An Exploratory Study of Two Caco-2 Cell Models for Oral Absorption: A Report on Their Within-laboratory and Between-laboratory Variability, and Their Predictive Capacity

In 2005 the European Centre for the Validation of Alternative Methods (ECVAM) sponsored a prevalidation study aimed at evaluating the reproducibility (between-laboratory and within-laboratory variability) and the predictive capacity of two in vitro cellular systems, Caco-2/ ATCC and Caco-2/TC7 clone, to estimate human oral fraction absorbed. Two laboratories, experienced with Caco-2 cultures participated in this study. Ten test chemicals with documented in vivo oral absorption data were selected by the Management Team. Atenolol, Cimetidine and propranolol were included as reference compounds for low, medium and high intestinal absorption, respectively. Transport experiments were independently carried out in the two laboratories, in accordance with the established protocol. The apparent permeability coefficient (Papp) was calculated either in apical to basolateral (absorption) or in basolateral to apical (efflux) direction. To investigate the involvement of possible active transport processes, experiments were also run in the presence of Sodium Azide plus 2-deoxy-D-glucose in the donor compartment. Before performing the permeability experiments the highest concentration that did not impair barrier integrity was identified for each test chemical in both cell models by applying the chemicals together with a marker of the paracellular pathway ([14C]-Mannitol or Lucifer Yellow). Measurement of trans-epithelial electrical resistance (TEER) was also used as a marker of barrier integrity. All permeability data obtained were collected and submitted to ECVAM for an independent biostatistical analysis. The coefficient of variation (CV) was selected as an appropriate measure of within-laboratory variability. Median CVs of 10.5% and 15.5% were found for each laboratory. Concerning between-laboratory reproducibility, comparable response levels were found for the three reference compounds and for Paracetamol while, for the other chemicals, results were less reproducible, in particular for compounds known to be actively transported. No significant differences in Papp values were reported between the two cell lines. A preliminary estimation of predictive capacity has been established using two mathematical models available from the literature. Good estimation of human fraction absorbed was obtained for well-absorbed compounds while moderate and poor absorbed compounds were rather overestimated.JRC.I.2-Validation of Alternative Method