PT - JOURNAL ARTICLE AU - Kayoko Ohura AU - Hisae Sakamoto AU - Shin-ichi Ninomiya AU - Teruko Imai TI - Development of a Novel System for Estimating Human Intestinal Absorption Using Caco-2 Cells in the Absence of Esterase Activity AID - 10.1124/dmd.109.029413 DP - 2010 Feb 01 TA - Drug Metabolism and Disposition PG - 323--331 VI - 38 IP - 2 4099 - http://dmd.aspetjournals.org/content/38/2/323.short 4100 - http://dmd.aspetjournals.org/content/38/2/323.full SO - Drug Metab Dispos2010 Feb 01; 38 AB - Both mRNA and protein levels of the carboxylesterase (CES) isozymes, hCE1 and hCE2, in Caco-2 cells increase in a time-dependent manner, but hCE1 levels are always higher than those of hCE2. In human small intestine, however, the picture is reversed, with hCE2 being the predominant isozyme. Drugs hydrolyzed by hCE1 but not by hCE2 can be hydrolyzed in Caco-2 cells, but they are barely hydrolyzed in human small intestine. The results in Caco-2 cells can be misleading as a predictor of what will happen in human small intestine. In the present study, we proposed a novel method for predicting the absorption of prodrugs in the absence of CES-mediated hydrolysis in Caco-2 cells. The specific inhibition against CES was achieved using bis-p-nitrophenyl phosphate (BNPP). The optimal concentration of BNPP was determined at 200 μM by measuring the transport and hydrolysis of O-butyryl-propranolol (butyryl-PL) as a probe. BNPP concentrations of more than 200 μM inhibited 86% of hydrolysis of butyryl-PL, resulting in an increase in its apparent permeability. Treatment with 200 μM BNPP did not affect paracellular transport, passive diffusion, or carrier-mediated transport. Furthermore, the proposed evaluation system was tested for ethyl fexofenadine (ethyl-FXD), which is a superior substrate for hCE1 but a poor one for hCE2. CES-mediated hydrolysis of ethyl-FXD was 94% inhibited by 200 μM BNPP, and ethyl-FXD was passively transported as an intact prodrug. From the above observations, the novel evaluation system is effective for the prediction of human intestinal absorption of ester-type prodrugs.Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics