Consumer Protection, European Commission Joint Research Centre, Ispra, Italy In international meetings, including 2 workshops of the European Partnership for Alternative Approaches to Animal Testing (EPAA), experts from research, industry and regulatory bodies agreed that questions of absorption, distribution, metabolism and excretion (ADME) are pivotal to the issue of systemic toxicity. It is recommended that ADME methods and models become an integral part of any Integrated Testing Strategies (ITS), aiming at replacing the systemic toxicity endpoints. Furthermore, current European legislation for cosmetics (Directive 2003/15/EC) and chemicals (REACH Regulation 1907/2006/EC) emphasises the need for the development of alternative methods and integrated non-animal test strategies. For regulatory purposes there is a strong need for a reliable and relevant human metabolic competent source, modelling the process of xenobiotic biotransformation. The Institute IHCP-JRC of the European Commission organised under the auspices of ECVAM a stakeholder meeting in the field of Toxicokinetics and Metabolism in which the basis for the current multi-study validation trial for cytochrome P-450 (CYP) induction were established. The objective of this trial is the provision of a reliable humanmetabolic competent test system for use in ITS. In this validation study the test systems cryopreserved HepaRG® and cryopreserved human hepatocytes will be used. Five test facilities are involved including, the CRO’s Pharmacelsus and Kaly-Cell as the lead laboratories, the pharmaceutical companies Astra Zeneca and Janssens Pharmaceutica, and the European Commission JRC ECVAM In VitroMethods Unit and Systems Toxicology laboratories. The result of this validation trial will be the starting point for a novel in vitro platform for assessing biotransformation and toxicity. doi:10.1016/j.toxlet.2011.05.066
S12-4 Extrapolation of mechanisms of toxicity from in vitro to the in vivo situation W. Pfaller Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, Austria The interest in biomarkers and intracellular pathways started way back when structure function correlation became capable of attributing certain biochemical measures obtained from body fluids