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Introduction: Conventional in vitro human hepatic models for drug testing are based on the use of cell lines or primary human hepatocytes (PHHs). However, limited availability, inter-donor functional variability and early phenotypic alterations of PHHs in vitro restrict their use; whilst cell lines such as HepG2/C3As lack a substantial and variable set of liver-specific functions, specifically, CYP450 activity. In this study we compared CYP450 activity/ metabolism between HepG2/C3A and human HepaRG cells as hepatic models for pre-clinical drug testing. Methods: Human hepatic cell lines [HepG2/C3A or HepaRG] were grown to >80% confluence on collagen-I-coated plates and treated (in triplicates) 24 h with prototypical inducers rifampicin (CYP3A4) and omeprazole (CYP1A2), [n=3]. 50μM testosterone or phenacetin were added and supernatant and cell samples taken after 2 hours of incubation at 37°C. CYP1A2/3A4 activity [P450-Glo™-Luminometry; Promega] was determined (Figure 1). Relative turnover of testosterone [HPLC] and phenacetin [LC-MS/MS] metabolites was also measured. Cell phenotype was assessed by light-microscopy, histology (PAS-Glycogen), CYP3A4, F-actin/phalloidin, and JC-1 fluorescent-staining. Results: Figure 1 shows HepaRG CYP1A2/3A4 activity was 40-80x fold >> HepG2/C3A cells [P