Oral caco-2 prediction

This model integrates existing in vitro data, such as Caco-2 permeability (Papp) and metabolic stability in liver S9 or microsomes, to estimate bioavailability as being either low, medium, or high. Oral bioavailability predictions for not only humans but also other species can be made by using the metabolic stability values of drugs in liver microsomal enzyme preparations from that species. A premise of this model is that metabolic clearance is more important than renal or biliary clearance in determining bioavailability. However, despite the lack of in vitro renal... 

The use of Caco-2 cell permeability studies has resulted in more accurate oral bioavailability predictions. Using the predicted hepatic clearance for compound X in humans (see above), estimating Fa by extrapolation from the Caco-2 cell Papp and assuming hepatic blood flow for humans (see, for example Rane et al., 1977) of 20 ml min 1 kg the human oral bioavailability of 69-98% is predicted for compound X. This compares well with the known oral bioavailability of this compound in rats and dogs (83 and 72%, respectively). 

In addition, the calculation of many different ID, 2D and 3D descriptors is possible using a range of commercially available software packages, such as Sybyl, Cerius2, Tsar, Molconn-Z and Hybot. Several new descriptor sets are based on quantification of 3D molecular surface properties, and these have been explored for the prediction of, e.g., Caco-2 permeability and oral absorption. It is pointed out here that a number of these new descriptors are strongly correlated to the more traditional physico-chemical properties. 

More than a decade ago, Caco-2 cells grown on permeable supports were introduced as an experimental tool for mechanistic studies of intestinal drug transport [1-4]. At the same time it was suggested that the Caco-2 model was suitable for screening intestinal drug permeability and predicting the oral absorption potential... 

The main reasons for the popularity of the Caco-2 cell line are that the cells are easy to maintain in culture, and they develop unusually high degree of differentiation spontaneously under standard culture conditions. In fact, Caco-2 is the only human intestinal cell line that has been found so far spontaneously to undergo functional enterocytic differentiation. The cells exhibit a good reproducibility, robustness and functional properties of human intestinal epithelial cells. The model has proved capable of predicting the oral absorption of a variety of drug compounds [see references in 10]. 

Many academic and industrial laboratories have shown that the drug permeability measured in Caco-2 cell monolayers can be used to predict the oral absorption of drugs in humans. Various datasets have therefore been used to establish correlations between Caco-2 permeability and the fraction absorbed orally in humans [85, 86, 96]. Taken together, these studies show good predictability, though with a relatively wide variation in the appearance of correlation profiles between different laboratories [86]. These studies emphasize the need to establish correlations and standardization procedures in each laboratory. 

Fig. 5.4. Relationship between the oral fraction absorbed in humans and apparent permeability coefficients obtained in Caco-2 cell monolayers. Papp bands for predicted fraction absorbed of <20% (low), 20-80% (moderate) and >80% (high) are indicated.

Caco-2 Cell line used to predict human oral absorption... 

Lau, Y.Y. et al. 2004. Evaluation of a novel in vitro Caco-2 hepatocyte hybrid system for predicting in vivo oral bioavailability. Drug Met. Disp. 32 937. 

Inspired by the successful implementation of the intestinal cell line, Caco-2, as a model to predict oral drug absorption, pulmonary-based models are used in a similar manner. The use of pulmonary cells which are covered by a comparatively thick fluid layer (liquid-interfaced deposition, LID) is probably... 

The two major determinants of oral bioavailability are intestinal absorption and hepatic first-pass elimination. Caco-2 cells are useful to predict intestinal absorption. The validity of this application has been demonstrated in a number of studies in which percent drug absorption in humans was correlated with Caco-2 permeability coefficients.35-39113114... 

To meet the need of conducting HTS for ADME-Tox properties, many slow and expensive in vivo ADME assays are now being replaced by in vitro cell models. For intestinal absorption, Caco-2 cell lines and Madin Darby canine kidney (MDCK) cell lines are widely used to predict the absorption rate of candidate drug compounds across the intestinal epithelial cell barrier. A number of models for Caco-2 cell permeability and MDCK cell permeability have been reported that predict the oral absorption properties of drugs, mostly limited to small organic molecules. Caco-2 and MDCK permeability are related to "A" and "D" in the ADME-Tox. 

The paracellular permeation pathway in the intestinal cell monolayer models is often limited. Therefore these models are not suitable for predicting permeability of paracellularly absorbed compounds. The average pore radius in Caco-2 cells (<6 A) is more representative of the colon than the small intestine (8-13 A)and paracellular transport can be up to 100-fold lower in Caco-2 cells than in the small intestine. Investigation of a rat intestinal cell line 2/4/Al, which forms polarized cell mono-layers and has an average pore radius (9 A) more representative of the small intestine, showed improved prediction of oral absorption for incompletely absorbed drugs [24, 25]. 

In this project, compound A from a potential lead series was a neutral compound of MW 314 with low aqueous solubility (Systemic clearance, volume and AUC following a 0.5mg/kg intravenous dose to rats were well predicted (within twofold) from scaled microsomal clearance and in silica prediction of pKa, logP and unbound fraction in plasma. Figure 10.3a shows the predicted oral profile compared to the observed data from two rats dosed orally at 2mg/kg. The additional inputs for the oral prediction were the Caco-2 permeability and measured human fed-state simulated intestinal fluid (FeSSIF, 92(tg/mL). The oral pharmacokinetic parameters Tmax. Cmax. AUC and bioavailability were well predicted. Simulation of higher doses of compound A predicted absorption-limited... 

Caco-2 cells, especially the human intestinal epithelial cell line, have been proposed and used for the simulation and prediction of intestinal drug absorption after oral administration. These membranes of cells have useful properties for correlation with in vivo data such as enzymatic and transporter systems [24]. 

Several papers have also been published in which a correlation has been sought between permeation across Caco-2 cells and physicochemical properties of the compounds. The review article by Ekins et al. (2000) discusses several studies to predict Caco-2 cell permeation. Correlations have been found with polar surface area, hydrogen bond descriptors, VolSurf, and other parameters. Van de Waterbeemd et al. (2001a) also discuss models for predicting oral absorption of compounds, including the use of Caco-2 cell lines. This paper also provides much useful information on the optimization of pharmacokinetic parameters in drug development. 

Absorption rate coefficients and permeability values obtained through different systems, i.e. in vitro or in situ, finally are determined with the objective in mind of predicting the fraction of a dose that will be absorbed through the intestine when the drug is orally administered. In order to use the data obtained in those systems it is essential to validate them properly. The present section reviews the capability of the parameters representatives of the absorption determining with different techniques to predict in vivo drug absorption in absence of any limited step (as dissolution or solubility) by means of the previously described model and Eq. (16). In particular, the absorption rate constant obtained with an in situ close loop assay, permeability through Caco-2 cell lines, and PAM PA models have been examined. 

Accordingly, the parameter used for the correlation was P0, permeability of the uncharged species. The intrinsic permeability results obtained in the PAMPA system (P0) were compared with more traditional in vitro methods, Caco-2 cell lines, as well as an in situ rat-based model which has already demonstrated a good ability for predicting in vivo oral absorption, as previously mentioned [50]. 

LION Bioscience—providerof iDEA, a modular ADME predictive system. The absorption module predicts Caco-2 cell permeation, and performs dose-response modeling of the oral absorption. The metabolism module predicts first-pass effects and models metabolic parameters. Future modules are planned for distribution and elimination (124). 

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