Chemical augmentation of the validated HepaRG ^TM CYP enzyme induction test method Part 1: The Goliath two laboratory study

Cytochrome P450 (CYP) enzymes play a key role in the metabolism of both xenobiotics and endogenous compounds, and the activity of some CYP isoforms are susceptible to induction and/or inhibition by certain chemicals. As CYP induction and inhibition can significantly alter the in vivo fate of xenobiotics i.e., levels of parent chemicals and/or metabolites, and thus toxicity, CYP induction/inhibition data is needed for regulatory chemical toxicity hazard assessment.

Utilizing available human in vivo pharmaceutical data, a successful validation was previously conducted on the in vitro HepaRG™ CYP induction test method for measurement of induction of three key human CYP enzymes CYP1A1/1A2, 2B6 and 3A4. However, further validation data was required to demonstrate applicability of the test method to also accurately detect CYP induction mediated by industrial and pesticidal chemicals. Here we report on the supplementary validation of the HepaRG™ CYP enzyme induction test method carried out in two laboratories under the auspices of the EU Horizon2020-funded project “GOLIATH”, to expand the chemical applicability domain beyond pharmaceutical chemicals. Successful transfer was demonstrated and reproducibility assessed for the original 10 selected proficiency pharmaceuticals, plus three reference inducers together with six additional non-pharmaceutical ‘augmentation chemicals’. The method and chemical selection were found to be reliable and relevant for the routine assessment of human CYP induction. For the augmentation chemicals being proposed as additional proficiency chemicals, the test method achieved a reasonable but not optimum reproducibility. Recommendations are proposed to improve the test method’s specificity, reflecting the inherent uncertainty around borderline CYP inducing chemicals.