ExITox-2 was built on the outcomes of ExITox-1 and aimed to develop an integrated approach for testing and assessment (IATA) to replace in vivo studies with repeated inhalation exposure. We established this IATA with the help of a read across (RAX) approach of ExITox-1, in which we tested groups of chemically similar compounds that share a specific mode of action (MoA) or adverse outcome pathway (AOP) in vivo. In ExITox-1 we showed that biological profiles based on the transcriptome changes and functional outcomes from in vitro and ex vivo models can be used to differentiate RAX groups with similar mode of action. Beside the RAX group vinyl ester from ExITox-1, we have included two new AOPs in second phase, namely pulmonary inflammation, and fibrosis. In the course of ExITox-2, geneXplain was expanded the “complete upstream analysis”, which is an integrated bioinformatics promoter analysis of the DEGs, identifying potential transcriptional regulators, with a proprietary pathway analysis controlling the activity of these transcriptional regulators and converge in defined sets of so-called master regulators (Kel et al., 2006).

Further the geneXplain platform was extended with lung-specific pathways up to newly constructed master pathways (for fibrosis and inflammation) to compare toxic effects to general systemic responses.

ExITox-2 integrated four new key aspects into the IATA:

• The uptake of compounds after inhalation exposure were estimated by physiological pharmacokinetic modeling and QSAR models.
• The onset of gene changes and miRNA regulation, by dose dependent testing, were investigated to better differentiate between group-specific changes and general stress responses related to high dosing.
• We generated and used master pathways per group to differentiate AOP related changes from general cellular stress responses.
• An IATA was developed, which allows to predict the toxicity of an untested compound in a read across context based on the generated data.