Drug-protein conjugates--XI. Disposition and immunogenicity of dinitrofluorobenzene, a model compound for the investigation of drugs as haptens.

The conjugation of drugs to autologous proteins is thought to be a key step in the hapten mechanism of drug hypersensitivity. We have studied the mild arylating agent dinitrofluorobenzene (DNP-F) as a model compound with which to investigate the relationship between the disposition and immunogenicity of drug haptens in two species, the rat and rabbit. Intramuscular administration of DNP-F (0.027-27 mumol/kg/day) for 4 days to male Wistar rats produced a dose-dependent (ED50 2.7 mumol/kg) IgG anti-DNP antibody response, measured by enzyme-linked immunosorbent assay. Subsequent monthly administrations (for 4 days) increased both the frequency and titre of antibody response. Intravenous administration of [3H]DNP-F (0.27 or 2.7 mumol/kg) for 9 days to male New Zealand White rabbits produced an IgG and IgM anti-DNP response in all animals from day 9 onwards. Formation of circulating (serum) DNP-protein conjugates was determined by radiometric analysis, and found to reach steady state (0.12-0.17% dose/ml) between days 6 and 8 and decline with a half-life of 7.4 days. The immunogenicity of fully characterized haptenated, autologous proteins was investigated in further experiments in which dinitrophenylated serum protein conjugates (DNP-RSP) and albumin conjugates (DNP-RSA) were prepared ex vivo and then administered (50 mg/kg; i.v.) to the rabbit from which the protein had been obtained. The plasma clearance and immunogenicity of DNP-RSA conjugates was dependent on epitope density. Anti-DNP antibodies were detected after administration of an RSA-DNP15 conjugate but not after either RSA-DNP0.5 or RSA-DNP5. Plasma concentrations of RSA-DNP15 conjugate declined slowly initially, but then fell rapidly between days 8 and 10. The plasma clearance of DNP-RSP conjugates showed a dependence on epitope density from day 1 onwards and anti-DNP antibodies were detectable after administration of all conjugates investigated (range of epitope densities 0.5-30 DNP/albumin equivalent). Thus conjugates derived from proteins other than albumin are likely to be the effective immunogens, for the model hapten DNP. These studies show that DNP-F is a useful model compound in studies of the disposition and immunogenicity of drugs acting as haptens, and may therefore be used as a positive control in experiments designed to assess the potential immunogenicity of drugs and other xenobiotics.