Development of orally active nonpeptidic inhibitors of human neutrophil elastase

Standardised Sonneratia apetala Buch.-Ham. fruit extract inhibits human neutrophil elastase and attenuates elastase-induced lung injury in mice

Chronic obstructive pulmonary disease (COPD) along with asthma is a major and increasing global health problem. Smoking contributes to about 80%-90% of total COPD cases in the world. COPD leads to the narrowing of small airways and destruction of lung tissue leading to emphysema primarily caused by neutrophil elastase. Neutrophil elastase plays an important role in disease progression in COPD patients and has emerged as an important target for drug discovery. Sonneratia apetala Buch.-Ham. is a mangrove plant belonging to family Sonneratiaceae. It is widely found in the Sundarban regions of India. While the fruits of this plant have antibacterial, antifungal, antioxidant and astringent activities, fruit and leaf extracts have been shown to reduce the symptoms of asthma and cough. The aim of this study is to find whether hydro alcoholic fruit extracts of S. apetala inhibit neutrophil elastase and thus prevent the progression of neutrophil elastase-driven lung emphysema. The hydroalcoholic extract, ethanol: water (90:10), of the S. apetala Buch.-Ham. fresh fruits (SAM) were used for neutrophil elastase enzyme kinetic assay and IC₅₀ of the extract was determined. The novel HPLC method has been developed and the extract was standardized with gallic acid and ellagic acid as standards. The extract was further subjected to LC-MS² profiling to identify key phytochemicals. The standardized SAM extract contains 53 μg/mg of gallic acid and 95 μg/mg of ellagic acid, based on the HPLC calibration curve. SAM also reversed the elastase-induced morphological change of human epithelial cells and prevented the release of ICAM-1 in vitro and an MTT assay was conducted to assess the viability. Further, 10 mg/kg SAM had reduced alveolar collapse induced by neutrophil elastase in the mice model. Thus, in this study, we reported for the first time that S. apetala fruit extract has the potential to inhibit human neutrophil elastase in vitro and in vivo.

Novel benzoxazinone derivative as potent human neutrophil elastase inhibitor: Potential implications in lung injury

Neutrophil elastase, a powerful physiological defence tool, may serve as drug target for diverse diseases due to its bystander effect on host cells like chronic obstructive pulmonary disease (COPD). Here, we synthesised seven novel benzoxazinone derivatives and identified that these synthetic compounds are human neutrophil elastase inhibitor that was demonstrated by enzyme substrate kinetic assay. One such compound, PD05, emerged as the most potent inhibitor with lower IC₅₀ as compared to control drug sivelestat. While this inhibition is competitive based on substrate dilution assay, PD05 showed a high binding affinity for human neutrophil elastase (Kd = 1.63 nM) with faster association and dissociation rate compared to notable elastase inhibitors like ONO 6818 and AZD9668, and its interaction with human neutrophil elastase was fully reversible.Preclinical pharmacokinetic studies were performed in vitro where protein binding was found to be 72% with a high recovery rate, aqueous solubility of 194.7 μM, low permeability along with a favourable hERG. Experiments with cell line revealed that the molecule successfully prevented elastase induced rounding and retracted cell morphology and cell cytotoxicity. In mouse model PD05 is able to reduce the alveolar collapse induced by neutrophil elastase. In summary, we demonstrate the in situ, in vitro and in vivo anti-elastase potential of the newly synthesised benzoxazinone derivative PD05 and thus this could be promising candidate for further investigation as a drug for the treatment of COPD.

Synthesis of 1,3,4-Oxadiazoles by Iodine-Mediated Oxidative Cyclization of Methyl Ketones with 4-Phenylsemicarbazide

An efficient one-pot method has been developed to access 5-amino-2-(het)aroyl-1,3,4-oxadiazoles through I2/DMSO-promoted oxidative cyclization of 4-phenylsemicarbazide with (het)aryl methyl ketones under mild conditions. This reaction proceeds smoothly with a wide range of methyl ketones containing various functional groups to give the corresponding products in moderate yields under mild conditions.

Optimization of peptide-based inhibitors targeting the HtrA serine protease in Chlamydia: Design, synthesis and biological evaluation of pyridone-based and N-Capping group-modified analogues

The obligate intracellular bacterium Chlamydia trachomatis (C. trachomatis) is responsible for the most common bacterial sexually transmitted infection and is the leading cause of preventable blindness, representing a major global health burden. While C. trachomatis infection is currently treatable with broad-spectrum antibiotics, there would be many benefits of a chlamydia-specific therapy. Previously, we have identified a small-molecule lead compound JO146 [Boc-Val-Pro-Val^P(OPh)₂] targeting the bacterial serine protease HtrA, which is essential in bacterial replication, virulence and survival, particularly under stress conditions. JO146 is highly efficacious in attenuating infectivity of both human (C. trachomatis) as well as koala (C. pecorum) species in vitro and in vivo, without host cell toxicity. Herein, we present our continuing efforts on optimizing JO146 by modifying the N-capping group as well as replacing the parent peptide structure with the 2-pyridone scaffold at P3/P2. The drug optimization process was guided by molecular modelling, enzyme and cell-based assays. Compound 18b from the pyridone series showed improved inhibitory activity against CtHtrA by 5-fold and selectivity over human neutrophil elastase (HNE) by 109-fold compared to JO146, indicating that 2-pyridone is a suitable bioisostere of the P3/P2 amide/proline for developing CtHtrA inhibitors. Most pyridone-based inhibitors showed superior anti-chlamydial potency to JO146 especially at lower doses (25 and 50 μM) in C. trachomatis and C. pecorum cell culture assays. Modifications of the N-capping group of the peptidyl inhibitors did not have much influence on the anti-chlamydial activities, providing opportunities for more versatile alterations and future optimization. In summary, we present 2-pyridone based analogues as a new generation of non-peptidic CtHtrA inhibitors, which hold better promise as anti-chlamydial drug candidates.

Azole-Based Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitors

The heme enzyme indoleamine 2,3-dioxygenase 1 (IDO1) plays an essential role in immunity, neuronal function, and aging through catalysis of the rate-limiting step in the kynurenine pathway of tryptophan metabolism. Many IDO1 inhibitors with different chemotypes have been developed, mainly targeted for use in anti-cancer immunotherapy. Lead optimization of direct heme iron-binding inhibitors has proven difficult due to the remarkable selectivity and sensitivity of the heme-ligand interactions. Here, we present experimental data for a set of closely related small azole compounds with more than 4 orders of magnitude differences in their inhibitory activities, ranging from millimolar to nanomolar levels. We investigate and rationalize their activities based on structural data, molecular dynamics simulations, and density functional theory calculations. Our results not only expand the presently known four confirmed chemotypes of sub-micromolar heme binding IDO1 inhibitors by two additional scaffolds but also provide a model to predict the activities of novel scaffolds.

Structure-Based Drug Design of Bisubstrate Inhibitors of Phenylethanolamine N-Methyltransferase Possessing Low Nanomolar Affinity at Both Substrate Binding Domains1

The enzyme phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) catalyzes the final step in the biosynthesis of epinephrine and is a potential drug target, primarily for the control of hypertension. Unfortunately, many potent PNMT inhibitors also possess significant affinity for the a₂-adrenoceptor, which complicates the interpretation of their pharmacology. A bisubstrate analogue approach offers the potential for development of highly selective inhibitors of PNMT. This paper documents the design, synthesis, and evaluation of such analogues, several of which were found to possess human PNMT (hPNMT) inhibitory potency <5 nM versus AdoMet. Site-directed mutagenesis studies were consistent with bisubstrate binding. Two of these compounds (19 and 29) were co-crystallized with hPNMT and the resulting structures revealed both compounds bound as predicted, simultaneously occupying both substrate binding domains. This bisubstrate inhibitor approach has resulted in one of the most potent (20) and selective (vs the a_2-adrenoceptor) inhibitors of hPNMT yet reported.

Carbon-nitrogen bond cleavage of pyridine with two molecular substituted allenoates: access to 2-arylpyrimidin-4(3H)-one

A DABCO-catalyzed annulation reaction of pyridin-2-amine and substituted allenoates has been disclosed. This strategy allows for the ring-opening of a pyridine ring system and the formation of two new rings including a pyrimidinone ring and a benzene ring in an efficient manner.

The Influence of Bioisosteres in Drug Design: Tactical Applications to Address Developability Problems

The application of bioisosteres in drug discovery is a well-established design concept that has demonstrated utility as an approach to solving a range of problems that affect candidate optimization, progression, and durability. In this chapter, the application of isosteric substitution is explored in a fashion that focuses on the development of practical solutions to problems that are encountered in typical optimization campaigns. The role of bioisosteres to affect intrinsic potency and selectivity, influence conformation, solve problems associated with drug developability, including P-glycoprotein recognition, modulating basicity, solubility, and lipophilicity, and to address issues associated with metabolism and toxicity is used as the underlying theme to capture a spectrum of creative applications of structural emulation in the design of drug candidates.

Synthesis of new 2,5-disubstituted-1,3,4-thiadiazole derivatives and their in vivo anticonvulsant activity

A series of 2,5-disubstituted-1,3,4-thiadiazole derivatives were synthesized by the reaction of 3-(2-cyanopropan-2-yl)-N-(5-(piperazine-1-yl)-1,3,4-thiadiazol-2-yl)benzamide with various sulfonyl chlorides and evaluated for their anticonvulsant activity in MES test. Rotorod method was employed to determine the neurotoxicity. The purity of the compounds is confirmed on the basis of their elemental analysis. The structures of all the new compounds are established on the basis of 1H NMR and mass spectral data. Out of fifteen compounds, three were found to be potent anticolvunstants. The same compounds showed no neurotoxicity at the maximum dose administered (100 mg/kg).

Synthesis and antifungal activity of 3-(1,3,4-oxadiazol-5-yl)-indoles and 3-(1,3,4-oxadiazol-5-yl)methyl-indoles

On the basis of the principle of combination of active structural moieties, a modified and efficient synthetic method for three series of novel indole-based 1,3,4-oxadiazoles is described. Bioassays conducted at Syngenta showed that several of the synthesized compounds exhibit higher antifungal activity than pimprinine, the natural product which inspired this synthesis. Two main structural alterations were found to broaden the spectrum of biological activity in most cases. Compounds 3g, 6c, 6e, 6h, 9d, 9e, 9h and 9m (Fig. 1) were identified as the most active on the biological assays, and will be studied further.

Synthesis of Mono-Substituted and Simmetrically 2, 5-Disubstituted 1, 3, 4-Oxadiazoles

This article is an extended abstract of a communication presented at the Conference Ecological Chemistry 2012.

Synthetic approaches and pharmacological activity of 1,3,4-oxadiazoles: a review of the literature from 2000-2012

This review provides readers with an overview of the main synthetic methodologies for 1,3,4-oxadiazole derivatives, and of their broad spectrum of pharmacological activities as reported over the past twelve years.

Targeting COPD: advances on low-molecular-weight inhibitors of human neutrophil elastase

Chronic obstructive pulmonary disease (COPD) is a major increasing health problem and the World Health Organization (WHO) reports COPD as the fifth leading cause of death worldwide. COPD refers to a condition of inflammation and progressive weakening of the structure of the lung as well as irreversible narrowing of the airways. Current treatment is only palliative and no available drug halts the progression of the disease. Human neutrophil elastase (HNE) is a serine protease, which plays a major role in the COPD inflammatory process. The protease/anti-protease imbalance leads to an excess of extracellular HNE hydrolyzing elastin, the structural protein that confers elasticity to the lung tissue. Although HNE was identified as a therapeutic target for COPD more than 30 years ago, only Sivelestat (ONO-5046), an HNE inhibitor from Ono Pharmaceutical, has been approved for clinical use. Nevertheless, Sivelestat is only approved in Japan and its development in the USA was terminated in 2003. Other inhibitors in pre-clinical or phase I trials were discontinued for various reasons. Hence, there is an urgent need for low-molecular-weight synthetic elastase inhibitors and the present review discusses the recent advances on this field covering acylating agents, transition-state inhibitors, mechanism-based inhibitors, relevant natural products, and major patent disclosures.

Unexpected active-site flexibility in the structure of human neutrophil elastase in complex with a new dihydropyrimidone inhibitor

Human neutrophil elastase (HNE), a trypsin-type serine protease, is of pivotal importance in the onset and progression of chronic obstructive pulmonary disease (COPD). COPD encompasses a group of slowly progressive respiratory disorders and is a major medical problem and the fifth leading cause of death worldwide. HNE is a major target for the development of compounds that inhibit the progression of long-term lung function decline in COPD patients. Here, we present the three-dimensional structure of a potent dihydropyrimidone inhibitor (DHPI) non-covalently bound to HNE at a resolution of 2.0 Å. The inhibitor binds to the active site in a unique orientation addressing S1 and S2 subsites of the protease. To facilitate further analysis of this binding mode, we determined the structure of the uncomplexed enzyme at a resolution of 1.86 Å. Detailed comparisons of the HNE:DHPI complex with the uncomplexed HNE structure and published structures of other elastase:inhibitor complexes revealed that binding of DHPI leads to large conformational changes in residues located in the S2 subsite. The rearrangement of residues Asp95-Leu99B creates a deep, well-defined cavity, which is filled by the P2 moiety of the inhibitor molecule to almost perfect shape complementarity. The shape of the S2 subsite in complex with DHPI clearly differs from all other observed HNE structures. The observed structural flexibility of the S2 subsite is a key feature for the understanding of the binding mode of DHPIs in general and the development of new HNE selective inhibitors.

Reversible competitive α-ketoheterocycle inhibitors of fatty acid amide hydrolase containing additional conformational constraints in the acyl side chain: orally active, long-acting analgesics

A series of α-ketooxazoles containing conformational constraints in the C2 acyl side chain of 2 (OL-135) were examined as inhibitors of fatty acid amide hydrolase (FAAH). Only one of the two possible enantiomers displayed potent FAAH inhibition (S vs R enantiomer), and their potency is comparable or improved relative to 2, indicating that the conformational restriction in the C2 acyl side chain is achievable. A cocrystal X-ray structure of the α-ketoheterocycle 12 bound to a humanized variant of rat FAAH revealed its binding details, confirmed that the (S)-enantiomer is the bound active inhibitor, shed light on the origin of the enantiomeric selectivity, and confirmed that the catalytic Ser241 is covalently bound to the electrophilic carbonyl as a deprotonated hemiketal. Preliminary in vivo characterization of the inhibitors 12 and 14 is reported demonstrating that they raise brain anandamide levels following either intraperitoneal (ip) or oral (po) administration indicative of effective in vivo FAAH inhibition. Significantly, the oral administration of 12 caused dramatic accumulation of anandamide in the brain, with peak levels achieved between 1.5 and 3 h, and these elevations were maintained over 9 h. Additional studies of these two representative members of the series (12 and 14) in models of thermal hyperalgesia and neuropathic pain are reported, including the demonstration that 12 administered orally significantly attenuated mechanical (>6 h) and cold (>9 h) allodynia for sustained periods consistent with its long-acting effects in raising the endogenous concentration of anandamide.

Conformational preferences of proline analogues with a fused benzene ring

The intrinsic conformational preferences of indoline-2-carboxylic acid (Inc) and its α-methylated derivative (αMeInc) have been investigated using quantum mechanical calculations. Specifically, the behavior of their N-acetyl-N'-methylamide derivatives, Ac-L-Inc-NHMe and Ac-L-αMeInc-NHMe, has been explored at the B3LYP/6-31+G(d,p) level. Such amino acids are analogues of proline and (α-methyl)proline, respectively, bearing a benzene ring fused to the C(γ)-C(δ) bond of the five-membered pyrrolidine ring. The additional aromatic group has been shown to significantly restrict the conformational space available to these residues by reducing the flexibility of both the five-membered cycle and the peptide backbone. The fused benzene ring also plays a critical role in determining the cis-trans arrangement of the amide bond involving the pyrrolidine nitrogen, which is also modulated by the presence of the α-methyl group in the αMeInc derivative. Furthermore, the influence of the environment on the conformational propensities of these compounds has been evaluated by using both a self-consistent reaction field model and a recently developed interface in a hybrid QM/MM scheme, in which the solvent molecules are treated explicitly with classical mechanics while the solute is described by quantum mechanics at the density functional theory level.

Novel potent and selective Ca2+ release-activated Ca2+ (CRAC) channel inhibitors. Part 3: synthesis and CRAC channel inhibitory activity of 4'-[(trifluoromethyl)pyrazol-1-yl]carboxanilides

From a series of 4'-[(trifluoromethyl)pyrazol-1-yl]carboxanilides derived from 4-methyl-4'-[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl]-1,2,3-thiadiazole-5-carboxanilide, one inhibited thapsigargin-induced Ca2+ influx in Jurkat T cells (IC(50)=77 nM) and exhibited high selectivity for the CRAC channel over the VOC channel (index: >130). Another acted as an inhibitor for both T lymphocyte activation-induced diseases and ovalbumin-induced airway eosinophilia in rats (ED(50)=1.3 mg/kg) p.o.

Delineation of a fundamental alpha-ketoheterocycle substituent effect for use in the design of enzyme inhibitors

The synthesis and examination of a systematic series of 5-substituted 2-keto oxazoles as inhibitors of fatty acid amide hydrolase (FAAH) defined a fundamental substituent effect that led to the discovery of inhibitors with Ki's as low as 400 pM. The intrinsic basis of the relationship (-log Ki vs sigmap), which relates Ki with the Hammett sigmap constant of the substituent, the magnitude of the effect (rho = 3.01), and its predictive value (R2 = 0.91) suggest a widespread applicability in studies beyond FAAH.

Optimization of Subsite Binding to the β5 Subunit of the Human 20S Proteasome Using Vinyl Sulfones and 2-Keto-1,3,4-oxadiazoles: Syntheses and Cellular Properties of Potent, Selective Proteasome Inhibitors

Beginning with the peptide sequence Cbz-Ile-Glu(OtBu)-Ala-Leu found in PSI (3), a series of vinyl sulfones (VS) were synthesized for evaluation as inhibitors of the chymotrypsin-like activity of the 20S proteasome. Variations at the key P3 position confirmed the importance of a long side chain capped with a hydrophobic group for optimal potency, consistent with a model of binding to the S3 subsite. The tert-butyl glutamic ester initially used at P3 gave plasma unstable, insoluble compounds and was replaced with the better isostere, N-beta-neopentyl asparagine. The inhibitors were shortened by replacing the N-terminal Cbz-isoleucine with a p-tosyl group without loss of potency. Small l-amino acids were used at P2, where d-substitution was not tolerated. The resulting optimized P4-P3-P2 sequence was grafted onto a novel proteasome inhibitor warhead, 2-keto-1,3,4-oxadiazoles (KOD), to produce reversible, subnanomolar proteasome inhibitors that were 1000-fold selective versus cathepsin B (CatB), cathepsin S (CatS), and trypsin-like as well as PGPH-like proteasome activity. A number of compounds in both the VS and the KOD series exhibited growth inhibitory effects against the human prostate cancer cell line PC3 at submicromolar concentrations.

Keto-1,3,4-oxadiazoles as cathepsin K inhibitors

We have prepared a series of cathepsin K inhibitors bearing the keto-1,3,4-oxadiazole warhead capable of forming a hemithioketal complex with the target enzyme. By modifying binding moieties at the P1, P2, and prime side positions of the inhibitors, we have achieved selectivity over cathepsins B, L, and S, and have achieved sub-nanomolar potency against cathepsin K. This series thus represents a promising chemotype that could be used in diseases implicated by imbalances in cathepsin K activity such as osteoporosis.

Inhibitors of hepatitis C virus NS3.4A protease 2. Warhead SAR and optimization

The alpha-ketoamide warhead (e.g., 15) was found to be a practical replacement for aliphatic aldehydes in a series of HCV NS3.4A protease inhibitors. Structure-activity relationships and prime side optimization are discussed.

Design, synthesis, and biological evaluation of simplified alpha-keto heterocycle, trifluoromethyl ketone, and formyl substituted folate analogues as potential inhibitors of GAR transformylase and AICAR transformylase

A series of simplified alpha-keto heterocycle, trifluoromethyl ketone, and formyl substituted folate analogues lacking the benzoylglutamate subunit were prepared and examined as potential inhibitors of glycinamide ribonucleotide transformylase (GAR Tfase) and aminoimidazole carboxamide transformylase (AICAR Tfase).

Novel inhibitor for prolyl aminopeptidase from Serratia marcescens and studies on the mechanism of substrate recognition of the enzyme using the inhibitor

Prolyl aminopeptidase from Serratia marcescens hydrolyzed x-beta-naphthylamides (x=prolyl, alanyl, sarcosinyl, L-alpha-aminobutylyl, and norvalyl), which suggested that the enzyme has a pocket for a five-member ring. Based on the substrate specificity, novel inhibitors of Pro, Ala, and Sar having 2-tert-butyl-[1,3,4]oxadiazole (TBODA) were synthesized. The K(i) value of Pro-TBODA, Ala-TBODA, and Sar-TBODA was 0.5 microM, 1.6 microM, and 12mM, respectively. The crystal structure of enzyme-Pro-TBODA complex was determined. Pro-TBODA was located at the active site. Four electrostatic interactions were located between the enzyme and the amino group of Pro inhibitors (Glu204:0E1-N:Inh, Glu204:0E2-N:Inh, Glu232:0E1-N:Inh, and Gly46:O-N:Inh), and the residue of the inhibitors was inserted into the hydrophobic pocket composed of Phe139, Leu141, Leu146, Tyr149, Tyr150, and Phe236. The roles of Phe139, Tyr149, and Phe236 in the hydrophobic pocket and Glu204 and Glu232 in the electrostatic interactions were confirmed by site-directed mutagenesis, which indicated that the molecular recognition of proline is achieved through four electrostatic interactions and an insertion in the hydrophobic pocket of the enzyme.

Structure-based drug design of pyrazinone antithrombotics as selective inhibitors of the tissue factor VIIa complex

Structure-based drug design coupled with polymer-assisted solution-phase library synthesis was utilized to develop a series of pyrazinone inhibitors of the tissue factor/Factor VIIa complex. The crystal structure of a tri-peptide ketothiazole complexed with TF/VIIa was utilized in a docking experiment that identified a benzyl-substituted pyrazinone as a P(2) surrogate for the tri-peptide. A 5-step PASP library synthesis of these aryl-substituted pyrazinones was developed. The sequence allows for attachment of a variety of P(1) and P(3) moieties, which led to synthesis pyrazinone 23. Compound 23 exhibited 16 nM IC(50) against TF/VIIa with >6250x selectivity versus Factor Xa and thrombin. This potent and highly selective inhibitor of TF/VIIa was chosen for pre-clinical intravenous proof-of-concept studies to demonstrate the separation between antithrombotic efficacy and bleeding side effects in a primate model of thrombosis.

Discovery of potent, selective human granzyme B inhibitors that inhibit CTL mediated apoptosis

A novel class of small molecule human granzyme B inhibitors is reported. Compound 20 has a K(i) of 7 nM against human granzyme B and blocks CTL mediated apoptosis with an IC(50) of 3 micromolar.

A novel oral neutrophil elastase inhibitor (ONO-6818) inhibits human neutrophil elastase-induced emphysema in rats

We investigated the effects of a novel oral neutrophil elastase inhibitor (ONO-6818) on acute lung injury and pulmonary emphysema induced by human neutrophil elastase (HNE). Young male Wistar rats were divided into four treatment groups: (1) control group (saline); (2) HNE group (HNE 200 U + 0.5% carboxymethyl-cellulose [solution for ONO-6818]); (3) low-dose ONO-6818 group (HNE 200 U + ONO-6818 10 mg/kg); and (4) high-dose ONO-6818 group (HNE 200 U + ONO-6818 100 mg/kg). Saline and HNE were applied via the trachea using a microsprayer. ONO-6818 was administered orally 1 hour before HNE application. Six hours after HNE application, neutrophil counts and hemoglobin concentration in bronchoalveolar lavage fluid and lung tissue myeloperoxidase activity were determined. Eight weeks after the application, FRC, TLC, lung compliance, and mean linear intercept were estimated. ONO-6818 attenuated dose-dependently HNE-induced increases in lung myeloperoxidase activity, hemoglobin, and neutrophil count in bronchoalveolar lavage fluid. Furthermore, it significantly attenuated HNE-induced increases in FRC, TLC, lung compliance, and mean linear intercept. ONO-6818 inhibited acute lung injury induced by HNE by minimizing lung hemorrhage and accumulation of neutrophils in the lung. ONO-6818 also inhibited the development of HNE-induced emphysematous changes including lung hyperinflation, degradation of elastic recoil, and airspace enlargement.

Neutrophil elastase inhibitors as treatment for COPD

Chronic obstructive pulmonary disease, characterised by a slowly progressive, irreversible airways limitation, is a major worldwide cause of chronic morbidity and mortality. The imbalance between human neutrophil elastase and endogenous antiproteases may cause excess human neutrophil elastase in pulmonary tissues, which may be considered a major pathogenic factor in chronic obstructive pulmonary disease. Great effort has been devoted to finding a method to restore the balance, resulting in the discovery of potent two-typed small-molecular-weight human neutrophil elastase inhibitors. In the application of chronic obstructive pulmonary disease therapy, the human neutrophil elastase inhibitors mainly focused upon include ONO-5046, MR-889, L-694,458, CE-1037, GW-311616 and TEI-8362 as the acyl-enzyme inhibitors; and ONO-6818, AE-3763, FK-706, ICI-200,880, ZD-0892 and ZD-8321 as the transition-state inhibitors. In this review, various problems that remain to be solved in the clinical use of human neutrophil elastase inhibitors are discussed.