Carrier-mediated hepatobiliary transport of a novel antifolate, N-[4-[(2,4-dianninopteridine-6-yl)methyl]-3,4-dihydro-2H-1,4-benzothiazin-7-yl]carbonyl-L-homoglutamic acid, in rats.
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 microM and Vmax = 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 microM) 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.
Han
Y H
YH
Graduate School of Pharmaceutical Sciences, University of Tokyo, Bunkyo-ku, Tokyo, Japan.
Kato
Y
Y
Watanabe
Y
Y
Terao
K
K
Asoh
Y
Y
Sugiyama
Y
Y
D015074:2-Aminoadipic Acid / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D000818:Animals; D027321:Anion Transport Proteins; D000838:Anions / Q000494:pharmacology; D000963:Antimetabolites / Q000494:pharmacology; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D004337:Drug Carriers; D005492:Folic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005493:Folic Acid Antagonists / Q000493:pharmacokinetics*; D005978:Glutathione / Q000031:analogs & derivatives / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008297:Male; D008727:Methotrexate / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013997:Time Factors; D022161:Transport Vesicles / Q000378:metabolism; D014316:Tritium
D027321:Anion Transport Proteins; D000838:Anions; D000963:Antimetabolites; D002352:Carrier Proteins; D004337:Drug Carriers; D005493:Folic Acid Antagonists; C104193:N-(1-((2,4-diamino-6-pteridinyl)methyl)-3,4-dihydro -2H-1,4-benzothiazine-7-carbonyl)-L-2-aminoadipic acid; D014316:Tritium; D015074:2-Aminoadipic Acid; C030190:S-(2,4-dinitrophenyl)glutathione; D005492:Folic Acid; D012964:Sodium; D005978:Glutathione; D008727:Methotrexate