Polyclonal and monoclonal antibodies directed against SK & F 94461, a specific H1 histamine receptor ligand

Abstract

SK & F 94461, an aminopentyl analogue of mepyramine, is a recently described H1 receptor antagonist. At variance with the other available H1 receptor ligands, SK & F 94461 offers the possibility of coupling to a protein carrier to render the molecule immunogenic. SK & F 94461 coupled to succinylated bovine serum albumin was used as an immunogen to raise polyclonal antibodies in rabbits and BALB/c mice. In parallel, spleen cells from immunized mice were used to produce hybridomas by somatic cell fusion. Thus, six different murine monoclonal antibodies sharing anti-SK & F 94461 specificity were selected for further detailed characterization of their binding properties. Pharmacologic studies of competitive inhibition using a set of 11 histaminergic agents allowed analysis of the fine specificity of anti-SK & F 94461 antibodies. Both polyclonal and monoclonal anti-SK & F 94461 antibodies showed very high affinity for the immunizing molecule (i.e., Ka values for monoclonal antibodies 8 and 12 were, respectively, 3 X 10(10) and 1.4 X 10(10) M-1). Both types of antibodies bound with high affinity (IC50 ranging from 10(-10) to 10(-12) M) to mepyramine, which has a chemical structure closely resembling that of SK & F 94461. Moreover, these antibodies displayed clear-cut stereoselectivity inasmuch as they bound the d-configuration of chlorpheniramine with significantly higher affinity than the l-form. Thus, all six monoclonal antibodies showed IC50 values 1 to 6 log units lower for d- than for l-chlorpheniramine. For some monoclonal antibodies, spectroscopic and fluorescence spectra studies showed that their different binding capacities correlated with their optical properties. Similarly, polyclonal anti-SK & F 94461 antibodies showed a 500-fold lower affinity for l- than for d-chlorpheniramine. All these results indicate that the polyclonal and the majority of monoclonal anti-SK & F 94461 antibodies recognized with high affinity structural configurations known to be important for the pharmacologic activity of H1 ligands, namely the presence of the dimethylaminoethyl side chain and, with stereochemical selectivity, the d-configuration of chlorpheniramine. These data extend for the first time to an H1 histamine receptor ligand results reported in other hormone systems.