N-anthraniloyl-Ala-Ala-Phe-4-nitroanilide, a highly sensitive substrate for subtilisins.

A new substrate for subtilisins, anthraniloyl-Ala-Ala-Phe-4-nitroanilide, has been synthesized and characterized. The peptide is a fluorogenic substrate that is intramolecularly quenched without loss of its chromogenic properties and offers a possibility for double-assay kinetic analysis. The kinetic parameters determined for subtilisin Carlsberg are Km = 0.004 mM, kcat = 104 s-1, and those for subtilisin BPN' are Km = 0.020 mM, kcat = 49 s-1. The substrate is extremely sensitive for subtilisins; the specificity constants are 10-fold higher than the corresponding values for the widely used substrate, succinyl-Ala-Ala-Pro-Phe-4-nitroanilide, and 200- to 1000-fold higher than the values obtained with succinyl-Ala-Ala-Phe-4-nitroanilide. The favorable effect of the anthraniloyl group as a P4 residue in the substrate sequence Ala-Ala-Phe-4-nitroanilide was assumed to be due to an ability to stiffen S4-P4 interactions. The mechanism proposed is hydrogen bond formation between the phenol group of tyrosine-104 and the amino group of the anthraniloyl moiety. In the spectrophotometric assay with the new substrate, the lower detection limit for subtilisin Carlsberg was 1 nM.     

Synthesis and mechanism of action of novel thiocarbamate inhibitors of human leukocyte elastase

Several peptidyl thiocarbamate inhibitors of human leukocyte elastase were synthesized in the molecular weight range of 700-800. Two different sequences with lysine at the P3 and ornithine at the P4 positions were synthesized. Most of the inhibitors with large molecular weights showed high inhibitory capacity with Ki values as low as 10(-8)M. Compounds immobilized on poly,alpha,beta-[N-(2-hydroxyethyl)-D,L-aspartamide] (PHEA) polymers with an average molecular weight of 36,000 showed higher inhibitory capacity than their free forms.     

Noncovalent inhibitors of human leukocyte elastase based on the 4-imidazolidinone scaffold

A central problem associated with the design of enzyme inhibitors in general, and serine protease inhibitors in particular, is the identification of templates capable of binding to the active site of an enzyme in a predictable and substrate-like fashion, orienting appended recognition elements in a correct spatial relationship so that favorable binding interactions with multiple sites are achieved. Described herein for the first time is the design of noncovalent inhibitors of human leukocyte elastase that employs a functionalized 4-imidazolidinone scaffold.     

白细胞弹性蛋白酶抑制剂

人白细胞弹性蛋白酶广泛参与体内的组织损伤反应,与炎症反应、自身免疫、肿瘤形成和转移等有密切关系。目前人白细胞弹性蛋白酶抑制剂已成为新药开发的热点,具有很高的应用价值,其中西维来司钠已经成功进入市场。本文对近几年发现的人白细胞弹性蛋白酶抑制剂的结构及其作用进行综述。     

Catalysis by human leukocyte elastase: proton inventory as a mechanistic probe

Proton inventories (rate measurements in mixtures of H2O and D2O) were determined for the human leukocyte elastase catalyzed hydrolyses of thiobenzyl esters and p-nitroanilides of the peptides MeOSuc-Val, MeOSuc-Alan-Pro-Val (n = 0-2), and MeOSuc-Alan-Pro-Ala (n = 1 or 2). The dependencies of k2/Ks on mole fraction of solvent deuterium for the p-nitroanilides are "dome-shaped" and were fit to a model that incorporates the mechanistic features of generalized solvent reorganization when substrate binds to enzyme and partial rate limitation of k2/Ks by physical and chemical steps [Stein, R. L. (1985) J. Am. Chem. Soc. 107, 7768-7769]. The proton inventories for the deacylation of MeOSuc-Val-HLE and MeOSuc-Pro-Val-HLE are linear while those for the deacylation of MeOSuc-Ala-Pro-Val-HLE and MeOSuc-Ala-Ala-Pro-Val-HLE are "bowl-shaped" and could be fit to a quadratic dependence of rate on mole fraction of deuterium. These results are interpreted to suggest that the correct operation of the catalytic triad is dependent on substrate structure. Minimal substrates, which cannot interact with elastase at remote subsites, are hydrolyzed via a mechanism involving simple general-base catalysis by the active site histidine and transfer of a single proton in the rate-limiting transition state. In contrast, tri- and tetrapeptide substrates, which are able to interact at remote subsites, are hydrolyzed by a more complex mechanism of protolytic catalysis involving full functioning of the catalytic triad and transfer of two protons in the rate-limiting transition state. Finally, the proton inventories for the deacylation of MeOSuc-Ala-Pro-Ala-HLE and MeOSuc-Ala-Ala-Pro-Ala-HLE are dome-shaped and suggest that the chemical events of acyl-enzyme hydrolysis are only partially rate limiting for these reactions and that some other physical step is also partially rate limiting.     

Synthesis and in vitro and in vivo evaluation of the 2-(6'methoxy-3',4'-dihydro-1'-naphtyl)-4H-3,1-benzoxazin-4- one as a new potent substrate inhibitor of human leukocyte elastase.

The title 2-vinyl-4H-3,1-benzoxazin-4-one has been synthesised and tested for inhibitory activity against human leukocyte elastase. The compound has shown activity both in vitro towards human sputum elastase and in vivo in an hemorrhagic assay.     

4-alkylidene-azetidin-2-ones: novel inhibitors of leukocyte elastase and gelatinase

In addition to their antibiotic potency, β-lactams have recently been investigated as inhibitors of serine proteinase such as leukocyte elastase (LE), released by inflammatory cells. We describe the synthesis of a series of 4-alkylidene-β-lactams, and investigate how substitutions on C-3, C-4, and N-1 of the β-lactam ring affect the activity of human LE and gelatinases MMP-2 and MMP-9. LE activity was measured using a chromogenic substrate, while gelatin-zymography assay was used to evaluate gelatinase activity. We demonstrate that C-4 unsaturation on the β-lactam ring determines the degree of biological activity, with a selectivity over LE by 3-[1-(tert-butyldimethylsilyloxy)-ethyl] derivatives (lowest IC₅₀ was 4 μM), and over gelatinase MMP-2 by C-3-unsubstituted 4-[1-ethoxycarbonyl]-ethylidene-β-lactams (lowest IC₅₀ was 60 μM). (3S)-3-[(1R)-1-hydroxyethyl]-4-(1-ethoxycarbonyl)-ethylidene-azetidin-2-one inhibits gelatinase MMP-9. The compounds tested showed no cytotoxicity against NIH-3T3 murine fibroblasts. This is the first example of beta-lactams inhibiting metallo-proteinases instrumental in cancer invasion and angiogenesis. These molecules are good candidates for prototype drugs showing selective antibiotic, anti-inflammatory, and anti-invasion properties.     

Synthetic inhibitors of human leukocyte elastase, Part 3. Peptides with alkyl groups at the N- or C-terminus. Non-toxic competitive inhibitors of human leukocyte elastase

A series of carboxy-alkylamidated and N-acetylated amino acids and peptides were synthesized and examined for their ability to inhibit human leukocyte elastase. The Boc-amino acid alkylamides were found to be potent specific and competitive inhibitors of this enzyme. They were found not to or only poorly inhibit several other serine proteinases such as bovine trypsin, alpha-chymotrypsin, porcine pancreatic elastase and human leukocyte cathepsin G at concentrations less than 10(-4) M. Specificity and maximum inhibition of human leukocyte elastase were achieved when the N-terminus of the amino acid was protected by a t-butyloxy-carbonyl (Boc) group, the oligopeptide fragment consisted of valine residues and when the alkyl chain was between 10 and 12 carbon atoms in length and attached to the C-terminus of the peptide fragment. Highest inhibition was obtained with the compound Boc-[Val]3-NH[CH2]11--CH3 (Ki = 0.21 microM). These specific inhibitors were also found to be non-toxic after oral administration to mice and rats (LD50 greater than 3.0 g/kg body weight).     

Interaction of human leukocyte elastase with a N-aryl azetidinone suicide substrate: Conformational analyses based on the mechanism of action of serine proteinases

The three-dimensional interaction of the enzyme-activated (suicide) inhibitor AA 231-1 [N(2-chloromethyl)-3,3-difluoro-azetidin-2-one] with human leukocyte elastase has been studied using computer graphics and molecular mechanics. Systematic conformational analyses and energy minimizations have been performed for the inhibitor AA 231-1 and its presumed complexes formed during the enzymatic process of inactivation, i.e., the Michaelis complex, the acyl-enzyme, and the inactivated enzyme with the covalently bound inhibitor. The β-lactam ring characteristics of modeled AA 231-1 were in agreement with crystallo-graphic data of related structures. Lowest energy conformatinos were found when the angle between the planes of the β-lactam ring and that of its phenyl substituent was about −60 or 60°. To study the interaction with the enzyne, the enzyme-inhibitor complexes were constructed by docking the inhibitor in the active site using enzyme coordinates from an X-ray crystallographic structure. The whole enzyme structure was used for conformational analyses and energy mechanics. Favorable conformations for the Michaelis complex have been obtained in which the carbonyl oxygen of the inhibitor was located in the oxyanion hole and the hydroxyl of Ser195 was in position to interact with the β-lactam carbonyl carbon on the α face of AA 231-1. Simulations of the approach of the benzylic carbon by the nucleophilic amino acid His40 or His57 through an S_N2 displacement on the halomethyl group of AA 231-1 were performed. The results agreed with the alkylation of the imidazole nitroge Nϵ2 of His57 leading to the inactivated enzyme (bis-adduct form).     

Mechanism for slow-binding inhibition of human leukocyte elastase by valine-derived benzoxazinones

Valine-derived benzoxazinones have been synthesized and found to be competitive, slow-binding inhibitors of human leukocyte elastase (HLE). Steady-state inhibition constants Ki are dependent on aryl substitution and reach a maximum of potency of 0.5 nM with the 5-Cl compound 6. UV-spectral data for the interaction of HLE and the unsubstituted inhibitor 3 indicate that the stable complex formed between enzyme and inhibitor is an acyl-enzyme that can either undergo ring closure, to reform intact benzoxazinone, or hydrolysis, to liberate an N-acylanthranilic acid. "Burst" kinetic data, derived from the direct observation of the interaction of HLE and 3, are consistent with results of the inhibition of catalysis experiments.     

Synthesis and in-vitro evaluation of novel low molecular weight thiocarbamates as inhibitors of human leukocyte elastase

A series of novel low molecular weight thiocarbamate esters (1e-6e) were synthesized and evaluated as inhibitors of human leukocyte elastase (HLE). The thiocarbamate esters studied consist of a substituted primary or secondary aliphatic or aromatic amine and a 1-phenyl-1H-tetrazole-5-thiol (Table I). The HLE catalyzed hydrolysis of N-methoxysuccinyl- L-Ala-L-Ala-L-Pro-L-Val-p-nitroanilide substrate was utilized as the measure of inhibition. N-n-butyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (1e) exhibited the highest inhibitory activity (k(obs) /[I] = 2.1 x 10(5) M(-1). min(-1) ) and N-allyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (2e) (K(obs) /[I] = 6.1 x 10(4) M(-1). min(-1) ) exhibited the second highest inhibitory activity of all the thiocarbamates. The aromatic N-phenyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (4e) showed the lowest inhibitory activity (K(obs) /[I] = 1.9 x 10(2) M(-1). min(-1) ) among the N-monosubstituted derivatives, similar to that of N-ethyl-N-n-butyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (5e) (K(obs) /[I] = 1.8 x 10(2) M(-1).min(-1) ). The N-isopropyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (3e) (K(obs) /[I] = 3.3 x 10(3) M(-1).min(-1) ) was about 10 fold more active than (4e) and N, N-diisopropyl, 1-phenyl-1H-tetrazole- 5-thiocarbamate (6e) showed no inhibitory activity against HLE. In the present work less than 3% of HLE specific activity was regained after 24 hours incubation with each of the tested N-monosubstituted thiocarbamates (1e-4e). The time-dependent inhibition of HLE by the thiocarbamate compounds (1e-5e) seems to involve the interaction and possible chemical modification of one enzyme residue. Straight chain nonpolar aliphatic substituents on the nitrogen of the thiocarbamate functionality may be essential for high inhibitory activity. As the degree of substitution (branching) on the nitrogen of the thiocarbamate functionality increases the inhibitory activity of the compounds decreases. The time-dependent inhibition of HLE and the slow deacylation rates by the N-monosubstituted thiocarbamates are consistent with irreversible inhibition.     

Catalysis by human leukocyte elastase: mechanistic insights into specificity requirements

Steady-state kinetic parameters were determined for the human leukocyte elastase catalyzed hydrolysis of a series of peptide-based thiobenzyl esters and p-nitroanilides. The peptide units are MeOSuc-Val, MeOSuc-Alan-Pro-Val (n = 0-2), and MeOSuc-Alan-Pro-Ala (n = 1 or 2). The results of this study suggest five important mechanistic features for HLE. Few important remote subsite contacts are established in the Michaelis complex. Full recognition and tight binding of the substrate occurs in the transition state for acylation. The P3-S3 interaction is critical during acylation. Subsite contacts are unimportant in deacylation. P1 specificity is regulated by peptide length. An important steady-state kinetic consequence of this specificity is that the rate-limiting step of kc for p-nitroanilide hydrolysis changes from acylation to deacylation as the peptide chain is lengthened.     

SC-39026, a specific human neutrophil elastase inhibitor

SC-39026, (+/-) 2-chloro-4-(1-hydroxyoctadecyl)benzoic acid, inhibits human neutrophil elastase with an IC50 of 0.5 microM (KI of 1.5 microM). Its inhibition of elastase is reversible and noncompetitive at low concentrations (0.5-1.25 microM). Inhibition is "mixed" at higher inhibitor concentrations. SC-39026 is inactive against hog pancreatic elastase, bovine alpha-chymotrypsin and Pseudomonas aeruginosa elastase, but does inhibit human neutrophil cathepsin G with an IC50 of approximately 2.5 microM. Neutrophil elastases isolated from rat, hamster, rabbit and hog are also inhibited by SC-39026.     

pH dependence of salt activation of human leukocyte elastase

The effects of pH on salt stimulation of the rates of hydrolysis of three substrates by human leukocyte elastase were studied. The enzyme was most active at pH 10.5, 8.0-8.5, and 9.5 for the hydrolyses of fluorescein isothiocyanate-labeled S-carboxymethylated bovine serum albumin (FITC-CM-BSA), succinyl-L-Ala-L-Pro-L-Ala-7-methylcoumaryl-4-amide (Suc-APA-MCA), and succinyl-L-Ala3-p-nitroanilide (Suc-Ala3-pNA), respectively, in the absence of NaCl. The enzyme was activated by 0.5 M NaCl similarly at all pHs tested for the hydrolysis of Suc-Ala3-pNA, but more at neutral and alkaline pH values, respectively, for the hydrolyses of FITC-CM-BSA and Suc-APA-MCA. Thus, in the presence of 0.5 M NaCl, the enzyme was most active at pH 8.0 and 10.0 with FITC-CM-BSA and Suc-APA-MCA, respectively. In contrast, the proteolytic activity of porcine pancreatic elastase was somewhat inhibited by 0.5 M NaCl.     

A new proteinase 3 substrate with improved selectivity over human neutrophil elastase

We report the synthesis and enzymatic studies on a new proteinase 3 intermolecular quenched substrate with enhanced selectivity over neutrophil elastase. Using combinatorial chemistry methods, we were able to synthesize the hexapeptide library with the general formula ABZ-Tyr-Tyr-Abu-X₁′-X₂′-X₃′-Tyr(3-NO₂)-NH₂ using the mix and split method. The iterative deconvolution of such a library allowed us to obtain the sequence ABZ-Tyr-Tyr-Abu-Asn-Glu-Pro-Tyr(3-NO₂)-NH₂ with a high specificity constant (k_cat/K_M = 1534 × 10³ M⁻¹ s⁻¹) and superior selectivity over neutrophil elastase and other neutrophil-derived serine proteases. Moreover, using the obtained substrate, we were able to detect a picomolar concentration of proteinase 3 (PR3). Incubation of the above-mentioned substrate with neutrophil lysate resulted in a strong fluorescent signal that was significantly reduced in the presence of a PR3 selective inhibitor.     

Proteolytic cleavage of annexin 1 by human leukocyte elastase

Annexin 1 has been shown to participate through its unique N-terminal domain in the recruitment and activation of leukocytes at sites of inflammation. Peptides derived from this domain are true mimetics of the annexin 1 action in all inflammation models tested and most likely serve as the active entities generated at sites of inflammation. To elucidate mechanisms underlying peptide generation we used isolated blood leukocytes and endothelial cell monolayers. We show that following endothelial adhesion, annexin 1 was externalized from leukocytes and rapidly cleaved. Addition of purified annexin 1 to degranulating leukocytes resulted in the truncation of annexin 1, which seemed to depend on the proteolytic activity of human leukocyte elastase (HLE). The capacity of elastase to proteolytically cleave annexin 1 was confirmed using both purified annexin 1 and HLE. The identification of annexin 1 as a substrate for HLE supports the model in which annexin 1 participates in regulating leukocyte emigration into inflamed tissue through N-terminal peptides generated at inflammatory sites.     

Enhancement of human leukocyte elastase activity by ionic strength

The activity of human leukocyte elastase is strongly enhanced by ionic strength. For instance, with 5 m NaCl, the rate of the elastase catalyzed hydrolysis of N-succinyl-trialanine-p-nitroanilide is increased by a factor of 20. Under these conditions elastase concentrations as low as 1 nm (35 ng/ml) may be assayed accurately. Pancreatic elastase is much less sensitive to ionic strength than the leukocyte enzyme. Between 0.2 and 0.75 m NaCl, the rate of solubilization of elastin by leukocyte elastase is also strongly enhanced.