Jing Zhang

Rising drug resistance underscores the urgent need for novel anti-influenza strategies. Targeting the hemagglutinin (HA)–sialic acid receptor interaction offers a promising broad-spectrum approach, yet progress is impeded by the lack of screening models that report the receptor-recognition step in a subtype-independent manner. Herein, we established a robust cell-based ELISA platform for high-throughput screening (HTS) that operates on the subtype-independent receptor-recognition step. The model utilizes ST6GAL1-overexpressing MDCK cells to enrich human-type α2,6-sialic acid receptors and employs horseradish peroxidase (HRP)-conjugated Sambucus nigra lectin (SNA) as a functional, though not structural, surrogate for the receptor-recognition step, yielding a high Z’ factor of 0.78. Given that SNA is a lectin rather than HA, the assay cannot by itself distinguish HA-specific blockade from membrane-mediated or virucidal effects. Orthogonal validation is therefore required for every hit. Screening a library of 2600 compounds identified two hits, Hypericin and protoporphyrin IX (PPIX), which effectively blocked SNA–receptor recognition with IC₅₀ values of 18.39 ± 6.23 μM and 9.77 ± 3.05 μM, respectively. An orthogonal flow cytometry assay with FITC-conjugated SNA reproduced this inhibition on intact cells in a dose-dependent manner (IC₅₀ = 17.68 ± 9.54 μM for Hypericin and 25.31 ± 19.47 μM for PPIX), confirming that the inhibition is not an artifact of the colorimetric readout. Hemagglutination inhibition (HA) assays with distinct pre-incubation strategies indicated that both compounds act on the viral particle rather than on the host receptor. Surface plasmon resonance (SPR) and molecular docking studies further indicated direct, dose-dependent but low-affinity binding to HA proteins. Notably, cytopathic effect (CPE) assays demonstrated their potent antiviral efficacy across H1N1 and H3N2 subtypes, with PPIX exhibiting exceptionally potent activity against H3N2 (EC₅₀ = 0.50 ± 0.17 μM). Taken together, these data identify Hypericin and PPIX as viral-side attachment inhibitors with weak HA binding and multimodal antiviral activity. Because neither a virucidal nor a fusion-blocking control was included, the relative contribution of HA engagement to their overall antiviral effect remains to be established. In conclusion, this BSL-1-compatible ELISA platform, which probes the subtype-independent receptor-recognition step, provides an efficient tool for discovering broad-spectrum influenza entry inhibitors, and the identified hits offer novel pharmacological scaffolds for further structural optimization.

Rising drug resistance undermines current anti-influenza virus therapies. Although targeting the hemagglutinin (HA)–sialic acid receptor interaction is a promising strategy, progress is impeded by the lack of subtype-independent screening models. Herein, we established a fluorescence-based cell high-throughput model using fluorescein isothiocyanate-conjugated Sambucus Nigra Lectin (FITC-SNA) as a stable HA surrogate and α-2,6-sialyltransferase (ST6GAL1)-overexpressing MDCK cells to mimic the HA–receptor interface. This platform was designed to serve as an efficient primary screening tool to rapidly filter large compound libraries for potential binders to the receptor-binding interface. Screening 10,000 compounds identified Obatoclax Mesylate and Ethylparaben as primary hits. Both exhibited broad-spectrum HA inhibition activity, validating the model’s capability to identify compounds interfering with viral attachment. Further cellular antiviral assays revealed cytotoxicity for both compounds, resulting in low selectivity indexes (SIs), indicating that while these molecules effectively target the interaction site, they require substantial structural optimization for therapeutic use. Molecular docking confirmed their binding to type A H1N1, H3N2, and B/Victoria HA proteins, while ADMET predictions highlighted specific structural optimization needs to mitigate toxicity. In conclusion, this subtype-independent, highly specific high-throughput screening (HTS) model provides an efficient and reliable platform for early-stage influenza drug discovery and lead compound development.

Osteoporosis is a systemic skeletal disease that severely impairs the health of the elderly population. The interaction between the receptor activator of the NF-κB ligand (RANKL) and its receptor RANK is critical for osteoclast differentiation and function. Therefore, targeting the RANKL/RANK interaction represents a promising strategy for osteoporosis. In this study, we employed a newly established yeast two-hybrid system based on RANKL/RANK interaction and identified IMB-R38, a novel benzamide compound that dose-dependently blocked RANKL/RANK interaction by inhibiting the growth of AH109 cells harboring pAD-RANKL/pBD-RANK plasmids in quadruple-dropout medium. IMB-R38 significantly suppressed osteoclast differentiation, disrupted F-actin ring formation, and downregulated the expression of osteoclast-specific genes, including NFATc1 and MMP9 in RANKL-induced RAW264.7 macrophages. IMB-R38 also promoted osteoblast differentiation by upregulating the expression of osteogenic genes. Importantly, in a dexamethasone (DXM)-induced osteoporotic zebrafish model, IMB-R38 significantly increased bone mineralization, with anti-osteoporosis efficacy superior to that of alendronate sodium (Alen). RT-qPCR assays showed that IMB-R38 significantly upregulated the mRNA expression of osteogenesis genes (Bmp2, Runx2a, Runx2b, Sp7, Alp, and Oc) while markedly downregulating that of the osteoclastogenesis genes (Mmp9, Mmp13, and Mmp2) compared with the DXM group. Mechanistically, an SPR assay confirmed that IMB-R38 directly binds with RANK but not RANKL to disrupt RANKL/RANK interaction. Furthermore, Asp168 of RANK was identified as a key amino acid that mediates both RANKL interaction and IMB-R38 binding. The inhibition of RANKL/RANK by IMB-R38 suppressed JNK phosphorylation and, consequently, osteoclast differentiation and function. Collectively, our findings identify IMB-R38 as a novel RANKL/RANK inhibitor with therapeutic potential for osteoporosis through its regulation of bone metabolism.

The recent coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has exerted considerable impact on global health. To prepare for rapidly mutating viruses and for the forthcoming pandemic, effective therapies targeting the critical stages of the viral life cycle need to be developed. Viruses are dependent on the interaction between the receptor-binding domain (RBD) of the viral Spike (S) protein (S-RBD) and the angiotensin-converting enzyme 2 (ACE2) receptor to efficiently establish infection and the following replicate. Targeting this interaction provides a promising strategy to inhibit the entry process of the virus, which in turn has both preventive and therapeutic effects. In this study, we developed a robust and straightforward assay based on the Yeast-Two Hybrid system (Y2H) for identifying inhibitors targeting the S-RBD-ACE2 interaction of SARS-CoV-2. Through high-throughput screening, two compounds were identified as potential entry inhibitors. Among them, IMB-1C was superior in terms of pseudovirus entry inhibition and toxicity. It could bind to both ACE2 and S-RBD and induce conformational change in the S-RBD+ACE2 complex. This is the first study to verify the feasibility of utilizing the Y2H system to discover potent SARS-CoV-2 inhibitors targeting the receptor recognition stage. This approach may also be applied in the discovery of other virus receptor recognition inhibitors.

Cathepsin L (CTSL), a lysosomal cysteine protease belonging to the papain-like protease family, is primarily involved in intracellular protein degradation, antigen processing, and extracellular matrix remodeling. It plays critical roles in pathological conditions, including cancer metastasis, neurodegenerative disorders, and viral infection, due to dysregulated activity or overexpression. Thus, inhibitors targeting CTSL are under investigation for therapeutic applications. Current approaches for identifying CTSL inhibitors predominantly rely on fluorescence-labeled substrates, fluorescence resonance energy transfer (FRET), and cell-based screening assays. Here, we applied the principle of fluorescence polarization (FP) to the detection of substrate cleavage activity by CTSL through changes in millipolarization unit (mp) values and established a cost-effective, quantitative, reagent- and time-saving inhibitor high-throughput screening (HTS) assay. We also provide detailed steps for the expression and purification of highly active CTSL from eukaryotic cells, which lays a solid foundation for the FP-based assay. A key advantage of this assay lies in its reduced susceptibility to fluorescence interference, as the fluorescein isothiocyanate (FITC) fluorophore exhibits high quantum efficiency with an emission peak at 535 nm—a wavelength range distinct from most naturally occurring fluorescent molecules. The assay’s adaptability to reaction time, temperature, and dimethyl sulfoxide (DMSO) concentration minimizes false-positive or false-negative results caused by minor experimental inconsistencies, streamlining the screening process. Furthermore, the protocol requires fewer operational steps, reduced incubation time, and lower quantities of CTSL and substrates compared to conventional methods. This rapid, cost-effective, and scalable approach aligns well with the demands of HTS platforms.

Mitochondria are the center of energy metabolism in eukaryotic cells and play a central role in the metabolism of living organisms. Mitochondrial diseases characterized by defects in oxidative phosphorylation are the most common congenital diseases. Meanwhile, mitochondrial dysfunction caused by secondary factors such as non-inherited genetic mutations can affect normal physiological functions of human cells, induce apoptosis, and lead to the development of various diseases. This paper reviewed several major factors and mechanisms that contribute to mitochondrial dysfunction and discussed the development of diseases closely related to mitochondrial dysfunction and drug treatment strategies discovered in recent years.

The need for novel antibiotics has become imperative with the increasing prevalence of antibiotic resistance in Gram-negative bacteria in clinics. Acting as a permeability barrier, lipopolysaccharide (LPS) protects Gram-negative bacteria against drugs. LPS is synthesized in cells and transported to the outer membrane (OM) via seven lipopolysaccharide transport (Lpt) proteins (LptA–LptG). Of these seven Lpt proteins, LptC interacts with LptA to transfer LPS from the inner membrane (IM) to the OM, and assembly is aided by LptD/LptE. This interaction among the Lpt proteins is important for the biosynthesis of LPS; therefore, the Lpt proteins, which are significant in the assembly process of LPS, can be a potential target for new antibiotics. In this study, a yeast two-hybrid (Y2H) system was used to screen compounds that could block LPS transport by inhibiting LptA/LptC interaction, which finally disrupts the biosynthesis of the OM. We selected the compound IMB-0042 for this study. Our results suggest that IMB-0042 disrupts LptA/LptC interaction by binding to both LptA and LptC. Escherichia coli cells, when treated with IMB-0042, showed filament morphology, impaired OM integrity, and an accumulation of LPS in the periplasm. IMB-0042 inhibited the growth of Gram-negative bacteria and showed synergistic sensitization to other antibiotics, with low cytotoxicity. Thus, we successfully identified a potential antibacterial agent by using a Y2H system, which blocks the transport of LPS by targeting LptA/LptC interaction in Escherichia coli.