Design of Selective Neuronal Nitric Oxide Synthase Inhibitors for the Prevention and Treatment of Neurodegenerative Diseases

Abstract

Nitric oxide (NO), which is produced from l-arginine by the nitric oxide synthase (NOS) family of enzymes, is an important second-messenger molecule that regulates several physiological functions. In endothelial cells, it relaxes smooth muscle, which decreases blood pressure. Macrophage cells produce NO as an immune defense system to destroy pathogens and microorganisms. In neuronal cells, NO controls the release of neurotransmitters and is involved in synaptogenesis, synaptic plasticity, memory function, and neuroendocrine secretion. NO is a free radical that is commonly thought to contribute to oxidative damage and molecule and tissue destruction, and thus it is somewhat surprising that it has so many significant beneficial physiological effects. However, the cell is generally protected from NO’s toxic effects, except under certain pathological conditions in which excessive NO is produced. In that case, tissue damage and oxidative stress can result, leading to a wide variety of diseases, including rheumatoid arthritis, Alzheimer’s disease, and Parkinson’s disease, among others. In this Account, we describe research aimed at identifying small molecules that can selectively inhibit only the neuronal isozyme of NOS, nNOS. By targeting only nNOS, we attained the beneficial effects of lowering excess NO in the brain without the detrimental effects of inhibition of the two isozymes found elsewhere in the body (eNOS and iNOS). Initially, in pursuit of this goal, we sought to identify differences in the second sphere of amino acids in the active site of the isozymes. From this study, the first class of dual nNOS-selective inhibitors was identified. The moieties important for selectivity in the best lead compound were determined by structure modification. Enhancement provided highly potent, nNOS-selective dipeptide amides and peptidomimetics, which were active in a rabbit model for fetal neurodegeneration. Crystal structures of these compounds bound to NOS isozymes showed a one-amino-acid difference between nNOS and eNOS in the second sphere of amino acids; this was the difference that we were searching for from the beginning of this project. With the aid of these crystal structures, we developed a new fragment-based de novo design method called “fragment hopping”, which allowed the design of a new class of nonpeptide nNOS-selective inhibitors. These compounds were modified to give low nanomolar, highly dual-selective nNOS inhibitors, which we recently showed are active in a rabbit model for the prevention of neurobehavioral symptoms of cerebral palsy. These compounds could also have general application in other neurodegenerative diseases for which excess NO is responsible.

Rational design of a fluorescent NADPH derivative imaging constitutive nitric-oxide synthases upon two-photon excitation

“…The biological activities of NO are closely linked to the specific NOS isoform involved in its synthesis and deregulation of its biosynthesis leads to various pathologies (5). Data support the notion that inhibition of the inducible and neuronal isoforms iNOS and nNOS have therapeutic utility in the treatment of a variety of diseases, including septic shock, neurodegeneration, inflammation, and cancer (5,6). It was shown that the endothelial isoform eNOS participates in tumor initiation and maintenance, thus its inhibition could be beneficial in this context (7,8).…”

Nitric Oxide Synthase Inhibitors

“…Using this moiety, compound 22 ( Figure 7) and its optical isomer showed to be selective against nNOS, although unable to penetrate the blood-brain-barrier (BBB) in in vivo studies [15,47,48]. Trying to increase the CNS permeability, prodrug design approach was used in primary and secondary amines.…”

On the Electronic Structure ofmer,trans‐[RuCl3(1H‐indazole)2(NO)], a Hypothetical Metabolite of the Antitumor Drug Candidate KP1019: An Experimental and DFT Study

“…[7] The pronounced effect of NAMI-A on angiogenesis was confirmed in the chick allantoic membrane and in the rabbit eye cornea model. [8,9] It should be also noted that NO, which is produced by a number of nitric oxide synthase (NOS) enzymes from larginine in the body, [10] plays a major role as a signaling molecule in biological signal transducing systems, for example, in blood pressure regulation, [11,12] neurotransmission, [13,14] inflammatory response, [15,16] as well as necrosis [17] and apoptosis. [18,19] Nitric oxide is therefore essential in biological systems, but both its excess as well as deficiency leads to pathologies.…”