title: Characterization of the uptake mechanism for a novel loop diuretic, M17055, in Caco-2 cells: involvement of organic anion transporting polypeptide (OATP)-B.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  The uptake of [14C]M17055 by Caco-2 cells cultured on multi-well dishes was measured after cultivation for 14 days. Uptake of [14C]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 Km 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Pharmaceutical Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Nishimura
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kubo
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kato
authors.forename: Yoshimichi
authors.initials: Y
authors.lastname: Sai
authors.forename: Takuo
authors.initials: T
authors.lastname: Ogihara
authors.forename: Akira
authors.initials: A
authors.lastname: Tsuji
mesh_terms: D000465:Algorithms; D001647:Bile Acids and Salts / Q000494:pharmacology; D018938:Caco-2 Cells; D003627:Data Interpretation, Statistical; D004232:Diuretics / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D027361:Organic Anion Transporters / Q000378:metabolism*; D010091:Oximes / Q000378:metabolism*; D015363:Quinolones / Q000378:metabolism*; D012964:Sodium / Q000502:physiology; D013431:Sulfates / Q000378:metabolism
chemical_list: D001647:Bile Acids and Salts; D004232:Diuretics; D027361:Organic Anion Transporters; D010091:Oximes; D015363:Quinolones; C450859:SLCO2B1 protein, human; D013431:Sulfates; C079648:7-chloro-2,3-dihydro-1-(2-methylbenzoyl)-4(1H)-quinolinone 4-oxime-O-sulfonic acid; D012964:Sodium