Antithrombotic potential of new direct thrombin inhibitors built on the azaphenylalanine scaffold in two rat venous thrombosis models

The antithrombotic potential of new direct thrombin inhibitors built on the azaphenylalanine scaffold (LK-732, LK-639 and LK-731) and their amidoxime prodrugs (LK-658, LK-633 and LK-730) was studied in comparison to argatroban and nadroparin in two rat models of venous thrombosis, induced either by complete stasis combined with hypercoagulability (model 1) or by partial stasis combined with vessel injury (model 2). In initial experiments LK-732 was established as the most promising antithrombotic of the LK inhibitors and as such was further tested. In model 1, intravenous bolus administration of LK-732 produced a dose-dependent inhibition of thrombus formation with an ID50 value of 1.3 mg/kg. This ID50 value was approximately four times higher than the ID50 value of argatroban (0.3 mg/kg; p=0.011). However, in model 2, LK-732 and argatroban decreased thrombus weight by 50% at similar ID50 values (3.8 mg/kg vs 3.0 mg/kg, respectively; p=0.726). The ex vivo anticoagulant effect of LK-732 was substantially weaker compared to argatroban at doses that produced comparable antithrombotic effects. After subcutaneous administration, in vivo thrombus weight reduction of LK inhibitors (10 mg/kg) ranged between 22 to 48%. However, their oral antithrombotic effect at a dose of 30 mg/kg was rather low. LK amidoxime prodrugs failed to produce a substantial antithrombotic effect after subcutaneous (10 mg/ kg) as well as after oral administration (30 mg/kg). In conclusion, thrombin inhibitors built on the azaphenylalanine scaffold represent a new group of intravenously effective antithrombotics. However, optimisation of the oral antithrombotic effect of amid-oxime prodrug LK-658 of the lead inhibitor LK-732 is required for justifying further development of these inhibitors.

Direct thrombin inhibitors built on the azaphenylalanine scaffold provoke degranulation of mast cells

The main structural feature of direct thrombin inhibitor LK-732 responsible for the appropriate interaction at the thrombin active site is a strong basic group. A possibility that a strong basic group of LK-732 might contribute to the mast cell degranulation effect and consequent reduction of tracheal air flow (TAF) and fall of mean arterial blood pressure (MAP) in rats was investigated in the present study. At doses up to5 mg/kg (i. v.), LK-732 did not cause significant changes of TAF and MAP. At 7 mg/kg (i. v.),a sudden reduction of TAF and a fall of MAP was observed within 5 min after LK-732 administration (75% mortality, p=0. 007). A less basic direct thrombin inhibitor LK-658 (21 mg/ kg, i. v.) did not significantly disturb TAF and MAP. A reduction of TAF and a fall of MAP caused by LK-732 (7 mg/kg, i. v.) was almost completely abolished in rats with degranulated mast cells (0% mortality, p=0. 008). LK-732 concentration-dependently degranulated rat peritoneal mast cells in vitro (pEC50=1. 92±0. 05 µM). A structure-activity relationship (SAR) study revealed that the terminal basic groups attached to the aromatic ring are responsible for the mast cell degranulation effect. A good correlation was observed between mast cell degranulation and pKb of analogues of LK-732 (R2=0. 49), but not between mast cell degranulation and thrombin Ki (R2=0. 23). LK-732-induced reduction of TAF, the fall of MAP and high mortality originate from LK732-induced mast cell degranulation. As judged by the SAR study, this effect could be overcome by reducing the basicity of LK-732.

Compatibility study between acetylcysteine and some commonly used tablet excipients

Differential scanning calorimetry (DSC), Fourier transform infra-red spectroscopy (FT-IR), HPLC and TLC were used to investigate the interactions between the mucolytic drug acetylcysteine and a number of commonly used tablet and capsule excipients. Acetylcysteine was found to be compatible with micro-crystalline cellulose (Avicel PH 101), sodium carboxymethylcellulose, amorphous silicon dioxide (Aerosil), PVP, cross-linked PVP (Polyplasdone XL), corn starch, saccharose and magnesium stearate. Acetylcysteine thermal stability (onset degradation temperature) was decreased in mixtures with corn starch, magnesium stearate, saccharose and lactose. Interactions of acetylcysteine with lactose, PEG 4000 and 6000, glycine, adipic acid and saccharin sodium were found using DSC and studied in detail with FT-IR, HPLC and TLC. The results suggest that acetylcysteine in mixtures with PEG 4000, glycine or saccharin sodium is degraded during storage at conditions of high temperature and humidity.

Inhibition of human sterol Δ7-reductase and other postlanosterol enzymes by LK-980, a novel inhibitor of cholesterol synthesis

Novel potential inhibitors of the postsqualene portion of cholesterol synthesis were screened in HepG2 cells. 2-(4-Phenethylpiperazin-1-yl)-1-(pyridine-3-yl)ethanol (LK-980) was identified as a prospective compound and was characterized further in cultures of human primary hepatocytes from seven donors. In vitro kinetic measurements show that the half-life of LK-980 is at least 4.3 h. LK-980 does not induce CYP3A4 mRNA nor enzyme activity. Target prediction was performed by gas chromatography-mass spectrometry, allowing simultaneous separation and quantification of nine late cholesterol intermediates. Experiments indicated that human sterol Δ(7)-reductase (DHCR7) is the major target of LK-980 (34-fold increase of 7-dehydrocholesterol), whereas human sterol Δ(14)-reductase (DHCR14), human sterol Δ(24)-reductase (DHCR24), and human sterol C5-desaturase (SC5DL) represent minor targets. In the absence of purified enzymes, we used the mathematical model of cholesterol synthesis to evaluate whether indeed more than a single enzyme is inhibited. In silico inhibition of only DHCR7 modifies the flux of cholesterol intermediates, resulting in a sterol profile that does not support experimental data. Partial inhibition of the DHCR14, DHCR24, and SC5DL steps, in addition to DHCR7, supports the experimental sterol profile. In conclusion, we provide experimental and computational evidence that LK-980, a novel inhibitor from the late portion of cholesterol synthesis, inhibits primarily DHCR7 and to a lesser extent three other enzymes from this pathway.

Revealing fosfomycin primary effect on Staphylococcus aureus transcriptome: modulation of cell envelope biosynthesis and phosphoenolpyruvate induced starvation

Background

Staphylococcus aureus is a highly adaptable human pathogen and there is a constant search for effective antibiotics. Fosfomycin is a potent irreversible inhibitor of MurA, an enolpyruvyl transferase that uses phosphoenolpyruvate as substrate. The goal of this study was to identify the pathways and processes primarily affected by fosfomycin at the genome-wide transcriptome level to aid development of new drugs.

Results

S. aureus ATCC 29213 cells were treated with sub-MIC concentrations of fosfomycin and harvested at 10, 20 and 40 minutes after treatment. S. aureus GeneChip statistical data analysis was complemented by gene set enrichment analysis. A visualization tool for mapping gene expression data into biological pathways was developed in order to identify the metabolic processes affected by fosfomycin. We have shown that the number of significantly differentially expressed genes in treated cultures increased with time and with increasing fosfomycin concentration. The target pathway - peptidoglycan biosynthesis - was upregulated following fosfomycin treatment. Modulation of transport processes, cofactor biosynthesis, energy metabolism and nucleic acid biosynthesis was also observed.

Conclusions

Several pathways and genes downregulated by fosfomycin have been identified, in contrast to previously described cell wall active antibiotics, and was explained by starvation response induced by phosphoenolpyruvate accumulation. Transcriptomic profiling, in combination with meta-analysis, has been shown to be a valuable tool in determining bacterial response to a specific antibiotic.

Physicochemical and preclinical pharmacokinetic and toxicological evaluation of LK-423--a new phthalimido-desmuramyl-dipeptide derivative with immunomodulating activity

INTRODUCTION

LK-423 is a new phthalimido-desmuramyl-dipeptide derivative with immunomodulating activity. As optimized delivery to the site of action appears crucial for further preclinical development of LK-423, the aim of this study was to perform a physicochemical and preclinical pharmacokinetic and toxicological evaluation.

METHODS

The solubility, partition coefficient, permeability, and stability profile were determined. Pharmacokinetics were evaluated in rats following intravenous and oral application of LK-423, and in dogs after intravenous administration and oral administration of microcapsules, designed for colon-specific delivery of LK-423 based on pH-, time-, and enzyme-controlled release mechanisms. Additionally, the acute and subchronic toxicity was examined.

RESULTS AND DISCUSSION

LK-423 is hydrophilic, sparingly to slightly soluble, and poorly permeable. Stability profile in aqueous solution is pH dependent. A pharmacokinetic study following intravenous application to rats and dogs revealed that LK-423 is rapidly eliminated with a short terminal phase half-life, and high plasma clearance, as well as a limited distribution to the peripheral tissue. Oral bioavailability of LK-423 is low, presumably due to low permeability. Debris of insoluble microcapsule coating in feces and obtained plasma concentration profiles confirm that LK-423 microcapsules are a promising approach for local treatment of inflammatory diseases of the large intestine. Acute and a subchronic toxicity results indicate that LK-423 is a safe and nontoxic drug under the applied experimental conditions.

New high-throughput fluorimetric assay for discovering inhibitors of UDP-N-acetylmuramyl-L-alanine: D-glutamate (MurD) ligase

A novel assay for monitoring the activity of the bacterial enzyme UDP-N-acetylmuramyl-L-alanine:D-glutamate ligase (MurD ligase) is presented. MurD, which belongs to an enzyme family of Mur ligases, is essential for the synthesis of bacterial peptidoglycan and therefore represents an attractive target for the discovery of novel antibacterial agents. The inhibition assay described in this article is amenable to high-throughput screening. It is based on the detection of the accumulation of adenosine 5'-diphosphate (ADP), a product of the reaction catalyzed by MurD ligase, by conversion to a fluorescent signal via a coupled enzyme system, using the ADP Quest assay kit from DiscoveRx. The novel assay has been validated by obtaining KM,app values for substrates D-Glu, UDP- N-acetylmuramyl-L-alanine (UMA) and ATP that are in agreement with the data reported in the literature. A counterscreen assay was introduced to eliminate false positives, and some of the known MurD inhibitors have been retested to compare the data measured with different methods. Moreover, a focused library of around 1000 compounds was screened for the inhibition of MurD to assess the performance and robustness of the assay. Finally, a novel MurD inhibitor belonging to a new structural class, with an IC50 value of 105 microM, was discovered.

Comparison of 3 cytotoxicity screening assays and their application to the selection of novel antibacterial hits

Cytotoxicity screening of new chemical entities in antibacterial drug discovery discerns between cytotoxic and antimicrobial activity, thus providing predictive evidence for selective toxicity. The objective of this study was to evaluate 3 cytotoxicity assays in identifying novel antibacterial hits with desired safety margins. The endpoints in assays comprised adenylate kinase (AK) release rate as an indicator of membrane rupture (Toxilight), intracellular adenosine triphosphate (CellTiter-Glo), and reduction of resazurin (CellTiter-Blue) both as indicators of cell metabolic activity. In the CellTiter-Glo and the CellTiter-Blue assays, 7 of 8 selected compounds showed cytotoxicity, whereas in the Toxilight assay, 3 of 8 compounds significantly reduced cell viability in the ChoK1 and the JurkatE6.1 cell line. The CellTiter-Glo assay proved to be the most sensitive among the evaluated assays, and excellent Z' values were obtained in the 96-well plate (Z' > 0.83). The CellTiter-Glo assay was clearly superior to the CellTiter-Blue and the Toxilight assay for the initial cytotoxicity screening. Moreover, the application of the CellTiter-Glo assay to determine mammalian cell toxicity versus the antibacterial effect ratio contributed to early identification of antibacterial hits with desired safety margins. The chemical structures of these novel antibacterial hits are disclosed herein.

In vitro activity of LK-157, a novel tricyclic carbapenem as broad-spectrum {beta}-lactamase inhibitor

LK-157 is a novel tricyclic carbapenem with potent activity against class A and class C beta-lactamases. When tested against the purified TEM-1 and SHV-1 enzymes, LK-157 exhibited 50% inhibitory concentrations (IC(50)s) in the ranges of the clavulanic acid and tazobactam IC(50)s (55 nM and 151 nM, respectively). Moreover, LK-157 significantly inhibited AmpC beta-lactamase (IC(50), 62 nM), as LK-157 was >2,000-fold more potent than clavulanic acid and approximately 28-fold more active than tazobactam. The in vitro activities of LK-157 in combination with amoxicillin, piperacillin, ceftazidime, cefotaxime, ceftriaxone, cefepime, cefpirome, and aztreonam against an array of Ambler class A (TEM-, SHV-, CTX-M-, KPC-, PER-, BRO-, and PC-type)- and class C-producing bacterial strains derived from clinical settings were evaluated in synergism experiments and compared with those of clavulanic acid, tazobactam, and sulbactam. In vitro MICs against ESBL-producing strains (except CTX-M-containing strains) were reduced 2- to >256-fold, and those against AmpC-producing strains were reduced even up to >32-fold. The lowest MICs (< or =0.025 to 1.6 microg/ml) were observed for the combination of cefepime and cefpirome with a constant LK-157 concentration of 4 microg/ml, thus raising an interest for further development. LK-157 proved to be a potent beta-lactamase inhibitor, combining activity against class A and class C beta-lactamases, which is an absolute necessity for use in the clinical setting due to the worldwide increasing prevalence of bacterial strains resistant to beta-lactam antibiotics.

Novel inhibitors of beta-ketoacyl-ACP reductase from Escherichia coli

Bacterial beta-ketoacyl-[acyl carrier protein] (beta-ketoacyl-ACP) reductase (FabG) is a highly conserved and ubiquitously expressed enzyme of the fatty-acid biosynthetic pathway of prokaryotic organisms that catalyzes NADPH-dependent reduction of beta-ketoacyl-ACP intermediates. Therefore, FabG represents an appealing target for the development of new antimicrobial agents. A number of trans-cinnamic acid derivatives were designed and screened for inhibitory activities against FabG from Escherichia coli. These inhibited FabG enzymatic activity with IC(50) values in the microM range, and were used as templates for the subsequent diversification of the chemotype. Introduction of an electron-withdrawing 4-cyano group to the phenol substituent showed improved inhibition over the non-substituted compound. The benzo-[1,3]-dioxol moiety also appeared to be essential for inhibitory activity of trans-cinnamic acid derivatives against FabG from E. coli. To explain the possible binding position, the best inhibitor from the present study was docked in the active site of FabG. The results for the best scoring conformers chosen by the docking programme revealed that cinnamic acid derivatives can be accommodated in the substrate-binding region of the active site, above the nicotinamide moiety of the NADPH cofactor. Additionally, a phage-displayed library of random linear 15-mer peptides was screened against FabG, to identify ligands with the common PPLTXY motif.

Treatment of health-care-associated infections caused by Gram-negative bacteria: a consensus statement

This consensus statement presents the conclusions of a group of academic and industrial experts who met in London in September, 2006, to consider the issues associated with the treatment of hospital infections caused by Gram-negative bacteria. The group discussed the severe clinical problems arising from the emergence of antibiotic resistance in these bacteria and the lack of new antibacterial agents to challenge the threat. The discovery of new drugs active against hospital-acquired Gram-negative bacteria is essential to prevent a future medical and social catastrophe. An important strategy to promote drug discovery will be the development of focused cooperations between academic institutions and small pharmaceutical companies.

Optimization of UDP-N-acetylmuramic acid synthesis

UDP-N-acetylmuramic acid (UDP-MurNAc) is a substrate of MurC, an important enzyme in the intracellular pathway of bacterial peptidoglycan biosynthesis. Various approaches towards preparation of UDP-MurNAc have been published but these synthetic preparations were shown to include many problematic steps. An optimization study with the focus on muramyl phosphate and UMP-morpholidate coupling was performed, resulting in a synthetic procedure enabling robust and easily reproducible production on a multi-gram scale.

4-Substituted trinems as broad spectrum beta-lactamase inhibitors: structure-based design, synthesis, and biological activity

A wide variety of pathogens have acquired antimicrobial resistance as an inevitable evolutionary response to the extensive use of antibacterial agents. In particular, one of the most widely used antibiotic structural classes is the beta-lactams, in which the most common and the most efficient mechanism of bacterial resistance is the synthesis of beta-lactamases. Class C beta-lactamase enzymes are primarily cephalosporinases, mostly chromosomally encoded, and are inducible by exposure to some beta-lactam agents and resistant to inhibition by marketed beta-lactamase inhibitors. In an ongoing effort to alleviate this problem a series of novel 4-substituted trinems was designed and synthesized. Significant in vitro inhibitory activity was measured against the bacterial beta-lactamases of class C and additionally against class A. The lead compound LK-157 was shown to be a potent mechanism-based inactivator. Acylation of the active site Ser 64 of the class C enzyme beta-lactamase was observed in the solved crystal structures of two inhibitors complexes to AmpC enzyme from E. cloacae. Structure-activity relationships in the series reveal the importance of the trinem scaffold for inhibitory activity and the interesting potential of the series for further development.

Design, synthesis and molecular modelling of 1-amidinopiperidine thrombin inhibitors

Design, synthesis and biochemical evaluation of a series of novel non-covalent thrombin inhibitors with a 1-amidinopiperidine moiety are presented. Replacement of the planar benzamidine group in azaphenylalanine derivatives with 1-amidinopiperidine resulted in lower activity but higher selectivity for this type of compounds. The binding conformation of inhibitors in the active site of thrombin was revealed by molecular modelling studies.

Recent advances in serine protease inhibitors as anticoagulant agents

The drawbacks and limitations of existing anticoagulant therapy which may result in serious adverse effects and a high mortality rate, have given rise to many anticoagulant development programmes in the last decade, focusing mainly at development of thrombin and FXa low-molecular weight inhibitors. A detailed understanding of blood coagulation pathways, functioning of the serine proteases thrombin, FXa, FVIIa and FIXa and elucidation of their crystal structures resulted in many potent compounds, among which some have entered the clinical phase or have been approved for use in clinical practice. Recently, the focus of anticoagulant research turned to inhibition of the TF:FVIIa complex, with some promising clinical candidates on the horizon. This article provides an overview of the current development status of serine protease inhibitors as anticoagulants, including new trends such as dual coagulation factor inhibitors.

Engineered staphylococcal protein A's IgG-binding domain with cathepsin L inhibitory activity

Inhibitory peptide of papain-like cysteine proteases, affinity selected from a random disulfide constrained phage-displayed peptide library, was grafted to staphylococcal protein A's B domain. Scaffold protein was additionally modified in order to allow solvent exposed display of peptide loop. Correct folding of fusion proteins was confirmed by CD-spectroscopy and by the ability to bind the Fc-region of rabbit IgG, a characteristic of parent domain. The recombinant constructs inhibited cathepsin L with inhibitory constants in the low-micromolar range.

Histamine release, an undesired effect of thrombin inhibitors with basic character, is mediated through direct activation of G(i) proteins

The common structural feature of LK direct thrombin inhibitors is a strong basic group attached to the azaphenylalanine scaffold, which is important for the appropriate interaction at the thrombin active site. Our previous results have shown that this basic group could be responsible for a reduction of tracheal air flow and a fall of mean arterial pressure in anaesthetized rats, an undesired effect of direct thrombin inhibitors which correlated with their ability to release histamine from mast cells. In the present study, we investigated the mechanism of LK direct thrombin inhibitors-induced histamine release from rat peritoneal mast cells. We demonstrated that thrombin inhibitors with basic character (LK-732, LK-639 and LK-6063) provoked release of histamine from mast cells, while less basic analogs (LK-658, LK-633 and LK-6062) had no effect. Histamine released by LK-732 and LK-639 was suppressed by removal of sialic acid residues by neuraminidase and by pertussis toxin, an inhibitor of G(i) protein activity. Additional demonstration that G proteins are the targets of LK-732 and LK-639 was provided by the increase of GTPgammaS binding rate to G proteins in rat brain cortical membranes. Our results indicate that basic direct thrombin inhibitors LK-732 and LK-639 provoke release of histamine from mast cells by direct activation of G(i) proteins through the similar biochemical pathway as basic secretagogues.

Comparison of bacterial and phage display peptide libraries in search of target-binding motif

Genetic engineering allows modification of bacterial and bacteriophage genes, which code for surface proteins, enabling display of random peptides on the surface of these microbial vectors. Biologic peptide libraries thus formed are used for high-throughput screening of clones bearing peptides with high affinity for target proteins. There are reports of many successful affinity selections performed with phage display libraries and substantially fewer cases describing the use of bacterial display systems. In theory, bacterial display has some advantages over phage display, but the two systems have never been experimentally compared. We tested both techniques in selecting streptavidin-binding peptides from two commercially available libraries. Under similar conditions, selection of phage-displayed peptides to model protein streptavidin proved convincingly better.

Synthesis, Conformation, and Stereodynamics of a Salt of 2-{[2-(3,4-Dichlorophenyl)- ethyl]propylamino}-1-pyridin-3-ylethanol

[reaction: see text] A novel synthetic route was developed for 2-{[2-(3,4-dichlorophenyl)ethyl]propylamino}-1-pyridin-3-ylethanol (4). A dynamic process due to nitrogen inversion at the central amine nitrogen has been identified by NMR spectroscopy for the dihydrobromide salt of this compound. The conformational properties of the diastereomeric pair were determined by analysis of NOE connectivities and MO calculations.

Structure of a Synthetic Fragment of the Lipopolysaccharide (LPS) Binding Protein When Bound to LPS and Design of a Peptidic LPS Inhibitor

Peptidic lipopolysaccharide (LPS) antagonists are the subject of intensive research. We report an NMR and modeling study of LBP-14 (RVQGRWKVRASFFK), a synthetic fragment of the LPS binding protein (LBP). In a mixture with LPS we observed the transferred nuclear Overhauser effect and determined the LPS-bound structure of LBP-14 that was used for docking calculations to LPS. The derived complex was used to design a peptide that displayed more than 50% increase in LPS inhibition in vitro.

Affinity selection to papain yields potent peptide inhibitors of cathepsins L, B, H, and K

Endogenous cysteine proteases were given much attention lately, as their role in a variety of pathophysiological disorders became evident. Amongst them cathepsins, which are thought to be implicated in mediation of osteoporosis, cancer progression, atherosclerosis, and many other conditions, are of considerable interest as drug targets. In the presented work, papain was chosen as a model cysteine protease and panning protocol was optimized for selection of papain-binding phage-displayed peptides from a commercially available combinatorial peptide library. Different selection strategies were applied in order to select high-affinity binders. Ultimately, five cyclic peptides (CNWAAGYNCGGGS-NH2, CWSMMGFQCGGGS-NH2, CWEWGGWHCGGSS-OH, CNWTLGGYKCGGGS-NH2 (all cyclized through formation of intramolecular disulphide bond), and GNWTLGGYKGG (cyclized head-to-tail)) were synthesized and tested for inhibitory activity towards papain and human cathepsins L, B, H, and K. The peptides possess inhibitory constants in the low micromolar to mid-nanomolar range and exhibit certain selectivity for different lysosomal cysteine proteases included in this study.

Internucleosomal DNA cleavage in apoptotic WEHI 231 cells is mediated by a chymotrypsin-like protease

Although several lines of evidence support a role for serine proteases in apoptosis, little is known about the mechanisms involved. In the present study, we have examined the apoptosis-inducing potential and dissected the death-signalling pathways of N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and N-tosyl-L-lysine chloromethyl ketone (TLCK), inhibitors of chymotrypsin- and trypsin-like proteases, respectively. Our results designate two distinct roles for serine proteases. Firstly, we show that both inhibitors induce biochemical and morphological characteristics of apoptosis, including proteolysis of poly(ADP-ribose) polymerase 1 (PARP-1) and inhibitor of caspase-activated DNase (ICAD), as well as mitochondrial dysfunction, and that their action is abrogated by the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp.fluoromethylketone (z-VAD.fmk). These results suggest that inhibition of anti-apoptotic serine proteases governs the onset of the caspase-dependant apoptotic cascade. Secondly, we also demonstrate the involvement of a serine protease in the terminal stage of apoptosis. We showed that chymotrypsin-like protease activity is required for internucleosomal DNA fragmentation in apoptotic cells. Hence, DNA fragmentation is abrogated in TPCK-pre-treated WEHI 231 cells undergoing apoptosis triggered either by anti-IgM or TLCK. These results indicate that internucleosomal DNA cleavage in apoptotic cells is mediated by a chymotrypsin-like protease.

Synthesis and in vitro evaluation of new azaphenylalanine derivatives as serine protease inhibitors

New inhibitors of serine proteases with azaphenylalanine scaffold were synthesized and their activity was evaluated in vitro. We studied the effect of different substituents in the part of a molecule that binds in the distal pocket of the thrombin active site. Modifications generally led to decreased activity, however two derivatives are promising lead compounds as new thrombin and dual thrombin-factor Xa inhibitors.

Novel non-covalent azaphenylalanine thrombin inhibitors with an aminomethyl or amino group at the P1 position

Design, synthesis and biological evaluation of a series of novel non-covalent azaphenylalanine thrombin inhibitors are presented. Replacement of the basic benzamidine moiety in azaphenylalanine derivatives by benzylamine (P1 part of a molecule) and the introduction of a N-cyclopentyl-N-methylamine moiety in the P2 part of a molecule resulted in the thrombin inhibitor LK-733 with greatly increased selectivity against trypsin and an in vitro Ki of 31 nM.

Modulation of cytokine production by some phthalimido-desmuramyl dipeptides and their cytotoxicity

Muramyl dipeptide (MDP) is the smallest bacterial cell wall peptidoglycan component having immunomodulatory activity. In an attempt to obtain MDP derivatives with improved and better defined pharmacological profiles we synthesized a new lipophilic phthalimido-desmuramyl dipeptide, LK 508. This novel MDP analogue and three structurally related phthalimido-desmuramyl dipeptides (LK 413, LK 511 and LK 512) were evaluated immunologically. Their ability to modulate the production of cytokines was measured in vitro by their inclusion in cultures of human peripheral blood mononuclear cells (PBMC) activated by ionomycin and phorbol-12-myristate-13-acetate (PMA). The results were compared with the analogous activity of MDP. All compounds tested are strong up-regulators of IL-12 synthesis. All compounds except LK 512 also stimulated IFNgamma synthesis. LK 508, LK 511 and LK 512 are effective in up-regulating IL-2 production. LK 508 and LK 512 considerably up-regulate the synthesis of IL-4 and IL-10. LK 413 and MDP stimulated the production of Th1 promoting and Th1 (IFNgamma and IL-12) cytokines, while LK 508, LK 511 and LK 512 non-selectively up-regulated the production of both Th1 and Th2-types of (IL-4 and IL-10) cytokines. None of the phthalimido-desmuramyl dipeptides was cytotoxic in vitro against the normal cell line HUVEC (human endothelial cells) thereby indicating their potential for use in vivo.

Thrombin inhibitors built on an azaphenylalanine scaffold

A series of azaphenylalanine derivatives were investigated as novel thrombin inhibitors based on the prodrug principle. By systematic structural modifications we have identified optimal groups for this series that led us to potent inhibitors of thrombin incorporating the benzamidine fragment at the P1 position, and their potentially orally active benzamidoxime prodrugs. The binding modes in the thrombin active site of two representative compounds were identified by X-ray crystallographic analysis.

Design and structure-activity relationship of thrombin inhibitors with an azaphenylalanine scaffold: potency and selectivity enhancements via P2 optimization

Theoretical and structural studies followed by the directed synthesis and in vitro biological tests lead us to novel noncovalent thrombin pseudopeptide inhibitors. We have incorporated an azapeptide scaffold into the central part of the classical tripeptide D-Phe-Pro-Arg inhibitor structure thus eliminating one stereogenic center from the molecule. A series of compounds has been designed to optimize the occupancy of the S2 pocket of thrombin. Increased hydrophobicity at P2 provides an enhanced fit into this active site S2 pocket. In the present paper, we also report on the structure of these inhibitors in solution and conformational analysis of inhibitors in the active site in order to asses the consequences of the replacement of the central alpha-CH by a nitrogen functionality. In vitro biological testing of the designed inhibitors shows that elimination of R, S stereoisomerism and restriction of conformational freedom influences the binding of inhibitors in a favorable fashion.

Novel thrombin inhibitors with azaphenylalanine scaffold

In this paper the synthesis and antithrombotic activity of a series of novel thrombin inhibitors with azaphenylalanine scaffold are described. By systematic structural modifications for this series we have identified optimal groups for achieving nanomolar potency, that led to potent inhibitors of thrombin with Ki values up to 11 nM.

Immunostimulatory effects of the muramyl dipeptide analogue LK415 in chickens immunized with a vaccine strain of infectious bursal disease virus

The effects of muramyl dipeptide (MDP) synthetic analogue LK415 on the immune response of chickens immunized with a live vaccine against infectious bursal disease (IBD) were studied in two independent trials, using levamisole hydrochloride as comparative immunostimulant. Groups of five-week-old commercial chickens (Isa Brown) were immunized orally with 10 doses of the vaccine strain of IBDV (Winterfield strain). The chickens were then given four injections of the MDP analogue LK415 in a dosage of either 0.25 mg/kg body weight (b.w.) or 2.5 mg/kg b.w. or levamisole at a daily dose of 15 mg/kg b.w. for four consecutive days, starting from the day of immunization. Histological examinations of bursal tissue collected on days 2, 4 and 7 postimmunization (p.i.) showed a lower degree of destruction of bursal follicles and earlier renewal of bursal tissue in LK415-treated chickens compared to levamisole-treated and untreated immunized groups. Compared to the other groups, the LK415-treated chickens showed a significantly higher antibody response to IBDV on days 14 and 28 p.i. (P < 0.01) as measured by commercial ELISA. The present study indicates some potent immunostimulatory effects of the MDP analogue LK415 on the chicken immune system.

Synthesis and modulation of cytokine production by two new adamantane substituted acyclic desmuramyldipeptide analogs

Two new adamantyl-desmuramyldipeptides LK 415 and LK 517 with 1-adamantylcarboxamido moiety as a replacement for muramyldipeptide's N-acetylglucosamine fragment were synthesized. Their efficacy to modulate the production of cytokines was measured in vitro in ionomycin and phorbol-12-myristate-13-acetate (PMA) activated cultures of human peripheral blood mononuclear cells (PBMC), co-incubated with the substances tested. The results were compared with the activity of muramyldipeptide (MDP). All three substances are strong up-regulators of IL-12 synthesis and hence of the IFN gamma synthesis as well. While MDP and LK 415 are relatively ineffective in modulation of IL-2, IL-4 and IL-10 production in vitro, the synthesis of all three cytokines is considerably up-regulated when peripheral blood mononuclear cells are co-incubated with LK 517. It seems likely that the introduction of the diethyl phosphonate moiety into LK 517 is of great importance for the augmented T-cell cytokine production.

Synthesis and biochemical evaluation of some novel N-acyl phosphono- and phosphinoalanine derivatives as potential inhibitors of the D-glutamic acid-adding enzyme

A series of N-(5-phthalimidopentanoyl)-, N-[2-(2-ethoxy)acetyl]-, and N-(7-oxooctanoyl)-phosphono and phosphinoalanine derivatives has been synthesized and evaluated for inhibition of the D-glutamic acid-adding enzyme (MurD) of peptidoglycan biosynthesis.

Screening for selective thrombin inhibitors in mushrooms

Thrombin is the key serine proteinase of the coagulation cascade and therefore a suitable target for inhibition of blood coagulation. A number of pharmacologically active secondary metabolites from mushrooms have already been isolated, thus providing the rationale for screening for new thrombin inhibitors in mushrooms. In this study, inhibitory activities of mushroom extracts on thrombin and trypsin were measured using the chromogenic substrates H-D-phenylalanine-L-pipecolyl-L-arginine-paranitroaniline dihydrochloride (S-2238) for thrombin and N-benzoyl-D,L-Arg-p-nitroanilide (BAPNA) for trypsin. The inhibitory activities of extracts from 95 Basidiomycete species have been determined. The majority of samples inhibited trypsin and thrombin with various potencies; however, some extracts showed no activity against one or both of the enzymes. An aqueous extract of Gleophyllum odoratum exhibited high inhibitory activity on both thrombin and trypsin (72 and 60%, respectively), while extracts of Clitocybe gibba, Amanita virosa, Cantharellus lutescens, Suillus tridentinus, Hypoloma fasciculare and Lactarius badiosanguineus considerably inhibited thrombin (49, 48, 36, 34, 32 and 31%, respectively) and showed no inhibitory activity on trypsin. The results at this point are promising for further research with the objective of finding an effective and safe thrombin inhibitor.

Modulation of tumour necrosis factor production with desmuramyldipeptide analogues

Some synthetic analogues of the immunomodulatory agent muramyl dipeptide (MDP), i.e. phthalimido- (LK-511, LK-413, LK-512, LK-423, LK-508), adamantyl- (LK-415, LK-517), 7-oxoalkyl-(LK-409) desmuramylpeptides were assessed for the tumour necrosis factor (TNF) inducing activity and the ability to modulate TNF production in in vitro phorbol 12-myristate 13-acetate (PMA) & ionomycin stimulated cultures of human peripheral blood mononuclear cells. A kinetic study over a 40-hour period indicated that desmuramyldipeptides were weak TNF inducers compared to romurtide, PMA & ionomycin or lipopolysaccharide. By contrast, they showed the potential to up- or down-regulate the production of TNF evoked by PMA & ionomycin, which was strongly dependent on the time of the stimulation. After 4h of stimulation, the TNF secretion was augmented by LK-508, LK-409 and LK-511, after 18 h by LK-409 and LK-423, and after 40 h by LK-423, LK-511, LK-415 and LK-512. However, LK-517 and LK-512 inhibited the secretion of TNF after the 18-h period.

The influence of magnesium stearate on the characteristics of mucoadhesive microspheres

Microspheres containing the mucoadhesive polymer chitosan hydrochloride, with matrix polymer Eudragit RS, pipemidic acid as a model drug and agglomeration preventing agent magnesium stearate were prepared by the solvent evaporation method. The amount of magnesium stearate was varied and the following methods were used for microsphere evaluation: sieve analysis, drug content and dissolution determination, scanning electron microscopy, x-ray diffractometry, DSC and FTIR spectroscopy. The results showed that average particle size decreased with increasing amount of magnesium stearate used for microsphere preparation. This is probably a consequence of stabilization of the emulsion droplets with magnesium stearate. Higher pipemidic acid content in the microspheres was observed in larger particle size fractions and when higher amounts of magnesium stearate were used. It was also found that these two parameters significantly influenced the dissolution rate. The important reason for the differences in drug content in microspheres of different particle sizes is the diffusion of pipemidic acid from the acetone droplets in liquid paraffin during the preparation procedure. The physical state of pipemidic acid changed from crystalline to mostly amorphous with its incorporation in microspheres, as shown by x-ray diffractometry and differential scanning calorimetry. No differences were observed in the physical state of pipemidic acid and in microsphere shape and surface between different size fractions of microspheres, prepared with different amounts of magnesium stearate. Additionally, no correlation between the physical state of the drug in different microspheres and their biopharmaceutical properties was found.

Therapeutic effects of LK 423, a phthalimido-desmuramyl-dipeptide compound, on dextran sulfate sodium-induced colitis in rodents through restoring their interleukin-10 producing capacity

A new phthalimido compound, N-[2-(2-phthalimidoethoxy)acetyl]-L-alanyl-D-glutamic acid (CAS 142489-47-2, LK 423), was examined for its possible activity to modulate levels and species of cytokines in mice carrying a specific inflamed organ. Colonic inflammation was induced in mice by giving 5% dextran sulfate sodium (DSS) solution as drinking water. The capacity of spleen cells obtained from the DSS-inflamed mice to produce interleukin-10 (IL-10) in response to mitogen was significantly reduced when compared with the capacity of spleen cells from intact mice. Treatment of the mice administered DSS by subcutaneous multiple injections with a low dose of LK423 resulted in delaying the progression to full-blown inflammation in the colon. The mitogen-stimulated spleen cells obtained from the LK423-treated mice yielded significantly greater amounts of IL-10 and IL-6 than the untreated DSS group, and the peritoneal cells from the LK423-treated mice produced significantly lower levels of tumor necrosis factor alpha (TNF alpha). Based on this prophylactic effect of LK423 in the murine colitis model, its therapeutic effect was examined in rats in which colitis had been induced by feeding 3% DSS for 12 days. Intracolonic administration of LK423 to these rats for 7 days resulted in diminishing the ulcerative area in the colon. The immunological characteristics of this new compound are discussed from the point of view of its possible application as a therapeutic agent for inflammatory bowel diseases (IBD) and other inflammatory diseases.

Qualitative determination of polyvinylpyrrolidone type by near-infrared spectrometry

Soluble polyvinylpyrrolidones are very useful and versatile pharmaceutical auxiliaries. The different types of povidone are characterised by their viscosity measured in water, expressed as a K-value. We have developed a rapid, accurate, reliable, and non-destructive near infrared (NIR) spectroscopy method for the determination of PVP type and consequently identification thereof. We have implemented chemometrics onto NIR spectra collected in diffuse reflectance mode using fibre optics to build a qualitative model that enables us to obtain useful analytical information. A principal component analysis and a modelling technique soft independent modelling of class analogy (SIMCA) were applied. An approach to validate the method was developed.

Interleukin-10 inducing activity of LK423, a phthalimido-desmuramyldipeptide compound

A new phthalimido compound, N-[2-(2-phthalimidoethoxy)acetyl]-L-alanyl-D-glutamic acid (CAS 142489-47-2, LK423), was examined along with other N-acyl-desmuramyldipeptide compounds for possible immunomodulating activities in cyclophosphamide (Cy)-treated mice. Reverse transcriptase-polymerase chain reaction (RT-PCR) and Northern blot assays demonstrated that multiple subcutaneous injections of LK423 (1 to 50 micrograms/days, for 4 days) into these mice resulted in upregulating interleukin-10 (IL-10) gene expression in the spleen. In contrast to IL-10, expression of interferon-gamma (IFN-gamma) gene was reduced by treating with this compound. The culture supernatant of spleen cells obtained from the mice that had received LK423 injections was found to contain a larger amount of IL-10 protein than in the culture supernatant of the spleen obtained from the mice that received no LK423 injections when tested by enzyme-linked immunosorbent assay (ELISA). Conversely to IL-10, the concentration of IFN-gamma was lower in the culture supernatant from the LK423-treated group than that in the control group. In contrast to this compound, other N-acyl-desmuramyldipeptide derivatives carrying a L-alanyl-D-isoglutamine moiety, and other immunological stimulants showed an activity to augment production of IFN-gamma and reduce the gene expression of IL-10. The immunological activities of this new phthalimido desmuramyldipeptide compound, LK423, are discussed from the point of view of its therapeutic application.

Synthesis of phthalimido-desmuramylpeptide analogues as potential immunomodulating agents

The preparation of immunologically active phthalimido desmuramylpeptide analogues 2e-h, 4c-d, and 7b is described. The N-acetylmuramic acid in the muramyl dipeptide has been replaced by a phthaloylated acyclic moiety such as N-phthaloylated amino acids 1a-c, 2-(2-phthalimidoethoxy)acetic acid 3, or by the carbocyclic rac. trans-2-(2'-phthalimidocyclohexyloxy)acetic acid 6.