RT Journal Article
SR Electronic
T1 Methotrexate Is Excreted into the Bile by Canalicular Multispecific Organic Anion Transporter in Rats
JF Cancer Research
JO Cancer Res
FD American Association for Cancer Research
SP 3506
OP 3510
VO 57
IS 16
A1 Masuda, Masayuki
A1 I'izuka, Yuji
A1 Yamazaki, Masayo
A1 Nishigaki, Ryuichiro
A1 Kato, Yukio
A1 Ni'inuma, Kayoko
A1 Suzuki, Hiroshi
A1 Sugiyama, Yuichi
YR 1997
UL http://cancerres.aacrjournals.org/content/57/16/3506.abstract
AB Methotrexate [(+) amethopterin, L-MTX] has two carboxyl groups in its structure and is eliminated mainly by excretion into urine and bile. To investigate the biliary excretion mechanism of L-MTX, we performed in vivo and in vitro studies using mutant rats, Eisai hyperbilirubinemic rats (EHBRs), whose canalicular multispecific organic anion transporter (cMOAT) is defective as a consequence of heredity. After i.v. administration of L-MTX to EHBRs, its plasma disappearance and biliary excretion was slower than in normal Sprague Dawley rat (SDR). ATP-dependence and overshoot phenomena were observed in the uptake of [3H]L-MTX by canalicular membrane vesicles (CMV) prepared from SDR, whereas no ATP-dependence was observed in CMV from EHBRs. The ATP-dependent uptake of L-MTX by SDR CMV exhibited saturable kinetics with a Km of 295 µm. L-MTX competitively inhibited the ATP-dependent uptake of [3H]2,4-dinitrophenyl-S-glutathione, a typical substrate for cMOAT, and the inhibition constant (Ki) of L-MTX was comparable with its own Km. These results suggest that L-MTX is excreted into bile by cMOAT. The inhibitory effects of L-MTX and its optical isomer, (-) amethopterin (D-MTX), on the uptake of [3H]L-MTX differed with Kis of 326 and 93 µm, respectively, indicating that the biologically inactive D form has a higher affinity for cMOAT than L-MTX. ©1997 American Association for Cancer Research.