SPECIAL ARTICLE www.jasn.org Frontiers in Nephrology: Targeting Inflammation Using Novel Nitric Oxide Donors Gordon Letts* and Joseph Loscalzo† *NitroMed, Inc., Lexington, Massachusetts; and †Brigham & Women’s Hospital and Harvard Medical School, Boston, Massachusetts ABSTRACT COX-1, an enzyme that produces a fam- Chimeric molecules are single-chemical entities that possess at least two separate ily of prostaglandins that are considered functions. In the design of new chimeric medicines, the two biologic actions are fundamental to maintaining the health often designed to be synergistic and, thereby, complement each other in activat- and integrity of many organs, including ing a specific target, such as a gene, a receptor, or an enzyme. In most chimeric platelets, blood vessels, and the kid- molecules, one functionality is designed to provide a high affinity to a designated ney.21,22 Inhibiting this enzyme and, site, thereby permitting the targeting of the second functionality, which is usually thereby, eliminating prostanoids that nonspecific. This review focuses on the development of two classes of chimeric promote normal homeostasis (beneficial medicines, anti-inflammatory and diuretic chimeric agents, both of which incorpo- prostanoids) results in a “deficient ” or- rate a nitric oxide moiety into the parent pharmacophore. gan whose ability to function is compro- mised. Reported reductions in various J Am Soc Nephrol 18: 2863–2869, 2007. doi: 10.1681/ASN.2007030321 organ functions (e.g., platelet adhesion and aggregation, renal blood flow, endo- scopic ulceration) all provide support for CHIMERIC NITRIC OXIDE ing enzyme inhibitor is both a direct ni- this mechanistic concept.23–26 DONORS trovasodilator and an effective angioten- The advantage of inhibiting selec- sin-converting enzyme inhibitor whose tively COX-2, an enzyme that is mainly 1 The development of novel chimeric ni- inhibitory activity is equivalent to the induced as a result of an inflammatory tric oxide (NO) donors had its origins in parent captopril. This series of studies set stimulus, is that it will not inadvertently 1,2 studies by Loscalzo’s group showing the stage for the development of many block the beneficial prostanoids that are that N-acetylcysteine potentiates the ac- other chimeric NO-donor compounds, produced by COX-1.10,27,28 The induced tivity of nitroglycerin and of authentic two of which are described next in detail. COX-2 enzyme was thought to generate endothelium-derived relaxing factor, excessive amounts of detrimental prosta- likely by generating S-nitroso-N-acetyl- noids at sites of injury, thereby amplify- cysteine. This S-nitrosothiol prolongs CHIMERIC CYCLOOXYGENASE-2 ing the damage and overwhelming local the bioactivity of NO and maintains the INHIBITORS host defense mechanisms. Although this intracellular thiol redox state of the effec- simple concept is generally true, excep- tor cell (platelet or vascular smooth mus- Selective cyclooxygenase-2 (COX-2) in- tions have become apparent as a result of cle cell). Subsequent studies by this hibitors were developed because they the clinical use of selective COX-2 inhib- group showed that S-nitrosothiols are were conceived to offer an improvement itors.29 In particular, prostacyclin, a ben- naturally occurring species in mammals, over existing nonselective nonsteroidal eficial prostanoid that is generated by the with S-nitroso–serum albumin serving anti-inflammatory drugs (NSAID).9–17 as a bioactive plasma reservoir for NO3,4 The existing NSAID are widely known to to which and from which NO is trans- cause adverse effects, such as gastrointes- Published online ahead of print. Publication date ferred via low molecular weight S-nitro- tinal irritation and/or bleeding; in addi- available at www.jasn.org. sothiols by thiol-nitrosothiol exchange.5 tion, their long-term use produces mild Correspondence: Dr. Joseph Loscalzo, Brigham & In a series of studies of the first true chi- hypertension and a detriment in renal Women’s Hospital, 75 Francis Street, Boston, MA 02115. Phone: 617-525-4833; Fax: 617-525-4830; meric NO-donor molecule, S-nitroso- function, among other abnormali- E-mail: [email protected] captopril, Loscalzo’s group6–8 showed ties.18–20 These unwanted actions have Copyright © 2007 by the American Society of that S-nitrosated angiotensin-convert- been shown to be a result of inhibition of Nephrology J Am Soc Nephrol 18: 2863–2869, 2007 ISSN : 1046-6673/1811-2863 2863 SPECIAL ARTICLE www.jasn.org flammatory mediators. For example, if DYSFUNCTIONAL the endothelium has this mutation in ENDOTHELIUM FUNCTIONAL its NOS-2 gene, then with inflamma- ENDOTHELIUM tion and activation of COX-2 in the vessel wall, oxidative inactivation of NO would occur by virtue of its rapid NSAID or COX-2 = PGI2 reaction with superoxide and the sub- PGI2 sequent generation of the cytotoxic Inflammation = NO – NO – OONO O2 peroxynitrite. In this setting, vascular relaxation would decrease and vascular NORMAL BLOOD PRESSURE ELEVATED BLOOD PRESSURE leukocyte adhesion would increase.35 ––Responsive to drugs and Enhanced response to vasoconstrictors This effect would be further enhanced homeostatic signals – Less responsive to drugs if a selective COX-2 inhibitor were Figure 1. How NSAID- or COX-2–induced inhibition of prostanoids at a site of endothelial given and local prostacyclin produc- inflammation can cause a perturbation in endothelial function, leading to an adverse effect on BP. tion also inhibited. In these cases, local homeostatic responses are virtually nonexistent. This concept is illustrated endothelium and whose actions are im- these cases, the levels of endogenous in Figure 1. portant in maintaining vascular integrity NO are bolstered by NOS-2, and a One way to combat this possible sce- and preventing the activation of circulat- heightened adverse oxidant effect may nario and to improve the clinical useful- ing platelets and the adhesion of neutro- be observed in the context of other in- ness of a COX-2 inhibitor is to transform it phils, is synthesized via both COX-1 and into a chimeric molecule that provides COX-2 pathways.11,30,31 Moreover, the NO. The concept of linking two separate reduction of prostacyclin production in functions into such a single molecule is ex- organs, such as the kidney, can lead to emplified in Figures 2 and 3. In this exam- abnormal organ function that is indistin- ple, the single-chemical entity, NMI-1093, guishable from that caused by nonspe- has two biologic functions: One is the po- cific NSAID.32 tent, selective inhibition of COX-2, and the Another enzyme that is induced along other is the ability to generate NO rapidly with COX-2 (and with similar kinetics) (Schroeder JL, Bandarage RR, Bandarage at the site of inflammation is NO syn- UK, Earl R, Gzawa M, Fang X, Garvey DS, thase-2 (NOS-2). The NO that is gener- Gaston RD, Khanapure SP, Stevenson CA, ated by NOS-2 is part of a local host de- and Wey SJ, NitroMed, Burlington, MA, fense response and has complex 2001, unpublished data).36 In Figure 2, the biology.33 The freshly generated NO is des-NO molecule, NMI-1089, is also capable of supplementing the local site shown, to illustrate the enhanced benefits Figure 2. Chemical structures of levels of constitutive NO as the low-flux NMI-1093 and NMI-1089. of the chimeric derivative. endogenous NO is rapidly oxidized and NMI-1093 has a potency and selectiv- eliminated at the site of an inflammatory ity for COX-2 comparable to the clini- insult.34 The NO reacts with superoxide cally approved drugs, such as rofecoxib. anions that are generated by COX-2 or The des-NO analogue (NMI-1089) also other downstream sources that are acti- retains excellent selectivity for COX-2 vated by inflammatory stimuli to form and is, thus, a good agent with which to an intermediate with powerful cytotoxic examine the benefit of the added NO do- actions, peroxynitrite (ONOOϪ), thereby nor functionality that has been incorpo- helping to eliminate the inflammatory rated into its structure (NMI-1093). The stimulus (if a biologic agent) and creating a relative potencies and selectivity of ac- “noninfective” boundary around the site tion are shown in Figure 4. of injury to localize or prevent further ex- The anti-inflammatory properties pansion of the inflammatory event itself. that are inherent in the chimeric COX-2 Figure 3. Mechanism by which a chimeric 14 Hobbs et al. showed that certain molecule with a high affinity for the COX-2 inhibitor are illustrated in Figure 5. This mutations in the NOS-2 gene result in active site is able to generate NO locally. classic animal model is often used to the generation of high fluxes of NO, The NO is formed by the action of nonspe- compare and rank the efficacies of both which can have severely adverse conse- cific esterases on the nitrate moiety of the selective COX-2 inhibitors and nonselec- quences at an inflammatory site. In chimeric molecule. tive NSAID. As shown, it is evident that 2864 Journal of the American Society of Nephrology J Am Soc Nephrol 18: 2863–2869, 2007 www.jasn.org SPECIAL ARTICLE NMI-1093 is a potent anti-inflammatory this anesthetized rat model, a short extra- nificant elevation in BP.32,39 This effect drug with a similar efficacy to that of ro- corporeal vascular loop is created, and a can be demonstrated by measurement fecoxib and celecoxib. The compounds silk thread is placed in the loop for 15 of the enhanced sensitivity to the vaso- have similar duration of action and also min. During the time the thread is in constrictor angiotensin II in animals exhibit similar potencies in a second an- contact with circulating blood, the for- after long-term drug administration at imal model of inflammation, the rat paw eign surface of the thread is the site of dosages of drug that do not directly af- edema model (data not shown; Trocha platelet deposition.