Current Drug Targets (v.13, #4)

The philosophy of enzymatic catalysis runs earth lives from generation to generation. Slightly structural alteration has allowed various physiological roles of these enzymes that belong to the same class. The substrate specificity distinguishes enzymes from one species to others, forming the base to design drugs specific for human and pesticides specific for pests. This characteristic even benefits the study of organic evolution and novel drugable sites against drug/pesticide resistance. N-acetyl- D-glucosamine and acetylchline related targets, most of which are enzymes, are two examples associated with both drug and pesticides. Various paths, such as biology, toxicology, physiology, chemicobiology and bioinformatics, have been tried. The theme of this issue is to review recent development of these targets in order to reveal how structural changes affect species specificity, efficacy and safety from the point of view of comparative biochemistry. N-acetyl-D-glucosamine is the building block of oligosaccharide linked to proteins (glycoproteins) or lipids (glycolipids) and chitin as the structural component of insect exoskeleton and cell wall of fungi. N-acetyl-D-glucosaminidases and chitinases are enzymes responsible for hydrolysis of glycosidic bonds joined by N-acetyl-D-glucosamine. The former is important for many life processes including post-translational N-glycan modification, glycoconjugate degradation as well as egg-sperm recognition. And the latter is found to play key roles in insect molting and metamorphism as well as human asthma caused by pathogenic bacteria. For agriculture economy, they are believed to be target potentials in the control of pests and protection of plants. For human, they are specific target potentials in the development of drugs against lysosomal-disorder diseases and pathogenic infection. Thus, the structural comparison of N-acetyl-D-glucosaminidases from different species gives clues to design speciesspecific drugs and pesticides. Acetylcholine is a neurotransmitter in many organisms including insects and humans. Acetylcholinesterase (AChE) is the most efficient enzyme in existence, which terminates the excitatory effects of neurotransmitter acetylcholine at cholinergic synapses by the hydrolysis of acetylcholine. The interference of the hydrolysis results in a build-up of acetylcholine leading to repeated firing of neurons and ultimately death by exhaustion. The significance of AChE in nerve system makes it an efficient target in developing pesticides. Vertebrate species possess a parallel hydrolase, butyrylcholinesterase (BChE) with detoxification function, which is differentiated from AChE by substrate preferences. This is the base for AchE as a species-specific target in developing insecticides with high selectivity. However given the strong similarities of the insect and mammalian cholinergic nervous system, these AChE-inhibited insecticides are responsible for the million of poisonings and thousands of deaths occurring annually. On the other hand, AChE inhibitors are active against human Alzheimer disease. It is therefore of great importance to reveal structural insights into differences in AChEs from various species.

Chitin-Related Enzymes in Agro-Biosciences by Yasuyuki Arakane (442-470).
Plants utilized for agricultural productions interact with insects, fungi, and bacteria under the field conditions, affecting thereby their productivity. Since chitin and its derivatives play important roles in the interactions between these organisms, chitin-related enzymes are effective tools or drug targets for controlling the interactions. Thus, the molecular biology, protein chemistry, and enzymology of the chitin-related enzymes have been intensively studied by many investigators. Identifications and classifications of the genes encoding chitin synthetases, chitinases, chitosanases, and chitin deacetylases in these organisms were conducted, and their physiological functions were defined by knockdown, knockout, or overexpression of the corresponding genes. Recombinant enzyme productions and mutation studies are also being conducted to understand their structure and function. All of these studies have opened the way to efficiently utilize these enzyme tools for enhancing the agricultural productions.

Insect pests are responsible for human suffering and financial losses worldwide. New and environmentally safe insecticides are urgently needed to cope with these serious problems. Resistance to current insecticides has resulted in a resurgence of insect pests, and growing concerns about insecticide toxicity to humans discourage the use of insecticides for pest control. The small market for insecticides has hampered insecticide development; however, advances in genomics and structural genomics offer new opportunities to develop insecticides that are less dependent on the insecticide market. This review summarizes the literature data that support the hypothesis that an insect-specific cysteine residue located at the opening of the acetylcholinesterase active site is a promising target site for developing new insecticides with reduced off-target toxicity and low propensity for insect resistance. These data are used to discuss the differences between targeting the insect-specific cysteine residue and targeting the ubiquitous catalytic serine residue of acetylcholinesterase from the perspective of reducing off-target toxicity and insect resistance. Also discussed is the prospect of developing cysteine-targeting anticholinesterases as effective and environmentally safe insecticides for control of disease vectors, crop damage, and residential insect pests within the financial confines of the present insecticide market.

Ladostigil [(N-propargyl-(3R) aminoindan-5yl)-ethyl methyl carbamate] is a dual acetylcholine-butyrylcholineesterase and brain selective monoamine oxidase (MAO)-A and -B inhibitor in vivo (with little or no MAO inhibitory effect in the liver and small intestine), intended for the treatment of dementia co-morbid with extrapyramidal disorders and depression (presently in a Phase IIb clinical study). This suggests that the drug should not cause a significant potentiation of the cardiovascular response to tyramine, thereby making it a potentially safer antidepressant than other irreversible MAO-A inhibitors. Ladostigil was shown to antagonize scopolamine-induced impairment in spatial memory, indicating that it can cause significant increases in rat brain cholinergic activity. Furthermore, ladostigil prevented gliosis and oxidative-nitrative stress and reduced the deficits in episodic and spatial memory induced by intracerebroventricular injection of streptozotocin in rats. Ladostigil was demonstrated to possess potent anti-apoptotic and neuroprotective activities in vitro and in various neurodegenerative rat models, (e.g. hippocampal damage induced by global ischemia in gerbils and cerebral oedema induced in mice by closed head injury). These neuroprotective activities involve regulation of amyloid precursor protein processing; activation of protein kinase C and mitogen-activated protein kinase signaling pathways; inhibition of neuronal death markers; prevention of the fall in mitochondrial membrane potential and upregulation of neurotrophic factors and antioxidative activity. Recent findings demonstrated that the major metabolite of ladostigil, hydroxy-1-(R)-aminoindan has also a neuroprotective activity and thus, may contribute to the overt activity of its parent compound. This review will discuss the scientific evidence for the therapeutic potential use of ladostigil in Alzheimer's and Lewy Body diseases and the molecular signaling pathways that are considered to be involved in the biological activities of the drug.

Acetylcholinesterase (AChE; EC 3.1.1.7) is a primary target of many insecticides including organophosphates (OP) and carbamates (CB). Because AChE is expressed in all invertebrate and vertebrate animals as a key enzyme of the cholinergic system, the toxicity of anticholinesterase insecticides to mammals and non-target species such as beneficial insects has been a great concern. In addition, the intensive use of OP and CB insecticides has resulted in the development of resistance in many insect pests, which has limited the use of anticholinesterase insecticides. Many aces encoding AChEs have been sequenced from a variety of vertebrates, insects and other invertebrates, and crystal structures of four AChEs have been determined in the past 20 years. Although the primary motifs and the three dimensional (3D) structures of different AChEs are similar, differences among AChEs are obvious. The catalytic properties and inhibition kinetics of AChEs from different groups of insects and mammals may be quite different, and two AChEs from a single insect may also show distinct differences. These differences may provide new opportunities for designing more selective insecticides for pest management.

Chitinases belong to family 18 glycosyl hydrolases that can hydrolyze chitin by cleaving β-1,4-glycosidic bond, and are at key points in the life cycles of organism. The inhibitors of chitinases not only have chemotherapeutic potential against fungi, insects, but also hold anti-inflammatory efficacy against asthma and allergic disease in human. This review summarizes the structural characters of chitinases, the proposed catalytic mechanism, furthermore, also gives descriptions of currently existing inhibitors. In addition, computational studies of the interaction modes of chitinases with different inhibitors and substrates, as well as the inhibitor design of chitinases, are summarized so as to obtain an overall understanding for chitinases.

Glycosyl hydrolase family 3, 20 and 84 β-N-acetyl-D-hexosaminidases are widely distributed enzymes that function in energy metabolism, cell proliferation, signal transduction as well as in pathogen-related inflammation and autoimmune diseases. Sharing the same retaining catalytic mechanism, they are distinguished from each other in terms of structure rather than substrate-enzyme transition state. Selective inhibition of each of these enzymes that exploits the structural differences would appear promising in the regulation and investigation of their corresponding life functions within the organism. Thanks to molecular structural biology, detailed structures of GH3, 20 and 84 β-N-acetyl-Dhexosaminidases have become available at the atomic level. This review gives a panoramic description and comparison of the enzymes catalytic mechanisms, overall structures, active site architectures as well as structure-based analysis of inhibition, with the hope of exploiting novel targets for developing novel drugs and pesticides.

The globally rising incidence of Type 1 diabetes (T1D) is no longer restricted to individuals with higher risk genotypes, but is now significantly increasing in a population with lower risk genotypes, likely as the result of environmental factors. In this review, we discuss the potential of advanced glycation end products (AGEs) as environmental contributors to the development of T1D. AGEs are nonenzymatically formed protein modifications found in the body, as well as, consumed in our daily diets. To date, many studies have provided evidence of AGE involvement in β cell dysfunction, whether by AGE modification itself or via interaction with AGE receptors. The receptor for AGE (RAGE) and AGE-receptor-1 (AGE-R1) are of particular interest, given that studies have demonstrated the deleterious effects of RAGE modulation and the protection afforded by AGE-R1 in the context of diabetes. More interestingly, we have recently found that two RAGE polymorphism are predictive of T1D in humans while the third is protective. Moreover, soluble RAGE (sRAGE) levels (a circulating competitive inhibitor of RAGE) were greatly reduced at seroconversion to autoantibodies in both children on high risk of T1D background and in an animal model of autoiummune diabetes. Taken together with the fact that AGEs have also shown to be involved in immunomodulation, it is tempting to postulate that dietary AGEs, RAGE and even AGE-R1 could be working synergistically or independently to breach the tightly regulated immune system, providing a missing link in the development of T1D.

Breast cancer is the most common non-cutaneous cancer diagnosed in women in the United States and the second most common cause of cancer-related mortality. Over the past two decades, the progress in screening and adjuvant systemic therapies noticeably improved the survival rate. However, traditional methods of characterizing tumors are imprecise and create heterogeneous groupings of tumors and patients. As a result, despite the important medical advances in diagnosis and treatment of breast cancer, one-third of the patients with initial breast tumor have recurrence of the disease 10 years after the diagnosis. Therefore, novel tools for discovery of strong prognostic and predictive markers that can be used to identify patients at high risk for relapse and aid in the selection of the most appropriate therapy are needed. This review analyzes some recent achievements in the development of such tools.

Long-Acting Antipsychotic Medications by Raman Baweja (555-560).
Antipsychotic medicines are the cornerstone pharmacotherapy for patients with psychotic disorders. Early and continuous management of psychoses improves the quality of life, decreases hospitalization and reduces medical costs. However, many psychotic patients are not fully compliant with treatment, and thus they more often experience a relapsing course with a suboptimal clinical outcome. Long-term parenteral antipsychotic agents may improve compliance by offering clear evidence of medication non-compliance and documented drug administration monitoring. Using injection therapy might be especially beneficial to poorly compliant individuals with their first-psychotic episode and those with severe psychopathology or comorbid substance abuse. The availability of five different antipsychotic drug depot medications offers diverse treatment options which can be individualized for each case.

The bone marrow-derived mesenchymal stem cells or mesenchymal stromal cells (MSCs), with pluripotent differentiation capacity, present an ideal source for cell transplantation or tissue engineering therapies, but exact understanding of regulating mechanism underling MSC proliferation and differentiation remains a critical issue in securing their safe and efficient clinical application. This review outlines current knowledge regarding MSC cell surface biomarkers and molecular mechanisms of MSC differentiation and proliferation with emphasis on Wnt/β-catenin signaling, Notch signaling pathway, bone morphogenesis proteins and various growth factors functioning in regulation of differentiation and proliferation of MSCs. Possible relation of oncogene and immunosuppressive activities of MSCs with tumorigenicity or tumor generation is also addressed for safe translational clinical application. Fast increase of MSC knowledge and techniques has led to some successful clinical trials and helped devising new tissue engineering therapies for bone and cartilage diseases that severely afflict human health. Production of adult MSC-derived functional neurons can further extend their therapeutic application in nerve injury and neurodegenerative diseases. It is promising that MSCs shall overcome ethical and immunorejection problems appeared in human embryonic stem cells, and specific molecular targeting manipulation may result in practical MSC therapy for personalized treatment of various diseases in the regeneration medicine.