Current Medicinal Chemistry - Volume 15, Issue 2, 2008

In this review, several aspects of virtual screening are presented. Although, docking and scoring have been the most widely employed techniques, ligand-based virtual screening has also gained momentum in recent years. We have classified the docking programs into four categories, based on their underline theories, and accordingly describe the most up-to-date algorithms and newest versions. Similarly, three categories of scoring functions are presented, while their weighting schemes on particular binding terms are discussed. The latter is important, since knowledge of the function can be used to select the ones that could be more appropriate for targets of similar nature. Challenging aspects, such as protein flexibility and practices to select the most appropriate docking/scoring schemes, are also discussed. Finally, a real-life example is presented where a pharmacophore-driven approach combined with a docking exercise were undertaken in an iterative manner to successfully enhance the virtual screening hit rates. In the end, we present our own perspective for best practices in the field based on our experiences.

Recognition of hepatitis C virus (HCV) as an etiological factor in mixed cryoglobulinemia (MC) has dramatically changed our point of view in its treatment. Emphasis is placed on abatement and clearance of viral load and deletion of clonal expansions of IgM molecules with rheumatoid factor activity-synthesising B cells. The purpose of this review is to discuss the underlying scientific rationale and results of clinical studies of new treatment approaches to MC, with a focus on cell-depleting therapies and chemokine blockade. Additional antiviral agents directed to several phases of HCV life cycle acting with different or alternate mechanisms are proposed with the goal to enhance response rates more broadly suitable for MC patients with vasculitis and peripheral neuropathies. The majority of the available data on these new treatment approaches stems from open-label studies, but controlled trials are under way. Therapy directed against chemokines and/or cytokines represents an interesting and promising future target.

For many bone and joint diseases in humans, including postmenopausal osteoporosis, rheumatoid arthritis, and ankylosing spondylitis, an immune-mediated etiology has either been proven or is considered as a co-factor in pathogenesis. The identification of the receptor activator of nuclear factor κB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG)-interplay and the in-depth characterization of the signaling pathways induced upon RANK activation, including molecules such as TNF receptor-associated factor 6 (TRAF6), nuclear factor-κB (NF-κB), and signal transducer and activator of T cells (STAT)-3, now promise to give the opportunity to target osteoclastogenesis specifically. Additionally, many byways influencing osteoclastogenesis have been elucidated, thus giving rise to additional therapeutic approaches. These are based mainly upon the effects of diverse cytokines on osteoclast differentiation with interleukin (IL)- 17 and interferone (IFN)-γ being most prominent at the moment. The same applies for the recently established signaling pathways in osteoblastogenesis, which have attracted much attention in the recent years. In this respect, much attention has been attributed towards bone morphogenetic proteins (BMPs) and the Wnt signaling cascade. In this review, an overview on the key molecules, which (could) serve as promising targets for novel therapeutic interventions with the aim of enhancing osteoblast formation or suppressing osteoclast development, is given. Further on, antibody-based therapeutical schemes as well as methodologically novel, albeit predominantly theoretical at the moment, strategies in the fight against immune-mediated osteopathologies are discussed.

Carcinogenesis of hormone-related cancers involves hormone-stimulated cell proliferation, which increases the number of cell divisions and the opportunity for random genetic errors. In target tissues, steroid hormones are interconverted between their potent, high affinity forms for their respective receptors and their inactive, low affinity forms. One group of enzymes responsible for these interconversions are the hydroxysteroid dehydrogenases, which regulate ligand access to steroid receptors and thus act at a pre-receptor level. As part of this group, the 17β-hydroxysteroid dehydrogenases catalyze either oxidation of hydroxyl groups or reduction of keto groups at steroid position C17. The thoroughly characterized 17β-hydroxysteroid dehydrogenase type 1 activates the less active estrone to estradiol, a potent ligand for estrogen receptors. This isoform is expressed in gonads, where it affects circulating levels of estradiol, and in peripheral tissue, where it regulates ligand occupancy of estrogen receptors. Inhibitors of 17β-hydroxysteroid dehydrogenase type 1 are thus highly interesting potential therapeutic agents for the control of estrogen-dependent diseases such as endometriosis, as well as breast and ovarian cancers. Here, we present the review on the recent development of inhibitors of 17β-hydroxysteroid dehydrogenase type 1 published and patented since the previous review of 17β-hydroxysteroid dehydrogenase inhibitors of Poirier (Curr. Med. Chem., 2003, 10, 453). These inhibitors are divided into two separate groups according to their chemical structures: steroidal and non-steroidal 17β- hydroxysteroid dehydrogenase type 1 inhibitors. Their estrogenic/ proliferative activities and selectivities over other 17β-hydroxysteroid dehydrogenases that are involved in local regulation of estrogen action (types 2, 7 and 12) are also presented.

Demyelination occurs in several central nervous system (CNS) disorders, including multiple sclerosis, viral infection and spinal cord injury and can result in severe functional impairment. Therefore there is great interest in developing therapies promoting repair in CNS demyelinating diseases and trauma. Cell replacement therapy is an attractive approach for myelin repair, and experimental transplantation has provided convincing evidence of the repair potential of grafted myelin-forming cells. Schwann cells (SCs), oligodendrocyte progenitors, olfactory ensheathing cells and embryonic and neural stem cells have been shown to form myelin after transplantation into the demyelinated CNS. SCs are among the most promising candidates for autologous grafting. They can remyelinate spinal cord lesions after experimental demyelination, leading in some cases to functional recovery in rodent and primate models. However, SCs do not normally enter the CNS, and migration of SCs transplanted in CNS white matter is inhibited by astrocytes. As SC migration and myelination is mediated by interactions of sets of extracellular matrix molecules with cell surface molecules, genetic engineering of SCs to alter aspects of these interactions is a possible way forward. Thus efforts towards the development of SC-based therapies are focused in enhancing their migration and functional integration into the lesioned CNS. In addition, efforts are being made to use these cells as gene delivery vehicles for an array of molecules with repair potential. In this review we summarize data from the recent literature regarding the use of SCs in CNS repair and discuss the prospects for future therapeutic applications

Malaria, one of the major reemerging parasitic diseases, is caused by protozoal parasites belonging to the genus plasmodia. Antimalarial drugs have played a mainstream role in controlling the spread of malaria through the treatment of patients infected with the plasmodial parasites and controlling its transmissibility. The current line of therapy against malaria is faced with the hurdles of a low or total lack of efficacy due to the evolution of drug-resistant strains of the malarial parasites. Preventive vaccination against malaria is an ideal solution to this problem but is not expected to arrive for at least a decade. Development of antimalarial drugs involving novel mechanisms of action is therefore of imminent importance. Several novel drug candidates of synthetic and natural products origin as well as their combination therapies are currently being evaluated for their efficacy against the drug-resistant strains of the parasites. Various plasmodial targets/pathways, such as the Purine salvage pathway, Pyrimidine biosynthesis pathway as well as the processes in the apicoplast, have been identified and are being utilized for the discovery and development of novel antimalarial therapies. This review provides an overview of the latest developments in terms of drugs, combination therapies and novel plasmodial targets being carried out to counter the menace of drug-resistant malaria.

Dihydropyridine-based calcium antagonists (DHPs) are widely used drugs for the treatment of hypertension and angina pectoris. We, along with others, have recently found that nifedipine, one of the most widely used DHPs, inhibits apoptotic cell death of endothelial cells (ECs) as well as vascular inflammation and subsequently improves endothelial function in patients with cardiovascular risk factors, including hypertension and/or diabetes, thus slowing the development and progression of atherosclerosis in these patients. Several papers have suggested that nifedipine exerts beneficial metabolic effects in vivo through its anti-inflammatory properties as well. However, the underlying molecular mechanisms for the cardiometabolic actions of nifedipine remain to be elucidated, because ECs do not possess voltage-operated L-type calcium channels. Meanwhile, we have very recently found that Bay w 9798, a dihydropyridine structurally related to nifedipine with no calcium antagonistic ability, has anti-oxidative and anti-inflammatory properties in vitro. In this paper, we review the role of oxidative stress in the development of vascular injury, especially focusing on the relationships between advanced glycation end products-receptor system, oxidized low-density lipoprotein and tumor necrosis factor-α and vasculopathy. We further discuss the potential clinical utility of anti-oxidative properties of nifedipine on various cardiometabolic disorders.

Parathyroid hormone (PTH) secreted from parathyroid cells is a key regulator of circulating levels of calcium ion, which is maintained within a narrow physiological range mainly by the action of a cell surface Ca2+-sensing receptor (CaSR) residing on parathyroid cells. The CaSR belongs to the family C of G-protein-coupled receptors (GPCRs), all members of which have a large extra cellular domain called Venus flytrap, akin to bacterial nutrient sensor. Promiscuity of the CaSR is reflected in its binding to several physiologically relevant di- or polyvalent cations that could elicit cellular signaling, yet the ligand specificity remains poor. This problem has been circumvented by the discovery of calcimimetics, the positive allosteric modulators of the CaSR that activate the CaSR on parathyroid cells, immediately suppressing PTH secretion. Out of several small molecules that act as calcimimetics, cinacalcet is the most extensively studied. The discovery of the CaSR and these specific agonists provides important insights into the discovery of new drugs that will be discussed in this review from the perspective of their structure-activity relationship. The calcimimetic compound cinacalcet has obtained regulatory approval for the treatment of hyperparathyroidism and is the first positive allosteric modulator of any GPCR to reach the market. It has other important uses in dialysis patients with end-stage renal disease, in whom it decreases Ca P product. Pharmaceutically converse to calcimimetics are calcilytic compounds, which antagonize parathyroid CaSR and stimulate PTH secretion. Antagonism of the CaSR has the potential to yield an anabolic therapy for osteoporosis that awaits clinical validation.

Apoptosis (programmed cell death) plays a key role in the pathogenesis of many disorders including cerebral and myocardial ischemia, autoimmune and neurodegenerative diseases, infections, organ and bone marrow transplant rejection, and tumor response to chemotherapy and/or radiotherapy. Apoptosis in itself represents a complex mechanism where numerous (pro-apoptotic and antiapoptotic) molecules interact in an elaborate manner. Since the original description by Kerr et al. in 1972, clinical assessment of apoptosis has always required biopsies or aspirated material for in vitro investigations. Several well-established methods are available for in vitro tests using tissue specimens. However, a noninvasive detection of apoptosis would be of great benefit for many patients in various situations. Today, non-invasive techniques for direct in vivo detection of apoptotic cells are rare and urgently need improvement. The early in vivo detection of apoptotic cells can provide the physician with important information to develop further therapeutic strategies in chemotherapy or radiotherapy of tumors, in transplantation of organs, or in healing of infarct areas. In some preliminary publications, several authors reported on the in vivo use of caspase-inhibitors and annexin V, labeled with indium- 111, technetium-99m, iodine-123, iodine-124 or fluoride-18. In the present paper, we review the current applicability of both techniques for in vivo apoptosis imaging, and discuss the methodical problems.

The Liver X Receptor (LXR) α and β isoforms are members of the type II nuclear receptor family which function as a heterodimer with the Retinoid X Receptor (RXR). Upon agonist binding, the formation of the LXR/RXR heterodimer takes place and ultimately the regulation of a number of genes begins. The LXR isoforms share 77% sequence homology, with LXRβ having highest expression in liver, intestine, adipose tissue, and macrophages and LXRα being ubiquitously expressed. The aim of this article is to review the reported medicinal chemistry strategies towards the optimisation of novel non-steroidal chemotypes as LXR agonists. An analysis of the structural features important for LXR ligand binding will be given, utilising both structural activity relationship data obtained from LXR assays as well as X-ray co-crystallographic data obtained with LXR ligands and the LXR ligand binding domain (LBD). The X-ray co-crystallographic data analysis will detail the key structural interactions required for LXR binding/agonist activity and reveal the differences observed between chemotype classes. It has been postulated that a LXRβ selective compound may have a beneficial outcome on the lipid profile for a ligand by dissociating the favourable and unfavourable effects of LXR agonists. Whilst there have been a few examples of compounds showing a modest level of LXRα selectivity, obtaining a potent LXRβ selective compound has been more challenging. Analysis of the SAR and X-ray cocrystallographic data suggests that the rational design of a LXRβ selective compound will not be trivial.