Current Pharmaceutical Design - Volume 11, Issue 19, 2005

Infectious diseases are a significant cause of morbidity and mortality worldwide, accounting for approximately 50% of all deaths in tropical countries and as much as 20% of deaths in the Americas. Despite the significant progress made in microbiology and the control of microorganisms, sporadic incidents of epidemics due to drug resistant microorganisms and hitherto unknown disease-causing microbes pose an enormous threat to public health. These negative health trends call for a global initiative for the development of new strategies for the prevention and treatment of infectious disease. For over 100 years chemical compounds isolated from medicinal plants have served as the models for many clinically proven drugs, and are now being re-assessed as antimicrobial agents. The reasons for this renaissance include a reduction in the new antibacterial drugs in the pharmaceutical pipeline, an increase in antimicrobial resistance, and the need of treatments for new emerging pathogens. Literally thousands of plant species have been tested against hundreds of bacterial strains in vitro and many medicinal plants are active against a wide range of gram positive and gram negative bacteria. However, very few of these medicinal plant extracts have been tested in animal or human studies to determine safety and efficacy. This review focuses on the medicinal plants and bacteria for which there is significant published in vitro, in vivo and clinical data available. The examples provided in this review indicate that medicinal plants offer significant potential for the development of novel antibacterial therapies and adjunct treatments (i.e. MDR pump inhibitors).

Secretory IgA (SIgA) is the antibody type produced in both mammals and birds that protects the body from infection at mucosal surfaces. While monoclonal IgG antibodies, particularly those against tumor antigens, have received a great deal of attention, both scientific and commercial, as immunotherapeutic agents, the potential of SIgA antibodies has only recently begun to be exploited. Part of the reason for this is that SIgA production in vivo normally requires the cooperation of two different cell types, and single animal cell systems for monoclonal SIgA production are inefficient. Transgenic plants are currently the most productive and economical system for making SIgA. The only monoclonal SIgA to be tested therapeutically in a human clinical trial is a product called CaroRx, made in transgenic tobacco, which is designed to block adherence to teeth of the bacteria that causes cavities. This antibody accumulates to high levels in the leaves of tobacco, where it is located primarily in the endoplasmic reticulum. The antibody can be efficiently purified using the affinity reagent protein G. Topical oral treatment in human subjects was safe and effective. Characterization of the expression, secretion, purification and therapeutic use of this antibody serves as a model for additional plant-made therapeutic SIgA antibodies under development.

Antibodies are an important class of proteins that can be used for the prevention, treatment and diagnosis of many diseases. Consequently, there is an intense and growing demand for recombinant antibodies, placing immense pressure on current production capacity which is based largely on microbial cultures and mammalian cells. Alternative systems for cost effective antibody production would be very welcome, and plants are now gaining widespread acceptance as green bioreactors with advantages in terms of cost, scalability and safety. Several plant-produced antibodies (plantibodies) are undergoing clinical trials and the first commercial approval could be only a few years away. The performance of the first generation of products has been very encouraging so far. In terms of product authenticity, differences in glycosylation between plantibodies and their mammalian counterparts have been defined, and the scientific evaluation of any possible consequences is underway. Ongoing studies are addressing the remaining biochemical constraints, and aim to further improve product yields, homogeneity and authenticity, particularly where the antibody is intended for injection into human patients. A remaining practical challenge is the implementation of large-scale production and processing under good manufacturing practice conditions that are yet to be endorsed by regulatory bodies. The current regulatory uncertainty and the associated costs represent an entry barrier for the pharmaceutical industry. However, the favourable properties of plants are likely to make the plant systems a useful alternative for small, medium and large scale production throughout the development of new antibody-based pharmaceuticals.

Plastid transformation technology is set to become a major player in the production of human therapeutic proteins. Protein expression levels that can be achieved in plant plastids are hundreds of times greater than the expression levels generally obtained via nuclear transformation. Plastids can produce human proteins that are properly folded and are biologically active. Effective protein purification strategies and strategies that can achieve inducible plastid gene expression are being developed within the system. Plastid transformation technology has been extended to edible plant species, which could minimize down-stream processing costs and raises the possibility of “edible protein therapies”. The system is limited by the fact that plastid-produced proteins are not glycosylated and that, at the moment, it can be difficult to predict protein stability within the plastid. The high level of protein expression that can be obtained in plastids could make it possible to produce high-value therapeutic proteins in plants on a scale that could be accommodated in contained glasshouse facilities and still be economically viable. Growing plastid-transformed plants under contained conditions, and coupled with the level of bio-safety conferred by maternal inheritance of plastid transgenes, would address many of the social and environmental concerns relating to plant based production of human therapeutic proteins.

Agitation is commonly seen in acute schizophrenic patients and core symptoms include a wide range of symptom. It requires rapid and effective treatment approaches in order to protect patient and caregiver from potential injury. Clinician's decision of pharmacological treatment should be individualized to the needs and circumstances of the patient. Benzodiazepines, typical antipsychotics, and combinations of typical antipsychotics and benzodiazepines have been widely used as treatment options. Atypical antipsychotics have clear advantages over the typical drugs as they generally show a much better safety and tolerability profile, particularly to EPS and related side effects, however clinical perception regarding efficacy in treating acutely agitated psychotic patient is controversial. New intramuscular atypical antipsychotic formulations offer evidence of being at least as effective as typical antipsychotics in controlling agitation. Therefore, they should be considered as first line therapy in agitated schizophrenic patients.

Ceramide is not only structurally but also functionally a key molecule in diverse kinds of sphingolipids. In the past decade, ceramide has been shown to be of crucial significance in several cell functions including apoptosis, cell growth, senescence, and cell cycle control. Among them, the role of ceramide in apoptosis induction has extensively been studied, and ceramide-targeting molecular medicine for apoptosis-based diseases such as malignant tumors, atherosclerosis and neurodegenerative disorders appears to come out to the clinical field. We here describe the recent advances in research of ceramide-mediated apoptosis signaling. We also show the relation of ceramide level through regulation of ceramide-related enzymes (sphingomyelinase, ceramidase, sphingomyelin synthase and glucosylceramide synthase) with diseases such as cancer, leukemia, bacterial infections, AIDS, Alzheimer's disease, atherosclerosis, diabetes mellitus and atopic dermatitis. The strategies to construct the ceramide-targeting medicine for intractable diseases such as cancer and leukemia are discussed.

Heparin is a sulphated glycosaminoglycan currently used as an anticoagulant and antithrombotic drug. It consists largely of 2-O-sulphated IdoA → N, 6-O-disulphated GlcN disaccharide units. Other disaccharides containing unsulphated IdoA or GlcA and N-sulphated or N-acetylated GlcN are also present as minor components. This heterogeneity is more pronounced in heparan sulphate (HS), where the low-sulphated disaccharides are the most abundant. Heparin/HS bind to a variety of biologically active polypeptides, including enzymes, growth factors and cytokines, and viral proteins. This capacity can be exploited to design multi-target heparin/HS-derived drugs for pharmacological interventions in a variety of pathologic conditions besides coagulation and thrombosis, including neoplasia and viral infection. The capsular K5 polysaccharide from Escherichia coli has the same structure as the heparin precursor N-acetyl heparosan. The possibility of producing K5 polysaccharide derivatives by chemical and enzymatic modifications, thus generating heparin/HS-like compounds, has been demonstrated. These K5 polysaccharide derivatives are endowed with different biological properties, including anticoagulant/antithrombotic, antineoplastic, and anti-AIDS activities. Here, the literature data are discussed and the possible therapeutic implications for this novel class of multi-target “biotechnological heparin/HS” molecules are outlined.

Collagen fibers are the most abundant components of the extracellular matrix in arteries and myocardium. Disturbances in the collagen turnover (synthesis and degradation) have been linked to inflammatory diseases including cardiovascular pathological syndromes. In the myocardium, changes in collagen turnover may result in ventricle dilatation and subsequent contractile dysfunction. In arteries, collagen synthesis and degradation are associated with the progression of atherosclerotic disease and intimal hyperplasia following injury. Collagen synthesis is tightly regulated at several levels: synthesis of procollagens, suitable folding of polypeptides, secretion and cross-linking of mature fibers. On the other hand, degradation of newly synthesised procollagen and mature collagen fibers depends on the action of Matrix-Metalloproteinases (MMPs). The major role of collagen turnover in cardiovascular disorders has stimulated the search for pharmacological agents that interfere with collagen turnover at different levels. These drugs can theoretically act through modulation of the synthesis of procollagens or by interference with their post-translational modifications. Another group of pharmacological agents inhibit collagen breakdown (MMP inhibitors). Beneficial effects of compounds that target collagen metabolism have been reported. Unfortunately, many of these compounds also give rise to serious adverse effects due to interference with vital biological processes in which collagen plays an important role. In this paper, we will review cardiovascular diseases in which altered local collagen turnover is a key feature. Subsequently, the effect of compounds that have been developed and tested to modulate collagen synthesis, cross-linking or breakdown will be discussed.

The recognition that asthma is an inflammatory disease opens a new field to find effective models for the evaluation and development of new drugs. In this scenario, many novel candidate molecules have been shown to work perfectly in animal models, but not in clinical studies. Ancillary models are reviewed in association with the findings obtained in either transgenic or knockout mice. In parallel, genetic studies in animal models and human populations have identified several genes that are asthma-related. Knowledge of these recent findings, in parallel with pharmacogenomic studies will be necessary to direct new strategies for the development of novel drugs to treat subgroups of patients with asthma.

Although well-differentiated thyroid carcinomas are usually curable by the combined effects of surgery, radioiodine ablation and thyroid stimulating hormone (TSH) suppressive therapy, recurrence develops in 20-40% of patients. During tumour progression, cellular de-differentiation occurs in up to 30% of cases and is usually accompanied by more aggressive growth, metastasis spread and loss of iodide uptake. The therapeutic options for de-differentiated thyroid cancer are limited and generally not efficient. Retinoic acids (RA) are biologically active metabolites of vitamin A that regulate growth and differentiation of many cell types, by binding to specific nuclear receptors: the retinoic acid receptors (RAR) and the retinoid X receptors (RXR). Recent studies have shown that RA can induce in vitro redifferentiation of thyroid carcinoma cell lines, as suggested by increased expression of the sodium/iodide symporter (NIS), type I iodothyronine deiodinase, alkaline phosphatase and by the increment of cellular 131I uptake. In addition to redifferentiating effects, RA also exert anti-proliferative actions, as the inhibition of mitosis and the induction of apoptosis. Previous clinical studies have shown that iodide uptake may be re-stimulated after RA in about 20-50% of patients with radioiodine non-responsive thyroid carcinoma. Longer follow-up of patients demonstrated that, besides iodide uptake increment, RA can induce tumour regression or at least tumour growth stabilisation. The therapy is generally well tolerated and the most frequent side effects are dryness of skin and mucosa, and hypertriglyceridemia. This paper describes the recent advances in the field of thyroid cancer therapy and reviews the use of RA as a promising novel therapeutic tool.