The most popular and acceptable route for administering drugs is orally. However, physico-chemical descriptors of drugs are not often adequate in predicting their oral bioavailability. Our research laboratory was interested in studying the oral bioavailability of prospective anticancer peptides. We were looking for an
in vitro model which would mimic the intestinal mucosa in order to evaluate strategies for investigating/enhancing drug absorption.
We chose the Caco-2 cell culture model for studying the intestinal permeability of our candidate peptides. Briefly, Caco-2 cells are seeded on collagen-coated cell culture inserts and allowed to differentiate into a confluent monolayer. The test drug is added in the top chamber and its transport to the lower chamber is monitored. The rate of transport from the apical to the basolateral chamber is a measure of the intestinal permeability of the test compound. However, performing the actual assay was an arduous and daunting task. The Caco-2 cell line is extremely difficult to grow. It is a slow growing cell line and it tends to grow in clumps on top of one another. Once the cells are seeded on the inserts they require 21 days to form a well-differentiated brush border on the apical surface of the filter. It is extremely laborious to culture these cells on the inserts. After 21 days, the rate of transport has to be checked by using a standard compound like radiolabeled mannitol and by measuring TEER. Additionally, we found a wide range of variability in our assays, which made it difficult to reproduce and interpret data.
Subsequently, we switched to the BD Biocoat HTS Caco-2 assay system. The inserts are precoated with collagen and the specialized media included in this kit can produce uniform differentiated CaCo-2 monolayers with tight junctions and well-differentiated brush border membranes within a few days, as compared to three weeks spent earlier. The cell culture inserts are provided in a 24-insert block format which makes it easier to handle than 24 separate inserts. The convienience of the block format is makes it easier to culture CaCo-2 cells on the inset and reduces risk of contamination The entire system is easy to use and can be adapted to perform a wide variety of time consuming studies like assessing the cellular permeability of drugs, elucidating pathways of drug transport and determination of optimal physicochemical characteristics for passive diffusion of drugs. The results obtained by this system are consistent and highly reproducible. As with all Biocoat products the disadvantage is the relatively high cost of this kit. However, the Caco-2 assay is one of the most labor intensive and difficult assays to perform. Keeping this in mind I think that the advantages of this assay system make it an asset for any research lab studying drug metabolism.
Piyali Dasgupta, Ph.D.
Post-Doctoral Fellow
Moffit Research Center