The Caco-2 cell line is a continuous cell of heterogeneous human epithelial colorectal adenocarcinoma cells, developed by the Sloan-Kettering Institute for Cancer Research through research conducted by Dr. Jorgen Fogh.
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. As a result, 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.
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. 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
This application of Caco-2 cells 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.
The considerable impact of the Caco-2 cell monolayer model can be measured in at least two ways. First, considering that poor pharmacokinetic properties accounted for ~40% of drug failures in development in the early 1990s and only ~10% by 2009, an interval in which Caco-2 monolayers were widely used throughout the pharmaceutical industry to predict absorption, it is not unreasonable to attribute some of that shift to this simple yet powerful model. Second, the 1989 Gastroenterology paper that demonstrated the utility of the model for this application has been cited more than 1000 times since its publication.
The versatility of Caco-2 cells is demonstrated by the fact that, even to this day, they are serving as the basis for the creation of innovative new models that are contributing to our understanding of drug efflux transporters such as P-glycoprotein (ABCB1) and BCRP (ABCG2). RNA interference has been used to silence the expression of individual efflux transporters, either transiently or long-term.
- Fogh J and Trempe G in Human Tumor Cells In Vitro (J. Fogh, ed.), Plenum, 1975, 115-141
- Pinto M; et al. (1983). "Enterocyte-like differentiation and polarization of the human colon carcinoma cell line Caco-2 in culture". Biol Cell. 47: 323–30.
- Hidalgo IJ; et al. (1989). "Characterization of the human colon carcinoma cell line (Caco-2) as a model system for intestinal epithelial permeability". Gastroenterology. 96 (3): 736–49. doi:10.1016/0016-5085(89)90897-4. PMID 2914637.
- Sambuy Y; et al. (2005). "The Caco-2 cell line as a model of the intestinal barrier: influence of cell and culture-related factors on Caco-2 cell functional characteristics". Cell Biol Toxicol. 21 (1): 1–26. doi:10.1007/s10565-005-0085-6. PMID 15868485.
- Artursson P (1990). "Epithelial transport of drug in cell culture. I: A model for studying the passive diffusion of drugs over intestinal absorbtive (Caco-2) cells". J Pharm Sci. 79 (6): 476–82. doi:10.1002/jps.2600790604. PMID 1975619.
- Artursson P & Karlsson J (1991). "Correlation between oral drug absorption in humans and apparent drug permeability coefficients in human intestinal epithelial (Caco-2) cells". Biochem Biophys Res Commun. 175 (3): 880–5. doi:10.1016/0006-291X(91)91647-U. PMID 1673839.
- Watanabe T; et al. (2005). "Construction of a functional transporter analysis system using MDR1 knockdown Caco-2 cells". Pharm Res. 22 (8): 1287–93. doi:10.1007/s11095-005-5270-z. PMID 16078138.
- Zhang W; et al. (2009). "Silencing the breast cancer resistance protein expression and function in Caco-2 cells using lentiviral vector-based short hairpin RNA". Drug Metab Disp. 37 (4): 737–44. doi:10.1124/dmd.108.023309. PMID 19131524.
- Darnell M; et al. (2010). "Investigation of the involvement of P-gp and MRP2 in the efflux of ximelagatran and its metabolites by using short hairpin RNA knockdown in Caco-2 cells". Drug Metab Disp. 38 (3): 491–7. doi:10.1124/dmd.109.029967. PMID 20023051.
- Artursson P, Palm K, Luthman K (2001). "Caco-2 monolayers in experimental and theoretical predictions of drug transport". Adv Drug Deliv Rev. 46 (1–3): 27–43. doi:10.1016/S0169-409X(00)00128-9. PMID 11259831.
- Shah P, Jogani V, Bagchi T, Misra A (2006). "Role of Caco-2 cell monolayers in prediction of intestinal drug absorption". Biotechnol Prog. 22 (1): 186–98. doi:10.1021/bp050208u. PMID 16454510.
- The use of Caco-2 to measure permeability in-vitro. The performance of Caco-2 permeability studies including analysis of the data.
- Cellosaurus entry for Caco-2