Conversion of methotrexate to 7-hydroxymethotrexate and 7-hydroxymethotrexate polyglutamates in cultured rat hepatic cells.
The formation of 7-hydroxymethotrexate and its diglutamate has been established in rat hepatic parenchymal cells in culture. The formation of 7-hydroxymethotrexate increases with the extracellular methotrexate concentration (1-50 microM) and with time over a 24-h period. The majority of the 7-hydroxy derivative is found in the medium after 6- and 24-h incubations at all concentrations examined. At high methotrexate concentration (50 microM) 7% of the total extracellular methotrexate was the 7-hydroxy derivative. 7-Hydroxymethotrexate diglutamate is accumulated within the cell, although longer chain length derivatives are not observed. The inability to form longer chain length polyglutamate derivatives is consistent with a limited capacity of hepatocytes to convert radiolabeled 7-hydroxymethotrexate to the tri- and tetraglutamates although the diglutamate is readily formed. A hepatoma cell line has an extremely limited capacity to form 7-hydroxy derivatives from methotrexate but form measurable amounts of mono-, di-, and triglutamates of 7-hydroxymethotrexate. 7-Hydroxymethotrexate was a good substrate for glutamylation in the hepatoma cells with large amounts of tri- through pentaglutamate derivatives. These studies confirm that 7-hydroxymethotrexate and the diglutamate must be considered when evaluating methotrexate pharmacology and demonstrate that this will be necessary with regard to methotrexate hepatotoxicity.
D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006900:Hydroxylation; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism; D008297:Male; D008727:Methotrexate / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000633:toxicity; D011099:Polyglutamic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D013997:Time Factors
D011099:Polyglutamic Acid; C014085:methotrexate polyglutamate; C011864:7-hydroxymethotrexate; D008727:Methotrexate