Current Medicinal Chemistry - Volume 13, Issue 22, 2006

There is an increasing amount of evidence showing the importance of intermediate aggregation species of amyloid β (Aβ) in the pathogenic cascade of Alzheimer's disease (AD). Different Aβ assembly forms may mediate diverse toxic effects at different stages of the disease. Mouse models for AD suggest that intraneuronal accumulation of Aβ oligomers might be involved in AD pathogenesis at a very early stage of the disease. The detrimental effect of oligomeric Aβ on synaptic efficacy is suggested to be an early event in the pathogenic cascade. Also early neuronal responses as activation of the unfolded protein response are processes likely to be associated with the increased occurrence of oligomeric or low fibrillar Aβ in AD pathology. In later stages of AD pathology, the fibrillarity of Aβ increases, concomitantly with a neuroinflammatory response, followed by tau related neurofibrillary changes in end stage pathology. We will review recent findings in in vitro cell models, in vivo mouse models, and post mortem AD brain tissue in view of the effects of different Aβ peptide species on neurodegeneration during AD pathogenesis. Insight into the role of different Aβ species during AD pathogenesis is essential for the development of disease modifying drugs and therapeutical strategies..

A promising way to interfere with biological processes is through the control of protein-protein interactions by means of small molecules that modulate the formation of protein-protein complexes. Although the feasibility of this approach has been demonstrated in principle by recent results, many of the smallmolecule modulators known to date have not been found by rational design approaches. In large part this is due to the challenges that one faces in dealing with protein binding epitopes compared to, e.g., enzyme binding pockets. Recent advances in the understanding of the energetics and dynamics of protein binding interfaces and methodological developments in the field of structure-based drug design methods may open up a way to apply rational design approaches also for finding protein-protein interaction modulators. These advances and developments include (I) computational approaches to dissect binding interfaces in terms of energetic contributions of single residues (to identify “hot spot” residues), (II) prediction of potential binding sites from unbound protein structures, (III) recognition of allosteric binding sites as alternatives to directly targeting interfaces, (IV) docking approaches that consider protein flexibility and improved descriptions of the solvent influence on electrostatic interactions, and (V) data-driven docking approaches. Here, we will summarize these developments with a particular emphasis on their applicability to screen for or design small-molecule modulators of protein-protein interactions.

The approach of chemical genetics has been widely used to study biological systems and to discover new drugs, signaling pathways and targets. The current review focuses on the development and utilization of a cell- and caspase-based apoptosis induction assay for the discovery of apoptosis inducers. We began with the development of a cell based phenotypic assay, which was used for the identification of small molecules that exhibit apoptosis inducing activities, including N-phenyl nicotinamides, gambogic acid, indole-2-carboxylic acid benzylidene-hydrazides, 4-aryl-4H-chromenes and 3-aryl-5-aryl-1,2,4-oxadiazoles. Through medicinal chemistry and biological studies, in vivo active compounds were identified, such as MX116407 as a tumor vascular disrupting agent with potent in vivo anticancer activity. The molecular targets of in vivo active compounds were identified using reagents designed and synthesized based on the SAR, including the identification of tail-interacting protein 47 (TIP47), an insulin-like growth factor II (IGF II) receptor binding protein, as the molecular target of 3-aryl-5-aryl-1,2,4-oxadiazoles; and Transferrin receptor I (TfR), a transmembrane protein that interacts with transferrin (Tf) for the transport of iron into cells, as the molecular target of gambogic acid. We demonstrated that chemical genetics is a very useful approach for anticancer drug research, from the discovery of potential drugs, to the understanding of signaling pathways and identification of druggable targets.

The structural and functional aspects of cytochrome P450 (CYP) enzymes are reviewed in the light of current developments in X-ray crystallography and other physical evidence, together with recent findings on the regulation of, and polymorphisms in, the human drug-metabolizing CYPs. It is emphasized that the crystal structures of eukaryotic CYPs are particuarly useful for constructing homology models of the human enzymes associated with drug metabolism, and that these models can aid in the high-throughput screening of novel compounds destined for human exposure.

Approximately 40%-60% of developing drugs failed during the clinical trials because of ADME/Tox deficiencies. Virtual screening should not be restricted to optimize binding affinity and improve selectivity; and the pharmacokinetic properties should also be included as important filters in virtual screening. Here, the current development in theoretical models to predict drug absorption-related properties, such as intestinal absorption, Caco-2 permeability, and blood-brain partitioning are reviewed. The important physicochemical properties used in the prediction of drug absorption, and the relevance of predictive models in the evaluation of passive drug absorption are discussed. Recent developments in the prediction of drug absorption, especially with the application of new machine learning methods and newly developed software are also discussed. Future directions for research are outlined.

Rimonabant (SR141716, Acomplia®) has been described as an antagonist/inverse agonist at the cannabinoid receptor type 1 (CB1). It has been widely used as a tool to evaluate the mechanisms by which cannabinoid agonists produce their pharmacological effects and to elucidate the respective physiological or pathophysiological roles of the CB1 receptor. It has become increasingly clear that rimonabant can exert its own intrinsic actions. These may be viewed as evidence of either the inverse agonist nature of rimonabant or of tonic activity of the endocannabinoid system. To date, data obtained from clinical trials (RIO North America, RIO Europe and RIO Lipid) indicate that rimonabant may have clinical benefits in relation to its anti-obesity properties and as a novel candidate for the treatment of metabolic and cardiovascular disorders associated with overweight and obesity. Other clinical trials, such as the STRATUS study, have also shown that rimonabant may be effective in smoking cessation, and that the drug has a reasonable safety profile. Recently, it has been shown that rimonabant prevents indomethacin-induced intestinal injury by decreasing the levels of pro-inflammatory cytokine tumour necrosis factor alpha (TNFα), thus indicating that CB1 receptor antagonists might exhibit potential antiinflammatory activity in acute and chronic diseases.

Breathing is generated and controlled by a brainstem neuronal network. Both intrinsic and synaptic interactions are involved in respiratory rhythm generation and their contribution is state-dependent, changing with hypoxia and the neuromodulatory state. Cellular mechanisms involved in acute or chronic pathological conditions are still unknown. A dysfunction in the neuronal network that controls breathing may be involved in several respiratory disorders such as central sleep apnea, sudden infant death syndrome, congenital hypoventilation, and in some clinical conditions that produce breathing dysfunction such as drug-induced respiratory depression, obesity hypoventilation syndrome, etc. Despite the fact that several drugs are currently used to treat these diseases, the probable effects of this pharmacotherapy on the central rhythm generator and on other neuronal networks related with breathing control is poorly understood. Here, we review the current pharmacological approaches in the treatment of respiratory disorders, such as acetazolamide, theophylline, aminophylline, progesterone, nitric oxide. Possible effects of these drugs on the central respiratory network are discussed and putative therapeutic targets for the development of future pharmacological therapies suggested.

Breakdown of glucose under physiological conditions gives rise to glucose degradation products (GDPs). GDPs are also formed during heat sterilization of glucose-containing peritoneal dialysis fluids (PDfluids). In PD-fluids GDPs have been shown in many different in vitro assays to be responsible for adverse effects such as growth inhibition, and impaired leukocyte function and impaired wound healing of peritoneal mesothelial cells. They have been linked to changes in the peritoneal membrane as well as to the decline in residual renal function of PD-patients. In diabetes one of the GDPs, 3-deoxyglucosone (3-DG), has been proposed as responsible for side-effects rather the glucose itself. 3,4-dideoxyglucosone-3-ene (3,4-DGE) was recently identified as the most bio-reactive GDP in PD-fluids. It exists in equilibrium with a pool of precursors, consisting of 3-DG but also of other hitherto unidentified GDPs. In PD-fluids the concentration of GDPs in this pool is 10-20 times as high as that of 3,4-DGE. In vitro 3,4-DGE induces caspase-dependent apoptosis of neutrophils and peripheral blood mononuclear cells. Such induction may explain immunosuppressive properties of 3,4-DGE and contribute to an impaired peritoneal antibacterial defense. 3,4-DGE also induces renal cell apoptosis. This may explain the better preservation of residual renal function in PD patients not exposed to GDPs. The concentration of 3-DG increases with worsening glycemic control and has been implicated in the genesis of diabetic microangiopathy. As 3,4-DGE is much more bio-reactive than 3-DG and as it may be easily recruited from the pool, it seems probable that 3,4-DGE is the molecule involved in the diabetic lesions rather than 3-DG itself. Thus, 3,4-DGE might contribute to diabetic nephropathy and to the impaired antibacterial defenses in diabetics. Unraveling of the pool dynamics of the GDPs and the molecular mechanisms of GDP-mediated cell injury may provide new therapeutic insights in PD and diabetes.

Cyclosporin-A (CsA) is a potent and selective immunosupressive agent that, due to its mechanism of action, may be used to inhibit both the inflammatory reaction and the synthesis of nitric oxide (NO), a wellknown neurotoxic agent. By these means CsA may diminish overproduction of free radicals and secondarily, lipid peroxidation (LP), both observed after acute spinal cord (SC) injury. Studies performed on reliable experimental models, using a well-standardized CsA dosing scheme, showed that a low dose of this drug inhibits the expression and activity of constitutive and inducible nitric oxide synthases (NOS), two enzymes strongly involved in the production of NO after SCI. Likewise, this compound inhibits LP. This inhibition is equivalent to the one induced by methylprednisolone (MP) at a high dose, but without the deleterious effects of the latter upon the survival of the animals. Moreover, inhibition of LP by CsA significantly correlates with a decrease in the demyelination process at the epicenter of the lesion, a significant survival of neurons in the red nucleus and enhanced motor recovery in animals submitted to a severe SC contusion. CsA acts as a neuroprotector agent after SC injury; hence, this drug may be useful in the treatment of acute SCI. CsA deserves further study in experimental animal models and in humans.

Histamine plays a prominent and diverse role in the pathophysiology of allergic disease and therapeutic intervention is therefore typically focused on blocking the effects of this biogenic amine. A new antihistamine, levocetirizine, is the R-enantiomer of cetirizine dihydrochloride and like its parent compound undergoes minimal hepatic metabolism. Levocetirizine has pharmacodynamically and pharmacokinetically favourable characteristics, including high bioavailability, rapid onset of action, limited distribution and a low degree of metabolism. Clinical trials indicate that it is safe and effective for the treatment of allergic rhinitis and chronic urticaria with a minimal number of untoward effects. Furthermore, several recent studies have demonstrated that, in addition to its being a potent antihistamine, levocetirizine has several anti-inflammatory effects that are observed at clinically relevant concentrations that may enhance its therapeutic benefit.

Thrombolysis has become an approved therapy for acute stroke. However, many stroke patients do not benefit from such treatment, since the presently used criteria are very restrictive, notably with respect to the accepted time window. Even so, a significant rate of intracranial hemorrhage still occurs. Conventional cerebral computed tomography (CT) without contrast has been proposed as a selection tool for acute stroke patients. Recently, more modern magnetic resonance imaging (MRI) and CT techniques, referred to as diffusion- and perfusion-weighted imaging, and perfusion-CT, have been introduced. They afford a comprehensive noninvasive survey of acute stroke patients as soon as their emergency admission, with accurate demonstration of the site of arterial occlusion and its hemodynamic and pathophysiological repercussions of the brain parenchyma. The objective of this review article is to present the advantages and drawbacks of CT, using iodinated contrast, and MRI, using gadolinium, in the evaluation of acute stroke patients.