Selected nucleophile/nitric oxide adducts [compounds which contain the anionic moiety, XN(O-)N = O] were studied for their ability to release nitric oxide spontaneously in aqueous solution and for possible vasoactivity. The diversity of structures chosen included those in which the nucleophile residue, X, was that of a secondary amine [Et2N, as in [Et2NN(N = O)O]Na, 1], a primary amine [iPrHN, as in [iPrHNN(N = O)O]Na, 2], a polyamine, spermine [as in the zwitterion H2N(CH2)3NH2+(CH2)4N[N(N = O)O-](CH2)3NH2, 3], oxide [as in Na[ON(N = O)O]Na, 4], and sulfite [as in NH4[O3SN(N = O)O]NH4, 5]. The rate constants (k) for decomposition in pH 7.4 phosphate buffer at 37 degrees C, as measured by following loss of chromophore at 230-260 nm, were as follows: 1, 5.4 x 10(-3) s-1; 2, 5.1 x 10(-3) s-1; 3, 0.30 x 10(-3) s-1; 4, 5.0 x 10(-3) s-1; and 5, 1.7 x 10(-3) s-1. The corresponding extents of nitric oxide release (ENO) were 1.5, 0.73, 1.9, 0.54, and 0.001 mol/mol of starting material consumed, respectively, as determined from the integrated chemiluminescence response. Vasodilatory activities expressed as the concentrations required to induce 50% relaxation in norepinephrine-constricted aortic rings bathed in pH 7.4 buffer at 37 degrees C (EC50) were as follows: 1, 0.19 microM; 2, 0.45 microM; 3, 6.2 microM; 4, 0.59 microM; and 5, 62 microM. Vasorelaxant potency (expressed as 1/EC50) was strongly correlated with the quantity of .NO calculated from the physicochemical data to be released in the interval required to achieve maximum relaxation at the EC50 doses (r = 0.995). This suggests that such nucleophile/.NO adducts might generally be useful as vehicles for the nonenzymatic generation of nitric oxide, in predictable amounts and at predictable rates, for biological purposes. The particular significance for possible drug design is underscored in the very favorable potency comparison between several of these agents and the established nitrovasodilators sodium nitroprusside and glyceryl trinitrate (EC50 values of 2.0 and greater than 10 microM, respectively) in parallel aortic ring tests.

No abstract

Joseph A. Hrabie received his entire education in the New York City public school system, including his Ph.D. degree in Chemistry (1981) under the guidance of Professor William F. Berkowitz at Queens College of the City University of New York. After postdoctoral research with Professor Herbert O. House at the Georgia Institute of Technology, he moved to the National Cancer Institute at Frederick and is currently a Senior Scientist with SAIC−Frederick, the primary NCI contractor at the site. In addition to many scientific publications, his continuing interest in nitric oxide chemistry has resulted in 15 U.S. patents. Larry K. Keefer received his B.A. degree from Oberlin College and his Ph.D. degree in Chemistry (1965) under the guidance of Professor Gloria G. Lyle at the University of New Hampshire. He held research positions at the Chicago Medical School and the University of Nebraska College of Medicine before coming to the National Cancer Institute in 1971. He and his colleagues in the NCI's Chemistry Section, Laboratory of Comparative Carcinogenesis, are intensively studying the chemistry and pharmacology of the diazeniumdiolates as nitric oxide sources for biomedical applications.This section contains a description of reactions that are used preparatively as well as those that do not

Ions of structure X[N(O)NO]- display broad-spectrum pharmacological activity that correlates with the rate and extent of their spontaneous, first-order decomposition to nitric oxide when dissolved. We report incorporation of this functional group into polymeric matrices that can be used for altering the time course of nitric oxide release and/or targeting it to tissues with which the polymers are in physical contact. Structural types prepared include those in which the [N(O)NO]- group is attached to heteroatoms in low molecular weight species that are noncovalently distributed throughout the polymeric matrix, in groupings pendant to the polymer backbone, and in the polymer backbone itself. They range in physical form from films that can be coated onto other surfaces to microspheres, gels, powders, and moldable resins. Chemiluminescence measurements confirm that polymers to which the [N(O)NO]- group is attached can serve as localized sources of nitric oxide, with one prototype providing sustained NO release for 5 weeks in pH 7.4 buffer at 37 degrees C. The latter composition, a cross-linked poly-(ethylenimine) that had been exposed to NO, inhibited the in vitro proliferation of rat aorta smooth muscle cells when added as a powder to the culture medium and showed potent antiplatelet activity when coated on a normally thrombogenic vascular graft situated in an arteriovenous shunt in a baboon's circulatory system. The results suggest that polymers containing the [N(O)NO]- functional group may hold considerable promise for a variety of biomedical applications in which local delivery of NO is desired.