2-Amino-3-methylimadazo[4,5-f]quinoline (IQ) induces cytochrome P450 1A through the canonical AhR-XRE pathway in human hepatocytes.

Heterocyclic aromatic amines (HAAs) are procarcinogens formed during the cooking of meat and fish and could potentially contribute to hepatocellular carcinoma. Although several HAAs are classified as possible or probable human carcinogens, most mechanistic studies have relied on rodent models, despite well-documented interspecies differences in HAA bioactivation by cytochrome P450 (CYP) isoforms. In this study, we investigated the regulation of CYP1A by the HAA 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) using complementary primary human hepatocytes and Hepoid® with HepaRG cells, a long-term 3D liver spheroid model. IQ at concentrations ranging from 0.1 to 20 µM strongly induced CYP1A1 and CYP1A2 expression and enzymatic activity following acute and chronic exposure, whereas other major hepatic CYP isoforms remained unaffected. This response was specific to IQ among other HAAs tested and to human hepatocytes and persisted for up to 28 days in 3D spheroids. IQ-induced CYP1A expression required transcriptional activation and involved the aryl hydrocarbon receptor (AhR). Using complementary pharmacological and genetic approaches, luciferase reporter assays and ligand-binding assays, we demonstrate that IQ is a direct AhR ligand that activates the canonical AhR-xenobiotic response element (XRE) signaling pathway in human hepatocytes. These findings indicate that IQ is a potent and selective inducer of CYP1A through the AhR and induces a sustained human-specific response upon repeated treatment. Persistent CYP1A induction and AhR activation may enhance the bioactivation of IQ and other co-occurring CYP1A substrates, highlighting the value of long-term human-relevant models to improve risk assessment of chemical carcinogens.