Characterization of the uptake mechanism for a novel loop diuretic, M17055, in Caco-2 cells: Involvement of organic anion transporting polypeptide (OATP)-B

Purpose. M17055 is under development as a novel loop diuretic for oral administration. To investigate the molecular mechanism of its gastrointestinal absorption, we initially aimed to clarify the mechanism of uptake of M17055 by Caco-2 cells, focusing on possible involvement of OATP-B (SLCO2B1), which is localized in the apical membranes of human intestinal epithelial cells. Materials and Methods. The uptake of [C-14]M17055 by Caco-2 cells cultured on multi-well dishes was measured after cultivation for 14 days. Uptake of [C-14]M17055 by HEK293 cells stably expressing OATP-B (HEK293/OATP-B cells) was also examined. Results. M17055 uptake by Caco-2 cells was saturable, and was inhibited by various organic anions, including other loop diuretics, and several bile acids. Uptake of M17055 by HEK293/OATP-B cells was much higher than that by mock cells. The inhibitory profiles of various organic anions and the estimated K-m values for M17055 uptake were similar in Caco-2 and HEK293/OATP-B cells. Moreover, the values of inhibition constants of several inhibitors for M17055 uptake were comparable in the two cell lines. Conclusion. Our data suggest that OATP-B plays a major role in the uptake of the novel loop diuretic M17055 from apical membranes in Caco-2 cells.