Anti-Inflammatory & Anti-Allergy Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Anti-Inflammatory and Anti-Allergy Agents) - Volume 8, Issue 4, 2009

Members of the S100 protein family comprise a multigenic group of non-ubiquitous cytoplasmic Ca2+-binding proteins of the EF-hand type, differentially expressed in a wide variety of cell types. They are small acidic proteins (10-12 kDa) that are found exclusively in vertebrates, and have been implicated in the regulation of many diverse processes such as signal transduction, cell growth and motility, cell-cycle regulation, transcription, differentiation, and cell survival. A large number of different human diseases have been associated with the variety of S100 proteins and their defective functions, e.g., cancer, inflammation, cardiomyopathies, neurodegenerative diseases, and allergies. Most S100 genes are located in a gene cluster near a region on human chromosome 1q21, which is responsible for a number of chromosomal abnormalities and has been frequently rearranged in human cancer. In addition, the S100 gene cluster is close to the epidermal differentiation complex as well as to a psoriasis susceptibility region, the PSORS4 locus. These data are important indications for the involvement of S100 genes in inflammatory as well as neoplastic disorders. The rearrangements may result in a deregulated expression of S100 genes associated with neoplasia. Furthermore, there is also an extensive interest in researching the possibility of using S100 proteins/specific antibodies in clinical diagnosis. It is worth mentioning that the first link between S100 family members and a specific disease was made for S100A8 and S100A9. It was speculated for considerable time that these two proteins could represent the proteins responsible for cystic fibrosis, a speculation now superseded by the cloning of the gene encoding the membrane protein cystic fibrosis conductance regulator. Nevertheless, it has been shown that S100A8- and S100A9-expressing cells belong to the early infiltrating cells and dominate acute inflammatory lesions. Phagocytes expressing S100A8 and S100A9 are found in a variety of inflammatory conditions, including rheumatoid arthritis, allograft rejections, and inflammatory bowel and lung diseases. Inflammatory disorders such as chronic bronchitis, cystic fibrosis, and rheumatoid arthritis are associated with elevated plasma levels of S100A8/A9. There are high correlations between S100A8/A9 plasma concentrations and clinical and laboratory markers of inflammation, as well as the rapid normalization following clinical improvement suggesting that these proteins track disease activity. Therefore, S100A8 and S100A9 are widely used as marker proteins for activated or recruited phagocytes as well as a diagnostic marker for disease activity. However, over the last decade they have gained increasing interest in many files of medicine due to their deregulated epidermal expression as a response to stress and in association with neoplastic disorders. S100A8 and S100A9 are predominantly expressed in myeloid cells. Except for inflammatory conditions, the expression of S100A8 and S100A9 is restricted to a specific stage of myeloid differentiation since both proteins are expressed in circulating neutrophils and monocytes but are absent in normal tissue macrophages and lymphocytes. Under chronic inflammatory conditions, such as psoriasis and malignant disorders, they are also expressed in the epidermis.

S100A8 and S100A9 are two soluble calcium-binding proteins highly expressed in myeloid cells, mainly neutrophils (45% of cytosolic proteins) or monocytes (1-5%) and also early differentiated macrophages. In neutrophils, they are believed to be expressed as a 1/1 non covalent heterodimer; the process of dimer and mainly tetramer formation is calcium dependent. The S100A8/S100A9 calcium loaded complex binds arachidonic acid and shuttles between cytosol and plasma membrane upon neutrophil stimulation. Neutrophils display, upon stimulation, a respiratory burst in which the cells catalyze NADPH oxidase activity through a redox membrane hemoprotein, cytochrome b558, which is constituted of 2 subunits: gp91-phox, the redox core and p22- phox the stabilizing partner. In neutrophils, this activity is transitory: to be active, regulatory cytosolic factors, p67-phox, p47-phox, p40-phox and Rac1/2 assemble with membrane cytochrome b558. Both S100A8 and S100A9 were recently introduced as partners for NADPH oxidase activation and associate with the cytosolic activating factors especially p67-phox and Rac1/2. Moreover, S100A8/S100A9 potentiates NADPH oxidase activity. This was observed ex vivo after co-transfection of genes encoding both S100A8 and S100A9 in B lymphocytes that express all the components of the phagocyte oxidase, but display a very low NADPH oxidase activity (in these cells, S100A8 and S100A9 are not present endogenously). In the biological function of S100A8/S100A9, S100A8 is a strategic protein that needs to be active in vivo as in vitro, its specific partner S100A9. New data introduce S100A8 and S100A9 as positive effectors in allosteric regulation of phagocyte NADPH oxidase activity.

The calgranulins are a subgroup of proteins in the S100 family (calgranulin A, S100A8; calgranulin B, S100A9 and calgranulin C, S100A12) that provide protective anti-infective and anti-inflammatory functions for the mammalian host. In this review, we discuss the structure-function relationships whereby S100A8 and S100A9, and for comparison, S100A12, provide intra- and extracellular protection during the complex interplay between infection and inflammation and how the calgranulins are regulated to optimally protect the host. Ideally located to support epithelial barrier function, calprotectin, a complex of S100A8/S100A9, is expressed in squamous mucosal keratinocytes and innate immune cells present at mucosal surfaces. The calgranulins are also abundantly produced in neutrophils and monocytes, whereas expression is induced in epidermal keratinocytes, gastrointestinal epithelial cells and fibroblasts during inflammation. The calgranulins show species-specific expression and function. For example, S100A8 is chemotactic in rodents but not in humans. In humans, S100A12 appears to serve as a functional chemotactic homolog to murine S100A8. Transition metalbinding and oxidation sites within calgranulins are able to create structural changes that may orchestrate new protective functions or binding targets. The calgranulins thus appear to adopt a variety of roles to protect the host. In addition to serving as a leukocyte chemoattractant, protective functions include oxidant scavenging, antimicrobial activity, and chemokine-like activities. Each function may reflect the concentration of the calgranulin, post-transcriptional modifications, oligomeric forms, and the proximal intracellular or extracellular environments. Calprotectin and the calgranulins are remarkable as multifunctional proteins dedicated to protecting the intra- and extracellular environments during infection and inflammation.

Asthma and chronic obstructive pulmonary disease (COPD) are persistent inflammatory conditions that have exhibited significantly increased prevalence in the past two decades. Though many current medications relieve the symptoms of obstructive airway disease, morbidity can still increase over time in individual patients. With particular respect to asthma, despite satisfactory control of symptoms in most patients with inhaled steroids, a sub-phenotype of subjects, representing ∼15% of all asthmatics, do not respond to steroids - these patients can exhibit severe asthma, which accounts for ∼50% of asthma health care costs. Moreover, inhaled steroids are not recommended as a sole therapy for COPD, and there is limited evidence for their effectiveness in preventing disease pathogenesis. Thus, it is important to better understand mechanisms for severe asthma and COPD and identify mediators released by cells, such as neutrophils, that are unresponsive to steroid therapy. This review focuses on the probable role of one the most abundant neutrophil proteins, called S100A8/A9, in asthma. S100A8/A9 is released in abundance in rheumatoid arthritis, inflammatory bowel disease and cancer, but there are no definitive studies on its role in obstructive airways disease. A primary receptor for S100A8/A9, which is uniquely expressed in high abundance in the lung, is the multi-ligand receptor for advanced glycated endproducts (RAGE) of the immunoglobin-like receptor family. RAGE participates in mediating fibroproliferative lung remodeling in idiopathic pulmonary fibrosis, and in bleomycin-exposed animal models. This review provides an overview of the S100A8/A9-RAGE axis, and discusses its potential in mediating chronic airway inflammation and tissue remodeling in asthma and COPD.

The S100A8/S100A9 heterodimer, commonly referred to as calprotectin (CP), is a member of the S100 subfamily of EF-hand calcium binding proteins that is largely expressed in activated monocytes and macrophages and has well-defined functions in acute and chronic inflammation. Indeed, certain S100 proteins including S100A8/A9 are exported from cells by an as-yet unknown mechanism. Once outside the cell, S100A8/A9 activates cell surface receptors such as the receptor for advanced glycation end products (RAGE) and has also been shown to inhibit the growth of pathogenic bacteria through the chelation of trace metal ions such as zinc (Zn2+) and manganese (Mn2+). The binding of these metal ions by S100A8/A9 has also been shown to induce apoptosis in various tumor cell lines. However, several lines of evidence have suggested that S100A8/A9-dependent apoptosis is not solely due to its ability to sequester Zn2+ from cells. Rather, it appears that trace metal binding to S100A8/A9 triggers a novel conformational switch in the protein, which promotes binding to specific sites on the surface of cells or through interaction with yet unidentified cell surface receptors. This review summarizes what is currently known regarding the molecular mechanisms by which S100A8/A9 performs its role as a novel apoptotic agent.

Human cancer is a chronic disease that originates from transformed tumor cells harboring genetic as well as epigenetic alterations. It develops via a multi-step process that can be divided both operationally and mechanistically into three phases: initiation, promotion and progression. However, cancer is not merely an autonomous mass of mutant cells, but is composed of multiple cell types, such as fibroblasts and epithelial cells, innate and adaptive immune cells, and cells forming blood vessels and lymphatic vasculature. A striking feature of many cancers is an underlying persistent and unresolved inflammation, which often orchestrates a tumor supporting microenvironment. Several lines of evidence identified an enhanced expression of S100A8 and S100A9 proteins in pathological conditions of chronic inflammation and inflammation- associated carcinogenesis in patient specimens as well as cell culture and experimental animal models. More recently, the analysis of genetically modified mouse models and cell lines derived thereof has provided important new insights into the regulation and molecular function of S100A8 and S100A9 proteins in vivo and in vitro. In this review, we will summarize our current knowledge on S100A8 and S100A9 regulation and function on tumor cell signaling and survival, as well as the establishment of an inflammatory, pro-tumorigenic microenvironment. Based on this knowledge, this review will discuss potential strategies to interfere with S100A8 and S100A9 function as a novel option to develop innovative strategies for cancer prevention or therapy.

Provoked by the discovery of metastasis-inducing endogenous ligands of TLR4 that has been recognized as a sensor for extrinsic pathogens, I propose an extended concept for danger signal that originally meant sentinels over tissue destruction by cancer. The so-called “homeostatic inflammation” concept includes signals before destruction actually takes place such as those in pre-metastatic microenvironment and possibly even in physiological conditions. It is orchestrated by tight cross-talks between growth factor and chemokine signaling.

The function of the exocrine pancreas is the production and secretion of digestive enzymes. Major pathologies of the exocrine pancreas are pancreatitis, a sterile inflammation, and pancreatic adenocarcinoma, a highly lethal tumor. Both diseases involve cells of the immune system and calcium binding proteins of the S100 family. Here, we review the known function of these proteins in pancreatitis and pancreas cancer. Few S100 proteins were detected during pancreatitis and only for the S100A8/A9 complex data are available that elucidate a presumable function. In a rodent model of caerulein-induced acute pancreatitis, pancreatic S100A8/A9 expression was exclusively detected in infiltrating leukocytes. S100A9 knockout animals developed less pancreatic tissue damage, no significant edema formation, and the intrapancreatic infiltration of leukocytes was inhibited. Purified S100A8/A9 dissociated calcium-dependent cell-cell contacts between pancreatic acinar cells in vitro and in vivo. These results indicate that the dissociation of epithelial cell-cell contacts mediated by secreted S100A8/A9 is crucial for the infiltration of leukocytes into the pancreas. Several studies revealed an expression of S100 proteins in pancreatic cancers. Especially S100A8/A9 proteins were found in myeloid cells within tumor-associated stroma. Whether these proteins contribute to a recruitment of specific immune cells to tumors or to other steps of pancreatic tumor progression is not clear. None of the S100 proteins has been clearly confirmed as a pancrea tumor marker. Taken together, S100A8/A9 proteins are essential for the inflammation induced infiltration of leukocytes in murine pancreatic tissue a mechanism which may also support tumor progression and metastasis.

Current vaccine research is now heavily focused on improving the efficacy and potency of sub-unit peptide vaccines. Many successful vaccines developed in past decades have been able to sufficiently prime proper immune responses without the use of any specific adjuvant immune mediators. Due to the intrinsic nature of more immune-evading pathogens and neoplasms, novel “tricks” are needed to elucidate a proper and protective immune response. It is important to note that without cytokines, proper execution of the immune response would be completely inhibited. They are responsible for the recruitment and chemo-tactic movement of most innate cellular effectors such as polymorphonucleocytes (PMN), macrophages, and dendritic cells. Most importantly, the entire Th1/Th2 balance is completely dependent on the unique nature and signature of differential cytokine production. These expression signatures are crucially needed to tip the scale either way, depending on which immune reaction is appropriate. This review will specifically explain the use of Th1 inducing cytokines as an adjuvant in current vaccine development. This rapidly developing field aims to produce more powerful and effective Th1 responses in the hopes of improving the treatment of cancer, intracellular infectious agents, and autoimmune diseases.

T cells specific for haptens determine immunopathology, as for the recognition of the β-lactamic ring by CD4+ T helper cells, responsible for the severe immune response to Penicillin in allergic patients. In this review we report studies that address functional and molecular aspects of hapten recognition by α/β T cells, enlightening the most relevant examples of hapten-specific T cells and their role in vivo. Using Trinitrophenyl as a contact allergen model and tumor associated carbohydrate antigens (TACA) as antigen models in cancer, our laboratory extensively studied T cell recognition by hapten-specific T cells suggesting new, unexplored avenues for T cell-based immunotherapy. In fact, the evidence of hapten recognition by “conventional” α/β T cells is of a critical importance in designing new immunotherapeutic approaches to treat allergies, cancer and chronic viral diseases.

Glucocorticoids (GCs) represent the cornerstone of treatment of patients with bronchial asthma; however, inflammation in bronchial asthma is sometimes incompletely controlled. GCs switch on the expression of anti-inflammatory genes by binding to DNA and recruiting transcriptional coactivator molecules. In contrast, they can switch off activated inflammatory genes by recruiting transcriptional repressor molecules such as histone deacetylase (HDAC) 2. Proinflammatory transcriptional element activator protein-1 (AP-1) and transcription factor nuclear factor kappa B (NF- κB), and upstream kinase p38 and c-Jun-N-terminal kinase (JNK) amplify inflammation and resistance to the actions of GCs. The activity of histoneacetyltransferase (HAT) and HDAC influences the expression of inflammatory genes. Cytokines, inflammatory mediators, allergens, viral or bacterial infections, oxidative stress, smoking, and vitamin D deficiency may all lead to a worsened clinical outcome by influencing these pathways. Conventional therapy acts by inhibiting NF-κB, enhancing glucocorticoid receptor (GR) functions, and restoring HDAC activity, resulting in helpful add-on therapy. Targeting kinases such as inhibitor of κB kinase (IKK)2, mitogen activated protein (MAP) kinase (MAPK)s and phospho-inositol (PI)3 kinase (PI-3K) should be effective as therapy. Decoy oligonucleotides for AP-1and NF-κB are also candidates for the treatment of glucocorticoid-resistant (GC-R) asthma. Since various factors affect GC response, the pathogenesis of GC-R asthma is considered to be heterogeneous. Most GC nonresponsiveness in these patients is relative and not absolute, suggesting that resistance is dependent on the intensity of localized inflammation. A better understanding of the inflammatory mechanisms of asthma may signal the management of GC-R asthma.