Current Medicinal Chemistry - Volume 14, Issue 11, 2007

Few public health problems have captured the attention of the biomedical and lay communities alike as has Alzheimer Disease (AD). Several questions remain still open in disease management, as the necessity to delineate disease process from “normal ageing”. In the last few years, Mild Cognitive Impairment (MCI) has received significant attention, thus it represents the major risk factor for AD. Not all people diagnosed as having MCI, however, will develop AD, hence there is a need to reliably predict progression. To this aim, different biomarkers have been proposed with the attempt to identify MCI people who already have pre-clinical AD. Neuropsychological assessment, peripheral and CSF biomarkers as well as neuroimaging findings (both structural and functional) have reported variable accuracy values, but better results have been obtained by combined biomarker approach. In this review, we summarise the most recent findings on combined biomarkers and their usefulness in clinical practice for the early and preclinical diagnosis of AD.

Post-translational modification of proteins by poly(ADP-ribosyl)ation is involved in the regulation of a number of biological functions. While an 18 member superfamily of poly(ADP-ribose) polymerases (PARP)s has been described PARP-1 accounts for more than 90% of the poly(ADP-ribosyl)ating capacity of the cells. PARP-1 act as a DNA nick sensor and is activated by DNA breaks to cleave NAD(+) into nicotinamide and ADP-ribose to synthesize long branching poly(ADP-ribose) polymers (PAR) covalently attached to nuclear acceptor proteins. Whereas activation of PARP-1 by mild genotoxic stimuli facilitate DNA repair and cell survival, severe DNA damage triggers different pathways of cell death including PARP-mediated cell death through the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus. PAR and PARP-1 have also been described as having a function in transcriptional regulation through their ability to modify chromatin-associated proteins and as a cofactor of different transcription factors, most notably NF-κB and AP-1. Pharmacological inhibition or genetic ablation of PARP-1 not only provided remarkable protection from tissue injury in various oxidative stress-related disease models but it result in a clear benefit in the treatment of cancer by different mechanisms including selective killing of homologous recombination-deficient tumor cells, down regulation of tumor-related gene expression and decrease in the apoptotic threshold in the co-treatment with chemo and radiotherapy. We will summarize in this review the current findings and concepts for the role of PARP-1 and poly(ADP-ribosyl)ation in the regulation of transcription, oxidative stress and carcinogenesis.

An inflammatory process in the central nervous system (CNS) is believed to play an important role in the pathway leading to neuronal cell death in a number of neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, prion diseases, multiple sclerosis and HIV-dementia. The inflammatory response is mediated by the activated microglia, the resident immune cells of the CNS, which normally respond to neuronal damage and remove the damaged cells by phagocytosis. Activation of microglia is a hallmark of brain pathology. However, it remains controversial whether microglial cells have beneficial or detrimental functions in various neuropathological conditions. The chronic activation of microglia may in turn cause neuronal damage through the release of potentially cytotoxic molecules such as proinflammatory cytokines, reactive oxygen intermediates, proteinases and complement proteins. Therefore, suppression of microglia-mediated inflammation has been considered as an important strategy in neurodegenerative disease therapy. Several anti-inflammatory drugs of various chemical ingredients have been shown to repress the microglial activation and to exert neuroprotective effects in the CNS following different types of injuries. However, the molecular mechanisms by which these effects occur remain unclear. In recent years, several research groups including ours have attempted to explain the potential mechanisms and signaling pathways for the repressive effect of various drugs, on activation of microglial cells in CNS injury. We provide here a comprehensive review of recent findings of mechanisms and signaling pathways by which microglial cells are activated in CNS inflammatory diseases. This review article further summarizes the role of microglial cells in neurodegenerative diseases and various forms of potential therapeutic options to inhibit the microglial activation which amplifies the inflammation-related neuronal injury in neurodegenerative diseases.

The blood-brain barrier (BBB) impedes the influx of intravascular compounds from the blood to the brain. The elements composing the BBB are endothelial cells, pericytes and the end-feet of astrocytes. Among them, the endothelial cell barrier line is the most critical for preventing toxic substances from entering the brain. In this review, we focus on the ultrastructural distribution of important components in the intracellular junction and cytoplasm of brain endothelial cells. The ultrastructural distribution of tight junction-specific integral membrane proteins such as occludin, junctional adhesion molecules, claudin, peripheral zonula occludens protein-1 (ZO-1), adherens junction-specific transmembrane protein cadherin, and adherens junction-associated peripheral proteins α-catenin, β-catenin, and p120 catenin is reviewed. P-glycoprotein and some other transporters recently discovered in endothelial cells prevent several compounds from entering the brain parenchyma. It is likely that the transient inhibition of P-glycoprotein by antidepressants enables other medicines to enter the brain. Vesicular transport with clathrin-mediated or adsorptive endocytosis through endothelial cells is also critical for transportation of bloodborn substances from the bloodstream to the brain. How medicines pass the BBB to reach the brain parenchyma is discussed.

A combination of different HIV inhibitors into a single molecular entity is a strategy that is growing in popularity in HIVchemotherapy research. The high levels of resistance elicited by both nucleoside and non-nucleoside reverse transcriptase inhibitors has prompted the design of double-drugs combining these two entities with the aim of addressing the emergence of resistance. The strategy involves combining two different inhibitors into a single chemical entity via a linker, with the aim of improving the physicochemical characteristics of the individual compounds. Linkers may be sub-divided into cleavable and non-cleavable. While the former result in regeneration of the parent drugs of the double-drug once in the cell cytoplasm, the latter type is designed to allow the double-drug to target two active sites in a simultaneous or bifunctional fashion, which are located in close proximity. The linkers have been attached at the C-5', C-5 or N-3 positions of the nucleoside, and in some of the substrates synthesized, a synergistic anti-HIV activity has been observed. This review focuses on the design and synthesis of anti-HIV double-drugs reported to date.

Significant advances in therapeutic applications of proteins and peptides have brought new challenges in the field of drug development. Ordered protein aggregation known as amyloid formation has recently emerged as a universal phenomenon due to extensive research in protein folding and amyloid diseases. The amyloid represents a new generic structure characterized by cross-β-sheet formation in its core, which implies that any polypeptide can adopt this conformation under amyloid-prone conditions. Some widely-used biopharmaceuticals such as insulin, glucagon, amylin and calcitonin have been shown to form amyloids and this list may be significantly extended upon further research. Compared to soluble precursor proteins and amorphous aggregates amyloids gain new properties such as remarkable stability and protease resistance, polymorphism, selfpropagation via seeding and cross-seeding, cytotoxicity and induced immunogenicity. Some of them can be hazardous in biopharmaceutical applications. The causes of amyloid aggregation and strategies for its prevention are reviewed here. They utilize the current knowledge of amyloid properties, structure-based design principles and protein chemistry. Once these challenges are met, they will ultimately lead to safer and surer pharmaceuticals.

The envelope that encapsulates the cell nucleus has recently gained considerable interest, as several clinical syndromes are linked to mutations in its molecular components. Most disorders recognized so far are caused by defects in the nuclear lamins, building blocks of a filamentous network lining the nucleoplasmic side of the inner nuclear membrane. Nuclear lamins are the evolutionary precursors of cytoskeletal intermediate filaments and associate in a head-to-tail manner into a stable lamina at the nuclear periphery and into a more dispersed structure in the nucleoplasm. Lamins have a scaffolding function for several nuclear processes such as transcription, chromatin organization and DNA replication, and maintain nuclear and cellular integrity. Mutations in the LMNA gene, encoding A-type lamins, can cause cardiac and skeletal muscle disease, lipodystrophy and premature ageing phenotypes. Hence, the integrity of the nuclear envelope seems essential for longevity. Furthermore, the laminopathies provide evidence that metabolism and ageing are as tightly linked in humans as they are in model organisms such as C. elegans. In this review, we elaborate on the structure and functions of nuclear lamins, the spectrum of syndromes related to mutations in nuclear envelope components and pathogenic concepts unifying these disorders.

Selective estrogen receptor modulators (SERMs), known previously as “antiestrogens”, are a new category of therapeutic agents used for the prevention and treatment of diseases such as osteoporosis and breast cancer. SERMs act as ERagonist in some tissues while acting as ER-antagonist in others based on conformational change of the receptors, particularly at the helix 12. Currently, there are two classes of clinically approved SERMs; triphenylethylene derivatives (e.g., tamoxifen) and benzothiophene derivatives (e.g., raloxifene). Tamoxifen, raloxifene and toremifene are the most widely used SERMs. Tamoxifen, an antagonist of the breast tissue, is the first clinically identified compound with noticeable SERM activity. Although tamoxifen has been very successful in breast cancer treatment, its agonistic effect on the uterus is said to be associated with increase risk of developing endometrial cancer. Ideally, it is presumed that SERMs should selectively act as an agonist in the bone and brain while simultaneously acting as an antagonist in the breast and uterus. Therefore, the therapeutic goal of SERMs is the prevention of estrogen deficiency diseases without promoting estrogen-associated tumor growth. Therefore, the objective of this review is to summarize various effects that have been applied in improving the tissue-selectivity of SERMs, highlighting the emerging understanding of their mechanism of actions in selected target tissues and the development of the SERMs. The significance in recent discovery of selective estrogen receptor alpha modulators, SERAMs will also be reviewed.

Serious infections caused by opportunistic molds remain a major problem for public health. Immune deficiency following organ transplantation and aggressive cancer treatment has greatly increased the incidence of systemic mycoses, and invasive aspergillosis in patients with AIDS is associated with significant morbidity and mortality. Amphotericin B is the first-line therapy for systemic infection because of its broad-spectrum and fungicidal activity. However, considerable side effects limit its clinical utility. The echinocandins are large lipopeptide molecules that inhibit the synthesis of 1,3-β-D-glucan, a key component of the fungal cell wall. Three echinocandins have reached the market, and some others are in early clinical development. Caspofungin was the first echinocandin to be licensed for clinical use in most countries. Micafungin is licensed for clinical use in Japan, China, Taiwan, Jordan, Korea, Hong-Kong and the US, and anidulafungin is currently licensed in the US. The novel class of echinocandins represents a milestone in antifungal drug research that has further expanded our therapeutic options. Studies to date have shown that micafungin exhibits extremely potent antifungal activity against clinically important fungi, including Aspergillus and azole-resistant strains of Candida. In animal studies, micafungin is as efficacious as amphotericin B with respect to improvement of survival rate. Micafungin is also characterized by a linear pharmacokinetic profile and substantially fewer toxic effects. Micafungin is a poor substrate for the cytochrome P450 enzymes, and compared to azoles, fewer drug interactions are described. No dose adjustments of the drug are required in the presence of mycophenolate mofetil, cyclosporin, tacrolimus, prednisolone, or sirolimus. Strategies using this new echinocandin agent will benefit a large number of patients with severe immune dysfunction.

In our review entitled “DNA Repair Helicases as Targets for Anti-Cancer Therapy“ by Brosh et al. in Current Medicinal Chemistry, 2007, 14, 503-517. We wish to correct a mistake in the reference section which was overlooked. Reference numbers 114 and 115 were duplicated and also appear as 70 and 71 in the Reference List. Therefore, readers are advised that reference numbers 116-146 correspond to references 114-144 in the text. Thus, in the Reference List, reference number 116 becomes reference number 114, 117 becomes 115, 146 becomes 144, etc. We apologize for our error and the inconvenience to the reader.