Immunological reactivity of angiotensin II receptor antagonists: possible implications for receptor binding sites

In the present study, we assessed the reactivity with seven anti-angiotensin II monoclonal antibodies of three nonpeptide and one peptide compounds described as selective antagonists of angiotensin II for AT1 (DuP 753, 2-n-butyl-4-chloro-5-(hydroxymethyl)-1-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl] methyl] imidazole; EXP 3174, 2-n-butyl-4-chloro-5-(carboxylic acid)-1-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl] methyl] imidazole) and AT2 receptor sites (CGP42112A, nicotinyl-Tyr-(N alpha-benzyloxycarbonyl-Arg)Lys-His-Pro-Ile-OH; PD123177, 1-[(4-amino-3-methylphenyl) methyl]-5-(diphenyl-acetyl)-4,5,6,7-tetrahydro-1H-imidazol[4,5-c] pyridine 6-carboxylic acid), respectively. These studies were undertaken because the reactivity of the monoclonal antibodies with peptide analogs of angiotensin II and the three-dimensional structure of an angiotensin II-immunoglobulin Fab fragment complex strongly suggested that the conformations identified by the monoclonal antibodies were relevant to those involved in receptor binding as defined by biophysical models supported by structure activity studies. Surprisingly although three of the compounds were described as competitive inhibitors of angiotensin II, binding of the various monoclonal antibodies to either ovalbumin-coupled angiotensin II adsorbed to plastic wells or 125I-labeled angiotensin II in liquid phase was unaffected by any of the nonpeptide antagonists and CGP42112A up to 10(-4) M concentration. The antagonists also failed to bind to rabbit polyclonal anti-angiotensin II antibodies. Direct binding experiments in which solid phase-immobilized angiotensin II and DuP 753 conjugates were incubated with anti-angiotensin II or anti-DuP 753 monoclonal antibodies, did not show any cross-reactivity.(ABSTRACT TRUNCATED AT 250 WORDS)