TY - JOUR T1 - Carrier-Mediated Hepatobiliary Transport of a Novel Antifolate,<em>N</em>-[4-[(2,4-Diamminopteridine-6-yl)methyl]-3,4-dihydro-2<em>H</em>-1,4-benzothiazin-7-yl]carbonyl-L-Homoglutamic Acid, in Rats JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 394 LP - 400 VL - 29 IS - 4 AU - Yong-Hae Han AU - Yukio Kato AU - Yuka Watanabe AU - Kimio Terao AU - Yoshinori Asoh AU - Yuichi Sugiyama Y1 - 2001/04/01 UR - http://dmd.aspetjournals.org/content/29/4/394.abstract N2 - The hepatic uptake and biliary excretion of a novel methotrexate derivative,N-[4-[(2,4-diamminopteridine-6-yl)methyl]-3,4-dihydro-2H-1,4-benzothiazin-7-yl]carbonyl-l-homoglutamic acid (MX-68), were examined in rats in vitro using isolated hepatocytes and bile canalicular membrane vesicles (CMVs), respectively. The uptake of MX-68 by isolated rat hepatocytes showed a saturable component (Km = 2.15 μM andVmax = 2.34 pmol/min/mg of protein) and was inhibited by ATP-depletors and anionic compounds such as taurocholate and probenecid. [3H]MX-68 uptake was also inhibited by folate analogs such as methotrexate and 5CH3-tetrahydrofolate, but the effect of these compounds was slightly less than that of unlabeled MX-68. On replacing Na+ with choline, MX-68 uptake remained unchanged, whereas the methotrexate uptake was reduced. Uptake of MX-68 increased as the extracellular pH fell from 7.5 to 5.5. These results suggest that MX-68 is taken up via active transport systems. The uptake of MX-68 by CMVs prepared from normal rats exhibited clear ATP dependence, whereas ATP had only a minimal effect on the uptake by CMVs from Eisai-hyperbilirubinemic rats with a hereditary deficiency in canalicular multispecific organic anion transporter (cMOAT). The initial uptake rate of ATP-dependent MX-68 transport showed saturation with kinetic parameters similar to those of methotrexate. MX-68 inhibited the ATP-dependent transport of 2,4-dinitrophenyl-S-glutathione, a typical substrate for cMOAT, the inhibition constant (162 μM) being comparable with the Km of ATP-dependent MX-68 transport. These results suggest that the biliary excretion of MX-68 via the bile canalicular membrane is mediated mainly by cMOAT. In conclusion, active transport systems are involved in membrane penetration of MX-68 both at sinusoidal and canalicular sides in the liver, the latter being mainly involved with methotrexate (MTX) whereas the former differs partially from that for MTX. The American Society for Pharmacology and Experimental Therapeutics ER -