Objective: According to the regulatory guidelines, one of the critical steps in using in-vitro permeability methods for permeability classification is to demonstrate the suitability of the method. Here, suitability of the permeability method by using a monolayer of cultured epithelial cells was verified with different criteria.
Methods: Imaging with a transmission electron microscope was used for characterisation of the cells. Monolayer integrity was confirmed by transepithelial electrical resistance measurements and permeability of zero permeability marker compounds. Real-time polymerase chain reaction was employed to evaluate expression levels of 84 known transporters. Samples for bidirectional permeability determination were quantified by ultra-performance liquid chromatography.
Key findings: The Caco-2 cells grow in an intact monolayer and morphologically resemble enterocytes. Genes of 84 known transporters were expressed at different levels; furthermore, expression was time depended. Functional expression of efflux transporter P-glycoprotein was confirmed. We established a correlation between permeability coefficients of 21 tested drug substances ranging from low, moderate and high absorption with human fraction absorbed literature data (R2 = 0.84).
Conclusions: Assay standardisation assures the consistency of experimental data. Only such fully characterised model has the ability to accurately predict drug's intestinal permeability at the early stage of research or for the BCS-based biowaiver application.
Keywords: Caco-2 cells; biopharmaceutics classification system; drug transport; in-vitro/in-vivo correlation; permeability.
© 2019 Royal Pharmaceutical Society.