Current Medicinal Chemistry - Volume 11, Issue 10, 2004

The pathogenesis of numerous cardiovascular, pulmonary, inflammatory, and thromboembolic diseases can be related to arachidonic acid (AA) metabolites. One of these bioactive metabolites of particular importance is thromboxane A2 (TXA2). It is produced by the action of thromboxane synthase on the prostaglandin endoperoxide H2 (PGH2), which results from the enzymatic degradation of AA by the cyclooxygenases. TXA2 is a potent inducer of platelet aggregation, vasoconstriction and bronchoconstriction. It is involved in a series of major pathophysiological states such as asthma, myocardial ischemia, pulmonary hypertension, and thromboembolic disorders. Therefore, TXA2 receptor antagonists, thromboxane synthase inhibitors and drugs combining both properties have been developed by several pharmaceutical companies since the early 1980s. Several compounds have been launched on the market and others are under clinical evaluation. Moreover, the recent literature reported the interest of thromboxane modulators, which combine another pharmacological activity such as, platelet activating factor antagonism, angiotensin II antagonism, or 5-lipoxygenase inhibition. In this review, we will propose a description of the recently described thromboxane modulators of major interest from both a pharmacological and a chemical point of view.

Prostacyclin (PGI2) is a potent endogenous inhibitor of platelet function and possesses a strong vasodilator effect. Furthermore, prostacyclin is currently presented as the physiologic antagonist of thromboxane A2 (TXA2), which exhibits pro-aggregatory and vasoconstrictor properties. So, the balance between PGI2 and TXA2 production is crucial for the cardiovascular system. Indeed, an imbalance in the production or effect of these products is deleterious for the circulatory system and can lead to characterized vascular diseases such as hypertension, stroke, atherosclerosis or myocardial infarction. Although the biological effects of PGI2 are considered to be clinically useful, its use as therapeutic agent is largely limited by both its chemical and metabolic instability. Actually, several prostacyclin agonists have been synthesized and pharmacologically evaluated. Among these, some have been clinically evaluated as therapeutic agents in several vascular diseases. This review focuses on the latest chemical and pharmacological developments in the field of the prostacyclin agonists.

Peptide nucleic acids (PNAs) are recently described DNA mimics, in which the sugar-phosphate backbone is replaced by N-(2-aminoethyl)glycine units. These molecules efficiently hybridize with complementary DNA, forming Watson-Crick double helices. In addition, the interest of PNAs and PNA-based analogs is related to the fact that they are resistant to DNases and proteinases. While applications of PNAs as antisense and antigéne molecules in non-viral gene therapy are well documented, their effects as potential transcription factor decoy (TFD) molecules is not demonstrated. PNA / PNA and PNA / DNA duplex are not suitable for TFD. In fact, PNA / PNA duplex does not recognize transcription factors, while, in the case of PNA / DNA hybrids containing nuclear factor binding sites, the interaction with transcription factors is unstable. By sharp contrast, double stranded molecules based on PNADNA chimeras exhibit strong TFD activity, display enzymatic stability in serum and cellular extracts and can be delivered to target cells after complexation with liposomes and microspheres. The TFD molecules based on PNA-DNA chimeras can be further engineered by addition of short peptides facilitating cell penetration and nuclear localization. Therefore, these engineered molecules could be of great interest for in vivo experiments on non-viral gene therapy of a variety of diseases, including neoplastic and viral diseases, for which the TFD approach has been already demonstrated as a very useful strategy.

Artemisinin, the first and last naturally occurring 1, 2, 4-trioxane originated from Artemisia annua, L. and its derivatives are a potent class of antimalarial drugs. The clinical efficacy of these drugs is characterized by an almost immediate onset and rapid reduction of parasitemia, and it is high in such areas as well where multidrug-resistance is rampant. Furthermore, artemisinin and many of its analog possess not only antiparasitic effect against Plasmodium falciparum, Schistosoma japonicum and Clonorchis sinensi but also immuno-modulation effects, and antitumor activities. This review covers the chemistry of artemisinin including synthesis of acetal-, non acetaltype C-12 analogs, C-11- and C-13 derivatives from artemisitene, ring-contracted derivatives, dimers, and trimers. Modes of biological action of artemisinin - derived analogs are also reviewed. The main objective of this article is to review the literatures of recent progress taken place in chemistry, mode of biological actions of artemisinin, and its derivatives as antimalarial and antitumor agents during the last three years (1999-2001).

Semicarbazide-sensitive amine-oxidase (SSAO) is present in various human tissues and in plasma. Oxidative deamination of short-chain aliphatic amines is catalyzed by this enzyme to afford the corresponding aldehydes, ammonia and hydrogen peroxide. Methylamine and aminoacetone have been recognized to be physiological substrates for SSAO. There are several pathological states where increased serum SSAO activity have been found, such as diabetes mellitus, congestive heart failure, multiple types of cerebral infarction, uraemia, and hepatic cirrhosis. The role of SSAO in pathophysiology of diabetes has been most extensively investigated. The elevated formation of the potentially cytotoxic products of the enzyme may contribute to the endothelial injury of blood vessels, resulting in the early development of severe atherosclerosis; it may also contribute to the pathogenesis of diabetic angiopathy. It is now suggested that SSAO inhibitors may prevent the development of atherosclerosis and diabetic complications as well. Inhibitors can be conveniently subdivided into the main groups of hydrazine derivatives, arylalkylamines, propenyl- and propargylamines, oxazolidinones, and haloalkylamines. Of them, aryl(alkyl)hydrazines, and 3-halo-2-phenylallylamines are generally very strong SSAO inhibitors. Most of these inhibitors of SSAO have been originally developed for other purposes, or they are simple chemical reagents with highly reactive structural element(s); these compounds have not been able to fulfil all criteria of high potency, selectivity, and acceptable toxicity. New potent compounds with selectivity and low toxicity are needed, which may prove useful tools for understanding the roles and function of SSAO, or they may even be valuable substances for treatment of various diseases.

Compelling experimental and epidemiological evidence involves oxygen radicals in carcinogenesis, acting reactive oxygen species both as endogenous genotoxins during cell initiation and as messenger molecules in mitogenesis and in tumor promotion. Moreover, oxidants stimulate neoangiogenesis, which is a prerequisite for tumor growth. However, while several natural as well as synthetic antioxidant compounds appear to be chemopreventive in mutagenicity assays, antioxidant-based treatments for the prevention or cure of cancer have led to non-conclusive if not disappointing results. This is likely due to the fact that oxygen radicals have also a major role in the natural defences against the propagation of cancer cells, i.e. tumor cell apoptosis and immune surveillance, and mediate the beneficial cytotoxic effect of both the chemo-and radio-therapy. In recent years, the mitochondrial antioxidant enzyme, Manganous Superoxide Dismutase (MnSOD), has received a growing attention as a negative modulator of cellular apoptosis and as a survival factor for cancer cells. In fact, while overexpression of this enzyme in cancer cells decreases proliferation and tumor incidence in transgenic models, it is clear that even small amounts of this enzyme are crucial for cell resistance to inflammatory stimuli and anticancer drugs, and prevent oncogene-induced apoptosis triggered by the tumor suppressor protein p53. A previously unexpected oncogenic potential of MnSOD is also suggested by the elevated levels of this enzyme in several classes of human neoplasms, in a fashion which often correlates with the degree of their malignancy. This review focuses on the debated issue of the pro- and / or anti-tumoral effect of MnSOD, with specialemphasis on recent observations suggesting that pharmacological inhibition of MnSOD may represent aneffective strategy to selectively kill cancer cells and to circumvent their resistance to the commonly usedanticancer treatments.

Cyclodepsipeptides comprise a wide variety of cyclic peptides of natural origin and are characterized by the occurrence of at least one ester linkage. The great interest that this class of natural products has elicited in scientific community is explained by their wide range of biological activities, intriguing mechanisms of action and attractive molecular architecture. For example, they display a variety of biological effects, such as immunosuppressant, antibiotic, antifungi, antiinflammatory or antitumoral activities. In addition, many of these cyclic depsipeptides represent useful tools for the research of biological processes involved in cellular regulation. The present review deals with the most interesting aspects of the biology and the chemistry of some of these compounds.

Estrogens are steroid hormones exhibiting a broad range of physiological activities, which are important in the homeostatic regulation of many cellular and biochemical events. Estradiol (E2) is an estrogen which is active in the development of the mammary glands and the uterus, in the maintenance of pregnancy and bone density, in protection from cardiovascular diseases, and in the relief of menopausal symptoms. However, it can also stimulate malignant growths, and hence contribute to the development of estrogen-dependent tumors, such as cancer of the breast and uterus. Phytoestrogens are plant-derived chemicals with estrogen-like activities, which could have a beneficial role in humans against estrogen deficiency. Several studies relate the lower incidence of estrogen deficiency-related disease among women in the Eastern word to a diet rich in phytoestrogens. This compound comprises a variety of structurally diverse chemicals, with flavonoids as their largest group. In the present review we summarize knowledge gained on the relationship between the structure of flavonoids to their ability to mimic estrogen activity, together with the methods adapted to perform these studies. The methods reviewed are qualitative and quantitative measurements of the estrogen-like activities of phytoestrogens, superposition analysis, docking analysis and quantitative structure-activity relationship (QSAR) models. The potential of various new flavonoid derivatives in hormone replacment therapy is discussed.

Polyphenolic compounds are widely distributed in higher plants and are an integral part of the human diet. Recent interest in these substances has been stimulated by their potential health benefits, which are believed to arise mainly from their antioxidant activity. In the past years, the antioxidant activity of flavonoids has been studied in detail. An important but often overlooked group of polyphenols is that of the proanthocyanidins. Therefore, the present review is focused mainly on the antioxidant activity of proanthocyanidins and its relevancy in vivo. The three most important mechanisms of their antioxidant action will be discussed, i.e. free radical scavenging activity, chelation of transition metals, and inhibition of enzymes. In addition, the protective role of proanthocyanidins against lipid peroxidation and peroxynitrite, as well as their antimicrobial properties will be discussed. To study the in vivo relevancy of the proanthocyanidin activities, the knowledge of their pharmacokinetic parameters is crucial. Although bioavailability and metabolism data on polyphenols in general and proanthocyanidins in particular are still largely unavailable, the first reports indicate that at least monomers and smaller oligomeric procyanidins are absorbed. There is also considerable scientific and public interest in the important role that antioxidants may play in health care, e.g. by acting as cancer chemopreventive and antiinflammatory agents and by reducing risk of cardiovascular mortality. Each of these aspects will be discussed, with special attention to the role of proanthocyanidins on apoptosis, gene expression and transcription factors, such as NF-kappa B.