Development of FRET-based high-throughput screening for viral RNase III inhibitors

Virtual Screening Combined with Phase Transition-FRET for Discovery of Small-Molecule FcRn Antagonists

Neonatal Fc receptor (FcRn) antagonists, which competitively block the binding of immunoglobulin G (IgG) to FcRn, offer a promising therapeutic strategy for treating IgG-mediated autoimmune disorders. However, all currently available FcRn antagonists are macromolecular therapeutic antibodies, which come with certain clinical limitations. The development of alternative small-molecule FcRn antagonists is therefore of considerable importance. To facilitate the discovery of small-molecule FcRn antagonists, we established a novel screening method based on phase transition induced Förster resonance energy transfer (PT-FRET) technique. The PT-FRET technique integrated fluorescence labeled pH-responsive polymers into the FRET system, which could not only amplify the fluorescence intensity but also obviate the necessity for labeling diverse small molecules with varying structures, addressing the labeling challenges in conventional FRET-based methods. Additionally, to further reduce the time and cost as well as improve hit rate, virtual screening was employed prior to PT-FRET, greatly narrowing the scope of small-molecule candidates with potential FcRn binding affinity. After verification and optimization, this novel strategy was successfully applied to the discovery of small-molecule FcRn antagonists. Through virtual screening of a small-molecule compound library containing over 2.0 × 106 compounds, 28 candidate compounds were selected, among which 3 compounds were further identified by PT-FRET. Confirmation results revealed significant antagonistic activity for these 3 identified compounds through a conventional competitive ELISA, demonstrating the reliability and feasibility of the proposed method. Action mechanism was further elucidated via molecular dynamics simulations and binding mode analysis.

Development and Application of Activity-based Fluorescent Probes for High-Throughput Screening

High-throughput screening facilitates the rapid identification of novel hit compounds; however, it remains challenging to design effective high-throughput assays, partially due to the difficulty of achieving sensitivity in the assay techniques. Among the various analytical methods that are used, fluorescence-based assays dominate owing to their high sensitivity and ease of operation. Recent advances in activity-based sensing/imaging have further expanded the availability of fluorescent probes as monitors for high-throughput screening of result outputs. In this study, we have reviewed various activity-based fluorescent probes used in high-throughput screening assays, emphasizing their structure-related working mechanisms. Moreover, we have explored the possibility of the development of additional and better probes to boost hit identification and drug development against various targets.

In Vitro Identification and In Vivo Confirmation of Inhibitors for Sweet Potato Chlorotic Stunt Virus RNA Silencing Suppressor, a Viral RNase III

Sweet potato virus disease (SPVD), caused by synergistic infection of Sweet potato chlorotic stunt virus (SPCSV) and Sweet potato feathery mottle virus (SPFMV), is responsible for substantial yield losses all over the world. However, there are currently no approved treatments for this severe disease. The crucial role played by RNase III of SPCSV (CSR3) as an RNA silencing suppressor during the viruses' synergistic interaction in sweetpotato makes it an ideal drug target for developing antiviral treatment. In this study, high-throughput screening (HTS) of small molecular libraries targeting CSR3 was initiated by a virtual screen using Glide docking, allowing the selection of 6,400 compounds out of 136,353. We subsequently developed and carried out kinetic-based HTS using fluorescence resonance energy transfer technology, which isolated 112 compounds. These compounds were validated with dose-response assays including kinetic-based HTS and binding affinity assays using surface plasmon resonance and microscale thermophoresis. Finally, the interference of the selected compounds with viral accumulation was verified in planta In summary, we identified five compounds belonging to two structural classes that inhibited CSR3 activity and reduced viral accumulation in plants. These results provide the foundation for developing antiviral agents targeting CSR3 to provide new strategies for controlling sweetpotato virus diseases.IMPORTANCE We report here a high-throughput inhibitor identification method that targets a severe sweetpotato virus disease caused by coinfection with two viruses (SPCSV and SPFMV). The disease is responsible for up to 90% yield losses. Specifically, we targeted the RNase III enzyme encoded by SPCSV, which plays an important role in suppressing the RNA silencing defense system of sweetpotato plants. Based on virtual screening, laboratory assays, and confirmation in planta, we identified five compounds that could be used to develop antiviral drugs to combat the most severe sweetpotato virus disease.