Mini Reviews in Medicinal Chemistry - Volume 13, Issue 1, 2013

In the last decades, no significant paradigm shifts in the psychopharmacology of major depressive disorder (MDD) have occurred. In fact, after the serendipitous discovery of the first antidepressant, the poor understanding of the pathophysiology of the illness has deeply limited the development of novel antidepressant agents. Although the discovery of the selective serotonin reuptake inhibitors and the dual-acting serotonin/norepinephrine reuptake inhibitors allowed to improve the treatment of MDD, there are still important unmet clinical needs, as the long latency of antidepressant action, the presence of relevant side effects and the lack of efficacy. In fact, even though the available antidepressants have consistently improved the prognosis of the disorder, the pharmacological treatment of MDD is far from being satisfactory and the disorder remains one of the major causes of morbidity and disability worldwide. Recently, besides the classical research involving the monoamines, other non-monoaminergic molecular mechanisms have been explored in search of new antidepressants. Amongst them, the investigation of the central neuropeptides, including substance P, corticotropinreleasing factor, neuropeptide Y, vasopressin and oxytocin, galanin and melanin-concentrating hormone, is increasingly attracting the attention of researchers worldwide. A number of novel compounds acting on neuropeptide receptors have been developed and tested in both animals and humans with different results. In this review, we provided a synthetic overview of the main neuropeptides, going through biochemical and molecular aspects up to preclinical and clinical evidence which link these molecules to the presence of MDD.

Biphalin (Tyr-D-Ala-Gly-Phe-NH-NH<-Phe<-Gly<-D-Ala<-Tyr) is an opioid octapeptide with a dimeric structure based on two identical pharmacophore portions, derived from enkephalins, joined “tail to tail” by a hydrazide bridge. This particular structure enhances the antinociceptive activity of the native enkephalins with an unknown mechanism, probably based on a cooperative binding and improved enzymatic stability. Biphalin has excellent binding affinity for μ and δ receptors and it is a highly potent analgesic, as potent as or more than ethorphine. A definitive explanation of the extraordinary in vivo potency shown by this compound, which has pronounced efficacy in pain modulation, is still not available; it has been suggested, however, that the high agonist activity may be related to its binding mode at both μ and δ opioid receptors. Biphalin has significantly higher potency than other analgesics with novel biological profiles; in particular, most recent data show that biphalin is unlikely to produce dependency in chronic use. In the past 20 years, there have been many attempts to modify its structure to obtain products unaffected by the action of enkephalinases, to enhance its antinociceptive activity and to modify the BBB penetration. In addition, structure-activity relationship studies (SAR) were performed in order to understand the elements responsible for biphalin's high activity. The aim of the studies reported in this review was to clarify: i) the role of the hydrazide bridge, ii) the role of residues in position 4, 4' and 3, 3', iii) the consequences of molecular simplifications (truncation, delection), iv) the consequences of cyclization through a disulfide bridge, v) conjugation with PEG and fluorescet residues, and vi) radiolabeling on Tyr1.

During the past 40 years, somatostatin (SST) has been a subject of intensive research. Apart from its substantial role in the neuroendocrine system, due to its dense localization in various areas in the brain, its functions as a neuromodulator have also been thoroughly investigated. Increasing evidence suggests that SST plays a crucial role in memory and cognition. Synthetic forms, biologically active peptide sequences, SST receptor agonists and SST depleting agents have been applied in animal models and in human studies of a number of neuropsychiatric disorders. The translation of experimental data into clinical use could provide novel therapies in neurodegenerative disorders involving cognitive dysfunctions. However in view of the controversial data reported concerning the different roles of the SST receptor subtypes, and the lack of SST analogs that are able to cross diffusion barriers and act selectively at these receptor subtypes, broader clinical use of SST analogs as cognitive enhancers is limited. This review covers the whole range of available experimental results relating to the behavioral effects of SST, and highlights the potential for further investigations.

Histamine H3 receptors are found mostly in central nervous system involved in the regulation of release of various neurotransmitters in brain. They have been implicated in diverse potential therapeutic applications such as sleepwake disorders, attention-deficient hyperactivity disorder, epilepsy, cognitive impairment and obesity. This review is an attempt to elucidate the function of H3 receptors and their role in various CNS disorders. Also, it is aimed at collating the information on efforts of various medicinal chemists to synthesize the H3 receptor agonists and antagonists in single article.

This article presents the potential of PLGA nanoparticles for the oral administration of drugs. Different strategies are used to improve oral absorption of these nanoparticles. These strategies are based on modification of nanoparticle surface properties. They can be achieved either by coating the nanoparticle surface with stabilizing hydrophilic bioadhesive polymers or surfactants, or by incorporating biodegradable copolymers containing a hydrophilic moiety. Some substances such as chitosan, vitamin E, methacrylates, lectins, lecithins, bile salts and RGD molecules are employed for this purpose. Of especial interest are nanoparticles production methods and, in order to improve oral bioavailability, the mechanism of each additive.

Now-a-days, cancer is becoming one of the major problems of public health in the world. Pharmacology treatment is a way to increase quality and long life. Predominantly, in last decade sulfonamide derivatives have been described as potential carbonic anhydrase inhibitors. In the present work, we describe recent advances during the last decade in medicinal chemistry of sulfonamides derivatives with some examples of rational design as anti-tumoral, antibacterial and anti-inflammatory agents. We show strategy design, structure-activity relationship, biological activity and advances of new sulfonamide compounds that have more health significance than some clinically used sulfonamides.

Chalcones (1, 3-Diphenyl-2-propen-1-one) are constituted by a three carbon α, β-unsaturated carbonyl system. The biosynthesis of flavonoids and isoflavonoids is initiated by chalcones. Notable pharmacological activities of chalcones and its derivatives include anti-inflammatory, antifungal, antibacterial, antimalarial, antituberculosis, antitumor, antimicrobial and antiviral effects respectively. Owing to simplicity of the chemical structures and a huge variety of pharmacological actions exhibited, the entities derived from chalcones are subjected to extensive consideration. This review article is an effort to sum up the anti-inflammatory activities of chalcone derived chemical entities. Effect of chalcones on lipid peroxidation, heme oxygenase 1(HO-1), cyclooxygenase (COX), interleukin 5 (IL-5), nitric oxide (NO) and expression of cell adhesion molecules (CAM) is summarized stepwise.

Inflammatory diseases including, different types of rheumatic diseases are the major problems associated with the presently available non-steroidal anti-inflammatory agents. The numbers of plant derived drugs have been screened for their anti-inflammatory and anti-arthritic activity. Drug development in the recent times often relies on use of natural and synthetic drugs, which are promising candidates as therapeutic agents for prevention of diseases and disorders. These drugs possess different chemical structures, with wide range of therapeutic activities. The mechanism of Inflammation mainly involve in development of serious diseases, such as cancer, rheumatoid arthritis, sprains, bronchitis, muscle pains, chronic inflammatory bowel disease, persistent asthma, and liver fibrosis. Development of inflammatory events basically related to various chemicals, such as glucocorticoids (GCs) and mometasone furoate (MF); endogenous factors such as tumor necrosis factor alpha (TNF-α); enzymes and proteins such as copper and zinc-superoxide dismutase (SOD), proinflammatory peptide substance (PPS), RGD peptides, interleukin-4 (IL-4), IL-10, interferon-γ (IFN-γ), COX, LOX, cytokines such as interleukin-1 (IL-1); reactive oxygen species (ROS), nitric oxide (NO) and prostaglandin E2; as well as pro-inflammatory cells such as T and NK cells are well known to have an important role. Based on these correlations, numerous assays were used for inflammatory mechanism research, which was described in this paper.

Chinese Herbal Medicines (CHM) have been used in disease prevention and treatment for centuries in China. A number of anti-breast cancer agents isolated from CHM recently, showed very interesting structures, although some of the mechanism of action is not quite clear. These unique chemical structures could be an important information resource for new anti-breast cancer drugs' design and discovery. This review summarizes these findings on anti-breast cancer agents from CHM.

Snakebite is a serious medical and socio-economic problem affecting the rural and agricultural laborers of tropical and sub-tropical region across the world leading to high morbidity and mortality. In most of the snakebite incidences, victims usually end up with permanent tissue damage and sequelae with high socioeconomic and psychological impacts. Although, mortality has been reduced markedly due to anti-venom regimen, it is associated with several limitations. Snake venom metalloprotease, hyaluronidase and myotoxic phospholipase A2 are the kingpins of tissue necrosis and extracellular matrix degradation. Thus, inhibition of these enzymes is considered to be the rate limiting step in the management of snakebite. Unfortunately, tissue necrosis and extracellular matrix degradation persists even after the administration of anti-venom. At present, inhibitors from snake serum and plasma, several synthetic compounds and their analogs have been demonstrated to possess anti-snake venom activities, but the use of plant metabolites for this purpose has an added advantage of traditional knowledge and will make the treatment cheaper and more accessible to the affected population. Therefore, the clinical and research forums are highly oriented towards plant metabolites and interestingly, certain phytochemicals are implicated as the antibody elicitors against venom toxicity that can be exploited in designing effective anti-venoms. Based on these facts, we have made an effort to enlist plant based secondary metabolites with antiophidian abilities and their mechanism of action against locally acting enzymes/toxins in particular. The review also describes their functional groups responsible for therapeutic beneficial and certainly oblige in designing potent inhibitors against venom toxins.

Menthol, a natural product of the peppermint plant Mentha x piperita (Lamiaceae), is a monoterpene which is widely used as a natural product in cosmetics, a flavoring agent, and as an intermediate in the production of other compounds. Various extracts from peppermint contain menthol as a major active constituent and have been used for centuries as traditional medicines for a number of ailments including infections, insomnia, and irritable bowel syndrome as well as an insect repellent. Menthol's characteristic cooling sensation is due, in part, to the activation of sensory neurons generally termed transient receptor potential (TRP) channels, in particular transient receptor potential melastatin family member 8 (TRPM8) and transient receptor potential subfamily A, member 1 (TRPA1). Menthol acts upon TRPM8 receptors by rapidly increasing intracellular calcium and mobilizing calcium flux through the channels to induce cold response signals at the application site. Aside from its cold-inducing sensation capabilities, menthol exhibits cytotoxic effects in cancer cells, induces reduction in malignant cell growth, and engages in synergistic excitation of GABA receptors and sodium ion channels resulting in analgesia. Notwithstanding its plethora of benefits, menthol's coldsensitivity response mechanism has been shown to inhibit mucosal recognition of nicotine and cigarette toxins common in mentholated cigarette brands thus potentially leading to toxic effects. Menthol may prove a valuable lead structure for the synthesis of drugs that target multiple receptors involved with a number of pharmacological effects.

Silent information regulator 2 (Sir2) enzymes or sirtuins are a family of evolutionarily conserved intracellular protein deacetylases that can catalyze the acetyl group removal from the specific Nε-acetyl-lysine (AcK) side chains on a variety of proteins from all kingdoms of life. Yeast Sir2 was the first sirtuin identified, and so far seven sirtuins (i.e. SIRT1-7) have been found in mammals including humans. The sirtuin-catalyzed deacetylation reaction has captured tremendous interest during the past a few years because of (i) its increasingly demonstrated importance in many crucial biological processes such as gene transcription, metabolism, and aging, and thus its therapeutic potential for metabolic and age-related diseases and cancer, and (ii) its unique deacetylation chemistry. Specifically, the sirtuin-catalyzed AcK side chain deacetylation is not merely an amide hydrolysis reaction, instead is coupled to the nicotinamide cleavage from β- nicotinamide adenine dinucleotide (β-NAD+ or NAD+) with the generation of three enzymatic products, i.e. the deacetylated protein species, nicotinamide, and 2'-O-acetyl-ADP-ribose (2'-O-AADPR). Here the author would like to review the past endeavors on developing mechanism-based sirtuin modulators (inhibitors and activators). The first part of this article will provide an updated mechanistic picture of the sirtuin-catalyzed deacetylation reaction. The second part will be focused on how the mechanistic knowledge has been exploited for the design of effective sirtuin modulators.

Candida albicans can invade humans and may lead to mucosal and skin infections or to deep-seated mycoses of almost all inner organs, especially in immunocompromised patients. In this context, both the host immune status and the ability of C. albicans to modulate the expression of its virulence factors are relevant aspects that drive the candidal susceptibility or resistance; in this last case, culminating in the establishment of successful infection known as candidiasis. C. albicans possesses a potent armamentarium consisting of several virulence molecules that help the fungal cells to escape from the host immune responses. There is no doubt that the secretion of aspartic proteases, designated as Saps, is one of the major virulence attributes produced by C. albicans cells, since these hydrolytic enzymes participate in a wide range of fungal physiological processes as well as in different facets of the fungal-host interactions. For these reasons, Saps clearly hold promise as new potential drug targets. Corroborating this hypothesis, the introduction of anti-human immunodeficiency virus drugs of the aspartic protease inhibitor-type (HIV PIs) have emerged as new agents for the inhibition of Saps. The introduction of HIV PIs has revolutionized the treatment of HIV disease, reducing the opportunistic infections, especially candidiasis. The attenuation of candidal infections in HIV-infected individuals might not solely has not only resulted from improved immunological status, but also as a result of direct inhibition of C. albicans Saps as well as the blockage of several biological processes controlled by these proteolytic enzymes. The present article will discuss the updates on the functional implications of HIV PIs on the development of candidiasis.