Current Medicinal Chemistry - Volume 19, Issue 21, 2012

The high distribution of CB2 receptors in immune cells suggests their important role in the control of inflammation. Growing evidence offers this receptor as an attractive therapeutic target: CB2 selective agonists are able to modulate inflammation without triggering psychotropic effects. This review will summarize the literature on the implication of CB2 in inflammation and CB2 selective agonists with anti-inflammatory activity.

DNA methyltransferases (DNMTs) are a family of epigenetic enzymes for which inhibition is an attractive strategy for the treatment of cancer and other diseases. In synergy with experimental approaches, computational methods are increasingly being used to identify and optimize the activity of inhibitors of DNMTs as well as to rationalize at the molecular level of the mechanism of established inhibitors. Recently, a crystallographic structure of the methyltransferase domain of human DNMT1 bound to unmethylated DNA was published encouraging the application of structure-based approaches to design and optimize the activity of currently known inhibitors. Herein, we review the progress in the discovery and optimization of inhibitors of DNMTs using computational approaches including homology modeling, docking, pharmacophore modeling, molecular dynamics, and virtual screening.

Camptothecins are still among the most widely prescribed and effective anticancer drugs. Unfortunately, important drawbacks including water insolubility, lactone instability, reversibility of the drug–target interaction, drug resistance and toxicity are responsible for treatment failure and often require suspension of the drug administration itself. In order to overcome such drawbacks, several options in chemical manipulation of natural camptothecin have been explored, and effective compounds have been identified in a novel series of 7- oxyiminomethyl derivatives. Among the compounds of this series, the hydrophilic derivative namitecan (7 (2-aminoethoxy) iminomethyl camptothecin) has been selected for further development. The relevant features of namitecan are: 1) marked cytotoxic potency - likely related to multiple factors, including i) a potent inhibition of topoisomerase I, ii) a persistent stabilization of the cleavable complex, iii) an increased intracellular accumulation, and iv) a peculiar subcellular localization; 2) enhanced lactone stability and favorable pharmacokinetics; 3) remarkable antitumor efficacy in a large panel of human tumor xenografts (including tumor models relatively resistant to topotecan and irinotecan), particularly on squamous cell carcinomas. The clinical development of namitecan is currently ongoing. Namitecan exhibited an acceptable toxicity profile, with neutropenia being the dose-limiting toxic effect, and clinical benefit was appreciable in patients with different tumor types, particularly bladder and endometrium carcinomas. In this article, we review the relevant features of namitecan, with particular reference to its advantages compared with the two analogues (topotecan and irinotecan) approved for clinical use.

Cardio-renal-anemia syndrome is a combination of heart failure, kidney failure, and anemia. Many advanced chronic kidney disease patients have both anemia and chronic heart failure. They have often hyperhomocysteinemia, high dimethylarginine values and low erythropoietin levels. Nephrologists treat advanced chronic kidney disease patients with erythropoiesis stimulating agents to improve anemia, renal and heart disease. Erythropoiesis stimulating agents, though considered essential to improve anemia in chronic kidney disease patients, have shown no significant protective effect on cardiovascular disease when used in large clinical trials targeting normal hemoglobin levels. It is possible that the high amounts of these drugs, given to reach normal hemoglobin values, may have counterbalanced the positive effect on endothelium obtained with low doses. Many studies have shown that erythropoietin improves endothelial function in animals with high dimethylarginine levels, lowering asymmetric dimethylarginine and increasing nitric oxide synthesis. Advanced chronic kidney disease patients have also high homocysteine levels which further reduce endothelial function by increasing asymmetric dimethylarginine. Homocysteine-lowering vitamin B treatment has been associated to a significant reduction of cardiovascular disease in advanced chronic kidney disease patients. Low doses of epoetin and B vitamins may improve cardiovascular morbidity by reducing asymmetric dimethylarginine and by increasing nitric oxide synthase activity. This review analyses the interaction between erythropoietin, dimethylarginine and homocysteine, and their role in cardio-renal-anemia syndrome.

Glaucoma is a chronic progressive optic neuropathy, which can result in visual impairment and blindness. Elevated intraocular pressure (IOP) is currently the only modifiable risk factor. Several recent studies have shown the benefits of IOP reduction in open-angle glaucoma. Therefore, current glaucoma drugs are IOP-lowering substances such as α2-adrenergic agonists, β2-adrenergic antagonists, carbonic anhydrase inhibitors and hypotensive lipids, which are used separately or in combination. In spite of the wide variety of antiglaucoma medicines, all therapies have several undesirable side effects. As a consequence, there are constant research attempts on the discovery of novel ocular hypotensive drugs. In the current paper, we review the latest available patents and literature for the pharmacological treatment of glaucoma, focusing on their molecular targets and/or their chemical characteristics and especially directed to melatoninergic drugs. Melatonin is a hormone secreted into the blood mainly from the pineal gland allowing the entrainment of the circadian rhythms of several biological functions. Melatonin and its analogues potently reduce IOP in rabbits, monkeys and humans. In addition, there are indications of long-term hypotensive effects and a proven neuroprotective role of melatoninergic substances. Furthermore, antidepressant and normalizing circadian rhythm actions of melatonin analogues might be beneficial for glaucoma patients. All the above mentioned facts suggest these agents as proper candidates for the glaucoma treatment. Consequently, the scientific research has given new and significant progress on the development of new, potent and selective melatonin ligands.

There is evidence that Trigonella foenum-graecum L. (fenugreek), a traditional Chinese herb, and its components are beneficial in the prevention and treatment of diabetes and central nervous system disease. The pharmacological activities of trigonelline, a major alkaloid component of fenugreek, have been more thoroughly evaluated than fenugreek’s other components, especially with regard to diabetes and central nervous system disease. Trigonelline has hypoglycemic, hypolipidemic, neuroprotective, antimigraine, sedative, memory-improving, antibacterial, antiviral, and anti-tumor activities, and it has been shown to reduce diabetic auditory neuropathy and platelet aggregation. It acts by affecting β cell regeneration, insulin secretion, activities of enzymes related to glucose metabolism, reactive oxygen species, axonal extension, and neuron excitability. However, further study of trigonelline’s pharmacological activities and exact mechanism is warranted, along with application of this knowledge to its clinical usage. This review aims to give readers a survey of the pharmacological effects of trigonelline, especially in diabetes, diabetic complications and central nervous system disease. In addition, because of its pharmacological value and low toxicity, the reported adverse effects of trigonelline in experimental animal models and humans are briefly reviewed, and the pharmacokinetics of trigonelline are also discussed.

The various physiological actions of the neurohormone melatonin are mediated mainly by two G-protein-coupled MT1 and MT2 receptors. The melatoninergic drugs on the market, ramelteon and agomelatine, as well as the most advanced drug candidates under clinical evaluation, tasimelteon and PD-6735, are high-affinity nonselective MT1 and MT2 agonists. However, exploring the exact physiological role of the MT1 and MT2 melatonin receptors requires subtype selective MT1 and MT2 ligands. This review covers novel melatoninergic agonists and antagonists published since 2010, focusing on high-affinity and subtype selective agents. Additionally, compounds not mentioned in the previous review articles and ligands selective for the MT3 binding site are included.

The emergence of bacterial strains with resistance to currently marketed antibacterial agents has spurred interest in the discovery of new antibacterial agents with novel modes of action. One set of potential novel targets are the family of bacterial aminoacyltRNA synthetases (AaRS). Aminoacyl-tRNA synthetases are the enzymes that catalyze the transfer of amino acids to their cognate tRNA. They play a pivotal role in protein biosynthesis and are necessary for growth and survival of all cells. Consequently, inhibition of these enzymes is an attractive target for antibacterial agents. In this review, we examine the latest developments and structure-activity relationship (SAR) analysis of aminoacyl-tRNA synthetases inhibitors, including methionyl-tRNA synthetase, isoleucyl-tRNA synthetase and phenylalanyl-tRNA synthetase inhibitors. It is expected that increasing knowledge of the SAR of aminoacyl-tRNA synthetase inhibitors will be beneficial to the rational design of new generation of antibiotics.

Diketopiperazines are the smallest cyclic peptides known. 90% of Gram-negative bacteria produce diketopiperazines and they have also been isolated from Gram-positive bacteria, fungi and higher organisms. Biosynthesis of cyclodipeptides can be achieved by dedicated nonribosomal peptide synthetases or by a novel type of synthetases named cyclopeptide synthases. Since the first report in 1924 a large number of bioactive diketopiperazines was discovered spanning activities as antitumor, antiviral, antifungal, antibacterial, antiprion, antihyperglycemic or glycosidase inhibitor agents. As infections are of increasing concern for human health and resistances against existing antibiotics are growing this review focuses on the antimicrobial activities of diketopiperazines. The antibiotic bicyclomycin is a diketopiperazine and structure activity studies revealed the unique nature of this compound which was finally developed for clinical applications. The antimicrobial activities of a number of other diketopiperazines along with structure activity relationships are discussed. Here a special focus is on the activity-toxicity problem of many compounds setting tight limitations to their application as drugs. Not only these classical antimicrobial activities but also proposed action in modulating bacterial communication as a new target to control biofilms will be evaluated. Pathogens organized in biofilms are difficult to eradicate because of the increase of their tolerance for antibiotics for several orders. Diketopiperazines were reported to modulate LuxR-mediated quorum-sensing systems of bacteria, and they are considered to influence cell-cell signaling offering alternative ways of biofilm control by interfering with microbial communication. Concluding the review we will finally discuss the potential of diketopiperazines in the clinic to erase biofilm infections.

Sulfonyl group-containing compounds constitute an important class of therapeutical agents in medicinal chemistry presumably because of the tense chemical structure and functionality of the sulfonyl, which could not only form hydrogen bonding interactions with active site residues of biological targets but also, as incorporated into core ring structure, constrain the side chains and allowed their specific conformations that fit the active sites. This review focuses on sulfonamides and sulfones, which cover more than 40 series and are associated with at least 10 potential pharmaceutical targets in pathways of glucose metabolism and insulin signaling. A large number of such compounds have been reported as pharmaceuticals every year in the last decade. In particular, increasing studies suggest that sulfonamides and sulfones play a key role in the design of pharmaceutical agents with potential application for the treatment of diabetes and its complications. First, they are inhibitors of a variety of enzymes including 11β-hydroxysteroid dehydrogenase type 1, α- glucosidase, carnitine palmitoyltransferase and cytosolic phosphoenolpyruvate carboxykinase, and in turn involved in the regulation of the metabolism of glucose. In addition, they are active as activators of glucokinase and as antagonists of ghrelin receptors. These enzyme and receptors are tightly associated with the regulation of glucose metabolism and the improvement of insulin resistance. Secondly, sulfonamides and sulfones act in the insulin secretion. As agonists, they activate insulin receptor tyrosine kinase and thus increase insulin sensitivity. Moreover, they as inhibitors suppress protein tyrosine phosphatase 1B and dipeptidyl peptidase IV, and thus normalize the insulin signaling pathway. Finally, a number of sulfonamides and sulfones are inhibitors of aldose reductase, which have been linked to diabetic complications.

Cytochrome P450 (CYP450) has widely been implicated for drug-drug interactions (DDI) in the pharmaceutical industry. Inhibition or induction of this enzyme family has led to withdrawal of multiple drugs from the market leading to major time and financial losses for the pharmaceutical industry. CYP450 plays a prevailing role in the biotransformation of a large number of structurally diverse drugs. Few isoenzymes of the CYP enzyme family (CYP3A4, 2D6 and 2C9 family) are mainly involved in metabolism of most of the drugs. To avoid such interactions and potentially minimize DDI, major pharmaceutical organizations prefer to incorporate CYP enzyme screening at an early stage of their discovery program. While this has been a prevalent practice in the pharmaceutical industry lately, there is very limited literature available reviewing the relationship between chemotypes and CYP isoforms. This review will collate literature pertaining to CYP-inhibition modulation through physicochemical parameters and chemical modification and thus bring to focus commonly used trends by medicinal chemists world-wide.

Hydrogen peroxide (H2O2) has entrapped the abundant concern of numerous researchers in the cutting edge of chemistry, biology and medicine since it is thought to be associated with various biological and pathological conditions. Fluorescent probes are the promising tools for the detection and understanding of the physiological roles of H2O2, considering that they are able to provide spatial and temporal information about target biomolecules in living cells. Nevertheless, the existent fluorescent probes have low selectivity and sensitivity on discerning H2O2. This review would like to demonstrate a comprehensive examination on the design, recognition, and performance of state-of-the-art boronate-based fluorogenic switch for the detection of H2O2, a field in which remarkable improvements have been accomplished over the last decade.

The antimicrobial and chemotherapeutic activities of a silver(I) glutamic acid complex with the synergistic concomitant generation of reactive oxygen species (ROS) were investigated here. The ROS generation system employed was via Fenton chemistry. The antimicrobial and chemotherapeutic activities were investigated on Staphylococcus aureus ATCC 43300 and Escherichia coli bacteria, and Vero and MCF-7 tumor cell lines, respectively. Antimicrobial activities were conducted by determining minimum inhibitory concentration (MIC), while chemotherapeutic efficacies were done by serial dilution using standard techniques to determine the half maximal inhibitory concentration (IC50). The antimicrobial and chemotherapeutic results obtained were compared with positive control drugs gentamicin, oxacillin, penicillin, streptomycin and cisplatin, a ubiquitously used platinum-based antitumor drug, and with the silver(I) glutamic acid complex and hydrogen peroxide separately. Based on MIC and IC50 values, it was determined that this synergistic approach was very effective at extremely low concentrations, especially when compared with the other drugs evaluated here. This finding might be of great significance regarding metronomic dosing when this synergistic approach is clinically implemented. Since silver at low concentrations exhibits no toxic, mutagenic and carcinogenic activities, this might offer an alternative approach for the development of safer silver-based antimicrobial and chemotherapeutic drugs, thereby reducing or even eliminating the toxicity associated with current drugs. Accordingly, the present approach might be integrated into the systemic clinical treatment of infectious diseases and cancer.

Recently, selected polyphenols were reported to exert proprotein convertase (PC) inhibitory activities on in vitro cleavage of a fluorogenic peptide substrate and it was concluded that this anti-protease activity might be responsible for the reported anti-cancer properties of these polyphenols. This prompted investigations to identify PC inhibiting polyphenols that could affect IGF-1R-mediated tumorigenesis since pro-IGF-1R is bioactivated by PCs like furin. Initial screening of polyphenols for their impact on in vitro cleavage of fluorogenic peptide substrate Pyr-RTKR-AMC by human furin (hfurin573) indeed revealed varying inhibitory effects. (-)EGCG, chrysin, and quercetin, were subsequently evaluated using uncleaved diphtheria toxin as substrate in vitro. However, none displayed any inhibitory impact on processing. Binding of (-)EGCG to both furin and the diphtheria toxin protein was demonstrated. Subsequently, it was found that for seven polyphenols tested, addition of casein or gamma globulin led to reduction or even annihilation of in vitro Pyr- RTKR-AMC cleavage inhibition. No such effect was seen with the furin inhibitor nona-D-arginine. Western blot studies to investigate possible effects of selected polyphenols on processing in cells of the tumorigenesis-linked proproteins pro-IGF-1R and pro-GPC3 also revealed no inhibitory effects. In conclusion, our results confirm the reported PC inhibitory effects of polyphenols on fluorogenic peptide substrate cleavage in vitro. However, the data show that polyphenolic inhibitory effects on hfurin573-mediated in vitro fluorogenic peptide substrate cleavage cannot be extrapolated to similar effects on processing of genuine proproteins, whether in vitro or in cells. This undermines the anti-protease rationale for the reported polyphenolic anti-cancer properties.