Current Medicinal Chemistry - Volume 19, Issue 34, 2012

The calcium ion is quite possibly the single most pervasive signaling molecule used by living organisms for the purpose of communicating internal and external states. It differs from other messengers in that it is neither created nor destroyed, but just moved around inside and outside the cell via transporters, pumps and channels to alter its concentration in specific cellular locations. These changes in free [Ca2+] are then detected by a wide array of Ca2+-binding effector proteins whose affinities are appropriately tuned to respond to a particular type of [Ca2+] change. This deceptively simple paradigm dominates the function of many cell types, for example in driving contraction of muscle, action potential generation in nerves, fluid, hormone, and enzyme secretion in secretory cells, and certain immune responses. However, the Ca2+ signal does not work in strict isolation, but rather is fine-tuned by many other signals, not the least of which is the other major second messenger, cyclic AMP (cAMP). Conversely, the cAMP pathway is subject to modification by the calcium signal and its various effectors at many different levels. These two fundamental second messengers, used throughout eukaryotes and even prokaryotes, are thus inextricably intertwined. The purpose of the present article is to provide an update on some of the recently described forms of reciprocal regulation between Ca2+ and cAMP signaling circuits, with emphasis on interactions that take place in localized domains of the cell.

The secretion of fluid, electrolytes, and protein by exocrine gland acinar cells is a vectorial process that requires the coordinated regulation of multiple channel and transporter proteins, signaling components, as well as mechanisms involved in vesicular fusion and water transport. Most critical in this is the regulation of cytosolic free [Ca2+] ([Ca2+]i) in response to neurotransmitter stimulation. Control of [Ca2+]i increase in specific regions of the cell is the main determinant of fluid and electrolyte secretion in salivary gland acinar cells as it regulates several major ion flux mechanisms as well as the water channel that are required for this process. Polarized [Ca2+]i signals are also essential for protein secretion in pancreatic acinar cells. Thus, the mechanisms that generate and modulate these compartmentalized [Ca2+]i signals are central to the regulation of exocrine secretion. These mechanisms include membrane receptors for neurotransmitters, intracellular Ca2+ release channels, Ca2+ entry channels, as well Ca2+ as pumps and mitochondria. The spatial arrangement of proteins involved in Ca2+ signaling is of primary significance in the generation of specific compartmentalized [Ca2+]i signals. Within these domains, both local and global [Ca2+]i changes are tightly controlled. Control of secretion is also dependent on the targeting of ion channels and transporters to specific domains in the cell where their regulation by [Ca2+]i signals is facilitated. Together, the polarized localization of Ca2+ signaling and secretory components drive vectorial secretion of fluid, electrolytes, and proteins in the exocrine salivary glands and pancreas. This review will discuss recent findings which have led to resolution of the molecular components underlying the spatio-temporal control of [Ca2+]i signals in exocrine gland cells and their role in secretion.

The control of cytosolic calcium is a major determinant not only of cardiac function, but also of the capability of myocardial tissue to survive damage. Increase of diastolic calcium leads rapidly to cell injury, and may be induced by a wide range of causes. In this review we describe the major points of calcium control in cardiac myocytes, mainly in mammalian ventricle, focusing on mechanisms of intracellular calcium influx during excitation, voltage gated channels of the sarcolemma and ryanodine receptors of the sarcoplasmic reticulum (SR), and efflux during relaxation, principally the sodium/calcium exchanger in membrane and the SR calcium complex. Mitochondria also depend on calcium concentration while also participating in its control. Moreover, we will outline receptor check points and their roles in physiology and pathology. We will focus on some new aspects of potential protective mechanisms that have been recently described and that involve peptide ligands and that in the case of the Neuregulin1beta/ErbB pathway are already reaching the clinical trial relevance.

Migration of neurons and neuronal precursors from the site of origin to their final location is a key process in the development of the nervous system and in the correct organization of neuronal structures and circuits. Different modes of migration (mainly radial and tangential) have been described in the last 40 years; for these, as for motility processes involving other cellular types, calcium signaling plays a key role, with influx from the extracellular medium representing the main mechanism, and a more delimited but specific role played by release from intracellular stores. Deciphering the involvement of the different calcium influx pathways has been a major task for cellular neurobiologists, and the availability - or lack – of reliable and selective pharmacological tools has represented the main limiting factor. This review addresses the strategies employed to investigate the role of voltage-dependent calcium channels and of neurotransmitter activated channels, either calcium permeable or not, that directly or indirectly can elicit cytosolic calcium increases; in addition, reference to recent findings on the involvement of other families of calcium permeable channels (such as the transient receptor potential superfamily) is presented. Finally, a brief description of the present - and limited - knowledge of the perturbations of calcium signaling involved in neuronal migration pathologies is provided.

Endothelial progenitor cells (EPCs) have recently been employed in cell-based therapy (CBT) to promote neovascularization and regeneration of ischemic organs, such as heart and limbs. Furthermore, EPCs may be recruited from bone marrow by growing tumors to drive the angiogenic switch through physical engrafting into the lumen of nascent vessels or paracrine release of pro-angiogenic factors. CBT is hampered by the paucity of EPCs harvested from peripheral blood and suffered from several pitfalls, including the differentiation outcome of transplanted cells and low percentage of engrafted cells. Therefore, CBT will benefit from a better understanding of the signal transduction pathway(s) which govern(s) EPC homing, proliferation and incorporation into injured tissues. At the same time, this information might outline alternative molecular targets to combat tumoral neovascularization. We have recently found that storeoperated Ca2+ entry, a Ca2+-permeable membrane pathway that is activated upon depletion of the inositol-1,4,5-trisphosphate-sensitive Ca2+ pool, is recruited by vascular endothelial growth factor to support proliferation and tubulogenesis in human circulating endothelial colony forming cells (ECFCs). ECFCs are a subgroup of EPCs that circulate in the peripheral blood of adult individuals and are able to proliferate and differentiate into endothelial cells and form capillary networks in vitro and contribute to neovessel formation in vivo. The present review will discuss the relevance of SOCE to ECFC-based cell therapy and will address the pharmacological inhibition of storedependent Ca2+ channels as a promising target for anti-angiogenic treatments.

Sixty years after its introduction, 1,5-bis(4-amidinophenoxy)pentane (Pentamidine) is still one of the most used drugs for the treatment of the first stage of Human African trypanosomiasis and other neglected diseases such as malaria and leishmaniasis. These protozoan infections are prevalent in the poorest world areas such as sub-saharian and developing countries, however the increasing immigration from these countries to the richest part of the world and the overlap of HIV with parasitic infections result in a growing number of cases in developed nations. A great effort has been made to develop new generations of diamidines for the treatment of these infections transmitted by insects. This review summarises the synthesis and evaluation of pentamidine analogues reported in the last years in the effort to find new drugs with better pharmaceutical activity, higher lipophilicity and lower citotoxycicty.

Visceral obesity is characterized by increased risk of cardiovascular disease as well as higher incidence of malignancies, including colorectal cancer (CRC), although the mechanisms linking excess adiposity with cancer are only partly characterized. Visceral obesity is currently acknowledged as a chronic inflammatory disorder and a growing body of evidence demonstrates the interconnections between obesity-related secretion pattern of adipo/cytokines and CRC. Specific molecules derived from the visceral adipose tissue (VAT), including adiponectin, leptin and resistin, are able to establish a positive feedback loop, thus increasing the proinflammatory and insulin resistant state and promoting tumorigenesis. Interestingly, these molecules have emerged as novel prognostic factors and therapeutic targets. This review will focus on current molecular and clinical evidence linking VAT-related inflammation to CRC initiation and progression, and summarize the role of dietary factors and lifestyle interventions aimed at promoting weight control and physical activity on CRC prevention and prognosis.

Adrenocortical carcinoma (ACC) is a rare but aggressive malignancy with a poor prognosis. Treatment options for advanced ACC are limited. Indeed, radical tumor resection can lead to local or metastatic recurrence, and mitotane (Lysodren®), the only recognized adrenolytic drug, offers modest response rates, notably due to some of its physico-chemical and pharmacological properties (i.e. hydrophobicity, low bioavailability). Meantime, high cumulative doses of Lysodren® usually cause systemic toxicities. To reduce adverse health effects, the search of safe and efficient mitotane nano-formulations as well as the full characterization and testing of its enantiomers can represent valuable therapeutic options. Interestingly, recent investigations showed that solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) could considerably improve the efficacy of mitotane (i.e. enhanced solubility and bioavailability, progressive release of the loaded drug into blood and targeted tissues) as well as its safety (i.e. lower toxicity, higher biocompatibility). These two nano-carriers for mitotane delivery and targeting are of particular interest over other polymeric particles (i.e. low-cost, efficient and simple scaling to an industrial production level following green methods). Besides, emerging studies suggested that the S-(-)- mitotane is more potent than the R-(+)-mitotane for ACC treatment. Therefore, the production of pure and active S-(-)-mitotane might offer synergic or additive benefits for ACC patients when combined to solid lipid-based nanocarriers. In this review, we first provide an updated overview of the ACC disease before emphasizing on the promising mitotane drug nano-systems, as well as on the separation, purification and production of single mitotane enantiomer using state-of-art chromatographic-based methods.

Cigarette smoking is one of the major risk factors for COPD and COPD severity. In turn COPD is a major independent risk factor for lung cancer. Genome-wide association (GWA) studies both in lung cancer and COPD highlighted the same variants (SNPs) on chromosome 15q25 marking the gene cluster CHRNA3-CHRNB4-CHRNA5 for these smoking related diseases, showing a stimulating connection between this common genetic region and smoking behavior and smoking related illnesses. Different authors identified two candidate regions associated with age at smoking initiation in patients with COPD. The nicotinic acetylcholine receptor polymorphism (rs1051730) on chromosome 15q25 is associated with major tobacco-related diseases in the general population with additional increased risk of COPD as well as lung cancer. Moreover variants on the gene cluster CHRNA3-CHRNB4-CHRNA5 are associated with nicotine addiction antismoking therapy and antismoking therapy side-effects. These findings not only support the notion that variants can influence any therapy for smoking cessation, but offer rational bases to develop new drugs and new therapeutic strategies. Scope of Proposed Topic (50 words): Genome-wide association (GWA) studies both in lung cancer and COPD highlighted the same variants (SNPs) on the gene cluster CHRNA3-CHRNB4-CHRNA5. These data not only support the notion that variants can influence any therapy for smoking cessation, but offer rational bases to develop new drugs and new therapeutic strategies.

Four different classes of HDACs have been identified in humans so far. Classes I, II and IV are zinc-dependent amidohydrolases, while III is a family of phylogenetically conserved NAD-dependent protein deacetylases/ADP-ribosyltransferase with a welldefined role in modifying chromatin conformation and altering the accessibility of the damaged sites of DNA for repair enzymes. Sirtuins are histone deacetylases (HDACs) of class III that cleave off acetyl groups from acetyl-lysine residues in histones and non-histone proteins. As sirtuins are involved in many physiological and pathological processes, their activity has been associated with different human diseases, including cancer. Especially two sirtuin members, SIRT1 and SIRT2, have been found to antagonize p53-dependent transcriptional activation and apoptosis in response to DNA damage by catalyzing p53 deacetylation. The findings that SIRT1 levels are increased in a number of tumors highlight the oncogenic role of sirtuins, in particular, in the down-modulation of p53 oncosuppressor activity. Along this lane, cancers carrying wild-type (wt) p53 protein are known to deregulate its activity by other mechanisms. Therefore, inhibition of SIRT1 and SIRT2, aimed at restoring wt-p53 transcriptional activity in tumors that retain the ability to express normal p53, might represent a valid therapeutic cancer approach specially when combined with standard therapies. This review will be focused on sirtuin inhibitors, with a specific attention on inhibitors of SIRT1 and SIRT2. Among them, nicotinamide and its analogs, sirtinol, A3 and M15, splitomicin, HR73 and derivatives, cambinol and derivatives, EX 527, kinase inhibitors, suramin, 4-dihydropyridine derivatives, tenovins, TRIPOS 360702, AC 93253, 3-arylideneindolinones, CSC8 and CSC13 will also be described.

Influenza is an infection of the upper respiratory tract caused by influenza virus. Neuraminidase (NA) plays an essential role in replication and infection of influenza virus. It is considered as a suitable target for antivirus agents development. Several potent NA inhibitors (NAIs) developed by using structure-based rational design have been widely used in clinic for treatment of influenza. However, the emergence of NA inhibitor-resistant virus mutations significantly limit their effectiveness. The molecular basis of virus resistance to NAIs has been a focus of intensive research. This review highlights recent progress in rational design and resistance mechanism of NAIs. We hope this review will be useful to not only researchers who are interested in developing novel NAIs but also clinical pharmacists.

Neurodegenerative diseases are accompanied by reduced activity of mitochondrial α-ketoglutarate dehydrogenase multienzyme complex (KGDHC). We present a new cellular model to study molecular mechanisms of this association. By application of the highly specific and efficient inhibitor of KGDHC, succinyl phosphonate (SP), to cultured neurons, we characterized the concentrationand time-dependent consequences of decreased KGDHC activity for neuronal metabolism and viability. Metabolic profiling of SP-treated neurons established accumulation of α-ketoglutarate and pyruvate as indicators of the KGDHC inhibition and ensuing impairment of pyruvate oxidation in the tricarboxylic acid cycle. Concomitant increases in alanine, glutamate and γ-aminobutyrate indicated a scavenging of the accumulated pyruvate and α-ketoglutarate by transamination and further decarboxylation of glutamate. Changes among other amino acids were in accordance with their potential to react with α-ketoglutarate or products of its transamination and serve as fuel compensating for the KGDHC block. Disturbances in neuronal amino acid pool were accompanied by changed polyamines, decreased total protein and increased thymine, suggesting increased catabolism of amino acids to decrease translation and affect DNA turnover/repair. The ensuing ATP salvage was observed as the paradoxical increase in neuronal ATP by mitochondrial inhibitor SP. Extensive exposure of neurons to SP reduced viability, as revealed by both the ATP- and NAD(P)H-dependent viability tests. Thus, we provide experimental evidence on the KGDHC impairment as a cause of neurodegeneration and decipher underlying molecular mechanisms, exposing the key regulatory complex of the tricarboxylic acid cycle as a promising target for directed regulation of neuronal function and survival.

The aggregation behavior of the amyloid peptide Aβ1-28 and the prion peptide PrP185-208 - both responsible for neurodegenerative disorders – was analyzed in the absence and in the presence of poly(propylene imine) (PPI) dendrimers at generation 5 (G5) with a dense shell of maltose and maltotriose units. Thioflavin T (ThT) fluorescence assay and circular dichroism (CD) experiments indicated that fibril formation is enhanced at low dendrimer concentration, while it is prevented at relatively high dendrimer concentrations. Computer aided EPR analysis by means of the selected spin probe 4-octyl-dimethylammonium,2,2,6,6-tetramethyl-piperidine-1-oxyl bromide (CAT8) further demonstrated this behavior, but also provided detailed information on the mechanism of fibril formation and on the different behavior of the differently decorated dendrimers. The CAT8 radicals were progressively trapped at the peptide interphase when peptide aggregates were formed, also monitoring pre-fibrillar structures. At later time, a phase separation of the CAT8 radicals monitors the formation of further supramolecular structures where the probes become squeezed among fibrillar aggregates. The addition of small amounts of dendrimers promotes the formation of peptide fibrils breaking them and providing a larger amount of ends that serve as sites of replications. Conversely, a high amount of dendrimers allows the peptides to well separate from each other such preventing their aggregation. EPR results also indicate that the perturbation played by PPI(G5)-Maltose are more effective onto PrP185-208 than onto Aβ1-28, while PPI(G5)-Maltotriose is less effective towards PrP185-208 in both promoting aggregation and preventing it by changing the dendrimer concentration. These results provide useful information about the mechanism and interactions which regulate the ability of macromolecules like the dendrimers to favor, prevent or cure neurodegenerative diseases.