Current Pharmaceutical Biotechnology - Volume 13, Issue 8, 2012

The female reproductive tract represents a great challenge to the residing immune cells: Concomitantly, those immune-competent cells have to provide tolerogenic mechanisms favoring the development of a successful pregnancy while permitting protection against harmful pathogens. The predominant cell population facing this “double edged” regulatory capacity within the reproductive tract is that of dendritic cells (DC). There is evidence that DC represent a highly adaptive cell type, which can either be transformed in an immune-stimulatory phenotype after exposure to inflammatory or infectious signals, or in an immune inhibitory phenotype preventing T cell activation when located in an adequate antiinflammatory microenvironment. Thus, this review highlights this two-faced character of DC focusing on their morphology and function within the human reproductive tract and especially during pregnancy.

More than 80% of all cancers are caused by solid malignancies. More than 90% of these tumours are of epithelial origin. The main principles in tumour treatment are surgery, radiotherapy, chemotherapy or combinations of these. Complete surgical removal of the tumour is the most effective therapy for solid malignancies. Recent advances in early cancer detection led to a higher rate of resectable primary tumours and therefore prognosis will be determined especially by metastasis. Even in early stages some tumour cells may disseminate for example into the bone marrow. If these occult metastasis get evident they are mostly incurable by surgery and often highly resistant to chemotherapy. Developing new therapeutic agents to destroy these resting cells is a major challenge for the improvement of cancer therapy in the future. Advances to reach these goals were made in immunological therapies with monoclonal antibodies (MABs). These MABs are for example directed against tumor-associated antigens (TAAs). By binding selectively on tumor cells they can activate immunological effector mechanisms, e.g. antibody dependent cell cytotoxicity (ADCC) or complement mediated lysis. Other mechanisms are the blocking of inhibiting molecules to re-activate anergic tumor infiltrating lymphocytes (TILs). Furthermore growing tumours depend on oxygen supply, i.e. on effective neovascularisation. Antibodies against VEGF are able to inhibit neovascularisation and are therefore used successfully in tumour therapy.

Unlike any other cell type, T cells have a unique potential to eliminate cancer cells and to eventually cure cancer patients. As a result, researchers have made extensive efforts over the past three decades to develop therapeutics with the potential to mount T cell responses against cancer cells. One way in which such T cell responses can be triggered is by vaccines and adjuvants, potentially leading to tumor-specific T cell clones and lasting immunity. Alternatively, they can be induced with the help of recombinant proteins that either are expressed in patients’ T cells by gene therapeutic means, or are delivered to patients as pharmaceuticals for temporary engagement of T cells. With both recombinant technologies, cytotoxic T cells can be engaged for cancer cell lysis regardless of T cell receptor specificity and with the prospect of bypassing both complex T cell regulation and frequent immune escape mechanisms of tumor cells. In this review, we will focus on recombinant approaches for T cell engagement that currently are in clinical development. Approaches transfecting patient T cells with genes encoding recombinant T cell receptors or antibody fusion proteins will be compared to those temporarily engaging T cells by infused recombinant bispecific proteins. Initial experience has recently been gained in the clinic with both technologies such that their fundamental differences can now be discussed on the basis of patient data.

Multiple sclerosis is the most common chronic inflammatory disease of the central nervous system and can cause severe neurological disability. Current immune therapy with beta-interferons, glatiramer acetate, immune suppressives, or selective adhesion molecule inhibitors can reduce the frequency and severity of acute attacks in a majority of patients but have little effect on the progressive phase of the disease. Patients who require aggressive immune therapy are also at risk for the development of potentially fatal opportunistic infections. Here current and emerging immune therapy options are discussed, and immune-mediated strategies to preserve normal immune surveillance and mediate tissue repair are proposed.

TNF has a critical role in inflammation and immunity, and therapeutic inhibition of TNF with antagonist could potentially lead to immune suppression. Data gathered from clinical trials and clinical observation show a minor but significant increased risk of infections in patients suffering from rheumatic diseases treated with monoclonal TNF antibodies and soluble TNF receptors. This increase risk applies to patients but also to the underlying disease. Pathogens causing these infections include intracellular bacteria, and to some extend opportunistic microorganisms as mycobacteria and fungi. Preventive strategies and patient selection have an important impact on the risk of these infections.

Tumor cells need to disrupt apoptosis pathways to escape the cytotoxic action of oncogene activation and microenvironmental stress during the carcinogenic process. However, the cytotoxic action of classical chemotherapy, and radiotherapy includes the induction of apoptotic cell death. Therefore, apoptosis resistance of tumor cells contributes to the failure of chemotherapy and radiotherapy. During the last two decades, extensive research aimed at an improved understanding of the complex signaling pathways that control apoptosis execution in normal cells and of the endogenous factors that mediate apoptosis resistance of cancer cells. Among these, the Bcl-2 protein family attracted major attention for the development of compounds that specifically target apoptosis resistance of cancer cells. Bcl-2 proteins are master regulators of the intrinsic apoptosis pathway that is crucial for apoptosis execution in response to DNA-damage. The review will highlight current knowledge on the regulation of apoptosis pathways and discuss several approaches that target the Bcl-2 rheostat to counteract tumor cell intrinsic apoptosis resistance that may therefore be of value for a biological modulation of apoptosis resistance.

Cloning techniques to identify genes and peptides of tumor-associated antigens have created new possibilities for the immunotherapy of patients with advanced cancer. Here, we review recent clinical trials of specific cancer vaccines, mainly HLA-restricted peptides, and epitope-encoding vectors for advanced colorectal cancer (CRC). Many researchers initially focused on carcinoembryonic antigen (CEA) as an immunologic target antigen that is overexpressed on virtually all CRCs. A recombinant vaccine containing the CEA gene and dendritic cells (DCs) loaded with CEA peptide was administered to patients with CEA-elevated CRC. Although CEA-specific responses were detected, the clinical responses were limited. Recently, new types of clinical trials-namely, a personalized protocol to take into account the immunological diversity of cytotoxic T cell responses among patients and a novel cancer-testis antigen protocol that uses multiple peptides derived from genes identified by the cDNA array method-have been introduced. The personalized protocol seemed to be better than the classical (non-personalized) protocol in terms of clinical response and survival. Novel cancertestis antigen protocols that use multiple CRC-derived peptides were recently conducted in patients with advanced CRC. The preliminary study yielded promising results regarding specific T cell responses to peptides and survival benefits. In this review, we summarize these results and discuss future perspectives.

Bacterial toxins share the ability to enter host cells to target various intracellular proteins and to modulate host immune responses. Over the last 20 years, toxins and their mutated variants, as well as live attenuated bacteria, have been exploited for vaccination and immunotherapy of various infectious, malignant and autoimmune diseases. The ability of Bordetella pertussis adenylate cyclase toxin to translocate its adenylate cyclase domain across the host cell membrane, as well as the pathways of intracellular trafficking of Bacillus anthracis lethal and edema toxins, Shigella dysenteriae shiga toxin or Escherichia coli shiga-like toxin, have been repeatedly exploited for the delivery of antigenic epitopes into host cells and for stimulation of antigen-specific T cell responses. Similarly, E. coli α-hemolysin, or effector proteins of Yersinia and Salmonella secreted by the type III secretion systems, were used to facilitate the delivery of fused heterologous proteins or peptides for antigenic presentation. Vibrio cholerae cholera toxin, E. coli heat-labile enterotoxin, B. pertussis pertussis toxin or the Cry1A protein of Bacillus thuringiensis have shown a great potential to act as adjuvants and to stimulate mucosal as well as systemic immune responses. The immunotherapeutic potential of some toxins, like Clostridium perfringens perfringolysin O, Streptococcus intermedius intermedilysin, or Streptococcus pneumoniae pneumolysin needs to be evaluated further. The Bordetella adenylate cyclase toxoid used as a vaccine delivery tool, or Corynebacterium diphtheriae diphtheria toxin and Pseudomonas aeruginosa exotoxin A-based immunotoxins, are currently in various phases of clinical trials for cancer immunotherapy, as are some antigen-delivering Salmonella and Listeria monocytogenes strains.

Schizophrenia is a severe mental disorder, characterized by a complex symptomatology and a chronic relapsing course, leading to a more or less intensive residual syndrome. The disorder has strong consequences on social functioning and on the patients’ quality of life and is associated with a huge economical burden for the society. The best possible drug treatment should be therefore provided. The introduction of the FGAs was an important step forward, since they were the first specific drug treatment for schizophrenia in the first place. However, the positive therapeutic effect was counterbalanced by problematic side-effects, predominantly different kinds of EPS. The SGAs have a much lower liability to induce EPS, with clozapine inducing no EPS. Additionally, SGAs demonstrated some advantages in terms of a broader spectrum of efficacy, including e.g. negative symptoms. However, for most of the single compounds this efficacy advantage was not as high as initially expected. Thus, there is a need for new developments. Currently, drugs in development are based on the classical transmitter related approaches, following especially the model of clozapine and several other multi-receptor compounds. More and more, the glutamatergic system is of interest in this context as well. Totally new directions, e.g. based on genetic findings or focussing more on brain plasticity are headed for. The question is, whether beside the classical concept of antipsychotics, which covers all symptomatic domains of schizophrenia, compounds demonstrating efficacy only in one syndrome such as e.g. negative symptoms will have a chance in the future development.

An important development within the last decades is the consideration of the patient's perspective and the acknowledgement that the majority of patients are able to judge their state of well-being. Several self-report scales such as the “The Subjective Well-being under Neuroleptics Scale” (SWN) have been established. Additionally to their beneficial impact, current antipsychotics have considerable limitations. Antipsychotic-related side effects, such as extrapyramidalmotor symptoms, weight gain and obesity, apathy and anhedonia have an important influence on the patient’s wellbeing. Evidence suggests that the so-called neuroleptic-induced deficit syndrome under antipsychotics might be caused by the inhibition of the dopaminergic reward system. A reduced activation of the ventral striatum, including the nucleus accumbens is associated with negative symptom severity. Second-generation antipsychotics (henceforth SGA) block striatal D2 receptors less and show a weaker binding to D2 receptors, have interactions with several other neurotransmitters and inhibit to a lesser degree the reward functions compared to first-generation antipsychotics (henceforth FGA). This may support the reduction of negative symptoms, contributes to a higher subjective well-being, a better medication adherence and thereby an improved therapeutic outcome. The involvement of the patient and the consideration of his/her subjective wellbeing will be a major aspect in the development of new treatment strategies in schizophrenia and has a significant impact on the adherence and the long-term prognosis.

Over the last 50 years, evidence for central involvement of glutamatergic neurotransmission in the pathophysiology of schizophrenia has accumulated. Recent advances in neuroimaging technology now allow several components of glutamatergic neurotransmission to be assessed in the living human brain. Positron emission tomography (PET) or single photon emission tomography (SPET) in combination with select radiotracers allows visualization of glutamatergic receptors in vivo, and magnetic resonance (MR) – based techniques allow mapping of the effects of glutamatergic agents on regional brain activation, and the measurement of regional glutamate concentrations. These imaging studies have provided evidence for regional glutamatergic abnormalities in psychosis, and are beginning to describe both the evolution of these abnormalities over the course of the illness and their response to therapeutic intervention. In parallel, advances in small animal imaging and the development of animal models have provided a platform to explore the neuropathological consequences of glutamatergic abnormality, and the potential antipsychotic efficacy of novel compounds. The molecular diversity of the glutamatergic system has driven the design of several compounds targeting aspects of glutamatergic transmission, and clinical trials have yielded encouraging results. Here, we review the contribution of imaging studies to date in understanding glutamatergic abnormalities in psychosis, and discuss the potential of new glutamatergic compounds for treatment of the disorder.

Introduction: In linkage and association studies the DTNBP1 gene has been identified as a major susceptibility gene for schizophrenia. Reduced expression of DTNBP1 was found in the hippocampus and prefrontal cortex in post mortem brains of schizophrenic patients. In vitro and animal models provide evidence that the DTNBP1 gene product dysbindin modulates the activity of the neurotransmitter glutamate in hippocampal neurons and is crucial for cell functioning and synaptogenesis. This study is the first to investigate the effects of genetic variants of DTNBP1 on the status of the glutamate system as well as neuronal integrity (N-acetylaspartate, NAA) in the hippocampus and a cortical region, the anterior cingulate cortex (ACC), in humans. Methods: In 79 healthy subjects, the association of single nucleotide polymorphisms (SNPs) rs760665 and rs909706 with absolute concentrations of glutamate and NAA in the left hippocampus and the ACC were investigated, using proton magnetic resonance spectroscopy (MRS) at 3 Tesla and a well established quantification procedure. Results: Hippocampal glutamate concentration was significantly affected by genotype of rs760665 (F=4.406, df=2,p=0.016) and rs909706 (F=3.171,df=2,p=0.048). For the concentration of NAA, a weak association with rs760665 was observed in the contrast analysis. None of the metabolites measured in the ACC showed a significant connection with either genotype. Conclusion: The results support a role of DTNBP1 gene variants in the glutamate neurotransmission system in the human brain at least in the hippocampus. This is compatible to growing evidence of a crucial role of glutamate in the pathobiology of schizophrenia. In addition, the weak association between DTNBP1 genotype and NAA is in line with a regulatory influence of dysbindin on synaptogenesis and neuronal survival.

In recent years metabotropic glutamate receptors have emerged as key targets for the design of new antipsychotic medications for schizophrenia, in particular mGluR5 and mGluR2/3. These receptors exhibit diverse interactions with other neurotransmitter receptors and critical elements of intracellular signalling cascades known to be important to the pharmacotherapy of schizophrenia. In addition, mGluR5 and mGluR2/3 are intimately involved in behavioural domains related to the symptoms of this disorder. Both animal and clinical studies using novel drugs targeting these receptors have provided encouraging results. The number of patents registered for drugs targeting metabotropic glutamate receptors has grown dramatically, and positive allosteric modulators for both receptors show particular promise.

The treatment of schizophrenia has been focused on modulation of dopamine receptors for over 50 years. Recent developments have implicated other neurotransmitter systems in the pathophysiology of this illness. The discovery and characterization of glutamate receptors and their roles in the brain has lead to novel approaches for the treatment of schizophrenia. In this article, we review drugs that modulate ionotropic gluamate receptors and discuss their efficacy for the treatment of this often debilitating severe mental illness.

Cognitive deficits are trait markers in schizophrenia and the improvement of these dysfunctions has been considered as a new frontier of treatment in this disease. A current model for the patophysiology of schizophrenia states that N-methyl-D-aspartate receptor (NMDAR) hypofunction leads to a dysregulation of gamma-amino butyric acid (GABA) fast- spiking interneurons, consequently disinhibiting pyramidal glutamatergic output and disturbing signal-to-noise ratio. In this way, the modulation of the glutamate activity might constitute a highly promising target for future therapeutic interventions of this disease. In the present review, we discuss key regulatory elements for glutamatergic neurotransmission and provide new insights into their potential role in developing pharmacological treatments. Also, we emphasize the role of certain chemical families as potential sources of new lead compounds with affinity for metabotropic glutamate receptors (mGluRs) with cognitive enhancing properties.

For decades treatment of schizophrenia was restricted to drugs, which mainly target positive symptoms by interfering with the dopaminergic neurotransmission. Since a large body of experimental and clinical data implicate that schizophrenia may primarily be a consequence of an imbalance in the glutamatergic system, specifically the networks containing GABAergic interneurons (γ-amino butyric acid), new drugs modulating glutamatergic neurotransmission are being developed. Targeting this dysfunction may follow different strategies, including application of direct or indirect NMDA (N-methyl-D-aspartate) receptor agonists or drugs modulating the function of metabotropic glutamate receptors. Meanwhile, the first substances have proven to be effective in animal models of schizophrenia and now enter the stage of clinical trials. The most promising data have been obtained in studies employing agonists of the metabotropic glutamate receptor. A choice of these substances is presented in this review.

Altered markers of cortical GABA neurotransmission are among the most consistently observed abnormalities in postmortem studies of schizophrenia. The altered markers are particularly evident between the chandelier class of GABA neurons and their synaptic targets, the axon initial segment (AIS) of pyramidal neurons. For example, in the dorsolateral prefrontal cortex of subjects with schizophrenia immunoreactivity for the GABA membrane transporter is decreased in presynaptic chandelier neuron axon terminals, whereas immunoreactivity for the GABAA receptor α2 subunit is increased in postsynaptic AIS. Both of these molecular changes appear to be compensatory responses to a presynaptic deficit in GABA synthesis, and thus could represent targets for novel therapeutic strategies intended to augment the brain’s own compensatory mechanisms. Recent findings that GABA inputs from neocortical chandelier neurons can be powerfully excitatory provide new ideas about the role of these neurons in the pathophysiology of cortical dysfunction in schizophrenia, and consequently in the design of pharmacological interventions.

It is being increasingly recognised that the future of drug development will need to be based on a comprehensive understanding of disease pathophysiology. Thus this review focuses on a growing body of information suggesting that decreases in muscarinic receptors are involved in the pathophysiology of schizophrenia. This review will address evidence to support the hypothesis that drugs that can increase the activity of muscarinic receptors have the potential to have antipsychotic affects and improve cognitive deficits in subjects with the schizophrenia. How drugs directed towards allosteric binding sites are overcoming the problem of using orthosteric receptor agonists in the treatment of disease, which cause agonist-induced receptor down-regulation and subsequent drug desensitisation, will be discussed. The discovery of allosteric binding sites on muscarinic receptors will be reviewed as will the ability of different classes of drugs to stimulate each muscarinic receptor without causing agonist-induced receptor down-regulation. Finally, progress in developing allosteric muscarinic receptor agonists and modulators will be discussed and it will be argued the muscarinic M1 receptor allosteric agonists and/or modulators may have the potential to improve the cognitive deficits associated with schizophrenia whilst muscarinic M4 receptor modulates may have antipsychotic effects.