Current Pharmaceutical Design - Volume 13, Issue 4, 2007

Proteases have been known for many years as protein-degrading enzymes. However, this view has dramatically changed and proteases are now considered as extremely important signalling molecules, involved in numerous vital processes. Their activity requires strict regulation and regulation defects can lead to pathologies, often associated with excessive proteolysis. The number of diseases, where proteases were identified to be important, if not essential, is increasing almost exponentially and proteases are therefore seriously considered as important drug targets in the areas of cardiovascular diseases, cancer, neurodegenerative diseases (Alzheimer, ...), osteoporosis, diabetes type II, pancreatitis, inflammation, arthritis and rheumatoid arthritis, to list just some of them. In addition, there has been a boom also in the area of infectious diseases, which were less seriously considered with few exceptions such as AIDS and hepatitis C. The recent determination of human, mouse, monkey and rat genomes, as well as the development of new technologies set new standards for more rapid target identification and validation, which is reflected also in the protease field. The major progress in the field resulted in successful development of drugs targeting new targets, such as dipeptidyl peptidase IV inhibitors (Novartis, Merck) for diabetes type II and a renin inhibitor for hypertension (Novartis), which are expected to be launched in 2007. Moreover, the number of new compounds being currently tested in advanced clinical trials suggests a major increase of new therapies based on protease inhibition in the coming years, which is also expected to largely increase the current ∼$11 billion market for protease-targeted drugs [1]. The goal of this issue, which is divided into two parts, is to review some of the current advances in the field. The first part contains 6 papers ([2-7], whereas the last four papers are in the second part of this issue [8-11]]. In the first paper, Fonovi and Bogyo describe development of activity based probes for proteases, and their applications to biomarker discovery, molecular imaging and drug screening [2]. In the next paper, Butler and Overall describe the power of proteomics in validation of protease drug targets, illustrated on an example from metalloprotease inhibition [3]. This is followed by a paper from Eder et al. [4], who describe the development of inhibitors against different aspartic proteases, including the development of renin inhibitors, where an NDA has been filed in this year. Prezeljz et al. discuss the recent advances in anticoagulant therapy based on the inhibition of serine protease inhibition [5]. In another paper based on serine proteases, Sommerhoff and Schaschke describe current advances in the development of tryptase inhibitors for treatment of allergic diseases, including bronchial asthma [6]. After the failure of broad spectrum MMP inhibitors in cancer and rheumatoid arthritis, the focus of MMP inhibition has shifted as described by Fingleton [7] in the last paper of the first part. In addition to MMPs, also metalloprotease exopeptidases can be attractive targets, as described by Arolas et al. [8] in the first paper of the second part. There are also important targets among cysteine proteases, as shown by the papers on caspase [9] and cysteine cathepsin [10] inhibition, where the compounds have also progressed into the clinical studies. Finally, the issue is concluded by a paper from Kido et al. on development of drugs against human influenza virus based on protease inhibition [11]. At the end, I would like to thank all the authors for their contributions, as well as Mr. Mirza Kazim Ali Baig from Bentham Science Publishers for all his help and support. References [1] Turk B. Targeting proteases: successes, failures and future prospects. Nat Rev Drug Disc 2006; 5: 785-99. [2] Fonovi M, Bogyo M. Activity based probes for proteases: applications to biomarker discovery, molecular imaging and drug screening. Curr Pharm Des 2007; 13(3): 253-261. [3] Butler GS, Overall CM. Proteomic validation of protease drug targets. Curr Pharm Des 2007; 13(3): 263-270. [4] Eder J, Hommel U, Cumin F, Martoglio B, Gerhartz B. Aspartic proteases in drug discovery. Curr Pharm Des 2007; 13(3): 271-285.........

Metallocarboxypeptidases (MCPs) are commonly regarded as exopeptidases that actively participate in the digestion of proteins and peptides. In the recent years, however, novel MCPs comprising a wide range of physiological roles have been found in different mammalian extra-pancreatic tissues and fluids. Among them, CPU, also known as thrombinactivatable fibrinolysis inhibitor (TAFI), has been shown to cleave C-terminal Lys residues from partially degraded fibrin, acting as inhibitor of clot fibrinolysis and therefore constituting an important drug target for thrombolytic therapies. Other MCPs such as CPE, CPN, CPM, and CPD function as pro-hormone and neuropeptide processors and display several structural differences with the pancreatic-like enzymes. In addition, important advances have been made in the discovery and characterization of new endogenous and exogenous proteinaceous inhibitors; the structural determination of their complexes with several MCPs has revealed novel binding modes. Finally, the use of MCPs in antibody-directed enzyme pro-drug therapy (ADEPT) has proved to be an efficient approach for the delivery of lethal levels of chemotherapeutic drugs specifically at tumor tissues. Taken together, these recent developments may help to understand potential biomedical implications of MCPs. Future perspectives for the regulation of these enzymes through the use of more selective and potent inhibitors are also discussed in this review and combined with earlier observations in the field.

This review provides an overview of the biochemistry and activation of inflammatory caspases, and focuses on their therapeutic potential as disease targets in pathologies such as sepsis, Crohn's disease, rheumatoid arthritis, traumatic brain injury and amyotrophic lateral sclerosis (ALS). We summarize the proof-of-principal evidence obtained by studies in several corresponding experimental disease models confirming the validity of strategies targeting inflammatory caspases. We discuss the use of inflammatory caspase inhibitors, such as VX-740 (Pralnacasan) and VX-765, in clinical studies for rheumatoid arthritis and osteoarthritis. Finally, we point out recent approaches identifying novel peptidomimetic or non-peptide caspase inhibitors with suitable clinical profiles.

The general view on cysteine cathepsins, which were long believed to be primarily involved in intracellular protein turnover, has dramatically changed in last 10 to 15 years. The discovery of new cathepsins, such as cathepsins K, V, X, F and O, and their tissue distribution suggested that at least some of them are involved in very specific cellular processes. Moreover, gene ablation experiments revealed that cathepsins play a vital role in numerous physiological processes, such as antigen processing and presentation, bone remodelling, prohormone processing and wound healing. Their involvement in several pathologies, including osteoporosis, rheumatoid arthritis, osteoarthritis, bronchial asthma and cancer have also been confirmed and today several of them have been validated as relevant targets for therapies. Compounds targeting cathepsins S and K are already in clinical evaluation, whereas others are in experimental phases. The cathepsin K inhibitor AAE-581 (balicatib) as the most advanced of them passed Phase II clinical trials in 2005. In this review, we discuss the current view on cathepsins as an emerging group of targets for several diseases and the development of cathepsin K and S inhibitors for treatment of osteoporosis and various immune disorders.

Influenza A virus (IAV) is one of the most common infectious pathogens in humans. Since IVA genome does not have the processing protease for the viral membrane fusion glycoprotein precursors, entry of this virus into cells is determined primarily by host cellular, trypsin-type, processing proteases that proteolytically activate the fusion glycoprotein precursors of IAV. At least five different processing proteases have been identified in the airways of animals and humans. These proteases determine the infectious organ tropism of IAV infection as well as the efficiency of viral multiplication in the airway, and sometimes in the brain. Proteases in the upper respiratory tract are suppressed by secretory leukoprotease inhibitor, and those in the lower respiratory tract are suppressed by pulmonary surfactant which, by adsorption, inhibits the interaction between the proteases and viral membrane proteins. Since protease activities predominate over those of endogenous inhibitory compounds under normal airway conditions, administration of protease inhibitors in the early-stage of infection significantly suppresses viral entry and viral multiplication. Several viral neuraminidase inhibitors are used clinically as anti-influenza virus agents, based on their inhibitory action on viral release from infected cells. Furthermore, protease inhibitors of viral entry could be potentially useful against influenza virus as well as neuraminidase inhibitor- resistant viruses. We also found that ambroxol, a mucolytic and anti-oxidant agent, up-regulates the levels of endogenous protease inhibitory compounds in the airway fluids in early-phase infection, and that clarithromycin, a macrolide antibiotic, increases IgA levels and mucosal immunity through augmentation of interleukin-12 levels in the airway. The combination of neuraminidase inhibitors and protease inhibitors, clarithromycin or ambroxol, could be potentially used as a potent anti-influenza therapy to minimize the emergence of drug-resistant mutant viruses.

The development of dendritic architecture with well-defined size, shape and controlled exterior functionality holds promise in pharmaceutical applications such as drug delivery, solubilization, DNA transfection and diagnosis. Highly branched, monodisperse, stable molecular level and low polydispersity with micelle-like behavior possessing nano-scale container property distinguish these structures as inimitable and optimum carrier for those applications. However reticuloendothelial system (RES) uptake, drug leakage, immunogenicity, hemolytic toxicity, cytotoxicity, hydrophobicity restrict the use of these nanostructures. PEGylation of dendrimers can generally overcome these shortcomings. Hemolytic and different cell line studies have shown reduced toxicity of PEGylated dendrimers than cationic dendrimers. PEGylation causes increased solubilization of hydrophobic drugs in dendritic framework as well as in PEG layers. PEGylated dendrimers have proved capable of forming stable complex with plasmid DNA and achieved improved gene transfection as compared to non-PEGylated dendrimers. Attachments of targeting moiety on the surface of partially PEGylated dendrimer created much interest as a delivery system for crossing of biological barriers and deliver the bioactive agent near the vicinity of target site. Recent successes also demonstrate potential of PEGylated dendrimers as magnetic resonance imaging contrast agent and in carbonyl metallo immunoassay. This review focuses on the current state of the art in the field and focuses on the potential of PEGylated dendrimers in pharmaceutical and biomedical area.

Primary chronic venous disease (CVD) is a common condition that can cause significant morbidity for sufferers and considerable burden on health care systems. Prolonged venous hypertension in conjunction with valvular incompetence and venous reflux is responsible for the diverse clinical manifestations of CVD and links all theories regarding CVD pathogenesis. Recent data suggest that valve damage may be acquired rather than congenital, and caused by inflammatory factors, notably leukocyte activation triggered by venous hypertension. Valve incompetence leads to reflux, reinforcing venous pressure elevation and initiating a vicious circle of disease progression. Loss of venous tone and lymphatic overload also play a role. Valve failure in superficial and perforating veins leads to elevated pressure in the veins and venules of the skin and subcutaneous tissue, resulting in skin hyperpigmentation, induration and ultimately ulceration. The inflammatory cascade may be ameliorated by pharmacologic intervention to decrease leukocyte activation and leukocyte endothelial interactions at both macro- and microcirculatory levels. Daflon 500 mg (micronized purified flavonoid fraction) offers great potential for achieving this with demonstrated efficacy in reducing inflammation and thus providing tissue protection at all stages of the disease. Experiments in animal and human models of CVD have shown that Daflon 500 mg modulates leukocyte rolling and adhesion and prevents endothelial damage in both veins and capillaries. Such treatment is useful for first-line management of edema as well as associated symptoms of CVD. A recent meta-analysis has confirmed that venous leg ulcer healing is accelerated by adding Daflon 500 mg to conventional treatment.