Development of natriuretic peptide analogs selective for the atrial natriuretic factor-R1A receptor subtype

A pharmacological characterization of subtypes of the atrial natriuretic factor (ANF) receptor ANF-R1, found in bovine adrenal cortex and rat papillary membrane preparations, has been carried out using various chimeric analogs based on rat ANF(99-126) [rANF(99-126)] and porcine brain natriuretic peptide 32 (pBNP32). Receptor binding and cGMP production assays in bovine adrenal cortex indicate that replacement of the amino-terminal segment of pBNP32 with that of rANF(99-126) enhances the affinity of the peptide for the ANF-R1A receptor subtype and its stimulation of associated guanylate cyclase activity. In rat kidney papillae, the substitution of amino- and/or carboxyl-terminal portions of pBNP32 with those of rANF(99-126) also results in a large increase in the affinity and agonistic potency for the ANF-R1A subtype but in only modest changes in those for the ANF-R1B receptor subtype. Interestingly, in this preparation the chimeric analogs could discriminate by their differential affinities and cGMP production potencies between the two receptor subtypes. In particular, pBNP1, obtained by combining the ring structure of pBNP32 with the amino- and carboxyl-terminal portions of rANF(99-126), is the most selective analog. pBNP1 displays higher affinity and agonistic potency for ANF-R1A receptor than for ANF-R1B receptor, with selectivity ratios between these two subtypes of 632- and 504-fold, respectively. Moreover, an excellent correlation is observed between the affinity of the peptides for the ANF-R1A receptor and their stimulation of particulate guanylate cyclase activity in bovine adrenal cortex (r = 0.99, p < 0.01) and rat papillary (r = 0.97, p < 0.01) membrane preparations. In addition, all the chimeric analogs in this study show affinities similar to those of rANF(99-126) and pBNP32 for the ANF-R2 receptor in NIH-3T3 membrane preparations. Importantly, the chimeric analogs pBNP1 and pBNP3, which contain the core of pBNP32 and the amino-terminal segment of rANF(99-126), display higher affinities for the ANF-R1A receptor type than for the ANF-R2 receptor type. These results indicate that the analogs combining the ring structure of pBNP32 with the amino- and/or carboxyl-terminal segments of rANF(99-126) are more selective for the ANF-R1A receptor subtype than are the natural peptides rANF(99-126) and pBNP32.