A primary human Gut/Liver microphysiological system to estimate human oral bioavailability

Oral bioavailability is a crucial pharmacokinetic (PK) parameter optimized by drug developers working on new therapeutic compounds. The goal is to obtain adequate systemic exposure and to establish safe and effective therapeutic dosages. Critical to optimizing oral bioavailability is understanding a compound's susceptibility to first-pass metabolism, determined by the intricate relationship between gut absorption, metabolism, and hepatic metabolism. Efforts to model this relationship in vitro have led to the emergence of microphysiological systems (MPSs) that consist of multiple, fluidically linked organs. Here, we describe an MPS that links the gut and liver, capable of simulating both oral and intravenous dosing routes and is made up of entirely primary human cells: a gut barrier tissue comprised of an intestinal epithelial monolayer derived from the human jejunum, and a liver microtissue, derived from primary human hepatocytes. Functionality of gut and liver tissues is maintained in coculture enabling the PK investigation of oral compounds. We combine the primary Gut/Liver MPS with a mechanistic mathematical model to generate organ-specific PK parameters and estimate human oral bioavailability and its components: the fraction absorbed (F_a), the fraction escaping gut wall elimination (F_g), and the fraction escaping hepatic elimination (F_h). We used the CYP3A-mediated compound midazolam, which is subjected to both intestinal and hepatic extraction, to demonstrate the transformative potential of the primary Gut/Liver MPS to mechanistically model the PKs of oral compounds in vitro. SIGNIFICANCE STATEMENT: Bioavailability underpins the success or when insufficient, can stall the development of oral therapeutics. The drug discovery process lacks in vitro assays that can profile the contribution to bioavailability by the gut and liver. The primary Gut/Liver MPS outlined in this study bridges this gap.