Toll-like receptor modulators: a patent review (2006-2010)

INTRODUCTION: The immune response is mediated via two parallel immune components, innate and adaptive, whose effector functions are highly integrated and coordinated for the protection of the human body against invading pathogens and transformed cells. The discovery of pathogen recognition receptors (PRRs), most notably toll-like receptors (TLRs), in innate immunity has evoked increased interest in the therapeutic handling of the innate immune system. TLRs are germ line-encoded receptors that play a potent role in the recognition of a diverse variety of ligands ranging from hydrophilic nucleic acids to lipopolysaccharide (LPS) or peptidoglycan (PGN) structures in pathogens. AREAS COVERED: This review discusses recent updates (2006-2010) in completed, ongoing and planned clinical trials of TLR immunomodulator-based therapies for the treatment of infectious diseases, inflammatory disorders and cancer. EXPERT OPINION: Since the discovery of human TLRs, modulating immune responses using TLR agonists or antagonists for therapeutic purposes has provoked intense activity in the pharmaceutical industry. The ability of TLRs to initiate and propagate inflammation makes them attractive therapeutic targets. We are now at the stage of evaluating such molecules in human diseases. Additionally, there is also extensive literature available on TLRs in diseased states. These data provide a basis for the identification of novel immunomodulators (agonists and antagonists) for the therapeutic targeting of TLRs.     

The active contribution of Toll-like receptors to allergic airway inflammation

Epithelia lining the respiratory tract represent a major portal of entry for microorganisms and allergens and are equipped with innate and adaptive immune signaling receptors for host protection. These include Toll-like receptors (TLRs) that recognize microbial components and evoke diverse responses in cells of the respiratory system. TLR stimulation by microorganism-derived molecules activates antigen presenting cells, control T helper (Th) 1, Th2, and Th17 immune cell differentiation, cytokine production by mast cells, and activation of eosinophils. It is clear that TLR are involved in the pathophysiology of allergic airway diseases such as asthma. Dendritic cells (DCs), a kind of antigen presenting cells, which play a key role in the induction of allergic airway inflammation, are privileged targets for pathogen associated molecular patterns (PAMPs). During the allergic responses, engagement of TLRs on DCs determines the Th2 polarization of the T cells. TLR signaling in mast cells increases the release of IL-5, and TLR activation of airway epithelial cells forces the generation of proallergic Th2 type of cytokines. Although these responses aim to protect the host, they may also result in inflammatory tissue damage in the airway. Under certain conditions, stimulation of TLRs, in particular, TLR9, may reduce Th2-dependent allergic inflammation by induction of Th1 responses. Therefore, understanding the complex regulatory roles of TLRs in the pathogenesis of allergic airway inflammation should facilitate the development of preventive and therapeutic measures for asthmatic patients.     

TLR based therapeutics

Toll-like receptors (TLRs) play a crucial role in innate immune responses to infection. Binding of agonists to TLRs promotes maturation of antigen presenting cells, such as dendritic cells, which in turn directs the induction of adaptive immune responses. For this reason TLR agonists are being exploited as vaccine adjuvants for infectious disease or cancer and as therapeutics against tumors. However TLR agonists also promote inflammatory cytokine production and have a pathogenic role in many diseases with an inflammatory basis, including autoimmune diseases. Consequently, antibodies to TLRs and inhibitors of TLR signalling pathways have considerable potential as therapeutics for inflammatory disorders. Some have shown to be efficacious in pre-clinical models, and have now entered clinical trials.     

Polymorphisms in TOLL-like receptor genes and their roles in allergic asthma and atopy

Allergic asthma is a chronic inflammatory disease of the lung airways cause by genetic and environmental factors. Two quantifiable phenotypes of this disease are airway hyperresponsiveness and atopy. TOLL-like receptors (TLRs) are a family of intracellular and cell surface receptors that can respond to pathogen associated molecular patterns involved in the pathogenesis of asthma. Macrophages, one of the main immune cells involved in asthma, express a variety of TLRs, including TLR 2, 4, 5, 6, 7, 8 and 9. This review focuses on polymorphisms found in TLR genes expressed in macrophages, and their role in asthma. Human studies have detected polymorphisms in TLR genes associated with asthma phenotypes, and studies using murine models have shown that some receptors and their agonistic or antagonistic ligands are capable of modulating the cytokine profile in asthmatics in a protective manner. Therefore, certain receptors and their ligands are being explored as potential immunotherapies for asthma. Recently, several patents have been filed protecting inventions for treating asthma through the use of TLRs and their ligands.     

The essential roles of Toll-like receptor signaling pathways in sterile inflammatory diseases

Toll-like receptors (TLRs) form a family of pattern recognition receptors with at least 11 members in human and 13 in mouse. TLRs recognize a wide variety of putative host-derived agonists that have emerged as key mediators of innate immunity. TLR signaling also plays an important role in the activation of the adaptive immune system by inducing pro-inflammatory cytokines and upregulating costimulatory molecules of antigen presenting cells. Inappropriate activation of TLRs by self-components generated by damaged tissues may result in sterile inflammation. This review discusses the contribution of TLR signaling to the initiation and progression of non-infectious inflammatory processes, such as ischemia and reperfusion (I/R) injury, tissue repair and regeneration and autoimmune diseases. The involvement of TLR signaling in the pathogenesis of sterile inflammation-related diseases may provide novel targets for the development of therapeutics.     

Toll-like receptor modulators: a patent review (2006 – 2010)

Introduction: The immune response is mediated via two parallel immune components, innate and adaptive, whose effector functions are highly integrated and coordinated for the protection of the human body against invading pathogens and transformed cells. The discovery of pathogen recognition receptors (PRRs), most notably toll-like receptors (TLRs), in innate immunity has evoked increased interest in the therapeutic handling of the innate immune system. TLRs are germ line-encoded receptors that play a potent role in the recognition of a diverse variety of ligands ranging from hydrophilic nucleic acids to lipopolysaccharide (LPS) or peptidoglycan (PGN) structures in pathogens.

Areas covered: This review discusses recent updates (2006 – 2010) in completed, ongoing and planned clinical trials of TLR immunomodulator-based therapies for the treatment of infectious diseases, inflammatory disorders and cancer.

Expert opinion: Since the discovery of human TLRs, modulating immune responses using TLR agonists or antagonists for therapeutic purposes has provoked intense activity in the pharmaceutical industry. The ability of TLRs to initiate and propagate inflammation makes them attractive therapeutic targets. We are now at the stage of evaluating such molecules in human diseases. Additionally, there is also extensive literature available on TLRs in diseased states. These data provide a basis for the identification of novel immunomodulators (agonists and antagonists) for the therapeutic targeting of TLRs.     

CD14 and toll-like receptors: potential contribution of genetic factors and mechanisms to inflammation and allergy

Innate and adaptive immune responses evolve as protective mechanisms against infectious microorganisms in humans. CD14 and toll-like receptors (TLRs) are examples of pattern recognition receptors that detect antigenic molecules on the surface of gram-positive (peptidoglycans, lipoteichoic acid) and gram-negative (lipopolysaccharide) bacteria. In vitro studies suggest that lipopolysaccharide is a potent inducer of interleukin-12 production that is mediated by both CD14 and TLR4. The associated increase in interferon-gamma steers our immune system away form the allergy-driven type-2 helper T cell phenotype. Epidemiological studies that shed light on the possible protective influences of natural microbial exposure on asthma and atopy development will be discussed. Recent insights into the complex mechanisms of human innate immunity suggest that genetic variability in genes encoding its components may alter the susceptibility to develop atopic disorders and other complex human diseases. The findings of these genetic association studies will be presented. Although highly conserved across a wide range of species, innate immunity genes demonstrate considerable inter-ethnic variability predominantly in the form of single nucleotide polymorphisms. The frequencies of these polymorphisms in CD14 and TLR genes in different ethnic groups will be discussed. Genetic variation in these genes may also play a role in the development of other human diseases that have an inflammatory component. Lastly, the prospect of using immunomodulatory agents targeting on the innate immunity to treat or even prevent asthma and other allergic diseases will be discussed.     

Toll-like receptors as therapeutic targets in cystic fibrosis

Background: Toll-like receptors (TLRs) are pattern recognition receptors that act as a first-line of defence in the innate immune response by recognising and responding to conserved molecular patterns in microbial factors and endogenous danger signals. Cystic fibrosis (CF)-affected airways represent a milieu potentially rich in TLR agonists and the chronic inflammatory phenotype evident in CF airway epithelial cells is probably due in large part to activation of TLRs. Objective/methods: To examine the prospects of developing novel therapies for CF by targeting TLRs. We outline the expression and function of TLRs and explore the therapeutic potential of naturally-occurring and synthetic TLR inhibitors for CF. Results/conclusion: Modulation of TLRs has therapeutic potential for the inflammatory lung manifestations of CF.     

Oxidants in asthma and in chronic obstructive pulmonary disease (COPD)

Experimental and clinical evidences suggest that oxidants play a role in the pathogenesis of respiratory disorders characterised by chronic airway inflammation such as asthma and chronic obstructive pulmonary disease (COPD). The respiratory system is chronically exposed to environmental pollutants, including oxidants. Exogenous sources of oxidants are particularly relevant to the pathogenesis of COPD, being cigarette smoke an extremely rich source of oxidants. In addition, the inflammatory cells recruited to the airways of patients with asthma and COPD, have an exceptional capacity to produce oxidants. Many decades of research have produced a significant amount of data indicating pro-oxidative molecular mechanisms putatively relevant in the pathogenesis of the oxidative stress which characterises these diseases, both locally and systemically. As a consequence, a drug therapy able to restore the redox imbalance in asthma and COPD would probably exert clinical and functional benefits. Indeed, currently available therapies for asthma and COPD can exert an inhibitory effect on oxidant production in the airways. However, it is unknown whether the efficacy of the treatment is somehow linked to the pharmacological modulation of the oxidant/antioxidant balance. So far, it appears that the potential role of antioxidant compounds in the treatment of asthma and COPD has not been fully explored.     

Small molecule inhibitors of cell signaling: novel future therapeutics for asthma and chronic obstructive pulmonary diseases

The respiratory diseases asthma and chronic obstructive pulmonary disease (COPD) exhibit common, key pathological features, including the development of airflow limitations such as thickening of the airway wall, and the presence of an inflammatory process. However, that is where their similarities end. A large number of medications for asthma are available to decrease inflammation and prevent or reverse airway constriction, while very few therapeutics, if any, exist for the effective management of COPD. Nonetheless, despite the availability of medications for asthma, the epidemic is continuing to increase and existing therapies offer little or no relief for chronic asthmatics. It is obvious that a high, unmet medical need remains for both asthma and COPD, and innovative therapeutic agents are urgently required. New therapies need to be developed to target not only the inflammatory component of asthma and COPD, but also the remodeling aspects of these diseases. This review summarizes the emerging treatments for chronic asthma and COPD, from early discovery to late clinical stages, and discusses the therapeutic rationale behind these treatments. We believe that there is still much to be learned about the mechanisms involved in the development and treatment of these debilitating respiratory diseases, however, much promise lies in the future of these new therapeutics.     

Respiratory Health Effects of Large Animal Farming Environments

With increases in large animal-feeding operations to meet consumer demand, adverse upper and lower respiratory health effects in exposed agriculture workers are a concern. The aim of this study was to review large animal confinement feeding operational exposures associated with respiratory disease with a focus on recent advances in the knowledge of causative factors and cellular and immunological mechanisms. A PubMed search was conducted with the keywords airway, farm, swine, dairy, horse, cattle inflammation, organic dust, endotoxin, and peptidoglycan, among items were published between 1980 and now. Articles were selected based on their relevance to environmental exposure and reference to airway diseases. Airway diseases included rhinitis, sinusitis, mucus membrane inflammation syndrome, asthma, chronic bronchitis, chronic obstructive pulmonary disease, hypersensitivity pneumonitis, and organic dust toxic syndrome. There is lower prevalence of immunoglobulin (Ig) E-mediated asthma and atopy in farmers and their children, but organic dust worsens existing asthma. Multiple etiologic factors are linked to disease, including allergens, organic dusts, endotoxins, peptidoglycans, and gases. Large animal confinement feeding operations contain a wide diversity of microbes with increasing focus on gram-positive bacteria and archaebacteria as opposed to gram-negative bacteria in mediating disease. Toll-like receptors (TLR) and nucleotide oligomerization domain (NOD)-like innate immune pathways respond to these exposures. Finally, a chronic inflammatory adaptation, tolerance-like response in chronically exposed workers occurs. Large animal confinement farming exposures produce a wide spectrum of upper and lower respiratory tract diseases due to the complex diversity of organic dust, particulates, microbial cell wall components, and gases and resultant activation of various innate immune receptor signaling pathways.     

Emerging oligonucleotide therapies for asthma and chronic obstructive pulmonary disease

Chronic respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD) are disorders of the airways largely related to the presence of persistent inflammation. The approval of inhaled corticosteroids in the early 1970s pioneered a new age of therapy in treating chronic inflammatory airway diseases. This was the first time that an anti-inflammatory product was available to reduce the characteristic lung inflammation in airways and the associated obstruction, inflammation and hyper-responsiveness. Fast forward 40 years: corticosteroids are still an important therapeutic intervention; however, they exhibit limited use in moderate to severe asthma and COPD. Oligonucleotide therapies are an emerging class which include the antisense, the RNAi (siRNA and miRNA), the immunomodulatory, the aptamer and the decoy approaches. As these approaches are rather recent in the respiratory field, most are still early in development. Nevertheless, with limitations of current small molecule therapies and the hurdles faced with biologics, the use of oligonucleotides is relevant and the door is open to the development of this category of therapeutics. This review focuses on the major classes of oligonucleotides that are currently in late stage preclinical or clinical development for the treatment of asthma and COPD, and discusses the implications for their use as therapies for respiratory diseases.     

Toll样受体在自身免疫性疾病中的作用机制研究现状

Toll样受体（Toll-like receptor,TLR）是近年来发现的一类模式识别受体,通过识别病原相关分子模式（pathogen associated molecular pattem,PAMP）,激活天然免疫。TLR信号还通过上调抗原提呈细胞（antigen presenting cells,APC）表面共刺激分子及APC分泌的炎症细胞因子调节获得性免疫。本文就TLR通过调节T、B淋巴细胞及TLR,MyD88信号通路在介导自身免疫性疾病中的作用机制以及其在皮肤病如系统性红斑狼疮等发病中的作用做一综述。     

Antimicrobial peptides in COPD--basic biology and therapeutic applications

A large number of studies have implicated activation of innate immune mechanisms in the pathogenesis of chronic obstructive pulmonary disease (COPD). Accumulation of inflammatory cells, chemokines and pro-inflammatory cytokines is a hallmark of activation of these mechanisms, but only a few studies have focussed on antimicrobial peptides in COPD. These peptides are a central component of innate immunity, and airway epithelial cells and neutrophils in the lung are the main cellular sources. In addition to their direct antimicrobial action, antimicrobial peptides have been shown to display a variety of activities that may implicate them in the pathogenesis of COPD. This is based on the observation that they not only contribute to defense against respiratory pathogens that have been associated with COPD, but may also contribute to the influx of inflammatory cells, activation of adaptive immunity and epithelial remodeling. The aim of this review is to provide an update on the basic biology of antimicrobial peptides in the lung, with a focus on their putative role in COPD. In addition, the implication of this knowledge for future treatment of COPD is discussed.     

TLR2、TLR4与类风湿关节炎

Toll样受体（TLRs）是天然免疫系统中特异性的Ⅰ型跨膜受体及病原模式识别受体,在急性炎症反应、细胞信号转导和细胞凋亡中起重要作用。TLRs通过选择性的识别病原体中病原相关分子模式的保守结构及某些内源性配体,触发髓样细胞分化因子88（MyD88）依赖性和非依赖性途径,导致基因编码的的促炎性细胞因子和趋化因子的激活,从而诱发局部的炎症,并通过上调抗原递呈细胞表面的共刺激分子,诱导T、B淋巴细胞分化,激动后继的适应性免疫应答。类风湿关节炎（RA ）主要表现为滑膜组织炎性增生和炎症细胞浸润最终导致组织破坏和功能障碍。与T细胞过度活化以及B细胞的过度刺激致大量自身抗体产生有关。研究发现,细胞表面的TLRs,尤其是TLR2和TLR4,在类风湿关节炎疾病的发生发展中起重要作用。该文就TLR2、TLR4在RA发病中的作用作一综述,旨在为后期药物干预提供一定的理论依据。     

Role of toll-like receptors in immune responses to chlamydial infections

Chlamydiae are important human pathogens which are leading causative agents for a variety of disease conditions including ocular, respiratory and sexually transmitted diseases, thus causing significant morbidity worldwide. Many of the human diseases caused by Chlamydia species are considered to be immunopathologically mediated. Toll like receptors (TLRs) have emerged as one of the major components of the immune system. Recognition of pathogen associated molecular patterns (PAMPs) by TLRs results in the activation of signaling events that induce the expression of effector molecules such as cytokines and chemokines which control the activation of adaptive immune responses. The precise immune mechanisms involved in resistance or pathogenesis to chlamydial infection, especially in the TLR signaling and downstream events during the innate phase of infection initiating the adaptive immune responses remains largely unknown. This review focuses on elaborating the current knowledge on the role of TLRs in immune responses to chlamydial infection. Although chlamydial components like lipopolysaccharide (LPS) and chlamydial heat shock protein 60 (cHSP60) are recognized by TLR4, the intact organisms stimulates the innate immune cells through TLR2, which also plays an important role as a PRR for Chlamydia. While the individual role of different TLRs such as TLR2, TLR4 and TLR9 in chlamydial infection is becoming delineated, studies have demonstrated the essential role of the TLR adapter molecule MyD88 in the generation of immune responses to Chlamydia infection. Given that there is no effective vaccine available for Chlamydia till date, a better understanding of the immunological and molecular mechanisms mediated by TLRs will greatly aid in possibly exploiting these molecules as immunotherapeutic targets.     

Anti-TNF-α therapies in chronic obstructive pulmonary diseases

Background: Chronic obstructive pulmonary disease (COPD) and asthma are chronic diseases in which inflammation of the airways leads to progressive transient airway obstruction and TNF-α plays an important pro-inflammatory role. Objective: To assess the plausibility of anti-TNF-α therapies playing an anti-inflammatory role in asthma and COPD. Methods: Scientific rationale of TNF-α targeting in asthma and COPD was assessed individually and the available data on the use of anti-TNF-α in each disease were reviewed. Results and conclusion: Anti-TNF-α therapies demonstrate different efficacies in asthma and COPD and further supportive preclinical and clinical data are needed, especially about subsets of certain diseases which could benefit the most from these therapies.     

Modulating toll-like receptor signalling as a novel antiinfective approach

The innate immune response against invading microorganisms results in the deployment of phagocytes, including macrophages and dendritic cells to recognize pathogen-associated molecular patterns. Activation of Toll-like receptors (TLRs) expressed on these cells is a critical step in the initiation of this response, triggering the production of pro- and antiinflammatory cytokines to dampen microbial pathogenesis. Importantly, TLR activation also mediates dendritic cell maturation, a critical step in bridging the innate and adaptive arms of the immune system. Balancing the role of TLRs as central mediators of overlapping signaling pathways, whether directly through ligand interactions or via secondary adaptor molecules, mandates exquisite specificity. Further, understanding the immunopharmacology of TLR cross-talk during infection may help to provide insight into innate immunity and the mechanisms of immune-response subversion by pathogens. The continual and rapid emergence of drug resistance to traditional antimicrobial agents highlights the medical need for new treatment approaches. Herein, the discovery and development of TLR agonist and antagonist therapies for infectious diseases as adjunct to, or in place of, conventional treatment paradigms is discussed.     

Toll-like receptors as targets for immune disorders

Since the identification of the first Toll-like receptor (TLR) in humans in 1997, understanding of the molecular basis for innate immunity has increased significantly. The TLR family and downstream signalling pathways have been extensively characterised, There is now significant evidence suggesting a role for TLRs in human inflammatory and immune diseases such as rheumatoid arthritis, diabetes, allergy/asthma and atherosclerosis. Various approaches have been taken to identify novel therapeutic agents targeting TLRs including biologics, small molecules and nucleic acid-based drugs. Several are now being evaluated in the clinic and showing promise against various diseases. This review paper outlines the recent advances in the understanding of TLR biology and highlights novel TLR agonists and antagonists in development for the treatment of immune diseases.     

Agents against cytokine synthesis or receptors

Various cytokines play a critical role in pathophysiology of chronic inflammatory lung diseases including asthma and chronic obstructive pulmonary disease (COPD). The increasing evidence of the involvement of these cytokines in the development of airway inflammation raises the possibility that these cytokines may become the novel promising therapeutic targets. Studies concerning the inhibition of interleukin (IL)-4 have been discontinued despite promising early results in asthma. Although blocking antibody against IL-5 markedly reduces the infiltration of eosinophils in peripheral blood and airway, it does not seem to be effective in symptomatic asthma, while blocking IL-13 might be more effective. On the contrary, anti-inflammatory cytokines themselves such as IL-10, IL-12, IL-18, IL-23 and interferon-gamma may have a therapeutic potential. Inhibition of TNF-alpha may also be useful in severe asthma or COPD. Many chemokines are also involved in the inflammatory response of asthma and COPD through the recruitment of inflammatory cells. Several small molecule inhibitors of chemokine receptors are now in development for the treatment of asthma and COPD. Antibodies that block IL-8 reduce neutrophilic inflammation. Chemokine CC3 receptor antagonists, which block eosinophil chemotaxis, are now in clinical development for asthma therapy. As many cytokines are involved in the pathophysiology of inflammatory lung diseases, inhibitory agents of the synthesis of multiple cytokines may be more useful tools. Several such agents are now in clinical development.