Current Medicinal Chemistry

ISSN: 0929-8673

Current Medicinal Chemistry
Volume 14, Number 5, 2007

Contents


DNA Repair Helicases as Targets for Anti-Cancer Therapy Pp. 503-517
Rigu Gupta and Robert M. Brosh, Jr
[Abstract]


Pgp and FLT3: Identification and Modulation of Two Proteins that Lead to Chemotherapy Resistance in Acute Myeloid Leukemia Pp. 519-530
János Kappelmayer, Miklós Udvardy and Péter Antal-Szalmás
[Abstract]


Synthetic Peptides for the Immunodiagnosis of Human Diseases Pp. 531-546
M.J. Gómara and I. Haro
[Abstract]


Chronic HCV-Related Autoimmunity: A Consequence of Viral Persistence and Lymphotropism Pp. 547-554
A. Kessel and E. Toubi
[Abstract]


Building a Bridge Between Clinical and Basic Research: The Phenotypic Elements of Familial Predisposition to Type 1 Diabetes Pp. 555-567
E. Matteucci and O. Giampietro
[Abstract]


Genetics of Gestational Diabetes Mellitus Pp. 569-583
Nael Shaat and Leif Groop
[Abstract]


Cardiovascular cGMP-Generating Systems in Physiological and Pathological Conditions Pp. 585-599
M.C. Cerra and D. Pellegrino
[Abstract]


Signaling Through RAS-RAF-MEK-ERK: from Basics to Bedside Pp. 601-623
Armin Zebisch, Armin P. Czernilofsky, György Keri, Julja Smigelskaite, Heinz Sill and Jakob Troppmair
[Abstract]




Abstracts


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DNA Repair Helicases as Targets for Anti-Cancer Therapy
Rigu Gupta and Robert M. Brosh, Jr

The genetic complexity of cancer has posed a formidable challenge to devising successful therapeutic treatments. Tumor resistance to cytotoxic chemotherapy drugs and radiation which induce DNA damage has limited their effectiveness. Targeting the DNA damage response is a strategy for combating cancer. The prospect for success of chemotherapy treatment may be improved by the selective inactivation of a DNA repair pathway. A key class of proteins involved in various DNA repair pathways is comprised of energy-driven nucleic acid unwinding enzymes known as helicases. DNA helicases have been either implicated or have proposed roles in nucleotide excision repair, mismatch repair, base excision repair, double strand break repair, and most recently cross-link repair. In addition to DNA repair, helicases have been implicated in the cellular processes of replication, recombination, transcription, and RNA stability/processing. The emerging evidence indicates that helicases have vital roles in pathways necessary for the maintenance of genomic stability. In support of this, a growing number of human genetic disorders are attributed to mutations in helicase genes. Because of their essential roles in nucleic acid metabolism, and more specifically the DNA damage response, helicases may be a suitable target of chemotherapy. In this review, we have explored this hypothesis and provided a conceptual framework for combinatorial treatments that might be used for combating cancer by inhibiting helicase function in tumor cells that already have compromised DNA repair and/or DNA damage signaling. This review is focused on helicase pathways, with a special emphasis on DNA cross-link repair and double strand break repair, that impact cancer biology and how cancer cells may be chemosensitized through the impairment of helicase function.


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Pgp and FLT3: Identification and Modulation of Two Proteins that Lead to Chemotherapy Resistance in Acute Myeloid Leukemia
János Kappelmayer, Miklós Udvardy and Péter Antal-Szalmás

Acute myeloid leukaemia (AML) comprises 80% of acute adult leukaemias and the disease has mostly an unfavourable outcome. Diagnostic criteria rely primarily on morphological classification, while prognostic evaluation is determined by cytogenetic methods. Survival is highly variable and it is a matter of debate, whether alternative therapeutic approaches may improve the effectiveness of conventional cytotoxic drug treatment. Two transmembrane proteins undoubtedly contribute to worse prognosis: P-glycoprotein (Pgp) and FLT3. Pgp is a transmembrane, ATP-cassette binding efflux pump that efficiently removes structurally unrelated xenobiotics from leukaemic blasts. This leads to inefficiency towards several cytotoxic drugs, hence the phenomenon is called multidrug resistance. FLT3 is a transmembrane tyrosine kinase and an internal tandem duplication can considerably augment its kinase activity. Both mechanisms lead to chemotherapy resistance and significantly shorter survival; thus several studies have been designed to treat patients via therapeutic measures that neutralize these proteins. This review focuses on the pathophysiological phenomena and the detection methods of Pgp and FLT3 as well as on novel therapeutic strategies that are offered by their inhibition.


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Synthetic Peptides for the Immunodiagnosis of Human Diseases
M.J. Gómara and I. Haro

Synthetic peptides have been shown to be valuable tools for viral laboratory diagnosis and can provide uniform, chemically well-defined antigens for antibody analysis, reducing inter- and intra-assay variation.

The main aim in the development of peptide-based diagnostic tests is to recognise specific antibodies induced by the whole viral proteins but using selected short fragments containing the most potent antigenic determinants. The success of this approach depends on the extent to which synthetic peptides are able to mimic the immunodominant epitopes of antigens. In recent years, synthetic peptides that mimic specific epitopes of infectious agents’ proteins have been used in diagnostic systems for various human diseases.

The present review summarizes some of the drawbacks of the use of relatively short linear peptides as antigenic substrates and the subsequent chemical strategies developed in order to overcome the low peptide reactivity against specific antibodies. Moreover, it outlines the most significant bibliography published in the last five years which provides validated peptide based tests potentially useful for diagnosis of viral, bacterial, parasitic and autoimmune diseases.


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Chronic HCV-Related Autoimmunity: A Consequence of Viral Persistence and Lymphotropism
A. Kessel and E. Toubi

Hepatitis C virus (HCV)-host interaction, namely the host immune reaction against various viral proteins, determines viral persistency and the severity of liver damage. The strong lymphotropism of HCV has been proven to be responsible in part for its ability to evade the peripheral immune response and possibly the frequency of HCV-related autoimmunity. Various mechanisms were reported to be responsible for HCV persistency and its association with autoimmunity. Of these, enhanced T cell apoptosis was reported to contribute to viral persistency and disease severity. The issue of HCV-related autoimmunity has partly been shown to be related to the resistance of CD5+ B cell subpopulation to apoptosis. Autoimmunity has been reported by many to include a wide range of autoantibodies such as rheumatoid factor, ani-cardiolipin and smooth muscle antibodies. In this review our aim is to summarize the data on the mechanisms responsible for HCV persistence and HCV-related autoimmunity. We will try to determine the importance of autoimmunity in the evaluation of chronic HCV infected patients.


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Building a Bridge Between Clinical and Basic Research: The Phenotypic Elements of Familial Predisposition to Type 1 Diabetes
E. Matteucci and O. Giampietro

Familial aggregation has been shown for type 1 diabetes (T1D) although the nature of the factors (environment and/or genetics) responsible remains unclear. Familial clustering of diabetic nephropathy as well as of increased cardiovascular morbidity and early mortality has also been observed.

This review describes the nearly 20 years history of our investigation in parallel with contemporary literature. The story is presented from the early years’ strong focus on possible markers of T1D nephropathy (urinary albumin, urinary enzymes, erythrocyte Na/Li countertransport, and erythrocyte Na/H exchange) to the last clinical investigations to determine relevant biological markers of familial predisposition to T1D. Our studies of case-families recruited unaffected first-degree relatives of sporadic T1D cases and population-based controls. Unlike multiple-case families, these families are those less likely to carry a strong genetic predisposition. Participants were both interviewed and provided biological material for a detailed functional characterisation of their biochemical phenotype. These studies have initially excluded that the erythrocyte Na/H exchange could be a marker of diabetic nephropathy. On the contrary, NHE activity was significantly higher in T1D family members independently of the presence of renal disease. Basic science knowledge of NHE and its functional implications have also been reviewed. Unexpectedly, we found evidence of increased oxidative stress in nondiabetic normotensive relatives of T1D patients, apart from soluble markers of autoimmunity and despite seemingly intact antioxidant defences. Markers of oxidation were associated with markers of inflammation and we concluded that the familial increase in NHE activity could be ascribed to the direct stimulatory effect of oxidative stress.

Relatives showed also immunological hallmarks and cardiovascular abnormalities that were related to indices of oxidative stress and metabolic syndrome. Other peculiarities emerged from measuring the erythrocytes redox system that exports electrons across the cell membrane to external oxidants as a function of cytoplasmic electron donor concentration. This electron transfer might reflect the functional state of membrane proton pumps that modulate intracellular redox levels. The transport system contributed to oxidation in T1D families, whereas in healthy people it protected from oxidation. Furthermore, dietary intake of vitamin C and sporting activities modulated erythrocyte electron transfer efficiency.

The contribution of environmental factors was investigated using the European Prospective Investigation of Cancer and Nutrition questionnaires that provided evidence of common unhealthy dietary behaviours, which could even predispose to the development of diabetes and cardiovascular complications, in subjects living in Pisa. However, lifestyle of T1D relatives was indistinguishable from those of controls, except for the higher daily intake of niacin and the lower physical activity levels. No difference in smoking or alcohol consumption emerged among families and controls.

The oxidative stress is a non-specific though certain component of pathogenesis at numerous diseases states of aerobic organisms. Although molecular genetic analysis has produced significant progress in T1D phenotype, much remains to be learned about the molecular sequence of events leading from a generic familial pro-oxidant background to a sporadic form of T1D (where oxidative damage targets the insulin-secreting cells).


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Genetics of Gestational Diabetes Mellitus
Nael Shaat and Leif Groop

About 2-5% of all pregnant women develop gestational diabetes mellitus (GDM) during their pregnancies and the prevalence has increased considerably during the last decade. GDM is a heterogeneous disorder that is defined as carbohydrate intolerance with onset or first recognition during pregnancy. It is manifested when pancreatic beta cells are no longer able to compensate for the increased insulin resistance during pregnancy, but the pathogenesis of the disease is still largely unknown. GDM is considered to result from interaction between genetic and environmental risk factors. Genetic predisposition to GDM has been suggested since GDM clusters in families. Also, women with mutations in MODY (Maturity onset diabetes of the young) genes often present with GDM. In addition, common variants in several candidate genes (e.g. potassium inwardly rectifying channel subfamily J, member 11 [KCNJ11], Glucokinase [GCK], Hepatocyte nuclear factor-1alpha [HNF1A] etc.) have been demonstrated to increase the risk of GDM. Old age, obesity and high fat diet represent some important non-genetic factors. There are several approaches to search for genes predisposing to a polygenic disease like GDM including linkage and association studies, expression profiling and animal models. A combination of several methods is usually necessary. Identification of the underlying genetic causes of GDM will eventually give a better view of the mechanisms that contribute to the pathophysiology of the disease. Furthermore, it may improve options to possibly prevent GDM and complications for the mother and her child. This review focuses on the genetics of GDM and possible implications in clinical practice.


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Cardiovascular cGMP-Generating Systems in Physiological and Pathological Conditions
M.C. Cerra and D. Pellegrino

The intracellular messenger cyclic GMP (cGMP) represents the key signal in several transduction pathways throughout the animal world. In the heart cGMP signaling contributes to functional interaction of different cell types. Nitric oxide (NO) and natriuretic peptides (NPs), major autocrine-paracrine cardiovascular regulators, increment intracellular cGMP through guanylate cyclases (GCs). NO and NPs interact with two GC types: cytosolic (soluble: sGC) and membrane bound [particulate: pGC (NP receptor types A and B)], respectively. Depending on sub-cellular localization and regulation of the enzymes, cGMP produced by either pGC or sGC exerts different complementary effects. The two pathways are reciprocally regulated. NPs-depending pGC is modulated by NO-cGMP signaling, and the activity of NO is influenced by cellular concentrations of both NO itself and NPs. This heterologous feedback regulates GCs, linking cardiovascular autocrine-paracrine activities of NPs and NO. Importance of these cGMP converging routes goes far beyond their role under normal conditions. They are of relevance especially in disease states when tissue and circulating levels of NPs, and local NO production are altered. An example is the endothelial dysfunction associated with deficient NO production and uncoupled endothelium-myocardium communications. In this case, NPs-pGC-cGMP could supplement the reduced activity of NO-scGC-cGMP pathway. In addition, these systems regulate cell growth and apoptosis, playing a role in myocardial pathological morpho-functional remodeling. Here we will review recent concepts on NO/NPs dependent control of heart function in vertebrates, also focusing on cGMP-activated downstream signaling and its role in health and disease conditions.


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Signaling Through RAS-RAF-MEK-ERK: from Basics to Bedside
Armin Zebisch, Armin P. Czernilofsky, György Keri, Julja Smigelskaite, Heinz Sill and Jakob Troppmair

Aberrant signaling caused by mutations in the RAS-RAF-MEK-ERK pathway and its upstream activators critically contributes to human tumor development. Strategies, which aim at inhibiting hyperactive signaling molecules, appear conceptually straight forward, but their translation into clinical practice has been hampered by many setbacks. Understanding structure, function and regulation of this intracellular pathway as well as its crosstalk with other signaling activities in the cell will be essential to ensure reasonable usage of new therapeutic possibilities. This review provides an understanding of this signaling cascade as revealed by genetic and biochemical approaches and discusses the existing or arising possibilities to interfere with unphysiological activation in cancer. Signaling aberrations and signal transduction therapies will be discussed exemplary for two types of hematological neoplasia, acute myeloid leukemia (AML) and the myelodysplastic syndromes (MDS). In the future understanding the role of tumor stem cells, both as a source of tumor recurrence and tumor heterogeneity, the signals controlling their fate as well as epigenetic changes in cancer will be the next critical steps to further advance the applicability of these novel therapeutic strategies.