HepaRGTM CYP induction test method augmentation part 1: The GOLIATH Study

Cytochrome P450 (CYP) enzymes play a key role in the metabolism of both xenobiotics and endogenous com-pounds, and some CYP isoforms are susceptible to induction and/or inhibition by certain chemicals. As CYP induction/inhibition can significantly alter the in vivo fate of xenobiotics, i.e., levels of parent chemicals and/or metabolites, and thus their toxicity, CYP induction/inhibition data is needed for regulatory chemical toxicity hazard assessment. Utilizing available human in vivo pharmaceutical data, a successful validation was previ-ously conducted on the in vitro HepaRG™ CYP induction test method for measurement of induction of the 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 a supplementary validation efforts to expand the chemical applicability domain beyond pharmaceutical chemicals for the HepaRG™ CYP induction test method. This was first carried out in two laboratories under the auspices of the EU Horizon2020-funded project GOLIATH. Laboratory trans-fer was demonstrated and reproducibility assessed for the original 10 selected proficiency pharmaceuticals plus three reference inducers together with six additional non-pharmaceutical 'augmentation chemicals'. For the proficiency pharmaceuticals, the method transferred well to one laboratory and was reasonably transfera-ble for the second laboratory. For the augmentation chemicals proposed as additional proficiency chemicals, the test method achieved reasonable but not optimum reproducibility. Recommendations are proposed to im-prove the test method's specificity regarding the uncertainty around borderline CYP inducing chemicals.