On the Process of Discovering Leads That Target the Heparin-Binding Site of Neutrophil Elastase in the Sputum of Cystic Fibrosis Patients

Merging cultures and disciplines to create a drug discovery ecosystem at Virginia commonwealth university: Medicinal chemistry, structural biology, molecular and behavioral pharmacology and computational chemistry

The Department of Medicinal Chemistry, together with the Institute for Structural Biology, Drug Discovery and Development, at Virginia Commonwealth University (VCU) has evolved, organically with quite a bit of bootstrapping, into a unique drug discovery ecosystem in response to the environment and culture of the university and the wider research enterprise. Each faculty member that joined the department and/or institute added a layer of expertise, technology and most importantly, innovation, that fertilized numerous collaborations within the University and with outside partners. Despite moderate institutional support with respect to a typical drug discovery enterprise, the VCU drug discovery ecosystem has built and maintained an impressive array of facilities and instrumentation for drug synthesis, drug characterization, biomolecular structural analysis and biophysical analysis, and pharmacological studies. Altogether, this ecosystem has had major impacts on numerous therapeutic areas, such as neurology, psychiatry, drugs of abuse, cancer, sickle cell disease, coagulopathy, inflammation, aging disorders and others. Novel tools and strategies for drug discovery, design and development have been developed at VCU in the last five decades; e.g., fundamental rational structure-activity relationship (SAR)-based drug design, structure-based drug design, orthosteric and allosteric drug design, design of multi-functional agents towards polypharmacy outcomes, principles on designing glycosaminoglycans as drugs, and computational tools and algorithms for quantitative SAR (QSAR) and understanding the roles of water and the hydrophobic effect.

A comprehensive overview of investigational elastase inhibitors for the treatment of acute respiratory distress syndrome

INTRODUCTION

Excessive activity of neutrophil elastase (NE), the main enzyme present in azurophil granules in the neutrophil cytoplasm, may cause tissue injury and remodeling in various lung diseases, including acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), in which it is crucial to the immune response and inflammatory process. Consequently, NE is a possible target for therapeutic intervention in ALI/ARDS.

AREAS COVERED

The protective effects of several NE inhibitors in attenuating ALI/ARDS in several models of lung injury are described. Some of these NE inhibitors are currently in clinical development, but only sivelestat has been evaluated as a treatment for ALI/ARDS.

EXPERT OPINION

Preclinical research has produced encouraging information about using NE inhibitors. Nevertheless, only sivelestat has been approved for this clinical indication, and only in Japan and South Korea because of the conflicting results of clinical trials and likely also because of the potential adverse events. Identifying subsets of patients with ARDS most likely to benefit from NE inhibitor treatment, such as the hyperinflammatory phenotype, and using a more advanced generation of NE inhibitors than sivelestat could enable better clinical results than those obtained with elastase inhibitors.

Homogeneous, Synthetic, Non-Saccharide Glycosaminoglycan Mimetics as Potent Inhibitors of Human Cathepsin G

Cathepsin G (CatG) is a pro-inflammatory neutrophil serine protease that is important for host defense, and has been implicated in several inflammatory disorders. Hence, inhibition of CatG holds much therapeutic potential; however, only a few inhibitors have been identified to date, and none have reached clinical trials. Of these, heparin is a well-known inhibitor of CatG, but its heterogeneity and bleeding risk reduce its clinical potential. We reasoned that synthetic small mimetics of heparin, labeled as non-saccharide glycosaminoglycan mimetics (NSGMs), would exhibit potent CatG inhibition while being devoid of bleeding risks associated with heparin. Hence, we screened a focused library of 30 NSGMs for CatG inhibition using a chromogenic substrate hydrolysis assay and identified nano- to micro-molar inhibitors with varying levels of efficacy. Of these, a structurally-defined, octasulfated di-quercetin NSGM 25 inhibited CatG with a potency of ~50 nM. NSGM 25 binds to CatG in an allosteric site through an approximately equal contribution of ionic and nonionic forces. Octasulfated 25 exhibits no impact on human plasma clotting, suggesting minimal bleeding risk. Considering that octasulfated 25 also potently inhibits two other pro-inflammatory proteases, human neutrophil elastase and human plasmin, the current results imply the possibility of a multi-pronged anti-inflammatory approach in which these proteases are likely to simultaneously likely combat important conditions, e.g., rheumatoid arthritis, emphysema, or cystic fibrosis, with minimal bleeding risk.

Factor XIa Inhibitors in Anticoagulation Therapy: Recent Advances and Perspectives

Factor XIa (FXIa) in the intrinsic pathway of the coagulation process has been proven to be an effective and safe target for anticoagulant discovery with limited or no bleeding. Numerous small-molecule FXIa inhibitors (SMFIs) with various scaffolds have been identified in the early stages of drug discovery. They have served as the foundation for the recent discovery of additional promising SMFIs with improved potency, selectivity, and pharmacokinetic profiles, some of which have entered clinical trials for the treatment of thrombosis. After reviewing the coagulation process and structure of FXIa, this perspective discusses the rational or structure-based design, discovery, structure-activity relationships, and development of SMFIs disclosed in recent years. Strategies for identifying more selective and druggable SMFIs are provided, paving the way for the design and discovery of more useful SMFIs for anticoagulation therapy.

Pharmacology of Heparin and Related Drugs: An Update

Heparin has been used extensively as an antithrombotic and anticoagulant for close to 100 years. This anticoagulant activity is attributed mainly to the pentasaccharide sequence, which potentiates the inhibitory action of antithrombin, a major inhibitor of the coagulation cascade. More recently it has been elucidated that heparin exhibits anti-inflammatory effect via interference of the formation of neutrophil extracellular traps and this may also contribute to heparin's antithrombotic activity. This illustrates that heparin interacts with a broad range of biomolecules, exerting both anticoagulant and nonanticoagulant actions. Since our previous review, there has been an increased interest in these nonanticoagulant effects of heparin, with the beneficial role in patients infected with SARS2-coronavirus a highly topical example. This article provides an update on our previous review with more recent developments and observations made for these novel uses of heparin and an overview of the development status of heparin-based drugs. SIGNIFICANCE STATEMENT: This state-of-the-art review covers recent developments in the use of heparin and heparin-like materials as anticoagulant, now including immunothrombosis observations, and as nonanticoagulant including a role in the treatment of SARS-coronavirus and inflammatory conditions.

Elastase Inhibitor Cyclotheonellazole A: Total Synthesis and In Vivo Biological Evaluation for Acute Lung Injury

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is one of the most common complications in COVID-19. Elastase has been recognized as an important target to prevent ALI/ARDS in the patient of COVID-19. Cyclotheonellazole A (CTL-A) is a natural macrocyclic peptide reported to be a potent elastase inhibitor. Herein, we completed the first total synthesis of CTL-A in 24 linear steps. The key reactions include three-component MAC reactions and two late-stage oxidations. We also provided seven CTL-A analogues and elucidated preliminary structure-activity relationships. The in vivo ALI mouse model further suggested that CTL-A alleviated acute lung injury with reductions in lung edema and pathological deterioration, which is better than sivelestat, one approved elastase inhibitor. The activity of CTL-A against elastase, along with its cellular safety and well-established synthetic route, warrants further investigation of CTL-A as a candidate against COVID-19 pathogeneses.

Neutrophil Elastase and Chronic Lung Disease

Neutrophil elastase (NE) is a major inflammatory protease released by neutrophils and is present in the airways of patients with cystic fibrosis (CF), chronic obstructive pulmonary disease, non-CF bronchiectasis, and bronchopulmonary dysplasia. Although NE facilitates leukocyte transmigration to the site of infection and is required for clearance of Gram-negative bacteria, it also activates inflammation when released into the airway milieu in chronic inflammatory airway diseases. NE exposure induces airway remodeling with increased mucin expression and secretion and impaired ciliary motility. NE interrupts epithelial repair by promoting cellular apoptosis and senescence and it activates inflammation directly by increasing cytokine expression and release, and indirectly by triggering extracellular trap release and exosome release, which magnify protease activity and inflammation in the airway. NE inhibits innate immune function by digesting opsonins and opsonin receptors, degrading innate immune proteins such as lactoferrin, and inhibiting macrophage phagocytosis. Importantly, NE-directed therapies have not yet been effective in preventing the pathologic sequelae of NE exposure, but new therapies are being developed that offer both direct antiprotease activity and multifunctional anti-inflammatory properties.

Sulfonated Nonsaccharide Heparin Mimetics Are Potent and Noncompetitive Inhibitors of Human Neutrophil Elastase

Human neutrophil elastase (HNE) is a serine protease that plays vital roles in inflammation, innate immune response, and tissue remodeling processes. HNE has been actively pursued as a drug target, particularly for the treatment of cardiopulmonary diseases. Although thousands of molecules have been reported to inhibit HNE, yet very few are being evaluated in early clinical trials, with sivelestat as the only approved HNE inhibitor. We report here a novel chemotype of sulfonated nonsaccharide heparin mimetics as potent and noncompetitive inhibitors of HNE. Using a chromogenic substrate hydrolysis assay, 14 sulfonated nonsaccharide heparin mimetics were tested for their inhibitory activity against HNE. Only 12 molecules inhibited HNE with IC₅₀ values of 0.22-88.3 μM. The inhibition of HNE by these molecules was salt-dependent. Interestingly, a specific hexa-sulfonated molecule inhibited HNE with an IC₅₀ value of 0.22 μM via noncompetitive mechanism, as demonstrated by Michaelis-Menten kinetics. The hexa-sulfonated derivative demonstrated at least 455-, 221-, 1590-, 21-, and 381-fold selectivity indices over other heparin-binding coagulation proteins including factors IIa, Xa, IXa, XIa, and FXIIIa, respectively. At the highest concentrations tested, the molecule also did not significantly inhibit other serine proteases of plasmin, trypsin, and chymotrypsin. Further supporting its selectivity, the molecule did not show heparin-like effects on clotting times of human plasma. The molecule also did not affect the proliferation of three cell lines at a concentration as high as 10 μM. Interestingly, the hexa-sulfonated molecule also inhibited cathepsin G with an IC₅₀ value of 0.57 μM alluding to a dual anti-inflammatory action. A computational approach was exploited to identify putative binding site(s) for this novel class of HNE inhibitors. Overall, the reported hexa-sulfonated nonsaccharide heparin mimetic serves as a new platform to develop potent, selective, and noncompetitive inhibitors of HNE for therapeutic purposes.

Glycosaminoglycan-Protein Interactions and Their Roles in Human Disease

Glycosaminoglycans (GAGs) are a family of linear and negatively charged polysaccharides that exist ubiquitously on the human cell surface as well as in the extracellular matrix. GAGs interact with a wide range of proteins, including proteases, growth factors, cytokines, chemokines and adhesion molecules, enabling them to mediate many physiological processes, such as protein function, cellular adhesion and signaling. GAG-protein interactions participate in and intervene in a variety of human diseases, including cardiovascular disease, infectious disease, neurodegenerative diseases and tumors. The breakthrough in analytical tools and approaches during the last two decades has facilitated a greater understanding of the importance of GAG-protein interactions and their roles in human diseases. This review focuses on aspects of the molecular basis and mechanisms of GAG-protein interactions involved in human disease. The most recent advances in analytical tools, especially mass spectrometry-based GAG sequencing and binding motif characterization methods, are introduced. An update of selected families of GAG binding proteins is presented. Perspectives on development of novel therapeutics targeting specific GAG-protein interactions are also covered in this review.

Polysulfated Hyaluronan GlycoMira-1111 Inhibits Elastase and Improves Rheology in Cystic Fibrosis Sputum

Cystic fibrosis (CF) lung disease is marked by high concentrations of neutrophil elastase (NE) and DNA polymers; both factors contribute to airway disease. Although inhaled recombinant human dornase alfa reduces the frequency of CF pulmonary exacerbations, it also increases free NE activity in the sputum. There are no approved anti-NE therapies for patients with CF. We investigated whether synthetic, low-molecular weight polysulfated hyaluronan GlycoMira-1111 (GM-1111) would be effective as an anti-NE drug using ex vivo CF sputum. Anti-NE activity of GM-1111 was tested in CF sputum in the presence or absence of dornase alfa and/or hypertonic saline using a spectrophotometric assay specific for human NE and was compared with unfractionated heparin. We tested whether GM-1111 disaggregated DNA from CF sputum (using gel electrophoresis analysis) or modified CF sputum viscoelastic properties (using a dynamic rheometer). GM-1111 and unfractionated heparin had near equivalent anti-NE activity in CF sputum in the presence of dornase alfa. Both GM-1111 and unfractionated heparin retained anti-NE activity in hypertonic saline but with decreased activity. GM-1111 increased the release of soluble DNA in CF sputum, resulting in improved depolymerization efficacy of dornase alfa. GM-1111 decreased CF sputum elasticity. GM-1111 inhibited NE activity, enhanced DNA depolymerization by deoxyribonuclease, and decreased viscoelastic properties of CF sputum, similar to effects reported previously for unfractionated heparin. Unlike heparins, GM-1111 is synthetic, with minimal anticoagulant activity, and is not derived from animal products. These key attributes provide advantages over unfractionated heparin as a potential therapeutic for CF.

Discovery of Sulfated Small Molecule Inhibitors of Matrix Metalloproteinase-8

Elevated matrix metalloproteinase-8 (MMP-8) activity contributes to the etiology of many diseases, including atherosclerosis, pulmonary fibrosis, and sepsis. Yet, very few small molecule inhibitors of MMP-8 have been identified. We reasoned that the synthetic non-sugar mimetics of glycosaminoglycans may inhibit MMP-8 because natural glycosaminoglycans are known to modulate the functions of various MMPs. The screening a library of 58 synthetic, sulfated mimetics consisting of a dozen scaffolds led to the identification of only two scaffolds, including sulfated benzofurans and sulfated quinazolinones, as promising inhibitors of MMP-8. Interestingly, the sulfated quinazolinones displayed full antagonism of MMP-8 and sulfated benzofuran appeared to show partial antagonism. Of the two, sulfated quinazolinones exhibited a >10-fold selectivity for MMP-8 over MMP-9, a closely related metalloproteinase. Molecular modeling suggested the plausible occupancy of the S₁^′ pocket on MMP-8 as the distinguishing feature of the interaction. Overall, this work provides the first proof that the sulfated mimetics of glycosaminoglycans could lead to potent, selective, and catalytic activity-tunable, small molecular inhibitors of MMP-8.

Glycosaminoglycans as Multifunctional Anti-Elastase and Anti-Inflammatory Drugs in Cystic Fibrosis Lung Disease

Neutrophil elastase (NE) is a major protease in the airways of patients with cystic fibrosis (CF) that activates airway inflammation by several mechanisms. NE stimulates epithelial toll like receptors (TLR) resulting in cytokine upregulation and release, upregulates MUC5AC, a major airway mucin, degrades both phagocytic receptors and opsonins resulting in both neutrophil and macrophage phagocytic failure, generates oxidative stress via extracellular generation and uptake of heme free iron, and activates other proteases. Altogether, these mechanisms create a significant inflammatory challenge that impairs innate immune function and results in airway remodeling. Currently, a major gap in our therapeutic approach to CF lung disease is the lack of an effective therapeutic strategy targeting active NE and its downstream pro-inflammatory sequelae. Polysulfated glycosaminoglycans (GAGs) are potent anti-elastase drugs that have additional anti-inflammatory properties. Heparin is a prototype of a glycosaminoglycan with both anti-elastase and anti-inflammatory properties. Heparin inhibits NE in an allosteric manner with high potency. Heparin also inhibits cathepsin G, blocks P-selectin and L-selectin, hinders ligand binding to the receptor for advanced glycation endproducts, and impedes histone acetyltransferase activity which dampens cytokine transcription and High Mobility Group Box 1 release. Furthermore, nebulized heparin treatment improves outcomes for patients with chronic obstructive pulmonary disease (COPD), asthma, acute lung injury and smoke inhalation. However, the anticoagulant activity of heparin is a potential contraindication for this therapy to be developed for CF lung disease. Therefore, modified heparins and other GAGs are being developed that retain the anti-elastase and anti-inflammatory qualities of heparin with minimal to no anticoagulant activity. The modified heparin, 2-O, 3-O desulfated heparin (ODSH), maintains anti-elastase and anti-inflammatory activities in vitro and in vivo, and has little residual anticoagulant activity. Heparan sulfate with O-sulfate residues but not N-sulfate residues blocks allergic asthmatic inflammation in a murine model. Polysulfated hyaluronic acid abrogates allergen- triggered rhinosinusitis in a murine model. Finally, nonsaccharide glycosaminoglycan mimetics with specific sulfate modifications can be designed to inhibit NE activity. Altogether, these novel GAGs or GAG mimetics hold significant promise to address the unmet need for inhaled anti-elastase and anti-inflammatory therapy for patients with CF.

Immunomodulation in Cystic Fibrosis: Why and How?

Cystic fibrosis (CF) lung disease is characterized by unconventional mechanisms of inflammation, implicating a chronic immune response dominated by innate immune cells. Historically, therapeutic development has focused on the mutated cystic fibrosis transmembrane conductance regulator (CFTR), leading to the discovery of small molecules aiming at modulating and potentiating the presence and activity of CFTR at the plasma membrane. However, treatment burden sustained by CF patients, side effects of current medications, and recent advances in other therapeutic areas have highlighted the need to develop novel disease targeting of the inflammatory component driving CF lung damage. Furthermore, current issues with standard treatment emphasize the need for directed lung therapies that could minimize systemic side effects. Here, we summarize current treatment used to target immune cells in the lungs, and highlight potential benefits and caveats of novel therapeutic strategies.

Inhibition of Human Cytomegalovirus Entry into Host Cells Through a Pleiotropic Small Molecule

Human cytomegalovirus (HCMV) infections are wide-spread among the general population with manifestations ranging from asymptomatic to severe developmental disabilities in newborns and life-threatening illnesses in individuals with a compromised immune system. Nearly all current drugs suffer from one or more limitations, which emphasizes the critical need to develop new approaches and new molecules. We reasoned that a ‘poly-pharmacy’ approach relying on simultaneous binding to multiple receptors involved in HCMV entry into host cells could pave the way to a more effective therapeutic outcome. This work presents the study of a synthetic, small molecule displaying pleiotropicity of interactions as a competitive antagonist of viral or cell surface receptors including heparan sulfate proteoglycans and heparan sulfate-binding proteins, which play important roles in HCMV entry and spread. Sulfated pentagalloylglucoside (SPGG), a functional mimetic of heparan sulfate, inhibits HCMV entry into human foreskin fibroblasts and neuroepithelioma cells with high potency. At the same time, SPGG exhibits no toxicity at levels as high as 50-fold more than its inhibition potency. Interestingly, cell-ELISA assays showed downregulation in HCMV immediate-early gene 1 and 2 (IE 1&2) expression in presence of SPGG further supporting inhibition of viral entry. Finally, HCMV foci were observed to decrease significantly in the presence of SPGG suggesting impact on viral spread too. Overall, this work offers the first evidence that pleiotropicity, such as demonstrated by SPGG, may offer a new poly-therapeutic approach toward effective inhibition of HCMV.