INVESTIGATION OF RAPAMYCIN TRANSPORT AND UPTAKE ACROSS ABSORPTIVE HUMAN INTESTINAL-CELL MONOLAYERS

An in vitro intestinal cell culture model was used to characterize and investigate factors affecting uptake and transport of rapamycin (RAPA ), a potent immunosuppressive drug. Studies were performed on three hu man intestinal cell monolayers (Caco-2, HCT-8, and T84), grown on micr oporous membrane inserts for 12 days. RAPA transport in all three mono layers was found to be dose dependent. The highest rates of transport were found at the highest tested final RAPA concentration of 10,000 mu g/L. Apical to basal RAPA transport was linear in Caco-2 cell monolay ers for up to 60 min, and in HCT-8 and T84 cell monolayers for up to 1 20 min. Temperature sensitive RAPA transport was found because incubat ion at 4 degrees C markedly attenuated transport by 97, 90, and 78% fo r Caco-2, HCT-8, and T84 monolayers, respectively. In all three monola yers RAPA transport was highly polarized because the apical to basal t ransport was greater than that in the opposite direction. RAPA uptake and transport across cell monolayers were compared when 10,000 mu g/L of RAPA (cold) plus 0.05 mu Ci C-14-RAPA was added in combination with varying final concentrations (1,000, 10,000, and 100,000 mu g/L) of t he immunosuppressive drugs, CsA or RS. Increasing concentrations of Cs A resulted in a significant dose-dependent decrease in C-14-RAPA trans port across cell monolayers. In contrast, at high (100,000 mu g/L) RS concentrations, C-14-RAPA transport was significantly increased. Uptak e of C-14-RAPA into cell monolayers was significantly decreased only w ith the 100,000 mu g/L CsA concentration. These studies suggest that c ombinations of immunosuppressive drugs given orally have a potential f or altering the intestinal transport and uptake of RAPA. More studies are currently being performed with this cell model using multiple comb inations of other immunosuppressive drugs, as well as in vivo in anima ls to further investigate this.