Evaluation of a chimeric (uPA+/+)/SCID mouse model with a humanized liver for prediction of human metabolism.

A model that predicts human metabolism and disposition of drug candidates would be of value in early drug development. In this study, a chimeric (uPA+/+)/SCID mouse model was evaluated with three structurally distinct compounds (GW695634, a benzophenone, SB-406725, a tetrahydroisoquinoline and GW823093, a fluoropyrrolidine) for which human metabolism and disposition was characterized. Human metabolite profiles in plasma and/or urine were compared to those of chimeric (uPA+/+)/SCID and control CD-1 or (uPA+/+)/SCID) mice. GW695634 and SB-406725 exhibited primarily hepatic metabolism and were chosen as probes to assess which human metabolites would likely circulate systemically. GW823093 exhibited a combination of hepatic and extrahepatic metabolism such that renal excretion of drug-related material was ~2-fold greater in humans than in mice, and thus chosen as a probe to assess if the chimeric (uPA+/+)/SCID mouse would predict the urinary excretion of human metabolites. We observed that human metabolism and disposition was well represented for GW695634, somewhat represented for GW823093 and minimally represented for SB-406725. Collectively, the results of this and other studies suggest that while limitations for prediction of human metabolism and disposition exist, humanized chimeric mouse models can potentially represent informative new tools in drug discovery and development.

An unexpected synergist role of P-glycoprotein and breast cancer resistance protein on the central nervous system penetration of the tyrosine kinase inhibitor lapatinib (N-{3-chloro-4-[(3-fluorobenzyl)oxy]phenyl}-6-[5-({[2-(methylsulfonyl)ethyl]amino}methyl)-2-furyl]-4-quinazolinamine; GW572016).

Lapatinib is a tyrosine kinase inhibitor approved for use in combination with capecitabine to treat advanced or metastatic breast cancers overexpressing human epidermal receptor 2 (ErbB2). This work investigated the role of P-glycoprotein (Pgp; the protein from the Mdr1a/b gene) and breast cancer resistance protein (Bcrp; the protein from the Bcrp1 gene) in modulating the central nervous system penetration of lapatinib at steady-state conditions in FVBn mice (wild-type), Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)/Bcrp1(-/-) knockout mice. After an intravenous infusion of lapatinib for 24 h to a targeted steady-state plasma concentration of 700 ng/ml (0.3 mg/kg/h) or 7000 ng/ml (3 mg/kg/h), lapatinib brain-to-plasma ratios were approximately 3- to 4-fold higher in Mdr1a/b(-/-) knockout mice (ratio range from 0.09 to 0.16) compared with wild-type mice (ratio range from 0.03 to 0.04). There was no difference in the brain-to-plasma ratio in the Bcrp1(-/-) knockout mice (ratio range from 0.03 to 0.04) compared with wild-type mice. In contrast, Mdr1a/b(-/-)/Bcrp1(-/-) triple knockout mice had a 40-fold higher brain-to-plasma ratio (ratio range from 1.2 to 1.7), suggesting that Pgp and Bcrp work in concert to limit the brain-to-plasma ratio of lapatinib in mice. This finding has important potential consequences for the treatment of brain tumors in breast cancer patients treated with tyrosine kinase inhibitors as well as the basic understanding of ATP binding cassette transporters expressed in the blood-brain barrier on the central nervous system disposition of drugs.