Understanding QSARs and read-across and their applications in regulatory toxicology


Objectives of the course

With regulators encouraging the reduction of in vivo tests according to the principles of the 3Rs this 2 day course will provide an understanding of methods for in silico toxicology with an emphasis on appropriate use in regulatory toxicology. 

Specifically the course will:

  • Review the current scientific basis and application of read-across and QSAR in toxicology

  • Interpret the meaning of in silico predictions

  • Describe the methods that will increase the probability of acceptance of predictions for regulatory use

  • Use hands-on activities on selected case studies to put theory into practice. 

Day 1: Understanding and using QSARs 




Welcome and Introduction

  • Introduction to the course outline, content and objectives


Chemical Structures    

  • Chemoinformatics: how you can characterise a chemical by informatics

  • Some of the most commonly used approaches will be discussed: identifiers, physico-chemical properties, activity/mechanism of action, ADME characteristics, molecular properties


Relationship with Activity

  • The relationship between structures and properties and how to describe this relationship will be discussed

  • Categories / series of molecules

  • What is a (Q)SAR (basics)



ChemSpider (identifiers and properties), ACD/Name and ACD/Percepta (chemical structure representation and properties), O-Chem (alerts)


Use and Assessment of (Q)SARs

  • Applications in toxicology (overview of endpoints and model types; focus on mutagenicity)

  • Example of QSAR

  • Assessing model validity and applicability domain (OECD Principles)

  • Analysis of nearest neighbours and identifying outliers (with examples)

  • Uncertainty


Practical example

  • Statistical-based model: how to interpret a model (in relation to the OECD principles) with examples

  • Rule-based model: how to interpret a model (in relation to OECD Principles) with examples

  • Combination of predictions to reduce uncertainty (e.g. as required in the ICH M7 guidelines), different combination schemes, WoE



Examples of freely available and some commercial QSAR software for regulatory tocicology (ToxTree; ToxGPS; ACD/Percepta)

Day 2: Understanding and applying read-across





  • Summary from Day 1 and Intro to Day 2


Intro to Read-Across

  • Basic principles: using data from "similar chemicals"

  • Applications in REACH, ICH M7 (drug impurities), pesticides, E&L



  • Determining similarity

  • Methods to group chemicals and find analogues

  • Justify analogue selection 



Finding data for source and target: COSMOS DB and OECD Toolbox





Software to Support Read-Across: OECD Toolbox and ToxGPS


Justifying and Reporting a Read-Across 

  • Support for the prediction

  • Reduction of uncertainty

  • Tips - avoiding pitfalls, increasing chance of acceptance


Summary and close     

ToxNavigation thanks MN-AM and ACD/Labs for providing ChemTunes, ToxGPS; ACD/Percepta and ACD/Name for the hands-od sessions. 

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