Drug-protein conjugates—VIII The metabolic fate of the dinitrophenyl hapten conjugated to albumin

Abstract

Dinitroflorobenzene has been used as a model chemically reactive metabolite to investigate factors which determine the fate of drug-protein conjugates formed in vivo. The disposition of homologous and heterologous albumin conjugated with 3H-dinitrophenyl groups ( 3H-DNP) has been investigated in the male Wistar rat. After intravenous administration, conjugates were cleared from plasma, predominantly through the liver, and the hapten was excreted into bile and urine as the novel amino acid derivative N 2-acetyl- N 6-DNP-lysine. It is assumed that the product arises from lysosomal hydrolysis of the conjugate, followed by N-acetylation, since its biliary excretion was significantly reduced in animals pretreated with suramin, an inhibitor proteolysis. The clearance of DNP-albumin conjugates was dependent upon the degree of conjugation; conjugates with an epitope density of > 20 had a short ( ca. 1 hr) half-life. In a second study, the disposition of DNP-autologous protein conjugates was monitored in the rabbit over 21 days. The plasma concentration-time profile of the serum conjugates indicated that clearance was dependent upon non-immune mechanisms and that intravenous administration of DNP-serum protein conjugates did not elicit an anti-DNP response.