title: Innovative Strategies to Develop Chemical Categories Using a Combination of Structural and Toxicological Properties.
abstract: Interest is increasing in the development of non-animal methods for toxicological evaluations. These methods are however, particularly challenging for complex toxicological endpoints such as repeated dose toxicity. European Legislation, e.g., the European Union's Cosmetic Directive and REACH, demands the use of alternative methods. Frameworks, such as the Read-across Assessment Framework or the Adverse Outcome Pathway Knowledge Base, support the development of these methods. The aim of the project presented in this publication was to develop substance categories for a read-across with complex endpoints of toxicity based on existing databases. The basic conceptual approach was to combine structural similarity with shared mechanisms of action. Substances with similar chemical structure and toxicological profile form candidate categories suitable for read-across. We combined two databases on repeated dose toxicity, RepDose database, and ELINCS database to form a common database for the identification of categories. The resulting database contained physicochemical, structural, and toxicological data, which were refined and curated for cluster analyses. We applied the Predictive Clustering Tree (PCT) approach for clustering chemicals based on structural and on toxicological information to detect groups of chemicals with similar toxic profiles and pathways/mechanisms of toxicity. As many of the experimental toxicity values were not available, this data was imputed by predicting them with a multi-label classification method, prior to clustering. The clustering results were evaluated by assessing chemical and toxicological similarities with the aim of identifying clusters with a concordance between structural information and toxicity profiles/mechanisms. From these chosen clusters, seven were selected for a quantitative read-across, based on a small ratio of NOAEL of the members with the highest and the lowest NOAEL in the cluster (< 5). We discuss the limitations of the approach. Based on this analysis we propose improvements for a follow-up approach, such as incorporation of metabolic information and more detailed mechanistic information. The software enables the user to allocate a substance in a cluster and to use this information for a possible read- across. The clustering tool is provided as a free web service, accessible at http://mlc-reach.informatik.uni-mainz.de.
authors.affiliation: Department Chemikalienbeureilung, Dantenbanken und Expertensysteme, Fraunhofer Institut für Toxikologie und Experimentelle Medizin Hannover, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Batke
authors.affiliation: Institut für Informatik, Johannes Gutenberg-Universität Mainz Mainz, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Gütlein
authors.affiliation: Institut für Arbeits-, Sozial- und Umweltmedizin, Universitätsmedizin Göttingen Göttingen, Germany.
authors.forename: Falko
authors.initials: F
authors.lastname: Partosch
authors.affiliation: Institut für Klinische Pharmakologie und Toxikologie, Charité Universitätsmedizin Berlin Berlin, Germany.
authors.forename: Ursula
authors.initials: U
authors.lastname: Gundert-Remy
authors.affiliation: In Silico Toxicology GmbH Basel, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Helma
authors.affiliation: Institut für Informatik, Johannes Gutenberg-Universität Mainz Mainz, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Kramer
authors.affiliation: Oncotest GmbH Freiburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Maunz
authors.affiliation: Institut für Informatik, Technische Universität München München, Germany.
authors.forename: Madeleine
authors.initials: M
authors.lastname: Seeland
authors.affiliation: Department Chemikalienbeureilung, Dantenbanken und Expertensysteme, Fraunhofer Institut für Toxikologie und Experimentelle Medizin Hannover, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Bitsch
keywords: Predictive Clustering Tree (PCT) method; QSAR; non-animal methods; read across; toxicological and structural similarity