Policresulen, a novel NS2B/NS3 protease inhibitor, effectively inhibits the replication of DENV2 virus in BHK-21 cells.

AIM: Dengue is a severe epidemic disease caused by dengue virus (DENV) infection, for which no effective treatment is available. The protease complex, consisting of nonstructural protein 3 (NS3) and its cofactor NS2B, plays a pivotal role in the replication of DENV, thus may be a potential target for anti-DENV drugs. Here, we report a novel inhibitor of DENV2 NS2B/NS3 protease and its antiviral action. METHODS: An enzymatic inhibition assay was used for screening DENV2 NS2B/NS3 inhibitors. Cytotoxicity to BHK-21 cells was assessed with MTT assay. Antiviral activity was evaluated in BHK-21 cells transfected with Rlu-DENV-Rep. The molecular mechanisms of the antiviral action was analyzed using surface plasmon resonance, ultraviolet-visible spectral analysis and differential scanning calorimetry assays, as well as molecular docking analysis combined with site-directed mutagenesis. RESULTS: In our in-house library of old drugs (~1000 compounds), a topical hemostatic and antiseptic 2-hydroxy-3,5-bis[(4-hydroxy-2-methyl-5-sulfophenyl)methyl]-4-methyl-benzene-sulfonic acid (policresulen) was found to be a potent inhibitor of DENV2 NS2B/NS3 protease with IC50 of 0.48 µg/mL. Furthermore, policresulen inhibited DENV2 replication in BHK-21 cells with IC50 of 4.99 µg/mL, whereas its IC50 for cytotoxicity to BHK-21 cells was 459.45 µg/mL. Policresulen acted as a competitive inhibitor of the protease, and slightly affected the protease stability. Using biophysical technology-based assays and molecular docking analysis combined with site-directed mutagenesis, we demonstrated that the residues Gln106 and Arg133 of DENV2 NS2B/NS3 protease directly interacted with policresulen via hydrogen bonding. CONCLUSION: Policresulen is a potent inhibitor of DENV2 NS2B/NS3 protease that inhibits DENV2 replication in BHK-21 cells. The binding mode of the protease and policresulen provides useful hints for designing new type of inhibitors against the protease.

[Study on Paddy Soil Chronosequences Based on Visiblc-Near Infrared Diffuse Reflectance Spectra].

To investigate spectral characteristics of different soil compositions, eight soil profiles from two paddy soil chronosequences developed on red clays and red sandstones respectively were collected in Jiangxi Province. A total of 37 soil samples were taken from each soil horizons of the profiles. The paddy soil chronosequences were chosen mainly because all soil profiles have the same land management and thus parent materials and rice cultivation time would be two major soil formative factors. This makes it possible to study spectral response characteristics of soil organic matter (SOM) and parent material characteristics. We measured diffuse reflectance spectra data of soil samples using the Cary 5000 spectrophotometer at 350-2500 nm spectral range. Spectral response characteristics of SOM and inorganic minerals in paddy soils were analyzed according to different soil horizons, soil forming times and parent materials. Experiment results showed that for soil samples from a single parent material, overall reflectance presented by PC_1 score can be calibrated for soil organic matter (SOM) content with high precision (R(RC)² = 0.91, R(RS)² = 0.79), even though the SOM content was low (not more than 20 g · kg⁻¹). The absorption strength (AS) at 1400, 1900 and 2200 nm was mainly affected by the minerals inherited from parent materials. And the more the sample was near to bottom of a soil profile, the higher the AS value. Samples with the same mineral components had the similar AS ratio among these three wavelength locations. The differences in parent materials can significantly affect spectral curve shape and spectral absorption strength. To make the calibration more interpretative, parent material factors should be considered.

[Study on the prediction of soil heavy metal elements content based on mid-infrared diffuse reflectance spectra].

The present paper analyzed the possibility of mid-infrared diffuse reflectance spectra for quick assessment of heavy metal element content in soil quickly. Soil samples were collected from Jiangning District and Baguazhou Island, and the numbers of sample were 103 and 58 separately. Jiangning District samples were used as calibration set while Baguazhou Island samples as validation set. To assess the utility of different pre-treatment process of MIR spectroscopy for soil heavy metal element content analysis, we used PLSR method to develop the calibration between spectral data and soil elements content. Three spectral pretreating techniques such as smooth, log(1/N), baseline correction, multiplicative scatter correction were used for promotion of predicting performance. The result showed that the progress of (log-BC-MSC) in turn achieved optimal calibration of MIR spectra and better prediction for ex-situ soils. Though the calibration data were treated by different pre-treating schema, the R2 of the 8 elements followed the same law: Ni > 0.8 > Cr, Cu, Zn, Pb, Hg > 0.6 > As, Cd. When we applied these calibrations to Baguazhou Island soils, (log-BC-MSC) treated data results in the smallest RMSEp-BGZ. We used the same calibration method to compare the predictive ability of MIR spectra to VNIR spectra. The R2 of 8 elements developed by VNIR spectral calibration are sometime larger than MIR's, but after we applied these calibrations to validation set, the RSME of MIR data for prediction of BGZ soil samples is 21% to 73% of VNIR's. This result showed us that for predicting ex-situ soils, MIR analysis substantially outperformed VNIR These results indicated that MIR spectra can be used to predict soil heavy metal content quickly and non-destructively.