Current Drug Discovery Technologies (v.6, #1)

Discovery of Medically Significant Lantibiotics by Clare Piper, Paul Cotter, R. Ross, Colin Hill (1-18).
The emergence of drug-resistant pathogens such as staphylococci and enterococci in the hospital setting has long being recognized as a serious clinical problem. Staphylococcus aureus is the causative agent of many nosocomial infections from minor skin abscesses to serious, potentially life threatening diseases such as bone and soft tissue intra-surgical infections, sepsis and invasive endocarditis, while enterococci are responsible for nosocomial bacteraemia, surgical wound infections and endocarditis. The most infamous drug-resistant forms of these include MRSA (methicillin resistant S. aureus), VISA (vancomycin insensitive S. aureus), hVISA (heterogenous vancomycin insensitive S. aureus) and VRE (vancomycin resistant S. aureus). While enhanced hygiene awareness is essential to any solution, the identification of effective novel antimicrobial compounds remains a major goal in eradicating these and other infections caused by multi-drug resistant pathogens. In recent years a class of antimicrobial peptides, the Lantibiotics, have been the focus of an ever increasing level of attention. This interest has been prompted by an enhanced appreciation of the mode of action of these peptides (including, in many cases, the ability to bind lipid II) and their frequently high levels of antimicrobial activity. Here we review lantibiotic- related issues in drug discovery, outline the strategies that have been employed to identify these peptides and summarize the use of bioengineering to generate enhanced forms of these peptides as well as the application of the associated biological machinery to generate novel forms of existing pharmaceutical compounds. In so doing we highlight how some, or all, of these approaches have the potential to result in the development of clinically important drugs.

The Kdo Biosynthetic Pathway Toward OM Biogenesis as Target in Antibacterial Drug Design and Development by Laura Cipolla, Alessandra Polissi, Cristina Airoldi, Paolo Galliani, Paola Sperandeo, Francesco Nicotra (19-33).
Despite important advances made in the last century, infectious diseases caused by pathogenic microrganisms are still a major threat to human health. This is worsened by the occurrence of new forms of bacterial resistance against antibiotics, that are the main remedy against infectious diseases, and their rapid spreading across bacterial species, pose additional threats to our health. Thus, the necessity to develop new weapons against pathogenic bacteria is widely recognized as a major challenge for modern drug research. Traditional antibiotic discovery procedures have so far focused on inhibiting the main processes of the bacterial cell (replication, transcription, translation, and peptidoglycan synthesis). This review will give an overview of the therapeutic strategies to cure infectious diseases caused by Gram-negative bacteria through the development of inhibitors of Kdo biosynthesis. Kdo is a monsaccharide essential for OM biogenesis, OM being an essential cellular structure shared by all Gram-negative bacteria. Hence, inhibitors of its biosynthesis can have a broad-spectrum antibacterial activity.

Ghrelin and Growth Hormone Secretagogues, Physiological and Pharmacological Aspect by Fernando Cordido, Maria Isidro, Rosa Nemina, Susana Sangiao-Alvarellos (34-42).
The first and#x201C;growth hormone secretagoguesand#x201D; (GHSs) were discovered by Bowers et al. in 1977. In 1996 the GHSs receptor (GHS-R 1a) was cloned. The endogenous ligand for this receptor, ghrelin, was not identified until 1999. Synthetic molecules termed GHSs are substances that stimulate growth hormone (GH) release, via a separate pathway distinct from GH releasing hormone (GHRH)/somatostatin. Ghrelin displays strong GH-releasing activity through the activation of the GHS-R 1a. Apart from stimulating GH secretion, ghrelin and many synthetic GHSs: 1) stimulate prolactin and ACTH secretion; 2) negatively influence the pituitary-gonadal axis; 3) stimulate appetite and positive energy balance; 4) modulate pancreatic endocrine function and affect glucose levels; 5) have cardiovascular actions. The control of ghrelin secretion is not well established at present, although nutrition is an important regulator. Investigators have exploited the ability of GHSs and ghrelin to release GH by mechanisms different from GHRH as a diagnostic tool, which is the present main clinical use of some GHSs. As an alternative to GH, GH deficient conditions could be treated with any substance which would release endogenous GH, such as synthetic GHSs. It is likely that GHSs, acting as either agonists or antagonists on different pathophysiological processes, might have some other clinical impact and therapeutic potential. At least theoretically ghrelin receptor antagonists could be anti-obesity drugs, as blockers of the orexigenic signal from the gastrointestinal tract to the brain. Inverse agonists of the ghrelin receptor, by blocking the constitutive receptor activity, might lower the set-point for hunger between meals.

Development of Multifunctional Nanoparticles for Targeted Drug Delivery and Noninvasive Imaging of Therapeutic Effect by Hari Sajja, Michael East, Hui Mao, Y. Wang, Shuming Nie, Lily Yang (43-51).
Nanotechnology is a multidisciplinary scientific field undergoing explosive development. Nanometer-sized particles offer novel structural, optical and electronic properties that are not attainable with individual molecules or bulk solids. Advances in nanomedicine can be made by engineering biodegradable nanoparticles such as magnetic iron oxide nanoparticles, polymers, dendrimers and liposomes that are capable of targeted delivery of both imaging agents and anticancer drugs. This leads toward the concept and possibility of personalized medicine for the potential of early detection of cancer lesions, determination of molecular signatures of the tumor by noninvasive imaging and, most importantly, molecular targeted cancer therapy. Increasing evidence suggests that the nanoparticles, whose surface contains a targeting molecule that binds to receptors highly expressed in tumor cells, can serve as cancer image contrast agents to increase sensitivity and specificity in tumor detection. In comparison with other small molecule contrast agents, the advantage of using nanoparticles is their large surface area and the possibility of surface modifications for further conjugation or encapsulation of large amounts of therapeutic agents. Targeted nanoparticles ferry large doses of therapeutic agents into malignant cells while sparing the normal healthy cells. Such multifunctional nanodevices hold the promise of significant improvement of current clinical management of cancer patients. This review explores the development of nanoparticles for enabling and improving the targeted delivery of therapeutic agents, the potential of nanomedicine, and the development of novel and more effective diagnostic and screening techniques to extend the limits of molecular diagnostics providing point-of-care diagnosis and more personalized medicine.

The surface coverage and leaflet anchoring of polymeric surfactants and other amphiphiles can be used to provide a particle with extensive modifiable and#x2018;stealthand#x2019; properties. This is not a new conceptual tool but one which has significant strategic advantage and recent proven clinical application in a and#x201C;drug-delivery-packageand#x201D;. This has been established and widely reported as a fundamental basis for optimal utility with long-circulation drug nanoparticles. The indirect and#x201C;disguisingand#x201D; of the medicinal payload presents itself as a form of and#x201C;pro-drugand#x201D; system that can be used to extend circulation lifetime and that is key to a number of essential current and future risk-bearing therapies. Appropriate particle sizing and leaflet chemical structuring, in terms of number of strata, complexity, extent and curvature can also be used as the means to and#x201C;drug anchoringand#x201D; for the incorporation of and#x201C;hydrophobicand#x201D; drugs. Actives that are chemo- or solvent labile can also be housed, often routinely, within the inner-protected chamber of such capsular systems. This has frequently formed the basis of a number of recently developed commercial preparations that are used ubiquitously in now standard chemotherapy. Additionally, the use of complementary and non-complementary phospholipid or other vesicle ingredient mixtures below, at or above the lipid and#x201C;gel transitionand#x201D; temperature or within a and#x201C;glassyand#x201D; crystalline packing configuration can provide a particle of varied physical and mechanical composition that provides a possible route to the production of fusogenic nano-drugs or control over the drug release profile. Successive layering of the nanoparticle can in principle provide the means to a step-wise or timed release of the particle contents and one that can be adapted to the site of intended use.

The Role of the RhoA/rho-kinase Pathway in Pulmonary Hypertension by Bobby Nossaman, Philip Kadowitz (59-71).
The small GTP-binding protein, RhoA, and its downstream effector protein, rho-kinase, have been implicated in the pathogenesis of a number of cardiovascular diseases. The activation of rho-kinase is involved in the development of increased vascular tone, endothelial dysfunction, inflammation, and restenosis; and that the inhibition of rho-kinase has been shown to have a beneficial effect in a variety of cardiovascular disorders. It is our hypothesis that rho-kinase inhibitors promote vasodilation independent of the mechanism that increases vasoconstrictor tone and moreover, the RhoA/rho-kinase pathway has a role in the regulation of smooth muscle tone under physiological conditions. The objective of this review is to improve our current understanding of the role of RhoA/rho-kinase pathway in the regulation of vasoconstrictor tone and the use of rho-kinase inhibitors in the treatment of cardiovascular disorders with an emphasis on pulmonary hypertension.

The surfaces of the abdomen and pelvis are an important anatomic site for the dissemination of gastrointestinal and gynecologic malignancy. This transcoelomic spread of cancer cells gives rise to peritoneal carcinomatosis which, without special treatments, is a fatal manifestation of these diseases. In order to control peritoneal carcinomatosis cytoreductive surgery to remove gross disease is combined with perioperative intraperitoneal and perioperative intravenous chemotherapy to eradicate microscopic residual disease. Chemotherapy agents are selected to be administered by the intraperitoneal or intravenous route based on their pharmacologic properties. A peritoneal- plasma barrier which retards the clearance of high molecular weight chemotherapy from the peritoneal cavity results in a large exposure of small cancer nodules on abdominal and pelvic surfaces. Tissue penetration is facilitated by moderate hyperthermia (41-42and#176;C) of the intraperitoneal chemotherapy solution. A constant dose of chemotherapy agent and volume of carrier solution based on body surface area allows prediction of systemic drug exposure and systemic toxicity. Timing of the chemotherapy as a planned part of the surgical procedure to maximize exposure of all peritoneal surfaces is crucial to success.