Current Enzyme Inhibition (v.9, #2)

Editorial by D. Hadjipavlou-Litina (i-i).

Tacrolimus Toxicity Reverses the Inhibitory Effects of Renin Angiotensin System Blockade on PAI-1 Expression in Cardiac Tissue by Mehmet Agirbasli, Emine Bas Bozkurtlar, Nurdan Papila-Topal, Hicran Deniz, Betul Ogutmen, Fulya Cakalagaoglu (83-88).
Introduction: PAI-1 is a potent fibrosis promoting glycoprotein in a tissue dependent manner. We previouslydisplayed that tacrolimus (FK506) toxicity increases vacuolar degeneration and arterial hyalinosis in cardiovascular tissue.FK506 toxicity induced transforming growth factor (TGF-β) expression. Renin angiotensin system (RAS) blockadepartially reversed histopathological changes associated with FK506 toxicity. In the same model, we investigated theeffects of FK506 and RAS blockade on PAI-1 expression.Materials and Methods: We examined cardiac expression of PAI-1 in a chronic FK506 toxicity model in Wistar rats.Study animals were divided into 4 groups. FK506 group was treated with FK506 intraperitoneally, FK506+Quinapril andFK506+Valsartan groups were treated Quinapril or Valsartan orally in addition to FK506. Control group was treated withsaline. Immunohistochemical staining of cardiovascular tissue was semiquantitatively scored for PAI-1 expression.Results: FK506 significantly induced PAI-1 expression in the cardiovascular tissue compared to the control group(semiquantitative scores were 25?5 versus (vs) 49±21, p =0.01). Adding renin angiotensin system blockade with anangiotensin converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) to FK506 increased FK506induced PAI-1 expression. Semiquantitative PAI-1 expression scores were 49±21, 87±14 and 95±10 for FK506,FK506+ACEI, and FK506+ARB groups respectively (p<0.01).Conclusion: FK506 toxicity is associated with up-regulation of PAI-1 expression at the tissue level which is not attenuatedafter RAS blockade. These observations suggest that FK506 induces an angiotensin II independent increase on PAI-1expression in cardiac tissue and/or elevated TGF-β and reduced BMP-7 levels with FK506 toxicity may reverse theinhibitory effects of RAS blockade on PAI-1 expression.

Targeting Lipoxygenases (LOs): Drug Design And Discovery by Eleni Pontiki, Dimitra Hadjipavlou&#8211;Litina (89-105).
Lipoxygenases (LOs) include several members and constitute a family of dioxygenases containing one nonhemeiron atom per molecule, which oscillates between Fe2+ (inactive enzyme) and Fe3+ (active form) during the catalyticcycle. They catalyze the oxygenation of polyunsaturated fatty acids containing a (1Z, 4Z)-penta-1, 4-diene system to thecorresponding hydroxyperoxy derivatives.Although the cyclooxygenases could be considered specialized in the arachidonate pathway, the detailed mechanism ofthe LO reaction still remains controversial.It has been found that LOs are implicated in several processes such as cell differentiation, inflammation and carcinogenesis.Development of drugs that interfere with the formation or effects of these metabolites would be important for thetreatment of various diseases like asthma, psoriasis, ulcerative colitis, rheumatoid arthritis, atherosclerosis, cancer andblood vessel disorders. Till now, asthma consists of the only pathological case in which improvement has been shown byLO inhibitors. Thus, the research has been directed towards the development of drugs that interfere with the formation ofleukotrienes.In this review we will update the research efforts within the LOs inhibition and we will present recent findings, of LO inhibitors.

Identifying the Structural Features of Pyrazolo[4,3-c]Quinoline-3-ones as Inhibitors of Phosphodiesterase 4: An Exploratory CoMFA and CoMSIA Study by Anand Gaurav, Vertika Gautam, Harish Kumar, Satya P. Gupta, Anees A. Siddiqui, Vijay Kumar (106-116).
Phosphodiesterases (PDEs) are responsible for the hydrolysis of cyclic nucleotides (cAMP and c-GMP). Cyclicnucleotides are important intracellular secondary messengers in cell function, relaying the signals from hormones atspecific cell-surface receptors. An increase of cAMP due to the stimulation of adenylyl cyclase or the inhibition of PDEsaffects the activity of immune system and inflammatory cells. Thus, PDE4, a cAMP specific PDE, received muchattention as a target for the treatment of the diseases like asthma and Chronic Obstructive Pulmonary Disease (COPD).Pyrazolo[4,3-c]quinoline-3-one nucleus has attracted considerable attention recently as PDE4 receptor antagonists whichhave shown remarkable therapeutic potential in the treatment of asthma and Chronic Obstructive Pulmonary Disease(COPD). In the present study, three dimensional quantitative structure activity relationship (3D QSAR) approach usingCoMFA and CoMSIA was applied to a series of 2, 5-dihydropyrazolo [4, 3-c] quinoline-3-ones as PDE4 receptorantagonists. For the purpose, 22 compounds from the series were used to develop and validate models. The robustness ofthe model was confirmed with the help of leave one out cross-validation method, while the predictive ability of modelswas tested using a test set containing three molecules. Novel compounds were designed on the basis of results of CoMFAand CoMSIA studies. Designed compounds were evaluated by Docking and Lipinski filters. 3D-QSAR models with highsquared correlation coefficient of up to 0.9590 for CoMFA and 0.9740 for CoMSIA were established. Robustness of themodels is demonstrated by R2cv values of up to 0.8600 and 0.8230 for CoMFA and CoMSIA, respectively. Predictiveability of the models is reflected by R2pred values of 0.865 and 0.926 for CoMFA and CoMSIA respectively. Predictedactivity of the designed molecules correlated well with the docking scores and the molecules also passed the Lipinskifilters. Developed models highlighted the importance of steric, electrostatic and hydrophobic properties of the moleculesfor PDE 4 receptor affinity. The designed compounds may serve as lead for the development of newer PDE4 inhibitorsbased on the 2, 5-dihydropyrazolo [4, 3-c] quinoline-3-one scaffold.

Advances in Design and Development of Inhibitors of Nitric Oxide Synthases by Harish Kumar, Satya P. Gupta, Anees A. Siddiqui, Vijay Kumar, Jennifer Rabjohns, Peter R. Williamson (117-141).
Nitric oxide synthase (NOS) is a dimeric enzyme that catalyses the production of nitric oxide (NO) in thehuman body. The nitric oxide has been identified as the most interesting and vital mediators for normal and pathologicalprocesses, including the regulation of blood pressure, neurotransmission, and macrophage defence system, but the overproduction of it can be toxic, hence their inhibitors are desired. In this article, the various isoforms of NOS and their rolesare described and a detail of the development of their inhibitors has been presented. The inhibitors studied includeaminopyridines, iminopiperidines, N-phenylamidines, benzoxazolones, isothioureas, oxazepanes, thiazepanes, diazepanes,4,5-disubstituted-1,3-oxazolidin-2-imine derivatives, thiazolidines, pyrazoles, pyrazolines, and some others.

Laccase Regulators in Anti-fungal Drug Discovery: Dark Lessons from the AIDS-related Pathogen, Cryptococcus by Jennifer Rabjohns, Peter R. Williamson, Julie O|Neal, Jason Chesney (142-151).
Fungal infections afflict an increasing number of patients due to increases in susceptible immunosuppressedpopulations such as those receiving chemotherapy, transplant conditioning or infections such as HIV. Poor responses toavailable therapy have prompted searches for novel drug targets, but screens can be difficult as expression of these targetsoften relies on specific inducing conditions present within the mammalian host. Cryptococcus is a yeast-likebasidiomycete fungus capable of causing fatal cryptococcocis in both immunocompetent and immunocompromisedindividuals, and is currently the fourth cause of infectious death in regions of Sub-Sahara Africa, excluding HIV. A keyvirulence factor of Cryptococcus is a cell-wall laccase, which produces melanin in the presence of exogenouscatecholamines. Screening melanin-deficient strains of the fungus is facile and has identified cellular processes critical forvirulence including copper homeostasis and autophagy. As demonstrated here through the analysis of laccase regulatorynetworks of Cryptococcus, genetic analysis targeting virulence-associated regulatory pathways can lead to the discoveryof promising novel drug candidates against fungal species.

Targeting Metabolic Enzymes in Cancer ? Clinical Trials Update by Julie O&#8217;Neal, Jason Chesney, Anand Gaurav, Vertika Gautam (152-160).
The uptake and utilization of glucose and glutamine by cancer cells are markedly higher than by most nontransformed,normal epithelial and mesenchymal cells. This metabolic shift enables the production of ATP and anabolicprecursors necessary for the synthesis of proteins, lipids and nucleotides required for survival, proliferation and invasiveness.The observations that certain oncogenic proteins (Ras, c-Myc and HIF-1 α) and tumor suppressors (p53, PTEN, Rband VHL) regulate the expression and activity of several metabolic enzymes have supported their potential as moleculartargets for the development of anti-neoplastic agents. Indeed, recent pre-clinical studies have shown that several establishedand novel inhibitors of metabolic enzymes exhibit reasonable therapeutic indices when tested in xenograft modelsof tumorigenesis. In this review, we will discuss the rationale of targeting metabolic enzymes for the treatment of cancerand then will describe published pre-clinical and clinical data for several inhibitors of metabolism in cancer.

The Proteasome as a Therapeutic Target for Lung Fibrosis by Leonard H.T. Go, Jinal K. Gangar, Manu Jain (161-167).
When extensive, fibrosis can impair the function of an affected organ. Despite a greater understanding of thecauses and processes leading to organ fibrosis, there are a limited number of treatment options with minimal data supportingtheir utility. Identifying compounds for clinical use that inhibit fibrosis is an active area of investigation. In recentyears, evidence for the utility of targeting the ubiquitin-proteasome system (UPS) in the inhibition of fibrosis has grown.Here we review the evidence for the interaction of the UPS with processes driving organ fibrosis, including the transforminggrowth factor beta pathway. We will also discuss the potential utility and harm of proteasome inhibition in the treatmentof organ fibrosis.