Current Medicinal Chemistry - Volume 14, Issue 20, 2007

Precisely localizing therapeutic agents in neoplastic areas would greatly improve their efficacy for killing tumor cells and reduce their toxicity to normal cells. Photodynamic therapy (PDT) is a promising cancer treatment modality, and near-infrared fluorescence imaging (NIRF-I) is a sensitive and noninvasive approach for in vivo cancer detection. This review focuses on the current efforts to engineer single molecule constructs that allow these two modalities to be combined to achieve a high level of selectivity for cancer treatment. The primary component of these so called killer beacons is a fluorescent photosensitizer responsible for both imaging and therapy. By attaching other components, e.g. various DNA- or peptide-based linkers, quenchers or cancer cell-specific delivery vehicles, their primary diagnostic and therapeutic functions as well as their target specificity and pharmacological properties can be modulated. This modular design makes these agents customizable, offering the ability to assemble a few simple and often interchangeable functional modules into beacons with totally different functions. This review will summarize following three types of killer beacons: photodynamic molecular beacons, traceable beacons and beacons with built-in apoptosis sensor. Despite the rapid progress in killer beacon development, numerous challenges remain before these beacons can be translated into clinics, such as photobleaching, delivery efficiency and cancerspecificity. In this review we outline the basic principles of killer beacons, the current achievements and future directions, including possible cancer targets and different therapeutic applications.

Bisphosphonates (BPs) are inhibitors of bone-resorption and have become the current standard of care for preventing skeletal complications associated with bone metastases. Among BPs, zoledronic acid (ZOL) has the strongest activity of anti-bone resorption and shows diverse direct anti-cancer effects in vitro. Some chemical and biological characteristics of ZOL indicate the potential for in vivo growth inhibition and the mechanisms responsible for the observed anti-cancer effects are beginning to be elucidated. ZOL inhibits farnesyl pyrophosphate synthase, a key enzyme in the mevalonate pathway. Consequently, it inhibits the prenylation of small G-proteins such as Ras, Rap1, Rho and Rab, reduces the signals they mediate, and thereby prevents the growth, adhesion/spreading, and invasion of cancer cells. ZOL, which has a high affinity for mineralized bone, rapidly localizes to bone, resulting in therapeutically effective local concentrations for the cancer cells in bone. ZOL also blocks osteolysis and osteoclastgenesis, thus preventing the release of various growth factors which are abundantly stored in bone. Moreover, ZOL stimulates γδ T cells, which play important roles in innate immunity against cancer. In addition, ZOL is also a potent inhibitor of angiogenesis, probably due to the modification of various angiogenic properties of endothelial cells. Furthermore, ZOL synergizes with a variety of anticancer agents including chemotherapeutic drugs, molecular targeted agents, and other biological agents. Based on these potential anti-cancer properties, several clinical trials have been initiated to test the combination of ZOL and other agents. The accumulated encouraging evidence to date indicate that ZOL is an attractive anti-cancer agent which promises to be the next exciting therapy for patients with various cancers.

Molecular recognition of DNA by small molecules and proteins is a fundamental problem in structural biology and drug design. Understanding of recognition in both sequence-selective and sequence neutral ways at the level of successful prediction of binding modes and site selectivity will be instrumental for improvements in the design and synthesis of new molecules as potent and selective gene-regulatory drugs. Minor groove is the target of a large number of non-covalent binding agents. DNA binding with specific sequences, mostly AT, takes place by means of a combination of directed hydrogen bonding to base pair edges, van der Waals interactions with the minor groove walls and generalized electrostatic interactions. These factors are also responsible for protein-DNA recognition, and a number of unifying rules governing the interactions have been elucidated although it has been realized that the earlier goal of a simple recognition code between amino acids and bases is not attainable. At present relatively little is understood about the mode of action at the molecular level of the majority of minor grooveinteracting drugs, although there is increasing evidence that they may act by directly blocking or inhibiting protein-DNA recognition. The present review has the aim to focus on interactions between minor groove binders and DNA through a variety of techniques that are commonly used to analyze the DNA binding properties of small molecules. In fact in the last years several articles dealing with in silico techniques on DNA minor groove binders (molecular modeling, molecular dynamics, QSAR) have been published. All these studies can be considered a support in defining valid predictive models. For this reason a compendium of all matter could be an useful support for future developments.

Prostacyclin (PGI2) is a major product of COX-2 catalyzed metabolism of arachidonic acid in the endothelium. Recent studies have demonstrated that PGI2 protects against atherothrombosis. The prostacyclin receptor knockout mice exhibit increased atherosclerosis, enhanced thrombosis, and enhanced proliferative response to carotid vascular injury with increased intima to media ratios [1-3]. Moreover, the recent withdrawal of rofecoxib (Vioxx™) due to increased cardiovascular events further supports the critical role of prostacyclin in inhibiting atherothrombosis in humans. Such studies have paralleled intense chemical biology studies to develop more stable prostacyclin analogues. Indeed a number of these analogues are currently being successfully used for the treatment of pulmonary hypertension. In this review we will summarize the current literature on some principles of prostacyclin analogue development, our current understanding of the receptor, and recent developments which implicate prostacyclin in atherothrombotic protection. More than 68 million Americans suffer from cardiovascular disease, which causes more deaths, disability and economic loss than any other group of diseases. Further clinical investigations of orally stable prostacyclin analogues for treatment of cardiovascular diseases other than pulmonary hypertension may now be warranted.

CD40-CD40L interactions have been involved in inflammation and thrombosis. Several diseases are characterized by inflammation, hypercoagulability and increased prevalence of thromboembolic events. In the past decade, a series of preclinical and clinical studies has provided more insight into the pathogenetic mechanisms linking inflammatory mediators to the activation and regulation of the haemostatic system. In particular, the study of CD40-CD40L interactions has greatly contributed to understanding the role of platelets in a variety of pathophysiological conditions, including atherothrombosis, immunoinflammatory diseases and, possibly, cancer. A wide variety of preclinical and clinical studies have generated clinical interest in the use of CD40L as a prognostic marker of thrombotic risk. However, the use of sCD40L in clinical studies requires reliable methods. For the correct interpretation of results, clinical and research laboratories and physicians must be aware of the limitations of immunoassays for this cytokine, which underlines the need for standardization of preanalytic conditions. This review will focus on biochemical evidence of CD40L involvement in platelet activation, contribution of platelet-derived CD40L to inflammation, thrombosis and neoangiogenesis, and possible methodological pitfalls regarding the appropriate specimen and preparation for laboratory evaluation of blood soluble CD40L as a biomarker in various human diseases characterized by underlying inflammation, such as atherothrombosis, cancer and immuno-inflammatory diseases.

Phosphodiesterases (PDE) are a class of proteins whose most relevant biological activity concerns the modulation of intracellular levels of cyclic nucleotides, e.g., cGMP and cAMP. PDE isoenzyme 5 (PDE5) is specifically involved in cGMP inactivation in the smooth muscle cell. Chemical inhibition of PDE5 by sildenafil, tadalafil or vardenafil recently became a valid therapeutic option aimed at overexpressing the molecular pathway originated from nitric oxide and expressed via increased cell cGMP availability. Based on the optimal tolerability and proven efficacy in various human disorders, EMEA and FDA have approved PDE5 inhibition as an efficient therapy in some cardiovascular, pulmonary and vascular diseases. More specifically, PDE5 inhibition appears successful for the treatment of idiopathic arterial pulmonary hypertension. Furthermore, PDE5 inhibition resulted in important protective effects in the myocardium, i.e., antyhypertrophic and antiapoptic, as well as vascular functions, i.e., increased tolerance to ischemia/reperfusion injury and improved endothelial function, thereby implying a potential usefulness in the treatment of patients with heart failure and coronary artery disease. Evidence currently available for considering PDE5-inhibition an additional opportunity in the treatment of common cardiopulmonary disorders is here provided.

Cardiac failure is a leading cause for the mortality of diabetic patients, in part due to a specific cardiomyopathy, referred to as diabetic cardiomyopathy, which occurs with or without co-existence of vascular diseases. Although several mechanisms responsible for diabetic cardiomyopathy have been proposed, oxidative stress is widely considered as one of the major causes for the pathogenesis of the disease. Thus, a few laboratories are trying to develop antioxidants used to prevent diabetic cardiomyopathy. Metallothioneins (MTs) are cysteine-rich metal-binding proteins with several biological roles including antioxidant property. We and others have indicated the significant cardiac protection of MT against diabetes using cardiac-specific MT-overexpressing transgenic mice and OVE26MT mice (cross-bred of cardiac MT transgenic mice with genetically engineered diabetic OVE26 mice). Several possible mechanisms responsible for MT's cardiac protection from diabetes were revealed. These include MT's important roles in calcium regulation, zinc homeostasis, insulin sensitization, and antioxidant action. Since MT is ubiquitously expressed in mammalian tissues and is highly inducible by a variety of reagents such as zinc, the clinical potential for inducing cardiac MT as an antioxidant by zinc supplementation to prevent various diabetic complications, including cardiomyopathy, has been explored in diabetic animal models and patients. Since zinc has been therapeutically used for several other non-diabetic diseases in clinics, it provides further potential use of zinc for diabetic patients. Therefore, this review will briefly introduce the biochemical features of MT along with its critical roles in redox homeostasis and antioxidant function in the heart, and then discuss the current research on the prevention of diabetic cardiomyopathy by MT with an emphasis on experimental evidence, possible mechanisms, and clinical implications.

New clinical practice guidelines for patients with asthma include the recommendation to monitor exhaled breath nitric oxide (NO) levels. NO concentrations in exhaled breath are increased in asthmatics and increased NO levels correlate with worsening airway inflammation and asthma symptoms. The multiple roles of NO in the lung have not been delineated clearly. Clinical trials are being performed presently that test the apparently conflicting hypotheses that either donors or inhibitors of NO in the lung are effective strategies for treating asthma. These strategies evolved, in part, from results of pre-clinical studies performed in mice and other animal models. This review evaluates the existing literature with regard to mouse models of asthma and explores the often conflicting data on the role of NO, the nitric oxide synthase (NOS) enzymes, and the arginase enzymes in allergic airway inflammation. While we will emphasize the ovalbumin exposure mouse model, we will also examine other models. Where inconsistencies are identified among the studies, we attempt to determine whether such inconsistencies arise from methodological differences or alternative mechanisms. Ultimately, we address whether the allergen-exposed mouse is a suitable model for identifying promising new drugs for the treatment of human asthma. While a consensus is building that NO is beneficial or protective in subsets of asthmatics, results from studies using mouse models to investigate the individual roles of NO and the NOS enzymes in airway inflammation are often contradictory. Further research efforts with this model will allow us to distinguish which asthma patients may benefit best from NO donors and which may benefit from NO inhibitors.