Improved clearance predictions for aldehyde oxidase substrates using a novel triculture human hepatocyte model

Over the last several decades, efforts in medicinal chemistry have aimed to reduce the extent of CYP metabolism of new chemical entities. This approach, however, has led to increased susceptibility to metabolism by non-CYP-mediated pathways, particularly involving other phase I enzymes such as aldehyde oxidase (AO). Commonly used in vitro models, such as suspended or cocultured primary human hepatocytes, have limitations in evaluating the disposition of compounds metabolized by AO due to low or variable levels of enzyme activity. Thus, an in vitro model that exhibits high to moderate levels of AO activity that can better predict the contribution of AO to drug metabolism and its impact on drug clearance is needed. A novel, 2D+ primary human hepatocyte model, TruVivo, was evaluated for its potential utility to improve hepatic clearance (CL_h) predictions and determine the contribution of AO to drug metabolism in humans. TruVivo demonstrated stable levels of AO activity for at least 2 weeks that were higher than levels in other hepatocyte models. CL_h predictions generated using TruVivo for the reference compounds carbazeran, zoniporide, zaleplon, and O6-benzylguanine were within 2-fold of reported in vivo CL values. Furthermore, the estimated fraction metabolized by AO for zaleplon and zoniporide was within 25% of reported in vivo values, whereas that for carbazeran and O6-benzylguanine was similar to those generated in other systems. These findings suggest TruVivo may offer a novel means to assess CL_h of AO substrates more accurately, even over extended incubation times for low clearance compounds. SIGNIFICANCE STATEMENT: The TruVivo in vitro primary human hepatocyte model maintains high levels of aldehyde oxidase (AO) activity for at least 14 days in culture, making the system suitable for evaluating slowly metabolized compounds, particularly those metabolized by AO. This novel system may therefore be useful for improving human clearance predictions for AO substrates.