Organs-on-a-chip: Current applications and consideration points for in vitro ADME-Tox studies.

Assay systems using in vitro cultured cells are increasingly applied for evaluation of the efficacy, safety, and toxicity of drug candidates. In vitro cell-based assays have two main applications in the drug discovery process: searching for a compound that is effective against the target disease (seed investigation) and confirmation of safety during use of the identified compounds (safety assessment). Currently available in vitro cell-based assays have been designed to evaluate the efficacy and toxicity in single organs, but the in vivo pharmacokinetics and pharmacodynamics of the administered drug candidates have not been considered. Thus, an evaluation system that interconnects cell culture units, one of which has appropriate drug metabolism activities and the other assesses the efficacy and toxicity of compounds, is needed. Accordingly, the in vitro ADME-Tox culture system known as organs-on-a-chip has been proposed. In this review, after introducing the organs-on-a-chip system, the evaluation of enterohepatic circulation and the gut-liver axis relationship will be presented as an example of the application of the organs-on-a-chip system for ADME studies based on inter-organ network. Additionally, the functions required for the organs-on-a-chip system and the necessity of standardization of cells mounted on the chip system will be discussed.