Current Pharmaceutical Design - Volume 12, Issue 35, 2006

Infection of viruses usually results in considerable mortality and morbidity worldwide for our human beings. Such as notorious HIV virus, it has imperiled the very fabric of human society as no disease in human history has before. It is estimated that deaths from this pandemic will rival those of the bubonic plague, which killed 93 million people. Epidemic infection of any other viruses has been always a deadly dream in human history. Identified as a novel species of coronavirus, the SARS-CoV has caused severe acute respiratory syndrome (SARS) in late 2002 [1]. Air travel spread it rapidly around the world, and ultimately this virus infected about 8000 people and caused about 800 deaths in 26 countries on 5 continents [2]. Aggressive quarantine measures have successfully terminated the disease, and most likely the virus no longer circulates in the human populations. On the other hand, the battle against virus remains to be everlasting, and top scientists from around the world are committed to develop antiviral drugs and vaccines. At this side, scientists in China together with others involved world-widely have contributed greatly to the latest advances of the scientific studies on SARS-CoV from a number of subjects, leading reasonable drug discovery and design targeting several corresponding key proteins of SARS-CoV. Using multiple strategies, from biochemical investigations to computational simulations, works in the lab of Dr. Xu Shen and Dr. Hualiang Jiang [3] have provided invaluable understanding for the structural and functional characteristics of major proteins responsible for the infection and replication of SARS-CoV, thus vital for the rational drug development and exploration of feasible therapy against this disease. To understand the catalytic mechanism of SARS-CoV, Dr. Luhua Lai [4] focused on the questions about the quaternary structures and substrate selectivity of this target protein using a variety of biophysical and biochemical methods. It is found that this atypical enzyme also follows the general base catalytic mechanism, and some positions at active site are found to be main determinants for substrate specificity as revealed by HPLC assay on synthesized peptides. As performed by Dr. Yexue Li [5], the functional genomics and molecular evolution studies on the SARS-CoV have also found that four proteins were absolutely responsible for nosogenesis of SARS, namely the spike (S) protein; small envelop (E) protien; membrane (M) protein; and nuleocaspid (N) protein. It is also demonstrated that SARS must be originated from wild animals, and particularly the Spike gene, is essential for the transition from animal-to-human transmission to human-to-human transmission. Studies through structural crystallization on various aspects of the main protease, as done in Dr. Zihe Rao's lab [6], have given fundamental insights for both the static and dynamics properties of coronavirus Mpro and functional assignment for different domains. Well-shaping on the catalytic site and substrate binding pocket has laid solid ground for further highly effective and selective inhibitor design against CoV Mpro. It is hopefully to discover a single agent with clinical potential through studies of enzyme activity assay, high-throughput screening, virtual screening and ab initio inhibitor design. As typically done in the area of drug discovery and design, Dr. Roman Osman [7] has performed combinatory computational and biochemical studies on the sweet taste receptor. The reasonable ligand binding sites are identified and verified by convincing site-directed mutagenesis experiments. These studies have led to a better understanding of the structure and function of the sweet taste receptor, and are guiding the rational structural-based design of novel sweeteners, of which could be used in the treatment of human obesity and diabetes. Starting from discovered lead compounds and analogs, Dr. Guangfu Yang [8] provided a unique way of relating the structural descriptors, especially derived from accurate quantum chemistry calculations, with measurable bio-activities. These descriptors cover the features of small molecules from steric, electronic to hydrophobic properties et al., and have been testified as an extension of traditional quantitative structure-activity relationships, also being powerful tools in the design of novel active compounds or positive modification of available low-activity compounds. Finally, I would like to give my sincere thanks to all the authors for their great contributions to this issue mainly focused on SARS-CoV and related advances in modern drug discovery, particularly thanks to Dr. Xu Shen and Dr. Hualiang Jiang for their kindly offering of the cover picture......

A severe atypical pneumonia designated as severe acute respiratory syndrome (SARS) by The World Health Organization broke out in China and menaced to more than other 30 countries between the end of the year 2002 and June of the year 2003. A novel coronavirus called severe acute respiratory syndrome coronavirus (SARS-CoV) has been recently identified as the etiological agent responsible for the infectious SARS disease. Based on extensively scientific cooperation and almost two-year's studies, remarkable achievements have been made in the understanding of the phylogenetic property and the genome organization of SARS-CoV, as well as the detailed characters of the major proteins involved in SARS-CoV life cycle. In this review, we would like to summarize the substantial scientific progress that has been made towards the structural and functional aspects of SARS-CoV associated key proteins. The progress focused on the corresponding key proteins' structure-based drug and vaccine developments has been also highlighted. The concerted and cooperative response for the treatment of the SARS disease has been proved to be a triumph of global public health and provides a new paradigm for the detection and control of future emerging infectious disease threats.

The SARS coronavirus 3C-like proteinase is recognized as a potential drug design target for the treatment of severe acute respiratory syndrome. In the past few years, much work has been done to understand the catalytic mechanism of this target protein and to design its selective inhibitors. The protein exists as a dimer/monomer mixture in solution and the dimer was confirmed to be the active species for the enzyme reaction. Quantitative dissociation constants have been reported for the dimer by using analytic ultracentrifuge, gel filtration and enzyme assays. Though the enzyme is a cysteine protease with a chymotrypsin fold, SARS 3C-like proteinase follows the general base catalytic mechanism similar to chymotrypsin. As the enzyme can cut eleven different sites on the viral polyprotein, the substrate specificity has been studied by synthesized peptides corresponding or similar to the cleavage sites on the polyprotein. Predictive model was built for substrate structure and activity relationships and can be applied in inhibitor design. Due to the lack of potential drugs for the treatment of SARS, the discovery of inhibitors against SARS 3C-like proteinase, which can potentially be optimized as drugs appears to be highly desirable. Various groups have been working on inhibitor discovery by virtual screening, compound library screening, modification of existing compounds or natural products. Highthroughput in vitro assays, auto-cleavage assays and viral replication assays have been developed for inhibition activity tests. Inhibitors with IC50 values as low as 60 nM have been reported.

Severe acute respiratory syndrome (SARS) first appeared in 2002 in China, which fastly affected about 8000 patients over 29 countries and caused 774 fatalities. As its pathogen was identified as a new kind of coronavirus (SARS_CoV), its genome was quickly sequenced on several isolates. Studies on its functional genomics were performed by combinatorial application of all the available bioinformatics tools and the development of new programs. In this way, it was found that the four proteins were absolutely responsible for nosogenesis of SARS, i.e. spike (S) protein; small envelop (E) protein; membrane (M) protein; and nucleocaspid (N) protein. Molecular evolution studies have revealed that SARS must be originated from wild animals, and it was demonstrated that the major genetic variations in some critical genes, particularly the Spike gene, was essential for the transition from animal-to-human transmission to human-tohuman transmission. Theoretical models, either Logistic model or SIR model, were developed to describe the transmission of SARS. The recorded difference of SARS spreading in Beijing and Hong Kong was also reasonably analyzed according to these models. The whole process of fruitful bioinformatics studies, along with other related scientific investigations have set up an unprecedented paradigm for human of how to battle against sudden-breaking and catastrophic epidemics.

Coronaviruses (CoVs), a genus containing about 26 known species to date, cause highly prevalent diseases and are often severe or fatal in humans and animals. In 2003, a previously unknown coronavirus was identified to be the etiological agent of a global outbreak of a form of life-threatening pneumonia called severe acute respiratory syndrome (SARS). No efficacious therapy is currently available, and vaccines and drugs are under development to prevent SARSCoV infection in many countries. The CoV main protease (Mpro), which plays a pivotal role in viral gene expression and replication through a highly complex cascade involving the proteolytic processing of replicase polyproteins, is an attractive target for drug design. This review summarizes the recent advances in biological and structural studies, together with development of inhibitors targeting CoV Mpros. It is expected that inhibitors targeting CoV Mpros could be developed into wide-spectrum antiviral drugs against existing and possible future emerging CoV-associated diseases.

The sweet taste receptor is a heterodimer of two G protein coupled receptors, T1R2 and T1R3. This discovery has increased our understanding at the molecular level of the mechanisms underlying sweet taste. Previous experimental studies using sweet receptor chimeras and mutants show that there are at least three potential binding sites in this heterodimeric receptor. Receptor activity toward the artificial sweeteners aspartame and neotame depends on residues in the amino terminal domain of human T1R2. In contrast, receptor activity toward the sweetener cyclamate and the sweet taste inhibitor lactisole depends on residues within the transmembrane domain of human T1R3. Furthermore, receptor activity toward the sweet protein brazzein depends on the cysteine rich domain of human T1R3. Although crystal structures are not available for the sweet taste receptor, useful homology models can be developed based on appropriate templates. The amino terminal domain, cysteine rich domain and transmembrane helix domain of T1R2 and T1R3 have been modeled based on the crystal structures of metabotropic glutamate receptor type 1, tumor necrosis factor receptor, and bovine rhodopsin, respectively. We have used homology models of the sweet taste receptors, molecular docking of sweet ligands to the receptors, and site-directed mutagenesis of the receptors to identify potential ligand binding sites of the sweet taste receptor. These studies have led to a better understanding of the structure and function of this heterodimeric receptor, and can act as a guide for rational structure-based design of novel non-caloric sweeteners, which can be used in the fighting against obesity and diabetes.

Over forty years have elapsed since Hansch and Fujita published their pioneering work of quantitative structure- activity relationships (QSAR). Following the introduction of Comparative Molecular Field Analysis (CoMFA) by Cramer in 1998, other three-dimensional QSAR methods have been developed. Currently, combination of classical QSAR and other computational techniques at three-dimensional level is of greatest interest and generally used in the process of modern drug discovery and design. During the last several decades, a number of different mythologies incorporating a range of molecular descriptors and different statistical regression ways have been proposed and successfully applied in developing of new drugs, thus QSAR method has been proven to be indispensable in not only the reliable prediction of specific properties of new compounds, but also the help to elucidate the possible molecular mechanism of the receptorligand interactions. Here, we review the recent developments in QSAR and their applications in rational drug design, focusing on the reasonable selection of novel molecular descriptors and the construction of predictive QSAR models by the help of advanced computational techniques.

Extensive research suggests that a number of plant-derived chemicals and traditional Oriental herbal remedies possess cognition-enhancing properties. Widely used current treatments for dementia include extracts of Ginkgo biloba and several alkaloidal, and therefore toxic, plant-derived cholinergic agents. Several non-toxic, European herbal species have pan-cultural traditions as treatments for cognitive deficits, including those associated with ageing. To date they have not received research interest commensurate with their potential utility. Particularly promising candidate species include sage (Salvia lavandulaefolia/officinalis), Lemon balm (Melissa officinalis) and rosemary (Rosmarinus officinalis). In the case of sage, extracts possess anti-oxidant, estrogenic, and antiinflammatory properties, and specifically inhibit butyryl- and acetyl-cholinesterase. Acute administration has also been found to reliably improve mnemonic performance in healthy young and elderly cohorts, whilst a chronic regime has been shown to attenuate cognitive declines in sufferers from Alzheimer's disease. In the case of Melissa officinalis, extracts have, most notably, been shown to bind directly to both nicotinic and muscarinic receptors in human brain tissue. This property has been shown to vary with extraction method and strain. Robust anxiolytic effects have also been demonstrated following acute administration to healthy humans, with mnemonic enhancement restricted to an extract with high cholinergic binding properties. Chronic regimes of aromatherapy and essential oil respectively have also been shown to reduce agitation and attenuate cognitive declines in sufferers from dementia Given the side effect profile of prescribed cholinesterase inhibitors, and a current lack of a well tolerated nicotinic receptor agonist, these herbal treatments may well provide effective and well-tolerated treatments for dementia, either alone, in combination, or as an adjunct to conventional treatments.

In recent years sphingolipids have emerged as important signaling molecules regulating fundamental cell responses such as cell death and differentiation, proliferation and aspects of inflammation. Especially ceramide has been a main focus of research since it possesses pro-apoptotic capacity in many cell types. A counterplayer of ceramide was found in sphingosine-1-phosphate (S1P), which is generated from ceramide by the consecutive actions of ceramidase and sphingosine kinase. S1P can potently induce cell proliferation via binding to and activation of the Edg family of receptors which have now been renamed as S1P receptors. Obviously, a delicate balance between ceramide and sphingosine-1- phosphate determines whether cells undergo apoptosis or proliferate, two cell responses that are critically involved in tumor development. Directing the balance in favor of ceramide, i.e. by inhibiting ceramidase or sphingosine kinase activities may support the pro-apoptotic action of ceramide and thus may have beneficial effects in cancer therapy. This review will summarize novel insights into the regulation of sphingolipid formation and their potential involvement in tumor development. Finally, we will pinpoint potential new targets for tumor therapy.

Hepatorenal syndrome is a severe, but not uncommon complication of decompensated liver cirrhosis. In particular, the rapidly progressive form of hepatorenal syndrome (type 1) is associated with a dismal prognosis. Established hepatorenal syndrome has a spontaneous reversibility below 5%. Hepatorenal syndrome is involved in more than 50% of cirrhosis-related mortality. Thus, any treatment capable of reversing hepatorenal syndrome would be expected to reduce morbidity and mortality from liver cirrhosis. A pathophysiological hallmark of hepatorenal syndrome is arterial underfilling due to an extreme splanchnic vasodilatation. Consequently, potent vasoconstrictors capable of reversing this vasodilatation have been investigated in hepatorenal syndrome. Several vasoconstrictors including the α-adrenergic agonists, midodrine and noradrenalin, and the vasopressor analogues, ornipressin and terlipressin, have all been associated with a significant improvement in renal function in 57 to 100% of cases and even reversal of hepatorenal syndrome in 42 to 100% of cases. The majority of recent studies are on terlipressin. A randomized, controlled trial showed a significant effect of terlipressin on reversal of hepatorenal syndrome. The contribution of volume expansion to the beneficial effects of vasoconstrictors on hepatorenal syndrome remains to be determined. In general, reversal of hepatorenal syndrome was associated with an improved survival. However, it remains to be determined if vasoconstrictor therapy should be used in hepatorenal syndrome in general, or if it should be reserved for potential candidates for liver transplantation. In conclusion, evidence for a beneficial effect of vasoconstrictor therapy for the treatment of hepatorenal syndrome is steadily accumulating. Confirmation of the preliminary data in larger randomized, controlled trials looking at long-term survival is required.

By searching the literatures, it was found that a total of 32 drugs interacting with herbal medicines in humans. These drugs mainly include anticoagulants (warfarin, aspirin and phenprocoumon), sedatives and antidepressants (midazolam, alprazolam and amitriptyline), oral contraceptives, anti-HIV agents (indinavir, ritonavir and saquinavir), cardiovascular drug (digoxin), immunosuppressants (cyclosporine and tacrolimus) and anticancer drugs (imatinib and irinotecan). Most of them are substrates for cytochrome P450s (CYPs) and/or P-glycoprotein (PgP) and many of which have narrow therapeutic indices. However, several drugs including acetaminophen, carbamazepine, mycophenolic acid, and pravastatin did not interact with herbs. Both pharmacokinetic (e.g. induction of hepatic CYPs and intestinal PgP) and/or pharmacodynamic mechanisms (e.g. synergistic or antagonistic interaction on the same drug target) may be involved in drug-herb interactions, leading of altered drug clearance, response and toxicity. Toxicity arising from drug-herb interactions may be minor, moderate, or even fatal, depending on a number of factors associated with the patients, herbs and drugs. Predicting drug-herb interactions, timely identification of drugs that interact with herbs, and therapeutic drug monitoring may minimize toxic drug-herb interactions. It is likely to predict pharmacokinetic herb-drug interactions by following the pharmacokinetic principles and using proper models that are used for predicting drug-drug interactions. Identification of drugs that interact with herbs can be incorporated into the early stages of drug development. A fourth approach for circumventing toxicity arising from drug-herb interactions is proper design of drugs with minimal potential for herbal interaction. So-called ”hard drugs” that are not metabolized by CYPs and not transported by PgP are believed not to interact with herbs due to their unique pharmacokinetic properties. More studies are needed and new approached are required to minimize toxicity arising from drug-herb interactions.