Importance of mechanistic drug metabolism studies in support of drug discovery: A case study with an N -sulfonylated dipeptide VLA-4 antagonist in rats.
N-(1-(3,5-dichlorobenzenesulfonyl)-2S-methyl-azetidine-2-carbonyl)-L-4-(2',6'-dimethoxyphenyl)phenylalanine (1) is a potent antagonist of the very late activating (VLA) antigen-4. During initial screening, 1 exhibited an apparent plasma clearance (CL) of 227 ml min(-1) kg(-1) in Sprague-Dawley rats following an intravenous bolus dose formulated in an aqueous solution containing 40% polyethylene glycol. Such a high CL value led to speculation that the elimination of compound 1 involved extra-hepatic tissues. However, the apparent plasma CL was reduced to 97 ml in(-1) kg(-1) when a 2-min time point was added to sample collections, and further decreased to 48 ml min(-1) kg(-1) after the dose was formulated in rat plasma. The lung extraction of 1 in rats was negligible whereas the hepatic extraction was > or =90%, based on comparison of area under the curve (AUC) values derived from intra-artery, intravenous, and portal vein administration. In rats dosed intravenously with [(14)C]-1, approximately 91% of the radioactivity was recovered in bile over 48 h, with 85% accounted for in the first 4-h samples. The biliary radioactivity profile consisted of approximately 30% intact parent compound, 20% 1-glucuronide, and 50% oxidation products resulting from O-demethylation or hydroxylation reactions. When incubated with rat liver microsomes, oxidative metabolism of 1 was inhibited completely by 1-aminobenzotriazole (ABT), whereas the oxidation and glucuronidation reactions were little affected in the presence of cyclosporin A (CsA). In contrast, the hepatic extraction of 1 in rats was unperturbed in animals pre-dosed with ABT, but was reduced approximately 60% following treatment with CsA. In vitro, 1 was a substrate of the rat organic anion transporter Oatp1b2, and its cellular uptake was inhibited by CsA. In addition, the hepatic extraction of 1 was approximately 30% lower in Eisai hyperbilirubinaemic rats which lack functional multidrug resistant protein-2 (MRP2). Collectively, these data suggest that the clearance of 1 in rats likely is a result of the combined processes of hepatic oxidation, glucuronidation and biliary excretion, all of which are facilitated by active hepatic uptake of parent compound and subsequent active efflux of both unchanged parent and its metabolites into bile. It was concluded, therefore, that multiple mechanisms contribute to the clearance of 1 in rats, and suggest that appropriate pharmacokinetic properties might be difficult to achieve for this class of compounds. This case study demonstrates that an integrated strategy, incorporating both rapid screening and mechanistic investigations, is of particular value in supporting drug discovery efforts and decision-making processes.
Tang
W
W
Department of Drug Metabolism and Pharmacokinetics, Rahway, NJ, USA. wei_tang@merck.com
Stearns
R A
RA
Chen
Q
Q
Bleasby
K
K
Teffera
Y
Y
Colletti
A
A
Hafey
M
M
Evers
R
R
Dean
D C
DC
Magriotis
P A
PA
Lanza
T J
TJ
Lin
L S
LS
Hagmann
W K
WK
Baillie
T A
TA
D000818:Animals; D002478:Cells, Cultured; D016572:Cyclosporine / Q000378:metabolism; D004285:Dogs; D008658:Inactivation, Metabolic; D039041:Integrin alpha4beta1 / Q000037:antagonists & inhibitors*; D008862:Microsomes, Liver / Q000378:metabolism; D029362:Organic Anion Transporters, Sodium-Independent / Q000378:metabolism; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D000074542:Solute Carrier Organic Anion Transporter Family Member 1B3; D013997:Time Factors; D014230:Triazoles / Q000494:pharmacology
D039041:Integrin alpha4beta1; C528738:N-(1-(3,5-dichlorobenzenesulfonyl)-2S-methyl-azetidine-2-carbonyl)-L-4-(2',6'-dimethoxyphenyl)phenylalanine; D029362:Organic Anion Transporters, Sodium-Independent; C421207:Slco1b2 protein, rat; D000074542:Solute Carrier Organic Anion Transporter Family Member 1B3; D014230:Triazoles; C033020:1-aminobenzotriazole; D010649:Phenylalanine; D016572:Cyclosporine