The prediction of drug bioavailability is one of the essential issues in the development of orally-administered drugs. Drug-induced intestinal abnormality is one of the most frequently-observed side effects and sometimes limits the clinical dose of anti-cancer drugs. However, their prediction at the preclinical stage is still a challenge due to the large species differences and the lack of an appropriate in vitro experimental system that mimics the functions of intestinal epithelial cells (e.g. Caco-2 cells). Therefore, we introduced the differentiated absorptive epithelial cells derived from intestinal stem cells at crypt region in humans/animals for the prediction of intestinal absorption and toxicity of drugs.
Advantages of this experimental system are that it is possible to use the unified protocol for the culture of intestinal stem cells and their differentiated ones regardless of any animal species and that it is also expected to reproduce the region-specific intestinal functions with our in vitro system since previous papers suggested that differentiated cells maintained the gene expression pattern at the crypt collection site. The expression and function of multiple transporters and metabolic enzymes in our differentiated intestinal cells were more similar to those in Caco-2 cells, which have been routinely utilized for characterization of drug intestinal absorption as a gold standard in the drug development. Furthermore, the intestinal availabilities of multiple CYP3A substrates were successfully predicted from their transcellular transport clearances. These evidences suggested that it is possible to predict the whole picture of intestinal absorption including its dynamic regulation by metabolic enzymes and transporters. Moreover, we demonstrated that PCFT and ASBT are limitedly expressed and uptake of methotrexate and taurocholate was only observed in the differentiated cells prepared from crypts at upper jejunum and terminal ileum, respectively, suggesting that region-specific function of detoxification system can also be well reproduced in this system.
Regarding the evaluation of the risk of drug-induced intestinal toxicity, we confirmed that the extent of the decrease in cellular ATP levels of spheroids by various EGFR tyrosine kinase inhibitors was well matched with clinical incidence of severe diarrhea and such toxicity was related to their inhibition potency against EGFR tyrosine kinase and mode of inhibition. We hope our in vitro system is expected to be widely used for the reproduction of various events at the intestinal tract such as drug intestinal absorption and drug toxicity.