Dose-dependent disposition of methotrexate in Abcc2 and Abcc3 gene knockout murine models

Methotrexate (MTX) is a substrate for numerous human ATP-binding cassette (ABC) efflux transporters, yet the impact of these transporters on MTX pharmacokinetics (PK) over a large dose range has not been examined. To investigate the effects of two transporters - ABC subfamily C member 2 (Abcc2; multidrug resistance protein 2) and ABC subfamily C member 3 (Abcc3; multidrug resistance protein 3) - involved in MTX hepatobiliary disposition in vivo, MTX plasma, urine, and feces concentrations were analyzed after 10, 50, and 200 mg/kg i.v. doses to groups of wild type (WT), Abcc2(-/-), and Abcc3(-/-) mice. The absence of Abcc2 caused a decrease in total clearance of MTX relative to WT mice at all dose levels yet was accompanied by compensatory increases in renal excretion and metabolism to 7-hydroxymethotrexate (7OH-MTX). In Abcc3(-/-) mice, total clearance was elevated at the two lower dose levels and was attributed to stimulation of biliary excretion and confirmed by elevated fecal excretion; however, at the high 200 mg/kg dose, clearance was severely retarded and could be attributed to hepatotoxicity because conversion to 7OH-MTX was diminished. The findings confirmed that both Abcc2 and Abcc3 significantly influenced the PK properties of MTX, and depending on the MTX dose and strain, alternate elimination pathways were elicited and saturable.