Nitric-oxide releasing molecules: a new class of drugs with several major indications.

Nitric oxide (NO) deficiency has been implicated in many pathological and physiological processes within the mammalian body providing a plausible biologic basis for the use of NO replacement therapy in these conditions. Exogenous NO sources may hopefully constitute a powerful way to supplement NO when the body cannot generate enough for normal biological functions. This theory has opened up the possibility of designing new drugs that are capable of delivering NO into tissues and the bloodstream in a sustained and controlled manner. This objective has been reached by grafting an organic nitrate structure onto existing molecules with various spacers such as aliphatic or aromatic chain, with different degree of complexity. This approach has led to the synthesis of several new chemical entities in various pharmacological classes, whose profile seems to challenge the parent drug not only on the basis of new pharmacological properties but also on a better toxicological and safety profile. In this article, general aspects on NO and NO donors are reviewed. Major focus is placed upon recent developments of novel NO donors, NO releasing device(s) as well as innovative improvements to conventional NO donors. Several examples are given in some important therapeutic indications such as cardiovascular diseases (NO-aspirin), pain and inflammation (NO-paracetamol), osteoporosis and urinary incontinence (NO flurbiprofen with aliphatic spacer), Alzheimer s disease (NO-flurbiprofen with anti-oxidant spacer), respiratory disorders (NO-steroids).

Nitric oxide-releasing NSAIDs: a review of their current status.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most widely prescribed drugs worldwide owing to their anti-inflammatory, antipyretic and analgesic properties. However, their use is hampered by gastrointestinal (GI) toxicity, the most common drug-related serious adverse event in industrialised nations. Nitric oxide (NO)-releasing NSAIDs, a recently described class of drugs, are generated by adding a nitroxybutyl or a nitrosothiol moiety to the parent NSAID via a short-chain ester linkage. While efficacy of nitrosothiol-NO-NSAIDs still awaits investigation, nitroxybutyl-NO-NSAIDs have been extensively studied in animals, thus the abbreviation NO-NSAIDs used here refers to the latter group of NSAID derivatives. NO-NSAIDs retain the anti-inflammatory and antipyretic activity of original NSAIDs, although they exhibit markedly reduced gastrointestinal toxicity. NO-NSAIDs are nonselective cyclo-oxygenase (COX) inhibitors, and they also exert COX-independent activities that are NO-dependent. Indeed, NO-NSAIDs suppress production of the cytokines interleukin (IL)-1beta, IL-18 and interferon-gamma by causing the S-nitrosilation/inhibition of caspase-1. In acute and chronic animal models of inflammation, it has been demonstrated that NO-NSAIDs abrogated prostaglandin E2 as well as thromboxane B2 generation. In a murine model, NO-naproxen was approximately 10-fold more potent than naproxen in reducing animal writhing after intraperitoneal injection of acetic acid. Similar data have been obtained in chronic models of pain such as rat adjuvant arthritis. In vivo and in vitro studies suggest that NO-aspirin (acetylsalicylic acid) exerts more potent antithrombotic action than aspirin, probably by coupling the ability to inhibit COX-1 with the anti-adhesive effect of NO. Moreover, in a model of renal injury NO-flurbiprofen not only has been demonstrated to be devoid of nephrotoxicity but also to ameliorate renal function. Finally, in an animal model of chronic neurodegenerative disease, NO-flurbiprofen and NO-aspirin attenuated the brain inflammatory response. The GI toxicity of NO-flurbiprofen and NO-naproxen is currently being investigated in healthy individuals.

Antiproliferative effects of nitrosulindac on human colon adenocarcinoma cell lines.

Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the incidence of colon cancer, but their use is limited by toxicity in the gastrointestinal tract. The coupling of a nitric oxide-releasing moiety to NSAIDs strongly reduces these side effects. We demonstrated that the NO-releasing sulindac (nitrosulindac) has much more potent effects on colon adenocarcinoma cell lines compared to sulindac. Moreover, it could inhibit the growth of cells in soft agar experiments, demonstrating the antineoplastic activity at low concentration of nitrosulindac. However, this reduction in the growth of colon cancer cells seemed to be independent of the classical apoptosis pathway and could be explained by a cytostatic effect. Nitrosulindac caused a light perturbation of the cell cycle parameters not linked to a modification of the levels of p21 or the proliferating cell nuclear antigen. Moreover, neither sulindac, nor nitrosulindac, were able to inhibit the NF-kappa B pathway. These data suggested that nitrosulindac could be a better solution compared to other NSAIDs in the treatment of colon cancer.

Involvement of cyclooxygenase 2 in the protective effect of 17beta-estradiol on hypercholesterolemic rabbit aorta.

The involvement of cyclooxygenase (COX) in the effects of 17beta-estradiol was investigated on hypercholesterolemic rabbits aorta. Acetylsalycilic acid, nimesulide, or SQ22536 was used as respective antagonist of COX-1, COX-2, or adenylate cyclase using aortic rings precontracted with phenylephrine and exposed to cumulative concentrations of acetylcholine (ACh). The relaxation effect of ACh was impaired by hypercholesterolemia and restored by an 8-week 17beta-estradiol treatment. In the control group treated with estrogen, nimesulide, acetylsalycilic acid, or SQ22536 slightly reduced the response to ACh. In hypercholesterolemic rabbits treated with estrogen, nimesulide significantly reduced the maximal relaxation and shifted to the right the relaxation curve of ACh, whereas acetylsalycilic acid did not modify the maximal response to ACh but displaced slightly the concentration-response curve. SQ22536 reduced the relaxant effect of ACh down to the level obtained in the presence of nimesulide. These results suggest that the protective effect of 17beta-estradiol against hypercholesterolemia involved COX-2/adenylate cyclase pathway.

Insulin-like growth factor-I receptor overexpression mediates cellular radioresistance and local breast cancer recurrence after lumpectomy and radiation.

The insulin-like growth factor-I receptor (IGF-IR) plays a critical role in cell growth regulation and transformation. The radiosensitivity of NIH 3T3 fibroblasts overexpressing either wild-type or mutant IGF-IR was examined. High levels of wild-type IGF-IR conferred radioresistance, and mutational analysis revealed that this effect correlated with the transforming capacity but not the mitogenic activity of the receptor. The radioresistant phenotype was reversed when the cells were incubated with antisense oligonucleotides targeted to IGF-IR mRNA, demonstrating that IGF-IR directly influences radioresistance. The clinical significance of these findings was examined in an immunohistochemical analysis of primary breast tumors, revealing that high levels of IGF-IR in tumor samples were highly correlated with ipsilateral breast tumor recurrence (IBTR) following lumpectomy and radiation therapy (P = 0.001). Subgroup analysis revealed that, for early breast tumor relapses (within 4 years of initial breast tumor diagnosis), elevated levels of IGF-IR were strongly associated with IBTR (P = 0.004) but IGF-IR expression was not prognostic for IBTR from breast cancer patients with late relapses (P was not significant). These studies provide evidence for the influence of IGF-IR on cellular radioresistance and response to therapy and raise the possibility that the radiocurability of selected tumors may be improved by pharmaceutical strategies directed toward the IGF-IR.

Melanin-concentrating hormone binding sites in human SVK14 keratinocytes.

Melanin concentrating hormone (MCH) is a cyclic peptide which regulates a broad array of functions in the mammalian brain and it may act as a paracrine factor in peripheral organs. In these studies a radiolabeled MCH derivative, the [125I]-[Phe13, Tyr19]-MCH, was synthesized and used as a tracer to perform binding experiments. A number of human or rodent cell lines displayed specific binding with [125I]-[Phe13, Tyr19]-MCH, the highest binding capacity being observed with human SVK14 keratinocytes. Saturation binding analysis with SVK14 cells indicated about 10,000 MCH binding sites per cell and a Kd of 0.7 nM for [125I]-[Phe13, Tyr19]-MCH. Surprisingly, the iodinated [Phe13, Tyr19]-MCH displayed about 10-fold higher affinity (Ki approximately 3.0 nM) for the putative MCH receptor than the noniodinated form (Ki approximately 25-30 nM). Competition binding analyses comparing various MCH-related peptides revealed a similar low binding potency for all these peptides (Ki approximately 65-160 nM). Strikingly, rat ANP and rat/human CNP but not rat BNP displaced [125I]-[Phe13, Tyr15]-MCH with Ki approximately 210-365 nM and may be due to topological similarities instead of partial sequence identities between MCH and some of the natriuretic peptides. However, other peptides such as CRF, alpha MSH, Arg-vasopressin, and MGOP-peptide I did not compete with the radioligand. Finally, the molecular mass of the MCH binding sites on SVK14 cells was estimated to be 47 kDa by crosslinking and SDS-PAGE experiments. Taken together, our data revealed the widespread expression of MCH binding sites on mammalian cells, particularly on skin carcinoma cells. However, the low affinity of these sites for the native MCH and MCH-related peptides as well as competitivity with ANP and CNP indicates that further biochemical and functional characterizations are needed to validate them as genuine physiological MCH receptors.

Intracellular transactivation of the insulin-like growth factor I receptor by an epidermal growth factor receptor.

Growth factor receptors may be transactivated not only by homologous receptors, but also by heterologous receptors. We have investigated this possibility, using for this purpose R-/EGFR cells, which are mouse embryo cells devoid of IGF-I receptors, but overexpressing the EGF receptor. At variance with mouse embryo cells with a wild-type number of IGF-I receptors and overexpressing the EGF receptor, R-/EGFR cells cannot grow in EGF only, nor can they form colonies in soft agar. However, if a wild type human IGF-I receptor is stably transfected into R-/EGFR cells, growth in EGF and colony formation in soft agar are restored. To determine a possible interaction between the two receptors, we transfected into R-/EGFR cells a number of IGF-I receptor mutants with different impaired functions. The only IGF-I receptor that cannot reverse the growth phenotype of R-/EGFR cells is a receptor with a point mutation at the ATP-binding site. All other mutant receptors, even when incapable of responding to IGF-I with a mitogenic signal, made R-/EGFR cells fully capable of responding with growth to EGF stimulation. IGF-I receptor mutants that are mitogenic but not transforming made R-/EGFR cells grow in EGF only, but were incapable of inducing the transformed phenotype. The mutant IGF-I receptors are activated (tyrosyl phosphorylation of IRS-I) in response to EGF. These experiments indicate that certain IGF-I receptor mutants with loss of function can be reactivated intracellularly by an overexpressed EGF receptor and confirm that the C-terminus of the IGF-IR is required for its transforming activity.

[Pharmacological approach of histamine H3 receptors: use of arterial and bronchiolar perfusion technique]. / Approche pharmacologique des récepteurs H3-histaminiques: utilisation d'une technique de perfusion artérielle et bronchiolaire.

The actions of histamine were believed to be mediated by H1 and H2 receptors, until the discovery of a novel class named H3 in the central nervous system. Initially identified as presynaptic autoreceptors, now, evidence has been obtained drawing that H3 receptors are also located on non histaminergic neurons in the brain and in peripheral organs. In the present study, H3 responses are studied on arterial and bronchiolar segments perfused at constant rate. In the rabbit middle cerebral artery (MCA), the endothelium-dependent relaxation to (R)-alpha-methylhistamine (an agonist H3) was competitively antagonized by thioperamide (an H3 antagonist). This relaxation is endothelium-dependent, involving both a prostanoid, probably prostacyclin, and an endothelium-derived relaxing factor: the nitric oxide. In guinea-pig perfused bronchioles (R)-alpha-methylhistamine induces an epithelium dependent relaxation via the release of metabolite(s) of arachidonic acid. Theses results indicate that H3 sites could exist in the rabbit cerebral arteries and in the guinea-pig bronchiole. Furthermore, the vasorelaxant and the bronchorelaxant effects of (R)-alpha-methylhistamine suggest that H3 agonists may constitute a novel approach for the treatment of diseases as asthma, for example.

Overexpression of insulin receptor substrate 1 (IRS-1) in the human breast cancer cell line MCF-7 induces loss of estrogen requirements for growth and transformation.

The synergistic action of estrogens and insulin-like growth factors (IGFs) promotes the growth of many human breast cancer cell lines. This synergistic effect involves estrogen-dependent induction of the IGF system, i.e., estrogens augment the number of IGF-I receptors, stimulate the secretion of IGF-II, and promote the synthesis of certain IGF-binding proteins. On the other hand, the sustained activation of the IGF-I receptor (IGF-IR) by the overexpression of IGF-II has been found to contribute to the development of the estrogen-independent phenotype in breast cancer cells. In this study, we have investigated whether the amplification of the IGF-IR intracellular signaling in MCF-7 cells can abolish or reduce estrogen requirements for growth and transformation. To this end we developed several MCF-7 clones that overexpressed insulin receptor substrate 1 (IRS-1), one of the principal substrates of the IGF-IR. We report here that in MCF-7 cells overexpressing IRS-1, estrogen requirements for growth in monolayer culture as well as in soft agar were reduced. The decreased estrogen requirements depended on the level of the overexpressed IRS-1 protein, and in cells which contained several-fold more functional IRS-1 than the parental cells, we observed total loss of estrogen dependence for growth. In addition, the importance of IRS-1 in proliferation of MCF-7 cells has been confirmed through the use of antisense strategies.

Mutant IGF-I receptors as dominant negatives for growth and transformation.

The insulin-like growth factor I receptor (IGF-IR) plays a crucial role in cell growth, transformation and protection from apoptosis. We have transfected several mutant IGF-IRs into C6 rat glioblastoma cells, in order to determine whether they can act as dominant negatives. We find that some of them can act as dominant negatives in growth assays (monolayer or soft agar), but that none of those examined can induce apoptosis in C6 cells.

Different effects on mitogenesis and transformation of a mutation at tyrosine 1251 of the insulin-like growth factor I receptor.

The wild type insulin-like growth factor I (IGF-I) receptor has both mitogenic and transforming activities. We have examined the effect of point mutations at tyrosine residues 1250 and 1251 on these two properties of the receptor. For this purpose, we stably transfected plasmids expressing mutant and wild type receptors into R- cells, which are 3T3-like cells, derived from mouse embryos with a targeted disruption of the IGF-I receptor genes, and therefore devoid of endogenous IGF-I receptors. A tyrosine to phenylalanine mutation of either the 1250 or 1251 residue, or both, has no effect on the ability of the receptor to transmit a mitogenic signal. However, the tyrosine 1251 mutant receptor and the double mutant have lost the ability to transform R- cells (colony formation in soft agar), even when the receptors are expressed at very high levels, while the Y1250F mutant is fully transforming. These experiments show that the 1251 tyrosine residue is required for the transforming activity of the IGF-I receptor.

Correlation between apoptosis, tumorigenesis, and levels of insulin-like growth factor I receptors.

We have investigated whether there is a quantitative relationship between the insulin-like growth factor I receptor (IGF-IR), the extent of apoptosis in vivo, and tumorigenesis. C6 rat glioblastoma cells were treated with increasing concentrations of antisense oligodeoxynucleotides to the IGF-IR RNA. The extent of apoptosis in vivo is correlated to the decrease in IGF-IR levels and, in turn, tumorigenesis in nude mice is correlated to the fraction of surviving cells. In syngeneic rats, a host response leads to complete inhibition of tumorigenesis. These findings establish, for the first time on a quantitative basis, the relationship between IGF-IR levels and the extent of apoptosis, as well as the relationship between the initial apoptotic event and the time of appearance of transplantable tumors.

NG-nitro-L-arginine methyl ester inhibits the effect of an H3-histaminergic receptor agonist on NANC contraction in guinea-pig perfused bronchioles.

A role for nitric oxide in the H3-histaminergic agonist-induced inhibition of the non-adrenergic, non-cholinergic (NANC) contraction has been studied in guinea-pig perfused bronchioles. (R)-alpha-Methylhistamine ((R)-alpha-MeHA), an agonist for H3 receptors, inhibited the NANC contraction induced by electrical field stimulation. NG-Nitro-L-arginine methyl ester (L-NAME) (50 microM), an inhibitor of nitric oxide synthesis, blocked the effect of (R)-alpha-MeHA. The effect of L-NAME was reversed by L-arginine (50 microM). L-NAME, L-arginine or (R)-alpha-MeHA were without effect on exogenous substance P- or neurokinin A-induced contractile responses of the perfused bronchioles. These results show that an H3-agonist inhibited the release of neurotransmitters in NANC nerve endings of guinea-pig perfused bronchioles presumably by production of nitric oxide.

Effect of an histaminergic H3 agonist on the non-adrenergic non-cholinergic contraction in guinea-pig perfused bronchioles.

From the bronchioles of guinea-pigs, preparations were isolated for registration of perfused pressure on electrical field stimulation (EFS) and by application of drugs. The perfused bronchioles contracted when EFS was applied in the presence of atropine and phentolamine suggesting a non-adrenergic non-cholinergic (NANC) response. (R)-alpha-Methylhistamine (methylhistamine), a selective H3 agonist, reduced the NANC bronchoconstrictor response in a concentration-dependent manner. beta-Adrenoceptors, muscarinic and histamine (H1 and H2 receptor) antagonists, epithelial removal and cyclooxygenase inhibition had no effect on this inhibitory action of methylhistamine whereas the H3 antagonist, thioperamide, reduced the inhibitory effect of methylhistamine with a Ki value of 2.98 x 10(-9) M. Methylhistamine had no effect on the concentration-dependent contraction induced by exogenous substance P and neurokinin A, demonstrating that an H3 receptor might inhibit the release of transmitter from NANC nerves on guinea-pig perfused bronchioles in-vitro.

Do perfused small caliber airways of guinea-pig release an epithelium-dependent relaxing factor?

The influence of epithelium removal on the effects of contractile substances on airway responsiveness was investigated on the guinea-pig perfused bronchioles. A gentle rubbing of the luminal surface with a pipe cleaner significantly shifted to the left the concentration-response curves evoked by histamine (3 x 10(-12)-10(-4) M) and acetylcholine (10(-9)-10(-3) M) and decreased the relaxation response to fenoterol (10(-12)-2 x 10(-5) M). In contrast, removal of epithelium did not alter the responses to K+ (4.7 x 10(-3)-1.2 x 10(-1) M), theophylline (10(-8)-10(-2) M), sodium nitroprusside (4 x 10(-10)-4 x 10(-5) M) or papaverine (10(-4) M). In intact preparations treated with indomethacin (10(-5) M), histamine and acetylcholine induced contractions similar to that produced by rubbed tissues whereas relaxation induced by fenoterol was not modified. 10(-5) M tranylcypromine (inhibitor of prostacyclin synthesis) or 10(-6) M L-NAME (NG Nitro-L-Arginine Methyl Ester, a nitric oxide synthesis inhibitor) did not alter any concentration-response curves. Whereas prostaglandin E2 had no effect, prostaglandin E1 (10(-12)-10(-5) M) induced concentration-dependent relaxation, indicating that this prostanoid could be an epithelium-derived relaxing factor. These results suggest that epithelium of small caliber airways could release a cyclooxygenase product, namely a prostanoid, involved in the epithelium-dependent modulation in response to contractile drugs.

Bronchodilatation of guinea-pig perfused bronchioles induced by the H3-receptor for histamine: role of epithelium.

1. The influence of epithelium on the effects of H3-histamine receptor agonist (R)alpha-methylhistamine [(R)alpha-MeHist] on airways was investigated on the guinea-pig perfused bronchioles. 2. In preparations under resting tone, removal of the bronchiolar epithelium or treatment with the cyclo-oxygenase inhibitor indomethacin (10(-5) M) increased the constriction induced by histamine and acetylcholine in a concentration-dependent manner without an alteration of the K(+)-induced contraction. 3. In this preparation (R)alpha-MeHist induced a concentration-dependent bronchodilatation which was antagonized in a competitive manner by thioperamide (an H3-antagonist) with a pA2 value of 8.6. 4. This bronchodilatation was reversed to a low concentration-dependent constriction after either removal of the epithelium or treatment with indomethacin (10(-5) M) but was unaffected by both 10(-5) M tranylcypromine (an inhibitor of PGI2 synthesis) and 5 x 10(-5) M NG-nitro-L-arginine methyl ester (an inhibitor of NO synthesis). 5. It is suggested that, in guinea-pig perfused bronchioles (R)alpha-MeHist induces an epithelium-dependent relaxation via the release of metabolite(s) of arachidonic acid.

Bronchodilator action of an agonist for histamine H3-receptors in guinea pig perfused bronchioles and lung parenchymal strips.

Isolated guinea pig perfused bronchioles and lung parenchymal strips were examined as an in vitro model for assessment of the direct effect of pharmacologic agents on the airway smooth muscle. The experiments were performed with a perfusion technique in bronchioles, the input pressure being measured as an index of the state of dilation, while changes in tension of the lung parenchymal strips were measured with an isometric force transducer. In both preparations, histamine and acetylcholine elicited dose-related contractile responses whereas fenoterol induced a concentration-dependent relaxation. After the 3 agonists' activities were compared in these 2 preparations, we tested the intrinsic effects of a specific H3 agonist, (R) alpha-methylhistamine ([R] alpha-MeHA). Statistical analysis was by Student's t test on the Emax (expressed as a percentage of 10(-4) M papaverine relaxation), EC50, and slopes of regression lines calculated from the concentration-response curves plotted for (R) alpha-MeHA alone or in presence of antagonists. Our results showed that (R) alpha-MeHA induced a concentration-dependent relaxation of perfused bronchioles and lung parenchymal strips competitively inhibited by 10(-7) M thioperamide (H3-antagonist), whereas 10(-5) M cimetidine (H2-antagonist) failed to prevent this effect. These results suggest the presence of H3-histaminergic dilatory receptors in the guinea pig airway.