title: Mechanisms underlying differences in systemic exposure of structurally similar active metabolites: comparison of two preclinical hepatic models.
abstract: Selection of in vitro models that accurately characterize metabolite systemic and hepatobiliary exposure remains a challenge in drug development. In the present study, mechanisms underlying differences in systemic exposure of two active metabolites, furamidine and 2,5-bis (5-amidino)-2-pyridyl furan (CPD-0801), were examined using two hepatic models from rats: isolated perfused livers (IPLs) and sandwich-cultured hepatocytes (SCH). Pafuramidine, a prodrug of furamidine, and 2,5-bis [5-(N-methoxyamidino)-2-pyridyl] furan (CPD-0868), a prodrug of CPD-0801, were selected for investigation because CPD-0801 exhibits greater systemic exposure than furamidine, despite remarkable structural similarity between these two active metabolites. In both IPLs and SCH, the extent of conversion of CPD-0868 to CPD-0801 was consistently higher than that of pafuramidine to furamidine over time (at most 2.5-fold); area under the curve (AUC) of CPD-0801 in IPL perfusate and SCH medium was at least 7-fold higher than that of furamidine. Pharmacokinetic modeling revealed that the rate constant for basolateral (liver to blood) net efflux (k(A_net efflux)) of total formed CPD-0801 (bound + unbound) was 6-fold higher than that of furamidine. Hepatic accumulation of both active metabolites was extensive (>95% of total formed); the hepatic unbound fraction (f(u,L)) of CPD-0801 was 5-fold higher than that of furamidine (1.6 versus 0.3%). Incorporation of f(u,L) into the pharmacokinetic model resulted in comparable k(A_net efflux,u) between furamidine and CPD-0801. In conclusion, intrahepatic binding markedly influenced the disposition of these active metabolites. A higher f(u,L) explained, in part, the enhanced perfusate AUC of CPD-0801 compared with furamidine in IPLs. SCH predicted the disposition of prodrug/metabolite in IPLs.
authors.affiliation: Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599-7569, USA.
authors.forename: Grace Zhixia
authors.initials: GZ
authors.lastname: Yan
authors.forename: Kim L R
authors.initials: KL
authors.lastname: Brouwer
authors.forename: Gary M
authors.initials: GM
authors.lastname: Pollack
authors.forename: Michael Zhuo
authors.initials: MZ
authors.lastname: Wang
authors.forename: Richard R
authors.initials: RR
authors.lastname: Tidwell
authors.forename: James E
authors.initials: JE
authors.lastname: Hall
authors.forename: Mary F
authors.initials: MF
authors.lastname: Paine
mesh_terms: D000578:Amidines / Q000493:pharmacokinetics* / Q000494:pharmacology*; D000818:Animals; D001550:Benzamidines / Q000493:pharmacokinetics* / Q000494:pharmacology*; D001646:Bile / Q000378:metabolism; D001711:Biotransformation; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003627:Data Interpretation, Statistical; D022781:Hepatocytes / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D008954:Models, Biological; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010599:Pharmacokinetics; D011355:Prodrugs; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000578:Amidines; D001550:Benzamidines; C555517:CPD 0801; D004364:Pharmaceutical Preparations; D011355:Prodrugs; C458513:pafuramidine