Nucleobase- and p-Glycoprotein-Mediated Transport of AG337 in a Caco-2 Cell Culture Model

Abstract

This study aimed to determine the intestinal transport characteristics of AG337. Caco-2 cell monolayers were used for directional transport of AG337. The results indicated that the rate of basolateral (BL) to apical (AP) or secretory transport of AG337 was always higher than the rate of AP to BL or absorptive transport. The BL-AP/AP-BL ratio increased from 7.6 to 17.2 as the concentration increased from 10 to 75 microM and stabilized afterward. The following results suggest that the p-glycoprotein is involved in the AP efflux of AG337. (1) Verapamil completely abolished the directional transport. (2) The apparent activation energy for secretory transport was high (33 kcal/mol). (3) Secretory transport was inhibited by verapamil (63%) and dipyridamole (35%), but not by probenecid. (4) AP to BL transport was enhanced by verapamil (232%) and dipyridamole (41%), but was not altered by probenecid or an AP pH change. An additional carrier mechanism may be involved in the AP uptake of AG337 because (1) absorptive permeabilities decreased as the concentration increased even though secretory permeabilities remained the same, (2) the absorptive transport rate was 37% lower in a medium containing verapamil and dipyridamole than in a medium containing only verapamil, and (3) the absorptive transport rate was also lower in a medium containing verapamil and a nucleobase mixture (consisting of adenine, hypoxanthine, and xanthine at 100 microM each) than in a medium containing verapamil only. Apical transport of AG337 in the Caco-2 cells is mediated, at least in part, by p-glycoprotein (efflux) and a nucleobase transporter that transports (uptake) nucleic bases.