The Caco-2 cell line is a continuous line of heterogeneous human epithelial colorectal adenocarcinoma cells, developed by the Sloan-Kettering Institute for Cancer Research through research conducted by Dr. Jorgen Fogh.
The application of Caco-2 cells in research was pioneered in the late 1980s by Ismael Hidalgo, working in the laboratory of Ron Borchardt at the University of Kansas, and Tom Raub, who was at the Upjohn Company at the time. Following stints at SmithKline Beecham and Rhone-Poulenc Rorer, Hidalgo went on to co-found a company, Absorption Systems, in 1996, where he remains as Chief Scientist.
Although derived from a colon (large intestine) carcinoma, when cultured under specific conditions the cells become differentiated and polarized such that their phenotype, morphologically and functionally, resembles the enterocytes lining the small intestine. Caco-2 cells express tight junctions, microvilli, and a number of enzymes and transporters that are characteristic of such enterocytes: peptidases, esterases, P-glycoprotein, uptake transporters for amino acids, bile acids, carboxylic acids, etc.
When looking at Caco-2 cell cultures microscopically, it is evident even by visual inspection that the cells are heterogeneous. Over the years, the characteristics of the cells used in different laboratories around the world have diverged significantly, which makes it difficult to compare results across labs. Despite such heterogeneity, Caco-2 cells have found applications in cell invasion studies, viral transfection research, and lipid transport.
Caco-2 cells are most commonly used not as individual cells, but as a confluent monolayer on a cell culture insert filter (e.g., Transwell). When cultured in this format, the cells differentiate to form a polarized epithelial cell monolayer that provides a physical and biochemical barrier to the passage of ions and small molecules. The Caco-2 monolayer is widely used across the pharmaceutical industry as an in vitro model of the human small intestinal mucosa to predict the absorption of orally administered drugs with different kits such as the CacoReady. The correlation between the in vitro apparent permeability (P¬app) across Caco-2 monolayers and the in vivo fraction absorbed (fa) is well established.Transwell diagram
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