Current Medicinal Chemistry - Volume 18, Issue 10, 2011

Asthma is now recognized as a heterogeneous disease, based on clinical parameters, the type of inflammation, the response to treatment, the rate of exacerbations and, finally, the underlying control and/or severity. Attempts to apply the above diverse characteristics to the clinical presentation of the disease have led to the identification of different phenotypes, with significant overlapping. The field of non invasive techniques has been rapidly developed since the time that the fraction of exhaled nitric oxide (FeNO) was recognized as an easily measured mediator in the exhaled air [1]. At approximately the same time, induced sputum was recognized as a valuable technique for the identification of the inflammatory cellular population as well as for the evaluation of different mediators in sputum supernatants [2]. Exhaled breath condensate (EBC), a totally non invasive technique, gave us the opportunity to sample the airways in an even more easily applicable approach, but the several methodological pitfalls of this method prevent it from being an accurate procedure for the evaluation of airways inflammation [3]. The attempt to connect the whole asthma entity and its numerous phenotypes using those minimally invasive techniques, i.e. FeNO, induced sputum and EBC, involves two major steps: First, these techniques must become more widely accepted and applied and, second, we need data from large multicenter studies that will identify the distinct inflammatory characteristics of specific phenotypes. Every single biomarker obtained by non invasive techniques must fulfill some requirements, in order to be applicable in every day clinical practice: it must be measurable in the field, be measurable in the specific disease, have a standardized methodology, have normal values that clearly discriminate normality from disease, present reproducibility and stability within measurements, be associated with an established inflammatory process and, finally, be applicable as a tool for guided treatment strategy. According to these requirements, it is quite difficult or even impossible for a single biomarker obtained from non invasive techniques to fulfill them. The majority of the numerous studies involving non invasive techniques for the assessment of airways inflammation evaluated the discriminative power of biomarkers in respect to the presence or absence of a specific disease. This approach has certain value, but does not add useful information for clinical practice in an inflammatory disease that presents significant day-to-day variability such as asthma. A more useful approach would be to evaluate a specific biomarker using statistical tools dedicated to test the diagnostic performance of a biomarker. For example, using receiver operating characteristics (ROC) analysis we can define specific cut-off values that may characterize the potential utility of a biomarker as a predictive tool for survival or disease progression or even as a tool for the prediction of other significant outcomes related to treatment response. There is additional need for the validation of such cut-off points in prospective trials involving decisionmaking. The current literature presents only limited data in that direction at the moment. The most promising data to-date are those published for induced sputum, that have used a specific cut-off value for eosinophils as predictors of severe exacerbations in respect to treatment intervention with inhaled steroids [4]. Similar data exist for FeNO in predicting multiple outcomes in asthma, both clinical and/or inflammatory [5]. The majority of the later studies have focused on sputum cellular population, and particularly on eosinophils. In contrast to those two widely evaluated biomarkers, the literature on EBC still does not include any data for the support of the aforementioned requirements. EBC pH is nowadays considered a promising parameter, since its values may discriminate between asthmatics and normal subjects [6] and present an association with eosinophilic inflammation [7], but the absence of robust longitudinal data still limits its application in clinical practice. Recently published data in a prospective study showed that EBC pH can be used to monitor asthma exacerbations, however with no associations with alterations in lung function or FeNO [8]. In this hot topic issue, the three most widespread techniques of non invasive or minimally invasive assessment of airways inflammation are described in details, all the way from the point of technical considerations to the implementation in clinical practice. It is widely accepted that all these techniques have provided clinicians and researchers with tools for the understanding of the underlying pathophysiology of the disease. But is this the main target? Definitely not. What we really need from non invasive techniques is to be implemented in clinical practice and provide useful information for the diagnostic approach, the identification of specific phenotypes, the evaluation of asthma control and the facilitation of decision-making. FeNO represents the only exhaled asthma biomarker that has reached clinical practice today. Despite some methodological issues, FeNO represents a good surrogate biomarker of eosinophilic airways inflammation, can serve as an aid to the diagnosis of asthma, may identify loss or restoration of asthma control as well as certain clinically relevant phenotypes (including an “at risk” phenotype in severe asthma), may predict steroid response and exacerbations, and may provide a possible aid for treatment guidance, especially in patients with difficult asthma [1]. Which is the contribution of EBC in the above requirements? Although promising, EBC is currently used only as a research tool, due to the lack of appropriate standardization and the absence of reference values [9]. Some of the biomarkers obtained by EBC can identify certain phenotypes, but with significant overlapping between measurements. Last but not least, sputum induction may share with FeNO some clinically useful applications mainly related to the detection of non-adherence to corticosteroid therapy, the assessment of the adequacy of inhaled corticosteroid therapy, the long-term management of asthma and the adjustment of oral corticosteroid dose in refractory asthma. Specifically, induced sputum may be used to study the dose-response effect of inhaled corticosteroids and may be useful to establish the relative potency of different corticosteroid formulations and delivery devices. Finally, prospective studies have shown that it is better than clinical assessment in reducing the rate of exacerbations [2], especially the eosinophilic ones [10]. What do we expect from the biomarkers obtained by non invasive methods in asthma? Based on the heterogeneity of the disease, the need for identification of the different disease phenotypes within the range of these syndromes is crucial for the proper management of the individual patient. Based on current knowledge, it is not likely that a single biomarker will suffice for the identification of the underlying pathophysiology and/or the clinically useful phenotyping of asthma. What is definitely needed is the proper combination of biomarkers, even from different techniques, in order to achieve their maximal effectiveness. Clinical assessment and physiologic parameters, such as spirometry, provide highly useful information, but they can not provide objective information in relation to the inflammatory process. The quest for a non invasive inflammometer has been a target for both clinicians and researchers in the past twenty years. Considering that the term inflammation is highly heterogeneous, we should be definitely seeking ways to combine the inflammatory characteristics with clinical features in order to characterize particular phenotypes. This concept may help physicians provide individualized treatment for each patient in the future......

During recent years there has been a growing interest in using non-invasive biomarkers to understand and monitor the airway inflammation in subjects with respiratory tract disorders and mainly asthma and chronic obstructive pulmonary disease (COPD). Sputum induction is generally a well-tolerated and safe procedure and a European Respiratory Society Task Force has published a comprehensive review on sputum methodology. Induced sputum cell count and, to a lesser extent, mediator measurements have been particularly well validated. In asthma, the sputum and the cell culture supernatant can be used for the measurement of a variety of soluble mediators, including eosinophil-derived proteins, nitric oxide (NO) derivatives, cytokines and remodelling-associated proteins. Sputum eosinophilia (> 3%) is a classic feature of asthma although half of the patients seems to be non eosinophilic. Measuring the percentage of sputum eosinophils has proved to be useful in the clinical arena in helping to predict short term response to inhaled corticosteroids (ICS) and tailor the dose of ICS in the severe patients but there is scope for the application of other induced sputum markers potentially useful in clinical practice. The widespread application of induced sputum in asthma across the spectrum of disease severity has given insight into the relationship between airway function and airway inflammation, proposed new disease phenotypes and defined which of these phenotypes respond to current therapy, and perhaps most importantly provided an additional tool to guide the clinical management of asthmatic patients. To date sputum induction is the only non-invasive measure of airway inflammation that has a clearly proven role in asthma management.

Approximately 20 years after the initial report of the measurement of exhaled nitric oxide (NO) in the exhaled air of humans, numerous publications have evaluated the possible applications of the fraction of exhaled NO (FeNO) in patients with asthma. The aim of the present review is to evaluate the technical issues and confounding factors related to FeNO measurements, as well as the role of FeNO in the diagnosis of asthma, the evaluation of asthmatic patients and the guidance of treatment. Several other issues, including the pursuit for “normal” and best personal values, the prediction of clinically relevant asthma outcomes and the identification of asthma phenotypes and future directions are discussed. FeNO represents the only exhaled biomarker that has reached clinical practice even in primary care settings and this review provides a critical view of the possible applications of this biomarker, both for the basic researcher and the clinician.

The need for non-invasive assessment of airway inflammation is imperative, since inflammatory airway diseases, such as asthma and COPD, are characterized by variation in their clinical presentation throughout their course. Exhaled breath condensate (EBC) collection represents a rather appealing method that can be used to conveniently and noninvasively collect a wide range of volatile and non-volatile molecules from the respiratory tract, without affecting airway function or inflammation. Although promising, EBC is currently used only as a research tool, due to the lack of appropriate standardization and the absence of reference values. A large number of mediators of inflammation, oxidative and nitrosative stress, including adenosine, ammonia, hydrogen peroxide, isoprostanes, leukotrienes, prostanoids, nitrogen oxides, peptides and cytokines, have been studied in EBC. This review focuses mainly on the presentation of the above biomarkers in asthma as well as on the effect of various factors on their concentrations. Concentrations of such mediators have been shown to be related to the underlying asthma and its severity and to be modulated by therapeutic interventions. Despite the encouraging positive results up-to-date, the introduction of EBC in everyday clinical practice requires the work-out of some methodological pitfalls, the standardization of EBC collection, and finally the identification of a reliable biomarker which is reproducible, has normal values and provides information for the underlying inflammatory process and the response to treatment. So far none of the parameters studied in EBC fulfils the aforementioned requirements.

The first demonstrations in the early seventies that adenosine had marked effects in the cerebral cortex, which were independent of its role in intermediary metabolism and could be antagonised by methylxanthines, were followed by the observations that other purine derivatives, notably ATP, may also play a critical role in cell function. In 1978 Burnstock first introduced the terms Pl for the nucleoside receptors and P2 for the nucleotide receptors, based on the most fundamental divisions of purine receptors between those for nucleosides such as adenosine and those for nucleotides such as ATP. At present, the P1 (adenosine) receptor family presents 4 subtypes, while the P2 (ATP, ADP and UTP) receptor family has been divided into P2X ionotropic receptors and P2Y metabotropic G proteincoupled receptors (GPCRs). While knowledge on the purinergic receptor pharmacology was increasing, the development of potent and selective ligands for these receptors has been a target of medicinal chemistry research for several decades. In particular, synthesis of 2- substituted adenosines was carried out in many laboratories starting from seventies aimed at finding adenosine derivatives more resistant than the parent nucleoside to rapid uptake into cells, to deamination by adenosine deaminase, and to phosphorylation by adenosine kinase. In the present review the synthesis of alkynyl derivatives of adenine, adenosine, N-alkylcarboxamidoadenosine, and adenine nucleotides, which have been tested on purinergic receptors, will be summarized. Furthermore, the contribution of chemistry, molecular modelling, and pharmacology to the development of structure-activity relationships in this class of purinergic receptor ligands will be outlined.

In this article the design of hybrid molecules that covalently connect two distinct drug entities in one molecule, at least one part being a biologically active natural product will be discussed. In the quest for novel drug entities, the hybrid approach is a promising path to drug molecules that can effectively target multifactorial diseases including neurodegenerative disorders like Alzheimer's and Parkinson's diseases (AD and PD). The hybrid approach can also be used to optimize certain biological properties like affinity and selectivity, but also to gain novel biological activities distinct from the ones of the components. Due to the high potential of natural products to exhibit pronounced biological activities, natural products have been one of the major sources of components in hybrid molecules. This review will cover their applications in developing drugs for neurodegenerative disorders, in the diverse field of anti-cancer agents (which represents the major application for natural products in medicinal chemistry), but also in miscellaneous areas of bioactive compounds including antioxidants, antimalarial drugs and estrogen-related hybrids to reach various therapeutic aims. The unique tasks of hybrid molecule design will be addressed, such as describing suitable ways to chemically connect the drug components, how to use the approach to enhance biological activity with respect to both activity and selectivity and potential drawbacks of the hybrid approach. It will be shown that hybrids can be more than the sum of their components, but in many cases should be considered as pharmacological entities in their own respect.

Atopic asthma results from airway inflammation triggered by an environmental allergen. Symptoms include wheezing, dyspnea and cough, airway narrowing and/or hyperresponsiveness to several inhaled stimuli. Inflammation develops in a two-phase fashion. The first phase after exposure to the allergen consists of degranulation and release of both histamine and other stored preformed inflammatory mediators as well as newly synthesized ones, including cytokines, all of which increase mucus secretion and smooth muscle contraction. The second phase occurs later and lasts longer; it is due to different molecules: several cytokines and chemokines, arachidonic acid derivatives, enzymes such as metalloproteinases and cell adhesion molecules. Cytokines are key players in the chronic inflammation in asthma patients, but details on their role and interactions still remain undetermined. Recent evidence suggests that allergic asthma is a multifaceted condition actively controlled by effector as well as regulatory T cells (Tregs). T helper (Th) 2 cells and Th17 cells increase airway inflammation, while Tregs are anti- inflammatory. Cytokines are involved in the development and activation of all T cell subpopulations. They are also involved directly or indirectly in most approaches to asthma treatment. Several cytokines have been tested as therapeutic targets and some of the currently used therapies like corticosteroids, beta agonists and allergen immunotherapy affect cytokine production. The increased knowledge on cytokine interplay and lymphocyte subsets should generate new therapeutic strategies in the near future.

Quinoline (1-azanaphthalene) is a heterocyclic aromatic nitrogen compound characterized by a double-ring structure that contains a benzene ring fused to pyridine at two adjacent carbon atoms. Quinoline compounds are widely used as “parental” compounds to synthesize molecules with medical benefits, especially with anti-malarial and anti-microbial activities. Certain quinoline-based compounds also show effective anticancer activity. This broad spectrum of biological and biochemical activities has been further facilitated by the synthetic versatility of quinoline, which allows the generation of a large number of structurally diverse derivatives. This includes numerous analogues derived from substitution of the quinoline ring system, and derivatization of quinoline ring structure. Quinoline and its analogs have recently been examined for their modes of function in the inhibition of tyrosine kinases, proteasome, tubulin polymerization and DNA repair. In this review, we have summarized our knowledge on quinoline compounds with respect to their anticancer activities, mechanisms of action, structure-activity relationship (SAR), and selective and specific activity against various cancer drug targets. In particular, we focus our review on in vitro and in vivo anticancer activities of quinoline and its analogs in the context of cancer drug development and refinement.

Drug discovery is costly and time-consuming, but it will become easier and simpler if a drug could be developed from an old one with well-documented investigations associated with pharmacology, pharmacokinetics, toxicology and clinical safety. In terms of hematological malignancies, several successful drugs have been discovered and developed from old ones such as arsenic trioxide for acute promyelocytic leukemia and thalidomide for multiple myeloma. In this review, we discussed the latest advancement in exploring old drugs for the treatment of hematological malignancies.

Cholesterol is essential to the functions of the brain, which contains approximately 20% of the body's stores of this sterol. Most brain cholesterol is found in compacted myelin. The operation of the blood brain barrier (BBB) precludes the uptake of cholesterol from the periphery and consequently this sterol is produced de novo in the brain. In contrast, oxysterols - a class of hydroxylated cholesterol catabolites - traverse the BBB readily and facilitate the elimination of cholesterol from the brain. Oxysterols not only act as a transport form of cholesterol, but serve as endogenous regulators of gene expression in lipid metabolism and behave as ligands to nuclear receptors. Two of the more important brain-derived oxysterols are 24S-hydroxycholesterol and 27-hydroxycholesterol. Aberrant cholesterol metabolism has been implicated in a number of neurological disorders. Since oxysterols are thought to reflect the cerebral cholesterol turnover there has been great interest in the diagnostic and prognostic value of these metabolites in neurodegenerative diseases of the brain. The following article provides an overview of the involvement of oxysterols in Alzheimer's disease, multiple sclerosis and spastic paraplegias.

Synthetic compounds with a tri- and tetra-substituted imidazole scaffold are known as selective inhibitors of the p38 mitogenactivated protein (MAP) kinase responsible for proinflammatory cytokine release. The scope is to review the literature describing their design, synthesis and activity studies. To date a great plethora of crystal structures of p38 in complex with small organic ligands have been published. Cocrystallized ligand information is of particular interest to our review study, i.e. ATP itself, the reference inhibitor SB203580 with its aryl-pyridinyl-imidazoles and related imidazole and pyrimidine-based derivatives. The selective inhibitors bind to the pocket of adenosine 5'-triphoshate (ATP) replacing the latter. The hydrophobic region II, however, is not occupied by the natural binder ATP, but accommodates the pyridine substituents preserving the 4-fluorophenyl ring occupation in pocket I as a prerequisite to gain higher binding selectivity and potency than the reference compound SB203580 (4-[5-(4-fluoro-phenyl)-2-(4-methanesulfinyl-phenyl)-3himidazol- 4-yl]-pyridine). Experimental and computed work is reviewed which evidence that the 2 position of the pyrimidine ring is amenable to the introduction of a side chain and the replacement of pyridine in SB203580 by a pyrimidine ring improves both inhibitory activity and selectivity for p38 over other kinases. All ligands with a pyridyl C2 side chain occupy the hydrophobic pocket II and in some cases a double hydrogen bond is reported between methionine 109 and glycine 110 of the hinge region, following an observed backbone shift. The substituted pyridine ring binds stronger than the two other side chains on the imidazole scaffold.

The development of the coxib family has represented a stimulating approach in the treatment of inflammatory disorders, such as arthritis, and for the management of acute pains, in relation to the well-known traditional Non-Steroidal Anti-inflammatory Drugs (t- NSAIDs). Prompted by the pursuit for new cyclooxygenase-2 (COX-2) inhibitors, endowed with fine tuned selectivity and high potency, in the past years we have identified novel classes of ether, ester and acid molecules characterized by the 1,5-diarylpyrrole scaffold as potentially powerful anti-inflammatory molecules (12-66). All compounds proved to exert an in vitro inhibition profile as good as that shown by reference compounds. Compounds bearing a p-methylsulfonylphenyl substituent at C5 displayed the best issues. In particular, ester derivatives proved to perform the best in vitro profile in terms of selectivity and activity toward COX-2. The cell-based assay data showed that an increase of hindrance at the C3 side chain of compounds could translate to activity enhancement. The human whole blood (HWB) test let to highlight that submitted compounds displayed 5-10 fold higher selectivity for COX-2 vs COX-1 which should translate clinically to an acceptable gastrointestinal safety and mitigate the cardiovascular effects highlighted by highly selective COX-2 inhibitors. Finally, to assess in vivo anti-inflammatory and analgesic activity three different tests (rat paw pressure, rat paw oedema and abdominal constriction) were performed. Results showed good in vivo anti-inflammatory and analgesic activities. The issues gained with these classes of compounds represent, nowadays, a potent stimulus for a further enlargement of the NSAIDs family. In this review we describe the results obtained by our research group on this topic.

There is a high demand for new drugs against malaria, which takes millions of lives annually. The abuse of classical antimalarials from the late 1940's to the early 1980's has bred resistant parasites, which led to the use of more potent drugs that ended up by refueling the resistance cycle. An example is chloroquine, once highly effective but now virtually useless against malaria. Structure-based rational drug design relies on high-resolution target structures to allow for screening of selective ligands/inhibitors. For the past two decades, and especially after the unveiling of the Plasmodium falciparum genome in 2002, enzymes of this lethal malaria parasite species have been increasingly attracting the attention of Medicinal Chemists worldwide as promising drug targets. There is particular emphasis on proteases having key roles on the degradation of host's hemoglobin within the food vacuole of blood-stage parasites, as these depend on such process for their survival. Among such enzymes, Plasmepsins (aspartic proteases) and, especially, Falcipains (cysteine proteases) are highly promising antimalarial drug targets. The present review will focus on the computational approaches made so far towards the unraveling of the structure, function and inhibition of Falcipains that, by virtue of their quite specific features, are excellent targets for highly selective inhibitors.