Preclinical profile of PF9404C, a nitric oxide donor with beta receptor blocking properties

PF9404C ((2'S),(2S)-3-isopropylamine, 1-[4-(2,3-dinitroxy)propoxymethyl]-phenoxy-2'-propranol) is the S-S diesteroisomer of a novel blocker of beta-adrenergic receptors with vasorelaxing properties. It causes a concentration-dependent relaxation of rat aorta helical strips precontracted with 10(-6) M norepinephrine (NE; IC50 33 nM). It is equipotent to nitroglycerin (NTG; IC50 49 nM), but much more potent than isosorbide dinitrate (ISD; IC50 15,000 nM). In rat aorta smooth muscle cells, at 10 microM, PF9404C increased the formation of cGMP from 3 pmol/mg protein in basal conditions to 53 pmol/mg protein, suggesting that the mechanism of its vasorelaxing effects involves the slow generation of NO. This is supported by the facts that (i) ODQ (a blocker of guanylate cyclase) inhibited the vasodilatory effects of PF9404C; and (ii) PF9404C generates NO, as indirectly measured by the Griess reaction. In the electrically driven guinea pig left atrium, PF9404C blocks the inotropic effects of isoproterenol in a concentration-dependent manner. Its IC50 (30 nM) was similar to that of S-propranolol (22.4 nM) and lower than that of metoprolol (120 nM) or atenolol (192 nM). The beta adrenergic ligand (-)-[3H]-CGP12177 (4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one hydrochloride) (0.2 nM) is displaced from its binding sites in rat brain membranes with a K(i) of 7, 17, 170, and 1200 nM for PF9404C, S-(-)propranolol, metoprolol, and atenolol, respectively. PF9404C blocks 45Ca2+ entry into bovine adrenal chromaffin cells induced by direct depolarization with 70 mM K+ or by the nicotinic agonist dimethylphenylpiperazinium (DMPP). PF9404C exhibits about 3-fold higher potency than NTG to relax the majority of the vessels studied, especially when they were contracted with K+, and shows a certain selectivity of action for the renal artery. It produces auto-tolerance that is ca. 20-fold less pronounced than that observed with NTG. Cross-tolerance in preparations pre-exposed to PF9404C and later relaxed with NTG, was much greater than auto-tolerance. This makes PF9404C a useful pharmacological tool for the development of novel NO-donor compounds with a lesser degree of vascular tolerance than those currently available.