Today the term “click chemistry” is often used equivalent with the copper-catalyzed 1,3-dipolar Huisgen cycloaddition. Originally, the concept was introduced in 2001 to describe reactions fulfilling a set of criteria that are most useful for chemical syntheses in drug research. In radiopharmaceutical chemistry where short lived radioisotopes are introduced into various different substance classes for in vivo imaging of biochemical processes, the expanding field of radioactive bioconjugation has become predominant. Labeled biomolecules such as peptides, proteins and oligonucleotides generated via bioconjugation of chelators for radiometal introduction as well as novel valuable secondary precursors for 18F labeling have enriched the growing field of molecular imaging substantially. When introducing radioactive nuclides with a very short half-life into biomolecules, some of the typical criteria defined by click-chemistry are more crucial than others. Time is always the most important issue, whereas avoiding the formation of by-products that have to be removed without chromatography is of minor importance. The short-lived radionuclide 11C for example has a physical half-life of only 20 min so that the labeling procedure cannot exceed 40-60 minutes (2-3 half-lifes). In this contribution, we outline reactions and molecules which meet the requirements of click chemistry reactions and are suitable for radiosyntheses of short lived SPECT (99mTc: t1/2 = 6 h, 111In: t1/2 = 2.81 d) and PET (11C: t1/2 = 20.3 min to 64Cu: t1/2 = 12.7 h) radiotracers for in vivo imaging of biological processes and review the contributions in the field of radiochemical “click-reactions” - 1,3-dipolar Huisgen cycloadditions and beyond.

Recently, the circulating anion nitrite (NO2-), the largest physiological reservoir of nitric oxide (NO) in the body, has revealed itself as a signalling molecule mediating numerous biological responses. Since it was estimated that as much as 70% of plasma nitrite originates from nitric oxide synthases (NOSs), mainly in the endothelium by endothelial NOS, nitrite is considered an index of NOSs activity. Exogenous sources, principally environmental pollutants and intake of vegetables, also contribute to this NO reserve. In mammalian blood, nitrite, present at nanomolar concentrations, can be reduced to bioactive NO along a physiological oxygen and pH gradient either non-enzymatically (acidic disproportionation) or by a number of enzymes including xanthine oxidoreductase, NOS, mitochondrial cytochromes and deoxygenated haemoglobin and myoglobin. The various NO-dependent nitrite-induced biological responses include hypoxic vasodilation, inhibition of mitochondrial respiration, cytoprotection following ischemia/reperfusion, and regulation of protein and gene expression. Since NO is a major paracrine-autocrine cardiovascular modulator and nitrite acts mainly as an endocrine store of NO, it is not surprising that NO2- exerts important cardiovascular actions both under normal and physio-pathological conditions. In the interdisciplinary framework of the NO cycle concept, this review illustrates the actions exerted by nitrite on the cardiovascular system. Since the majority of the NO2- -oriented studies focused on the systemic and regional control of blood flow both under physiological and ischemia/reperfusion conditions, we will firstly consider this issue. Secondly, the nitrite-induced effects on myocardial contractile and relaxation processes will be discussed, emphasizing the biomedical interest of nitrite as a new therapeutic agent. The importance of cardiac myoglobin as nitrite-reductase able to exert cardioprotection through a novel function, in addition to its role as classical respiratory protein, will be highlighted. Finally, using recent data from others and our labs, we will emphasize the importance of fish and amphibian heart models with diverse morphologies and blood supply for providing remarkable insights on “ancestral” functions of the nitrite-NO system in vertebrates, which, in turn, may help to expand its actual significance in human physiology.

Protein C is a vitamin K-dependent anticoagulant serine protease zymogen in plasma which upon activation by the thrombin-thrombomodulin complex down-regulates the coagulation cascade by degrading cofactors Va and VIIIa by limited proteolysis. In addition to its anticoagulant function, activated protein C (APC) also binds to endothelial protein C receptor (EPCR) in lipid-rafts/caveolar compartments to activate protease- activated receptor 1 (PAR-1) thereby eliciting antiinflammatory and cytoprotective signaling responses in endothelial cells. These properties have led to FDA approval of recombinant APC as a therapeutic drug for severe sepsis. The mechanism by which APC selects its substrates in the anticoagulant and antiinflammatory pathways is not well understood. Recent structural and mutagenesis data have indicated that basic residues of three exposed surface loops known as 39-loop (Lys-37, Lys-38, and Lys-39), 60-loop (Lys-62, Lys-63, and Arg-67), and 70-80-loop (Arg-74, Arg-75, and Lys-78) (chymotrypsin numbering) constitute an anion binding exosite in APC that interacts with the procoagulant cofactors Va and VIIIa in the anticoagulant pathway. Furthermore, two negatively charged residues on the opposite side of the active-site of APC on a helical structure have been demonstrated to determine the specificity of the PAR-1 recognition in the cytoprotective pathway. This article will review the mechanism by which APC exerts its proteolytic function in two physiologically inter-related pathways and how the structure-function insights into determinants of the specificity of APC interaction with its substrates in two pathways can be utilized to tinker with the structure of the molecule to obtain APC derivatives with potentially improved therapeutic profiles.

Ambient level of γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter of the brain is mediated by neuronal and glial GABA transporters (GATs), members of the sodium and chloride ion-dependent solute carrier family. The neuronal GABA transporter subtype (GAT-1) has already been proven to be the target for the antiepileptic drug Tiagabine. However, druggability of glial GAT-2 and GAT-3 is yet to be established. Recent advances in structure elucidation of a bacterial orthologue leucine transporter in complex with different substrates substantiate homology modeling of human GATs (hGATs). These modeling studies can provide mechanistic clues for structure-based prediction of the potential of medicinal chemistry campaigns. A recently identified characteristic structural feature of the occluded conformation of hGATs is that similar extra- and intracellular gates are formed by middle-broken transmembrane helices TM1 and TM6. Binding crevice formed by unwound segments of broken helices facilitates symport of GABA with Na+ ion via fitting of GABA to TM1-bound Na+(1) closely inside. Favored accommodation of substrate inhibitors with high docking score predicts efficient inhibition of the neuronal hGAT-1 if the TM1-TM8 binding prerequisite for GABA was used. Docking, molecular dynamics and transport data indicate, that amino acids participating in substrate binding of the neuronal hGAT-1 and the glial hGAT-2 and hGAT-3 subtypes are different. By contrast, substrate binding crevices of hGAT-2 and hGAT-3 cannot be distinguished, avoiding sensible prediction of efficient selective substrate inhibitors. Glial subtypes might be specifically distinguished by interfering Zn2+ binding in the second extracellular loop of hGAT-3. Formation of the unique ring-like Na+-GABA complex in the occluded binding crevices anticipates family member symporters exploring chemiosmotic energy via reversible chemical coupling of Na+ ion.

As the central energy source, the mitochondria are of great importance in the maintenance of the glia cells of the brain. It is presumed that mitochondrial energy production is affected not only by well-characterized genetic mutations of the mitochondria, which are associated with severe malfunctions and resultant acute glia and neuronal cell death, but also by a number of other unfavorable genetic variants. The genetic variants of the kinesin motor proteins and mitochondrial uncoupling proteins (UCPs) are believed to influence the mitochondrial energy production in different distress states of the glia cells. The kinesin motor proteins carry the mitochondria from the central parts to the peripheral parts of the glia cells, where myelin protein synthesis takes place. The UCPs are essential for regulation of the mitochondrial membrane potential under different physiological conditions, thereby finally attuning mitochondrial energy production in environmental states such as cold exposure, fasting or chronic mild hypoxia. While the capacity of the kinesin motor proteins can affect the number of mitochondria in the peripheral parts of the glia cells, the functional features of the UCPs can affect the degree of energy production of the mitochondria by influencing the mitochondrial membrane potential. The different genetic variants may display different activities, and some may result in a slowly developing energy shortage in the glia cells. In this context, this article discusses the roles of genetic variants of the kinesin motor proteins and UCPs in slowly developing diseases of the white matter of the brain as multiple sclerosis and leukoaraiosis.

A major concern for helminth parasite control in human and animal health is the development of anthelmintic resistance. The mutations that lead to such resistance do so in several ways including, loss of drug binding, modification of response once the drug has bound and loss of the drug target altogether. Benzimidazole resistance is best characterized by amino acid substitutions at three positions of the beta-tubulin protein: F167Y, E198A and F200Y, each of which causes loss of drug binding. Macrocyclic lactone resistance has been linked in the laboratory to mutations in different ligand- gated chloride-channel subunit genes, Hco-glc-5, Hco-lgc-37 and Con-avr-14 with substitutions A159V, K159R and L256F. These alter the channel response to drug binding, reducing its effects, which can also be seen in vivo. Levamisole resistance, including pyrantel and other related compounds, has been more difficult to characterize. More recently, loss of specific acetylcholine gated ion-channels that are targeted by the drug has been demonstrated with functional and molecu- lar evidence. The loss of specific ion-channel targets of both the macrocyclic lactones and the new monepantel also seems to be a more general mechanism of anthelmintic resistance that requires further study. Praziquantel resistance is associated with SNPs in the β subunit forming voltage-gated Ca2+ channels. By placing our knowledge of the characteristics of these mutations in a framework of their biochemistry, functional characteristics, population genetics and effects in vivo gives us a more comprehensive understanding of how these mutations behave. This in turn should ultimately help us to minimize their impact.

Identification of artworks is mainly based on a few characteristics which can be observed using non-invasive tools (sight, touch, simple instruments), the investigated properties being geometry, weight, colours, texture, etc. Nowadays, technology allows reproducing all these characteristics to such an extent that even expert conservators can be deceived: in particular at the present time even the geometry of an artwork can be easily reproduced with the help of laser scanner analysis and with a rapid prototyping machine or a computer numerical control (CNC) milling machine. We propose a new tool, the Sonic Imprint, producing a code capable of identifying a rigid artefact from its vibrational resonance frequencies beyond doubt. In fact the vibration modes of an artefact strongly depend on the spatial distributions of its density and elastic parameters, as well as on its internal defects, definable in terms of abrupt changes of elastic properties in a small portion of the object. Then even small differences of these properties (differences usually present even among “identical” objects produced with industrial methods, at least in terms of defects) give appreciable variations of the Sonic Imprint codes, allowing secure identification of artworks, prevention of clonation and even damage monitoring. Moreover the procedure is really robust, rapid, inexpensive and not invasive. We tested it on a large number of commercial objects with the same shape and dimension and on many artworks in archaeological museums: an example is described. The application of this methodology to small-size artefacts (from small stones, vessels, pottery to medium-large coins) involves some problems in the detection of the Sonic Imprint. The problems, just due to the smaller sizes of this kind of objects, arise from the presence of higher resonance frequencies and larger damping of the induced vibrations. This implies that probes and instrumentation should be replaced to be adapted to the new experimental conditions.

Normal pregnancy is associated with significant vascular remodeling in the uterine and systemic circulation in order to meet the metabolic demands of the mother and developing fetus. The pregnancy-associated vascular changes are largely due to alterations in the amount/activity of vascular mediators released from the endothelium, vascular smooth muscle and extracellular matrix. The endothelium releases vasodilator substances such as nitric oxide, prostacyclin and hyperpolarizing factor as well as vasoconstrictor factors such as endothelin, angiotensin II and thromboxane A2. Vascular smooth muscle contraction is mediated by intracellular free Ca2+ concentration ([Ca2+]i), and [Ca2+]i sensitization pathways such as protein kinase C, Rho-kinase and mitogen-activated protein kinase. Extracellular matrix and vascular remodeling are regulated by matrix metalloproteases. Hypertension in pregnancy and preeclampsia are major complications and life threatening conditions to both the mother and fetus, precipitated by various genetic, dietary and environmental factors. The initiating mechanism of preeclampsia and hypertension in pregnancy is unclear; however, most studies have implicated inadequate invasion of cytotrophoblasts into the uterine artery, leading to reduction in the uteroplacental perfusion pressure and placental ischemia/hypoxia. This placental hypoxic state is thought to induce the release of several circulating bioactive factors such as growth factor inhibitors, anti-angiogenic proteins, inflammatory cytokines, reactive oxygen species, hypoxia-inducible factors, and vascular receptor antibodies. Increases in the plasma levels and vascular content of these factors during pregnancy could cause an imbalance in the vascular mediators released from the endothelium, smooth muscle and extracellular matrix, and lead to severe vasoconstriction and hypertension. This review will discuss the interactions between the various circulating bioactive factors and the vascular mediators released during hypertension in pregnancy, and provide an insight into the current and future approaches in the management of preeclampsia.

Molecular recognition and ligand binding involving proteins underlie the most important life processes within the cell, such as substrate transport, catalysis, signal transmission, receptor trafficking, gene regulation, switching on and off of biochemical pathways. Despite recent successes in predicting the structures of many protein-substrate complexes, the dynamic aspects of binding have been largely neglected by computational/theoretical investigations. Recently, several groups have started tackling these problems with the use of experimental and simulation methods and developed models describing the variation of protein dynamics upon complex formation, shedding light on how substrate or inhibitor binding can alter protein flexibility and function. The study of ligand-induced dynamic variations has also been exploited to review the concept of allosteric changes, in the absence of major conformational changes. In this context, the study of the influence of protein motions on signal transduction and on catalytic activities has been used to develop pharmacophore models based on ensembles of protein conformations. These models, taking flexibility explicitly into account, are able to distinguish active inhibitors versus nonactive drug-like compounds, to define new molecular motifs and to preferentially identify specific ligands for a certain protein target. The application of these methods holds great promise in advancing structure-based drug discovery and medicinal chemistry in general, opening up the possibility to explore broader chemical spaces than is normally done in an efficient way. In this review, examples illustrating the extent to which simulations can be used to understand these phenomena will be presented along with examples of methodological developments to increase physical understanding of the processes and improve the possibility to rationally design new molecules.

Monoclonal antibodies have yet considerably modified the field of clinical oncology. The growing knowledge of key cellular pathways in tumor induction and progression, targeted therapies represent an increasing proportion of new drugs entering clinical trials. Some molecules such as trastuzumab, rituximab, alemtuzumab, cetuximab are now widely used in clinical practice. These antibodies are now tested in different indications alone or in combination with standard chemotherapy. They are also developed for the treatment of inflammatory diseases (rituximab). Numerous others antibodies are currently in pre-clinical and clinical development phases for several malignancies including renal carcinoma, melanoma, lymphomas, leukaemia, breast, ovarian and colorectal cancer. An alternative approach is to conjugate the monoclonal antibody to a toxin, a cytotoxic agent, or a radioisotope. In other cases these antibodies aim to modify the tumour microenvironnement through inhibition of angiogenesis or enhancing host immune response against cancer. If the molecule targeted by the antibodies is clearly identified, most often the precise mechanism of action of these immunoglobulins is not fully understood.They can have direct effects in inducing apoptosis or programmed cell death. They can block growth factor receptors, efficiently arresting proliferation of tumor cells. Indirect effects include recruiting cells that exert cytotoxicity, such as monocytes and macrophages (ADCC). Monoclonal antibodies also bind complement, leading to toxicity known as complement dependent cytotoxicity (CDC).The side effects associated with these new treatments were in part foreseeable depending on the affected cell or function. But new or surprising side effects emerged from clinical studies. We present an overview of the monoclonal antibodies used in clinical oncology or currently in development phases. We particularly focus on recent development including new indications, clinical trial results and specific side effects of monoclonal antibodies used in the treatment of cancer.