Immobilized enzyme reactors in HPLC and its application in inhibitor screening:A review

This paper sets out to summarize the literatures based on immobilized enzyme bio-chromatography and its application in inhibitors screening in the last decade.In order to screen enzyme inhibitors from a mass of compounds in preliminary screening,multi-pore materials with good biocompatibility are used for the supports of immobilizing enzymes,and then the immobilized enzyme reactor applied as the immobilized enzyme stationary phase in HPLC.Therefore,a technology platform of high throughput screening is gradually established to screen the enzyme inhibitors as new anti-tumor drugs.Here,we briefly summarize the selective methods of supports,immobilization techniques,co-immobilized enzymes system and the screening model.

Colorimetric detection of α-glucosidase activity using Ni-CeO_(2)nanorods and its application to potential natural inhibitor screening

In this work,we established an exceptionally facile method for the preparation of Ni-CeO_(2)nanorods in a kind of deep eutectic solvents(DESs)composed of l-proline and Ce(NO_(3))_(3)·6H_(2)O.First,Ni-CeO_(2)nanorods were successfully prepared by adding Ni(NO_(3))_(3)·6H_(2)O to DESs.Then,we found that Ni-CeO_(2)nanorods prepared in DESs have more prominent oxidase-like activity than pure CeO_(2).The outstanding catalytic activity of Ni-CeO_(2)could be ascribed to its high Ce^(3+)/Ce^(4+)ratio.As a proof-of-concept application,the Ni-CeO_(2)nanorods were successfully acted as a colorimetric platform for the sensitive determination of ascorbic acid andα-glucosidase activity,which displays excellent analytical performance.Moreover,this sensing platform was applied for screening naturalα-glucosidase inhibitors,such as terpenoids from natural products.The results indicated that ursolic acid and oleanolic acid had good inhibitory rates.This strategy not only provides a new way to construct more kinds of nanomaterials from DESs,but also offers a facile and effective tool to screen theα-glucosidase natural inhibitors as potential anti-diabetic drugs.

Recent advances in screening of enzymes inhibitors based on capillary electrophoresis

Capillary electrophoresis with many advantages plays an important role in pharmaceutical analysis and drug screening. This review gives an overview on the recent advances in the developments and applications of capillary electrophoresis in the field of enzyme inhibitor screening. The period covers 2013 to 2017. Both the pre-capillary enzyme assays and in-capillary enzyme assays which include electrophoretically mediated microanalysis（EMMA） and immobilized enzyme microreactor（IMER） are summarized in this article.

A colorimetric method for α-glucosidase activity assay and its inhibitor screening based on aggregation of gold nanoparticles induced by specific recognition between phenylenediboronic acid and 4-aminophenyl-α-D- glucopyranoside

A colorimetric method has been established for a-glucosidase activity assay and its inhibitor screening. The method is based on the specific recognition between 1,4-phenylenediboronic acid （PDBA） and 4-aminophenyl-a-D-glucopyranoside （pAPG）, which may induce aggregation of pAPG-functionalized gold nano- particles （AuNPs） to achieve color change of the test solution. Because pAPG is the substrate of α-glucosidase, the aggregation of AuNPs will be influenced by α-glucosidase since there is no coordination reactivity between PDBA and 4-aminobenzene, the hydrolyzed product of pAPG catalyzed by the enzyme. Therefore, a simple and easily-operated colorimetric method for the assay of a-glucosidase activity can be developed. Under the optimized experimental conditions, the ratios of absorbance at a wavelength of 650 nm to that at 520 nm vary linearly with the α-glucosidase activity within a range from 0.05 to 1.1 U/mL with a lowest detection limit of 0.004 U/mL. Moreover, using the proposed method, the inhibition effect of gallic acid and quercetin on a-glucosidase activity can be tested with IC50 values of 1.16 mM and 1.82 μM, respectively. Thus, the method has a great potential not only for the detection of a-glucosidase activity, but also for the screening of its inhibitors.

Preparation of Magnetic Microsphere-Gold Nanoparticle- Immobilized Enzyme Batch Reactor and Its Application to Enzyme Inhibitor Screening in Natural Extracts by Capillary Electrophoresis

A novel strategy for screening the enzyme inhibitors from the natural products by capillary electrophoresis （CE） with a pre column enzyme batch reactor prepared by magnetic microsphere （MB）-gold nanoparticles （AuNPs） is reported. The enzyme batch reactor was prepared by immobilizing the enzymes on the MB conjugated AuNPs （MB-AuNPs）. To demonstrate this strategy, xanthine oxidase （XOD） was employed as a model for the activity of the enzyme, inhibition study, and inhibitor screening. With the developed CE method, the enzyme activity was de- termined by the quantification of the peak area of the product. Enzyme inhibition can be read out directly from the reduced peak area of product in comparison to a reference electropherogram obtained in the absence of any inhibitor A statistical parameter Z＇ factor was recommended for evaluation of the accuracy of a drug screening system. In the present study, it was calculated to be 0.7, implying a good accuracy. The screening of two natural extracts from Cortex Phellodendri and Rhizoma Galangae showed that they were positive for XOD inhibition by the present method. Using this immobilized enzyme technology combined with CE separation not only provides the advantages such as convenience, rapidity and low cost, but also provides a new platform for discovering enzyme-inhibitor drug lead compounds.

Strategies for Antiviral Screening Targeting Early Steps of Virus Infection

Viral infection begins with the entry of the virus into the host target cell and initiates replication. For this reason, the virus entry machinery is an excellent target for antiviral therapeutics. In general, a virus life cycle includes several major steps: cell-surface attachment, entry, replication, assembly, and egress, while some viruses involve another stage called latency. The early steps of the virus life cycle include virus attachment, receptor binding, and entry. These steps involve the initial interactions between a virus and the host cell and thus are major determinants of the tropism of the virus infection, the nature of the virus replication, and the diseases resulting from the infection. Owing to the pathological importance of these early steps in the progress of viral infectious diseases, the development of inhibitors against these steps has been the focus of the pharmaceutical industry. In this review, Herpes Simplex Virus (HSV), Hepatitis C Virus (HCV), and Human Enterovirus 71 (EV71) were used as representatives of enveloped DNA, enveloped RNA, and non-enveloped viruses, respectively. The current mechanistic understanding of their attachment and entry, and the strategies for antagonist screenings are summarized herein.

High-throughput fluorescent screening of thioredoxin reductase inhibitors to inhibit Mycobacterium tuberculosis

Tuberculosis(TB)is a chronic infectious disease,which is caused by the pathogen Mycobacterium tuberculosis(Mtb)and reemerged as a global health risk with a significant proportion of multi-drug resistant and extensively drug resistant TB cases.It is very urgent to find some novel high-confidence drug targets in Mtb for discovering the effective anti-TB agents.Thioredoxin reductase(TrxR)has been identified to be a highly viable target for anti-TB drugs for its important role in protecting the pathogen from thiol-specific oxidizing stress,regulating intracellular dithiol/disulfide homeostasis and DNA replication and repair.In the present work,a near-infrared(NIR)fluorescent probe DDAT was developed for the detection of TrxR activity and used to high-throughput screen the TrxR inhibitors from natural products.Two screened TrxR inhibitors from Sappan Lignum and microbial metabolites that were further used to inhibit Mycobacterium tuberculosis.All the results indicate that DDAT is a practical fluorescent molecular tool for the discovery of potential anti-TB drugs.

Screening potential P-glycoprotein inhibitors by combination of a detergent-free membrane protein extraction with surface plasmon resonance biosensor

P-glycoprotein(P-gp)highly expressed in cancer cells can lead to multidrug resistance(MDR)and the combination of anti-cancer drugs with P-gp inhibitor has been a promising strategy to reverse MDR in cancer treatment.In this study,we established a label-free and detergent-free system combining surface plasmon resonance(SPR)biosensor with styrene maleic acid(SMA)polymer membrane proteins(MPs)stabilization technology to screen potential P-gp inhibitors.First,P-gp was extracted from MCF-7/ADR cells using SMA polymer to form SMA liposomes(SMALPs).Following that,SMALPs were immobilized on an SPR biosensor chip to establish a P-gp inhibitor screening system,and the affinity between P-gp and small molecule ligand was determined.The methodological investigation proved that the screening system had good specificity and stability.Nine P-gp ligands were screened out from 50 natural products,and their affinity constants with P-gp were also determined.The in vitro cell verification experiments demonstrated that tetrandrine,fangchinoline,praeruptorin B,neobaicalein,and icariin could significantly increase the sensitivity of MCF-7/ADR cells to Adriamycin(Adr).Moreover,tetrandrine,praeruptorin B,and neobaicalein could reverse MDR in MCF-7/ADR cells by inhibiting the function of P-gp.This is the first time that SMALPs-based stabilization strategy was applied to SPR analysis system.SMA polymer can retain P-gp in the environment of natural lipid bilayer and thus maintain the correct conformation and physiological functions of P-gp.The developed system can quickly and accurately screen small molecule ligands of complex MPs and obtain affinity between complex MPs and small molecule ligands without protein purification.

Paper-based fluorescent devices for multifunctional assays:Biomarkers detection,inhibitors screening and chiral recognition

The development of a single analytical platform with different functions is highly desirable but remains a challenge at present.Here,a paper-based device based on fluorescent carbon dots(CDs)functionalized paper/MnO_(2)nanosheets(MnO_(2)NS)hybrid devices(PCD/NS)was proposed for single-device multi-function applications.MnO_(2)NS functioned as a fluorescence quencher of CDs and recognizer of H_(2)O_(2)released from the oxidase catalyzed system.Fluorescence recovery would occur after the decomposition of MnO_(2)NS induced by H_(2)O_(2),by which a simple and effective strategy could be developed for fluorescence monitoring multiplex biological events.Xanthine(XA)sensing,xanthine oxidase(XOD)inhibitors screening analysis and chiral recognition of glucose enantiomers were performed on PCD/NS to investigate the multifunctional application of the paper-based device.By means of PCD/NS,XA could be determined in the range of 0.1–40μmol/L with a low detection of limit of 0.06μmol/L.The IC_(50)value of allopurinol,the model inhibitor of XOD,was sensitively detected to be 7.4μmol/L.Glucose enantiomers were also recognized in terms of the specific fluorescence response to d-glucose.This work firstly presented a paper-based device capable of biomarkers detection,inhibitors screening and chiral recognition,which enlightened a promising strategy for the construction of multifunctional devices and hold the great potential application in clinical diagnosis and drug discovery.

Rapid screening of SARS-CoV-2 inhibitors via ratiometric fluorescence of RBD–ACE2 complexes in living cells by competitive binding

To the Editor:The current coronavirus disease-19(COVID-19)pandemic spurs the development of antiviral drugs for SARS-CoV-2,as the number of patients with viral infections continues to rise globally in the context of widespread vaccination.Targeting the interaction between the receptor binding domain(RBD)of SARS-CoV-2 spike protein and the host cell ACE2 is a promising therapeutic strategy to effectively inhibit viral entry.

A High-Affinity Methyl-CpG-Binding Protein for Endonuclease-Free and Label-Free DNA Methyltransferase Activity Detection

DNA methyltransferase(MTase)activity detection has received increasing attention as a promising biomarker and therapeutic target.However,most of these detection methods rely on endonuclease digestion and signal groups labeling.Herein,we present a novel platform for sensing DNA MTase activity that overcomes these limitations.Our approach is both endonuclease-free and label-free,utilizing a combination of a high-affinity streptavidin-methyl-CpG-binding domain(SA-MBD)protein and surface plasmon resonance(SPR)technology.The SA-MBD protein specifically recognizes a hairpin probe containing methylated CpG sites,which is treated with M.SssI MTase.This recognition event generates a corresponding SPR response signal.The limit of detection is as low as 0.016 U/mL,owing to the high-affinity of the SA-MBD protein.Notably,we have demonstrated the feasibility of our method for M.SssI MTase activity analysis in serum and inhibitor screening,which implies the potential prospects for biomedical research.

Sphingomyelin synthase activity measurement by the fluorescent product in cell culture medium or animal plasma

Sphingolipids, a new class of lipid mediators, are involved in a variety of important physiological and pathological processes. Sphingomyelin synthase （SMS） is an enzyme to convert the ceramide （Cer.） and phosphatidylcholine into sphingomyelin （SM） and diacylglycerol, which plays a key role in sphingolipid biosynthesis. Two SMS isoforms, SMS1 and SMS2, have been identified with different subceUular localizations and expression level in tissues. Previous studies have shown that SMS may serve as a potential therapeutic target for the treatment of various diseases, such as cardiovascular and metabolic diseases. Thus, there is an urgent need for a rapid and sensitive method for SMS activity analysis. In our study, we developed a novel method for SMS activity by monitoring the appearance of the product, NBD-SM, in the tissue culture medium or blood and applied this method in cells and mice. In Huh7 cells, the interassay coefficient of variation of the SMS activity assay was （3.60±0.07）% . In wild type （WT） mice, we observed accumulation of NBD-SM in blood in a time dependent fashion. In SMS2 KO mice, NBD-SM in plasma collected at 5- （0%, P〈0.01）, 30- （16%, P〈0.01）, and 60 min （21%, P〈0.01） after injection of fluorescence liposome solution was significantly decreased compared with WT mice. However, in SMS1 KO mice, NBD-SM in plasma collected 5- and 30 min is similar to that in WT mice. Our results suggest that this method could be used for SMS activity measurement in vitro and in vivo.

Expression, purification and activity assay of recombinant human thymidylate synthase

Thymidylate synthase （TS, E.C.2.1.1.45） catalyzes a critical reaction in the only pathway of de novo synthesis of thymidylate （dTMP） in human cells, and is an important target of chemotherapy. To evaluate the inhibitory activities of novel compounds to TS, a convenient method of activity assay using 6x His-tagged recombinant human TS （rhTS） was established and 49 novel synthetic folate analogues were screened to discover potential TS inhibitors. During the process, 4 novel compounds were found to effectively inhibit TS, while the IC 50 of a positive control raltitrexed was 3.4 μM in this assay.