Endocrine, Metabolic & Immune Disorders-Drug Targets (Formerly Current Drug Targets - Immune, Endocrine & Metabolic Disorders) - Volume 6, Issue 3, 2006

Tumors produce several factors, such as Prostaglandins (PGs), Interleukin (IL)-10, Vascular Endothelial Growth Factor (VEGF) and Transforming Growth Factor (TGF)-β , which may directly or indirectly inhibit the immune response and may hamper immunotherapy. Furthermore, cells of innate or adaptive immunity, recruited by tumor-derived factors, may contribute in immunosuppression. Regulatory T (Treg) cells such as the “naturally occurring” CD4+/CD25+ Treg and the IL-10-induced Tr1 cells are major players in this arena. Paradoxically Treg cells are stimulated by IL-2, which is used in tumor immunotherapy. Treg cells suppress T cell responses through soluble factors or by contactdependent mechanisms, such as the Cytotoxic T Lymphocyte Antigen (CTLA)-4-mediated induction of Indoleamine 2,3- Dioxygenase (IDO) in dendritic cells (DC). IDO inhibits T cell responses by depleting Tryptophan and producing Kynurenine, which is toxic to lymphocytes. Macrophages, granulocytes or myeloid suppressor cells (MSC) suppress immunity by other enzymatic mechanisms, involving Arginase and Nitric Oxide Synthase (NOS). Subversion of tumor immunosuppression is required for successful immunotherapy. Attempts to block or eliminate Treg cells have been made by the use of chemotherapy, anti-CD25 or anti-CTLA-4 antibodies, IL-2-toxin chimeric proteins or Glucocorticoidinduced TNF-like Receptor (GITR) and CD134/OX-40 ligands. Tumor cells genetically modified to secrete IL-21 (an immune-stimulatory “IL-2-like” cytokine, which is not involved in immune regulation) cured experimental metastases in combination with anti-CD25 monoclonal antibodies (mAbs). Also strategies aimed at blocking enzyme-based immunesuppressive mechanisms are suitable, as suggested by experimental evidences in mouse tumor models.

Conventional drug screening has been targeted, in many cases, on cell surface receptors, e.g., G-Protein coupled receptors, to regulate cellular signaling and thus function. There is emerging evidence, however, that such targets can be expanded to effector enzymes of receptors because effector enzymes have multiple subtypes that differ in tissue distribution, and thus targeting such molecules may lead to organ-specific pharmacological regulation. An example is phosphodiesterase, which degrades cyclic nucleotides. Subtype-specific phosphodiesterase inhibitors, such as sildenafil citrate, a type 5 phosphodiesterase inhibitor, and milrinone, a type 3 phosphodiesterase inhibitor, are now widely used in the treatment of erectile dysfunction and heart failure, respectively. Adenylyl cyclase, which synthesizes cyclic AMP, has at least 9 isoforms that differ in tissue distribution. Transgenic mouse studies utilizing such isoforms have identified the roles of each isoform. Forskolin, a natural plant extract, was first identified as a general stimulator of adenylyl cyclase more than 20 years ago. Recently, 6-[3-(dimethylamino)propionyl]forskolin, a water-soluble forskolin derivative with high selectivity for type 5 (cardiac) adenylyl cyclase was developed and has been widely used in the treatment of acute heart failure. Adenine analogs or P-site inhibitors, which are classic, but not isoform-specific adenylyl cyclase inhibitors, are now utilized to develop isoform-specific inhibitors as well. Putting together, targeting adenylyl cyclase isoforms, either of isoform-specific stimulation or inhibition, may be a novel strategy to develop new drugs in the next decade.

Hyponatremia is a very common electrolyte disorder often caused by the dysregulation of arginine vasopressin (AVP) secretion and the effects of the hormone at its receptors and is associated with significant morbidity and mortality. Recent developments in the understanding of water homeostasis and AVP actions at the kidney, both in normal circumstances and in pathologic conditions, has created the possibility of new therapies that directly target the inappropriate excess of AVP stimulation of vasopressin V2 receptors (V2Rs) in the kidney. Preclinical and clinical trial results indicate that AVP V2R antagonism is a highly promising and rational approach for the treatment of dilutional hyponatremia caused by excessive retention of water. This review of hyponatremia and its therapy is intended to educate clinicians who manage patients who have hyponatremia and its complications. Background information on hyponatremia is presented and the pertinent published literature with regard to the diagnosis and therapy of this disorder is summarized with a specific focus on AVP-receptor antagonists. Agents that antagonize AVP V2Rs and promote aquaresis, the electrolyte-sparing excretion of free water, are likely to be effective and well tolerated therapies for the treatment of dilutional hyponatremia.

Glucocorticoid hormones play essential roles in adaptation to stress, regulation of metabolism and inflammatory responses. Their effects primarily depend on their binding to intracellular receptors leading to altered target gene transcription as well as on cell-type specific biotransformation between 11β -hydroxy glucocorticoids and their 11- oxo metabolites. The latter effect is accomplished by two different 11 β-hydroxysteroid dehydrogenase isozymes, constituting a shuttle system between the receptor ligand cortisol and its non-binding precursor cortisone. Whereas the type 1 enzyme (11β-HSD1) is in vitro a NADP(H)- dependent bidirectional enzyme, it reduces in most instances in vivo cortisone to active cortisol. The type 2 enzyme is an exclusive NAD+ dependent dehydrogenase of glucocorticoids, thus “protecting” the mineralocorticoid receptor against illicit occupation by cortisol. Inhibition of tissue-specific glucocorticoid activation by 11 β-HSD1 constitutes a promising target in the treatment of metabolic and cardiovascular diseases. Pharmacological inhibition leads in animal models to lowered hepatic glucose production and increased insulin sensitivity, the primary goals in therapy of diabetes mellitus. Importantly, 11 β-HSD1 activity appears to be intrinsically linked to all features of the metabolic syndrome, which could at least in animal experiments be modulated by use of synthetic selective inhibitors. Importantly, these features include not only insulin resistance but also dyslipidemia, obesity and arterial hypertension. Animal studies and pharmacological experiments suggest further unrelated target areas, for example improvement of cognitive function and treatment of glaucoma, due to the role of glucocorticoids and cellular activation by 11 β-HSD1 in these pathologies. The recent development of specific 11 β-HSD1 inhibitors coupled with advances on structural knowledge and regulation of the 11 β-HSD1 target has undoubtedly promoted the understanding of glucocorticoid control of metabolic regulation. Taken together, it appears that inhibitors against 11 -HSD1 constitute a promising avenue for novel treatment strategies against the underlying causes of cardiovascular and other metabolic diseases.

Angiogenesis is necessary for growth and the spread of human tumors. Animal studies also suggest that angiogenesis is an important interspecies biological mechanism of tumor development. Angiogenesis is a complex multistep cascade modulated by both positive soluble factors, such as vascular endothelial growth factor, thymidine phosphorylase, basic-fibroblast growth factor and negative soluble factors such as angiostatin and endostatin. From the imbalance of the above angiogenesis regulators, tumor endothelial cells may divide up to 50 times more frequently than endothelial cells of normal tissue. Published studies have suggested that the assessment of microvessel density (MVD) or endothelial area (EA) can be considered as surrogate markers of angiogenesis with biological and prognostic relevance. Literature data on angiogenesis of mesothelioma are inconclusive, with only a few studies performed in primary peritoneal mesothelioma (PPM) due to the rarity of the disease. We assessed immunohistochemically MVD and EA and their biological and clinical significance in a consecutive series of 23 PPM cases. MVD and EA were detected in “hot spots” by a computerized image analyzer. The mean value of MVD and EA was 27 ± 14 and 26.04 ± 8.35 x10-2 μ2 per field (400x), respectively. Patients with a high MVD or EA tumors showed a more clinical aggressiveness due to the presence of ascites and a shorter overall survival. Our results suggest that PPM is an angiogenesis-dependent neoplasia. Therefore, antiangiogenic compounds should be tested particularly in those patients with highly vascularized PPM.

The aim of this investigation was to establish potential oxidative effects of glucose, advanced glycation end products (AGE) and nicotine (N) in a fibroblast cell culture model using the anti-oxidants glutathione (G) and insulin like growth factor (IGF). Assays of androgen metabolites were used as biomarkers of healing in this context. Confluent monolayer cultures of human gingival fibroblasts were established in 24 well multiwell plates and incubated in Eagle's MEM for 24h using two radiolabelled androgen substrates 14C-testosterone/14C-4-androstenedione. The established effective concentrations of G1000, glutathione and AGE were used alone and in combination with nicotine and insulin-like growth factor. The medium was then solvent extracted for steroid metabolites, evaporated to dryness and subjected to thin layer chromatography in a benzene acetone solvent system 4:1 v/v for separation of formed metabolites. The metabolites were quantified, using a radioisotope scanner. Significant reduction in the yields of DHT in response to G1000, AGE and nicotine (n=6; p<0.003) were overcome by glutathione (n=6; p<0.002). The stimulatory effect of IGF when combined with AGE was further enhanced by the antioxidant effect of glutathione (n=6; p<0.003). Glucose, AGE and nicotine had a significant inhibitory effect on the yields of the androgen biomarker DHT, overcome by the antioxidant glutathione and IGF, suggestive of an oxidant role for the former agents and an anti-oxidant one for the latter. These agents affected yields of androgen metabolites, biomarkers of oxidative stress and repair, with potential implications on healing in uncontrolled diabetic smokers.

Microparticles (MPs) are small vesicles released from the membrane surface during eukaryotic cell activation or apoptosis. They originate from various cell types, displaying the typical surface cell proteins and cytoplasmic components of their cell origin. Their procoagulant properties are linked to phosphatidylserine exposed at their surface. Numerous reports have shown that MPs are able to mediate long-range signaling, acting on different targets from those of their own cellular origin. MPs-mediated binding to other cells occurs by integration into the membrane, by adhesion to the cell surface or by ligand-receptor interaction. Elevated levels of circulating MPs have been detected in cardiovascular and immune-mediated diseases. Despite extensive studies of the procoagulant and pro-inflammatory properties of MPs, little is known about their effect on vascular function. MPs accumulate in atherosclerotic plaques and injured vascular wall. Circulating MPs from patients with myocardial infarction induce endothelial dysfunction by impairing the endothelial nitric oxide (NO) pathway, without causing changes in endothelial NO-synthase (eNOS) expression. However, MPs from T-cells may induce endothelial dysfunction, altering gene expression of eNOS and caveolin-1. Moreover, MPs may promote the expression of pro-inflammatory proteins implicated in vascular contractility alterations. This review describes the origin of MPs and their biological role in physiological conditions and in various pathological states, with special reference to the possible linkage between their pro-inflammatory and procoagulant properties and vascular dysfunction.

Despite the existence of a wealth of structural and theoretical data relating to palindromic sequences in the genome, the mechanism of cruciform formation in the presence of anthracyclines in miscellaneous biological processes is still poorly understood. Generally, DNA intercalators influence the DNA superhelicity, which plays a key role in the cruciform formation in DNA molecules. The potential of DNA intercalating ligands on the stabilization/destabilization of cruciform in DNA is discussed. Here, the indirect impact of anthracyclines to cell developing and surviving is analyzed for the first time. Primarily, the anthracycline modifies the helical properties of DNA and the overall DNA structure, and secondarily alters any cruciform-dependent processes, mainly DNA replication and transcription.