Recent development of two chitinase inhibitors, Argifin and Argadin, produced by soil microorganisms

The Exploitation of the Glycosylation Pattern in Asthma: How We Alter Ancestral Pathways to Develop New Treatments

Asthma has reached epidemic levels, yet progress in developing specific therapies is slow. One of the main reasons for this is the fact that asthma is an umbrella term for various distinct subsets. Due to its high heterogeneity, it is difficult to establish biomarkers for each subset of asthma and to propose endotype-specific treatments. This review focuses on protein glycosylation as a process activated in asthma and ways to utilize it to develop novel biomarkers and treatments. We discuss known and relevant glycoproteins whose functions control disease development. The key role of glycoproteins in processes integral to asthma, such as inflammation, tissue remodeling, and repair, justifies our interest and research in the field of glycobiology. Altering the glycosylation states of proteins contributing to asthma can change the pathological processes that we previously failed to inhibit. Special emphasis is placed on chitotriosidase 1 (CHIT1), an enzyme capable of modifying LacNAc- and LacdiNAc-containing glycans. The expression and activity of CHIT1 are induced in human diseased lungs, and its pathological role has been demonstrated by both genetic and pharmacological approaches. We propose that studying the glycosylation pattern and enzymes involved in glycosylation in asthma can help in patient stratification and in developing personalized treatment.

Discovery and Optimization of a Novel Macrocyclic Amidinourea Series Active as Acidic Mammalian Chitinase Inhibitors

Our research group has been involved for a long time in the development of macrocyclic amidinoureas (MCAs) as antifungal agents. The mechanistic investigation drove us to perform an in silico target fishing study, which allowed the identification of chitinases as one of their putative targets, with 1a showing a submicromolar inhibition of Trichoderma viride chitinase. In this work, we investigated the possibility to further inhibit the corresponding human enzymes, acidic mammalian chitinase (AMCase) and chitotriosidase (CHIT1), involved in several chronic inflammatory lung diseases. Thus, we first validated the inhibitory activity of 1a against AMCase and CHIT1 and then designed and synthesized new derivatives aimed at improving the potency and selectivity against AMCase. Among them, compound 3f emerged for its activity profile along with its promising in vitro ADME properties. We also gained a good understanding of the key interactions with the target enzyme through in silico studies.

Chitinases and Chitinase-Like Proteins as Therapeutic Targets in Inflammatory Diseases, with a Special Focus on Inflammatory Bowel Diseases

Chitinases belong to the evolutionarily conserved glycosyl hydrolase family 18 (GH18). They catalyze degradation of chitin to N-acetylglucosamine by hydrolysis of the β-(1-4)-glycosidic bonds. Although mammals do not synthesize chitin, they possess two enzymatically active chitinases, i.e., chitotriosidase (CHIT1) and acidic mammalian chitinase (AMCase), as well as several chitinase-like proteins (YKL-40, YKL-39, oviductin, and stabilin-interacting protein). The latter lack enzymatic activity but still display oligosaccharides-binding ability. The physiologic functions of chitinases are still unclear, but they have been shown to be involved in the pathogenesis of various human fibrotic and inflammatory disorders, particularly those of the lung (idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease, sarcoidosis, and asthma) and the gastrointestinal tract (inflammatory bowel diseases (IBDs) and colon cancer). In this review, we summarize the current knowledge about chitinases, particularly in IBDs, and demonstrate that chitinases can serve as prognostic biomarkers of disease progression. Moreover, we suggest that the inhibition of chitinase activity may be considered as a novel therapeutic strategy for the treatment of IBDs.

Discovery of , a First-in-Class Chitinase Inhibitor as Potential New Therapeutics for Idiopathic Pulmonary Fibrosis

Chitotriosidase (CHIT1) and acidic mammalian chitinase (AMCase) are the enzymatically active chitinases that have been implicated in the pathology of chronic lung diseases such as asthma and interstitial lung diseases (ILDs), including idiopathic pulmonary fibrosis (IPF) and sarcoidosis. The clinical and preclinical data suggest that pharmacological inhibition of CHIT1 might represent a novel therapeutic approach in IPF. Structural modification of an advanced lead molecule 3 led to the identification of compound 9 (OATD-01), a highly active CHIT1 inhibitor with both an excellent PK profile in multiple species and selectivity against a panel of other off-targets. OATD-01 given orally once daily in a range of doses between 30 and 100 mg/kg showed significant antifibrotic efficacy in an animal model of bleomycin-induced pulmonary fibrosis. OATD-01 is the first-in-class CHIT1 inhibitor, currently completed phase 1b of clinical trials, to be a potential treatment for IPF.

De novo transcriptome of the whole-body of the gastropod mollusk Philomycus bilineatus, a pest with medical potential in China

Philomycus bilineatus is a highly common gastropod mollusk pest in China and is also utilized to treat infectious diseases. However, no genomic resources are available for this non-model species. In the present study, the transcriptomic analysis of P. bilineatus was completed. After sequencing using the next generation sequencing technology, 9.11 Gb of clean reads were obtained, which led to the assembly and annotation of 145,523 transcripts and 125,690 unigenes. Unigenes were functionally classified using Gene Ontology (GO), euKaryotic Ortholog Groups of proteins (KOG), and Kyoto Encyclopedia of Genes and Genomes (KEGG). A total of 27,554 unigenes were assigned into 55 GO terms, 13,989 unigenes were differentiated into 26 KOG categories, and 16,368 unigenes were assigned to 229 KEGG pathways. Furthermore, 16,614 simple sequence repeats (SSRs), 38 olfactory genes, and 40 antimicrobial peptide/protein genes were identified. The transcriptome profile of P. bilineatus will provide a valuable genomic resource for further study, will promote the development of new pest management strategies through interference of chemosensory communication, and will support potential medicinal uses of this species.

Benzoxazepine-Derived Selective, Orally Bioavailable Inhibitor of Human Acidic Mammalian Chitinase

Human acidic mammalian chitinase (hAMCase) is one of two true chitinases in humans, the function of which remains elusive. In addition to the defense against highly antigenic chitin and chitin-containing pathogens in the gastric and intestinal contents, AMCase has been implicated in asthma, allergic inflammation, and ocular pathologies. Potent and selective small-molecule inhibitors of this enzyme have not been identified to date. Here we describe structural modifications of compound OAT-177, a previously developed inhibitor of mouse AMCase, leading to OAT-1441, which displays high activity and selectivity toward hAMCase. Significantly reduced off-target activity toward the human ether-à-go-go-related gene (hERG) and a good pharmacokinetic profile make OAT-1441 a potential candidate for further preclinical development as well as a useful tool compound to study the physiological role of hAMCase.

A Series of Compounds Bearing a Dipyrido-Pyrimidine Scaffold Acting as Novel Human and Insect Pest Chitinase Inhibitors

Chitinases not only play vital roles in the human innate immune system but are also essential for the development of pathogenic fungi and pests. Chitinase inhibitors are efficient tools to investigate the elusive role of human chitinases and to control pathogens and pests. Via hierarchical virtual screening, we have discovered a series of chitinase inhibitors with a novel scaffold that have high inhibitory activities and selectivities against human and insect chitinases. The most potent human chitotriosidase inhibitor, compound 40, exhibited a K_i of 49 nM, and the most potent inhibitor of the insect pest chitinase OfChi-h, compound 53, exhibited a K_i of 9 nM. The binding of these two most potent inhibitors was confirmed by X-ray crystallography. In a murine model of bleomycin-induced pulmonary fibrosis, compound 40 was found to suppress the chitotriosidase activity by 60%, leading to a significant increase in inflammatory cells and suggesting that chitotriosidase played a protective role.

Progress and prospects of arthropod chitin pathways and structures as targets for pest management

Chitin is a structural component of the arthropod cuticular exoskeleton and the peritrophic matrix of the gut, which play crucial roles in growth and development. In the past few decades, our understanding of the composition, biosynthesis, assembly, degradation, and regulation of chitinous structures has increased. Many chemicals have been developed that target chitin biosynthesis (benzoyphenyl ureas, etoxazole), chitin degradation (allosamidin, psammaplin), and chitin regulation (benzoyl hydrazines), thus resulting in molting deformities and lethality. In addition, proteins that disrupt chitin structures, such as lectins, proteases, and chitinases have been utilized to halt feeding and induce mortality. Chitin-degrading enzymes, such as chitinases are also useful for improving the efficacy of bio-insecticides. Transgenic plants, baculoviruses, fungi, and bacteria have been engineered to express chitinases from a variety of organisms for control of arthropod pests. In addition, RNA interference targeting genes involved in chitin pathways and structures are now being investigated for the development of environmentally friendly pest management strategies. This review describes the chemicals and proteins used to target chitin structures and enzymes for arthropod pest management, as well as pest management strategies based upon these compounds, such as plant-incorporated-protectants and recombinant entomopathogens. Recent advances in RNA interference-based pest management, and how this technology can be used to target chitin pathways and structures are also discussed.

The functional difference of eight chitinase genes between male and female of the cotton mealybug, Phenacoccus solenopsis

The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) is a polyphagous insect that attacks tens of plant and causes substantial economic loss. Insect chitinases are required to remove the old cuticle to allow for continued growth and development. Though insect chitinases have been well studied in tens of insects, their functions in mealybug are still not addressed. Here, we sequenced the transcriptomes of adult males and females, from which eight chitinase genes were identified. We then used the method of rapid amplification of cDNA ends to amplify their full length. Phylogenetic analysis indicated that these genes clustered into five subgroups. Among which, group II PsCht2 had the longest transcript and was highly expressed at second instar nymph. PsCht10, PsCht3-3 and PsIDGF were highly expressed in the adult females, whereas PsCht4 and PsCht4-1 were significantly expressed at the male pupa and adult male. Next, we knocked down all eight chitinase genes by feeding the double-stranded RNA. Knockdown of PsCht4 or PsCht4-1 led to the failure of moult and, silencing PsCht5 resulted in pupation defect, while silencing PsCht10 led to small body size, suggesting these genes have essential roles in development and can be used as a potential target for pest control.

Guanidinylation of Chitooligosaccharides Involving Internal Cyclization of the Guanidino Group on the Reducing End and Effect of Guanidinylation on Protein Binding Ability

In order to synthesize a promising material for developing a novel peptide/protein delivery system, guanidinylation of chitooligosaccharides with 1-amidinopyrazole hydrochloride was investigated herein. The production of guanidinylated chitooligosaccharides was demonstrated by infrared spectroscopy (IR), nuclear magnetic resonance (NMR), and elemental analyses. Interestingly, we found that the reducing end in the guanidinylated chitooligosaccharides was converted to a cyclic guanidine structure (2-[(aminoiminomethyl)amino]-2-deoxy-d-glucose structure). This reaction was carefully proven by the guanidinylation of d-glucosamine. Although this is not the first report on the synthesis of the 2-[(aminoiminomethyl)amino]-2-deoxy-d-glucose, it has provided a rational synthetic route using the high reactivity of the reducing end. Furthermore, we found that the interaction between chitooligosaccharides and bovine serum albumin is weak when in a neutral pH environment; however, it is significantly improved by guanidinylation. The guanidinylated chitooligosaccharides are useful not only for the development of a novel drug delivery system but also as a chitinase/chitosanase inhibitor and an antibacterial agent.

Target identification and intervention strategies against amebiasis

Entamoeba histolytica is the etiological agent of amebiasis, which is an endemic parasitic disease in developing countries and is the cause of approximately 70,000 deaths annually. E. histolytica trophozoites usually reside in the colon as a non-pathogenic commensal in most infected individuals (90% of infected individuals are asymptomatic). For unknown reasons, these trophozoites can become virulent and invasive, cause amebic dysentery, and migrate to the liver where they cause hepatocellular damage. Amebiasis is usually treated either by amebicides which are classified as (a) luminal and are active against the luminal forms of the parasite, (b) tissue and are effective against those parasites that have invaded tissues, and (c) mixed and are effective against the luminal forms of the parasite and those forms which invaded the host's tissues. Of the amebicides, the luminal amebicide, metronidazole (MTZ), is the most widely used drug to treat amebiasis. Although well tolerated, concerns about its adverse effects and the possible emergence of MTZ-resistant strains of E. histolytica have led to the development of new therapeutic strategies against amebiasis. These strategies include improving the potency of existing amebicides, discovering new uses for approved drugs (repurposing of existing drugs), drug rediscovery, vaccination, drug targeting of essential E. histolytica components, and the use of probiotics and bioactive natural products. This review examines each of these strategies in the light of the current knowledge on the gut microbiota of patients with amebiasis.

Structural dissection reveals a general mechanistic principle for group II chitinase (ChtII) inhibition

Small-molecule inhibitors of insect chitinases have potential applications for controlling insect pests. Insect group II chitinase (ChtII) is the most important chitinase in insects and functions throughout all developmental stages. However, the possibility of inhibiting ChtII by small molecules has not been explored yet. Here, we report the structural characteristics of four molecules that exhibited similar levels of inhibitory activity against OfChtII, a group II chitinase from the agricultural pest Asian corn borer Ostrinia furnacalis These inhibitors were chitooctaose ((GlcN)₈), dipyrido-pyrimidine derivative (DP), piperidine-thienopyridine derivative (PT), and naphthalimide derivative (NI). The crystal structures of the OfChtII catalytic domain complexed with each of the four inhibitors at 1.4-2.0 Å resolutions suggested they all exhibit similar binding modes within the substrate-binding cleft; specifically, two hydrophobic groups of the inhibitor interact with +1/+2 tryptophan and a -1 hydrophobic pocket. The structure of the (GlcN)₈ complex surprisingly revealed that the oligosaccharide chain of the inhibitor is orientated in the opposite direction to that previously observed in complexes with other chitinases. Injection of the inhibitors into 4th instar O. furnacalis larvae led to defects in development and pupation. The results of this study provide insights into a general mechanistic principle that confers inhibitory activity against ChtII, which could facilitate rational design of agrochemicals that target ecdysis of insect pests.

Functional analysis of eight chitinase genes in rice stem borer and their potential application in pest control

Insect chitinases participate in numerous physiological processes such as nutrition, parasitism, morphogenesis and immunity. These properties make chitinases good targets for pest control. Rice striped stem borer (SSB), Chilo suppressalis Walker, is one of the most destructive pests of rice causing huge yield losses. In our previous work, we reported the identification of 12 SSB chitinase (CsCht) genes, and studied the functions of CsCht1 to 4. Here, we have extended our study to investigate the expression patterns and functions of CsCht5 to 12. All eight chitinase genes displayed distinct temporospatial expression profiles. We looked at the effect of knocking down each gene at the developmental stage where highest expression was observed. Knocking down CsCht5, CsCht6 and CsCht8 resulted in high mortality and delayed development. Although silencing CsCht7, CsCht9, CsCht10, CsCht11 and CsCht12 had no apparent effect on development, knocking down CsCht10 in SSB individuals that were simultaneously treated with Beauveria bassiana (Bb84) led to higher mortality rates and quicker death, suggesting CsCht10 has an essential role in protecting SSB from exogenous microorganisms. In summary, we elucidated the functions of eight SSB chitinase genes and found that CsCht10 could be a good candidate for pest control.

Marine chitinolytic enzymes, a biotechnological treasure hidden in the ocean?

Chitinolytic enzymes are capable to catalyze the chitin hydrolysis. Due to their biomedical and biotechnological applications, nowadays chitinolytic enzymes have attracted worldwide attention. Chitinolytic enzymes have provided numerous useful materials in many different industries, such as food, pharmaceutical, cosmetic, or biomedical industry. Marine enzymes are commonly employed in industry because they display better operational properties than animal, plant, or bacterial homologs. In this mini-review, we want to describe marine chitinolytic enzymes as versatile enzymes in different biotechnological fields. In this regard, interesting comments about their biological role, reaction mechanism, production, functional characterization, immobilization, and biotechnological application are shown in this work.

Targeting Acidic Mammalian chitinase Is Effective in Animal Model of Asthma

This article highlights our work toward the identification of a potent, selective, and efficacious acidic mammalian chitinase (AMCase) inhibitor. Rational design, guided by X-ray analysis of several inhibitors bound to human chitotriosidase (hCHIT1), led to the identification of compound 7f as a highly potent AMCase inhibitor (IC₅₀ values of 14 and 19 nM against human and mouse enzyme, respectively) and selective (>150× against mCHIT1) with very good PK properties. This compound dosed once daily at 30 mg/kg po showed significant anti-inflammatory efficacy in HDM-induced allergic airway inflammation in mice, reducing inflammatory cell influx in the BALF and total IgE concentration in plasma, which correlated with decrease of chitinolytic activity. Therapeutic efficacy of compound 7f in the clinically relevant aeroallergen-induced acute asthma model in mice provides a rationale for developing AMCase inhibitor for the treatment of asthma.

Discovery of selective, orally bioavailable inhibitor of mouse chitotriosidase

This article describes our work towards the identification of a potent and selective inhibitor of mouse chitotriosidase (mCHIT1). A series of small molecule inhibitors of mCHIT1 and mAMCase have been developed from early lead compound 1. Examination of synthetized analogues led to discovery of several novel highly potent compounds. Among them compound 9 (OAT-2068) displays a remarkable 143-fold mCHIT1 vs. mAMCase selectivity. To explain the observed SAR molecular docking experiments were performed, which were in line with the experimental data from the enzymatic assays. Inhibitor 9 (OAT-2068) was found to have an excellent pharmacokinetic profile. This, together with high activity and selectivity, makes the compound an ideal and unique tool for studying the role of CHIT1 in biological models.

Genome-wide analysis of chitinase genes and their varied functions in larval moult, pupation and eclosion in the rice striped stem borer, Chilo suppressalis

Some insect chitinases are required to degrade chitin and ensure successful metamorphosis. Although chitinase genes have been well characterized in several model insects, no reports exist for the rice striped stem borer, Chilo suppressalis, a highly destructive pest that causes huge yield losses in rice production. Here, we conducted a genome-level analysis of chitinase genes in C. suppressalis. After amplification of full-length transcripts with rapid amplification of cDNA ends, we identified 12 chitinase genes in C. suppressalis. All these genes had the conserved domains and motifs of glycoside hydrolase family 18 and grouped phylogenetically into five subgroups. C. suppressalis chitinase 1 (CsCht1) was highly expressed in late pupae, whereas CsCht3 was abundant in early pupae. Both CsCht2 and CsCht4 were highly expressed in larvae. CsCht2 was abundant specifically in the third-instar larvae and CsCht4 showed periodic high expression in 2- to 5-day-old larvae in each instar. Tissue specific expression analysis indicated that CsCht1 and CsCht3 were highly expressed in epidermis whereas CsCht2 and CsCht4 were specifically abundant in the midgut. Knockdown of CsCht1 resulted in adults with curled wings, indicating that CsCht1 might have an important role in wing expansion. Silencing of CsCht2 or CsCht4 arrested moulting, suggesting essential roles in larval development. When the expression of CsCht3 was interfered, defects in pupation occurred. Overall, we provide here the first catalogue of chitinase genes in the rice striped stem borer and have elucidated the functions of four chitinases in metamorphosis.

[Study on the discovery of novel chitinase inhibitors based on natural products]

Chitin, the second most abundant polysaccharide in nature, is a constituent of fungal cell walls, the exoskeletons of crustaceans and insects and the microfilarial sheaths of parasitic nematodes. Chitin has, so far, not been found in mammals. Accumulation of chitin by organisms is modulated by chitin synthase-mediated biosynthesis and by chitinase-mediated hydrolytic degradation. Thus, chitinases are expected to be specific targets for antifungal, insecticidal and antiparasitic agents. Paradoxically, while chitin does not exist in mammals, human chitinase family members, such as acidic mammalian chitinase, have recently been described, and offer significant potential for the treatment of asthma and other related diseases in humans. This review covers the development of two chitinase inhibitors of natural origin, Argifin and Argadin, isolated from the cultured broth of microorganisms in our laboratory. In particular, the practical total synthesis of these natural products and discovery methods that generate only highly-active compounds using a kinetic target (chitinase)-guided synthesis approach (termed in situ click chemistry) are described.

Identification and characterization of a novel chitinase-like gene cluster (AgCht5) possibly derived from tandem duplications in the African malaria mosquito, Anopheles gambiae

Insect chitinase 5 (Cht5), a well-characterized enzyme found in the molting fluid and/or integument, is classified as a group I chitinase and is usually encoded by a single gene. In this study, a Cht5 gene cluster consisting of five different chitinase-like genes (AgCht5-1, AgCht5-2, AgCht5-3, AgCht5-4 and AgCht5-5) was identified by a bioinformatics search of the genome of Anopheles gambiae. The gene models were confirmed by cloning and sequencing of the corresponding cDNAs and gene expression profiles during insect development were determined. All of these genes are found in a single cluster on chromosome 2R. Their open reading frames (ORF) range from 1227 to 1713 bp capable of encoding putative proteins ranging in size from 409 to 571 amino acids. The identities of their cDNA sequences range from 52 to 66%, and the identities of their deduced amino acid sequences range from 38 to 53%. There are four introns for AgCht5-1, two for AgCht5-2 and AgCht5-3, only one for AgCht5-4, but none for AgCht5-5 in the genome. All five chitinase-like proteins possess a catalytic domain with all of the conserved sequence motifs, but only AgCht5-1 has a chitin-binding domain. Phylogenetic analysis of these deduced proteins along with those from other insect species suggests that AgCht5-1 is orthologous to the Cht5 proteins identified in other insect species. The differences in expression patterns of these genes at different developmental stages further support that these genes may have distinct functions. Additional searching of the genomes of two other mosquito species led to the discovery of four Cht5-like genes in Aedes aegypti and three in Culex quinquefasciatus. Thus, the presence of a Cht5 gene cluster appears to be unique to mosquito species and these genes may have resulted from gene tandem duplications.

Potent family-18 chitinase inhibitors: x-ray structures, affinities, and binding mechanisms

Six novel inhibitors of Vibrio harveyi chitinase A (VhChiA), a family-18 chitinase homolog, were identified by in vitro screening of a library of pharmacologically active compounds. Unlike the previously identified inhibitors that mimicked the reaction intermediates, crystallographic evidence from 14 VhChiA-inhibitor complexes showed that all of the inhibitor molecules occupied the outer part of the substrate-binding cleft at two hydrophobic areas. The interactions at the aglycone location are well defined and tightly associated with Trp-397 and Trp-275, whereas the interactions at the glycone location are patchy, indicating lower affinity and a loose interaction with two consensus residues, Trp-168 and Val-205. When Trp-275 was substituted with glycine (W275G), the binding affinity toward all of the inhibitors dramatically decreased, and in most structures two inhibitor molecules were found to stack against Trp-397 at the aglycone site. Such results indicate that hydrophobic interactions are important for binding of the newly identified inhibitors by the chitinase. X-ray data and isothermal microcalorimetry showed that the inhibitors occupied the active site of VhChiA in three different binding modes, including single-site binding, independent two-site binding, and sequential two-site binding. The inhibitory effect of dequalinium in the low nanomolar range makes this compound an extremely attractive lead compound for plausible development of therapeutics against human diseases involving chitinase-mediated pathologies.