Surface Plasmon Resonance Binding Assays Research Articles

Polymerized Type I Collagen Downregulates STAT-1 Phosphorylation Through Engagement with LAIR-1 in Circulating Monocytes, Avoiding Long COVID

The intramuscular administration of polymerized type I collagen (PTIC) for adult symptomatic COVID-19 outpatients downregulated hyperinflammation and improved symptoms. We inferred that LAIR1 is a potential receptor for PTIC. Thus, a binding assay and surface plasmon resonance binding assay were performed to estimate the affinity of the interaction between LAIR1 and PTIC. M1 macrophages derived from THP-1 cells were cultured with 2–10% PTIC for 24 h. Lysates from PTIC-treated THP-1 cells, macrophage-like cells (MLCs), M1, M1 + IFN-γ, and M1 + LPS were analyzed by Western blot for NF-κB (p65), p38, STAT1, and pSTAT1 (tyrosine701). Serum cytokine levels and monocyte LAIR1 expressions (Mo1 and Mo2) were analyzed by luminometry and flow cytometry in symptomatic COVID-19 outpatients on PTIC treatment. PTIC-bound LAIR1 had a similar affinity to collagen in M1 macrophages. It downregulated pSTAT1 in IFN-γ-induced M1. COVID-19 patients under PTIC treatment showed a significant decrease in Mo1 percentages and cytokines (IP-10/MIF/eotaxin/IL-8/IL-1RA/M-CSF) associated with STAT1 and an increase in the Mo2 subset. The inflammatory mediators and Mo1 downregulation were related to better oxygen saturation and decreased dyspnea, chest pain, cough, and chronic fatigue syndrome in the acute and long-term phase of infection. PTIC is an agonist of LAIR1 and downregulates STAT-1 phosphorylation. PTIC could be relevant for treating STAT1-mediated inflammatory diseases, including COVID-19 and long COVID.

Dual-function natural products: Farnesoid X receptor agonist/inflammation inhibitor for metabolic dysfunction-associated steatotic liver disease therapy

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most prevalent chronic liver disease globally, with only one Food and Drug Administration (FDA)-approved drug for its treatment. Given MASLD’s complex pathophysiology, therapies that simultaneously target multiple pathways are highly desirable. One promising approach is dual-modulation of the farnesoid X receptor (FXR), which regulates lipid and bile acid metabolism. However, FXR agonists alone are insufficient due to their limited anti-inflammatory effects. This study aimed to dto identify natural products capable of both FXR activation and inflammation inhibition to provide a comprehensive therapeutic approach for MASLD. Potential FXR ligands from the Natural Product Library were predicted via virtual screening using the Protein Preparation Wizard module in Schrodinger (2018) for molecular docking. Direct binding and regulation of candidate compounds on FXR were analyzed using surface plasmon resonance (SPR) binding assay, reporter gene analysis, and reverse transcription-polymerase chain reaction (RT-PCR). The anti-inflammatory properties of these compounds were evaluated in AML12 cells treated with tumor necrosis factor-alpha (TNF-α). Dual-function compounds with FXR agonism and inflammation inhibition were further identified in cells transfected with Fxr siRNA and treated with TNF-α. The effects of these dual-function compounds on lipid accumulation and inflammation were evaluated in cells treated with palmitic acid. Results revealed that 17 natural products were predicted via computational molecular docking as potential FXR agonists, with 15 exhibiting a strong affinity for FXR recombinant protein. Nine isoflavone compounds significantly enhanced FXR reporter luciferase activity and the mRNA expressions of Shp and Ostb. Structure-activity relationship analysis indicated that introducing isopropyl or methoxy groups at the C7 position or a methoxy group at the C6 position could enhance the agonistic efficacy of isoflavones. Three compounds (2, 6, and 8) were identified as dual-function natural products functioning as FXR agonists and inflammatory inhibitors, while one compound (12) acted as an FXR agonist to inhibit inflammation. These natural products protected hepatocytes against palmitic acid-induced lipid accumulation and inflammation. In conclusion, compounds 2, 6, and 8 (genistein, biochanin A, and 7-methoxyisoflavone, respectively) were identified as dual-function bioactive products that transactivate FXR and inhibit inflammation, serving as potential candidates or lead compounds for MASLD therapy.

Structural and Biochemical Requirements for Secretory Component Interactions with Dimeric IgA.

Secretory (S) IgA is the predominant mucosal Ab that protects host epithelial barriers and promotes microbial homeostasis. SIgA production occurs when plasma cells assemble two copies of monomeric IgA and one joining chain (JC) to form dimeric (d) IgA, which is bound by the polymeric Ig receptor (pIgR) on the basolateral surface of epithelial cells and transcytosed to the apical surface. There, pIgR is proteolytically cleaved, releasing SIgA, a complex of the dIgA and the pIgR ectodomain, called the secretory component (SC). The pIgR's five Ig-like domains (D1-D5) undergo a conformational change upon binding dIgA, ultimately contacting four IgA H chains and the JC in SIgA. In this study, we report structure-based mutational analysis combined with surface plasmon resonance binding assays that identify key residues in mouse SC D1 and D3 that mediate SC binding to dIgA. Residues in D1 CDR3 are likely to initiate binding, whereas residues that stabilize the D1-D3 interface are likely to promote the conformational change and stabilize the final SIgA structure. Additionally, we find that the JC's three C-terminal residues play a limited role in dIgA assembly but a significant role in pIgR/SC binding to dIgA. Together, these results inform models for the intricate mechanisms underlying IgA transport across epithelia and functions in the mucosa.

18F]AlF-NOTA-PCP2: a novel PET/CT tracer for enhanced PD-L1 heterogeneity imaging and comparative analysis with [18F]AlF-NOTA-WL12 in glioblastoma xenografts.

The unsatisfactory efficacy of PD-L1 antibodies in glioblastoma (GBM) is largely due to the temporal and spatial heterogeneity of PD-L1 expression. Molecular imaging can enhance understanding of the tumor immune microenvironment and guide immunotherapy. However, highly sensitive imaging agents capable of effectively visualizing PD-L1 heterogeneity are limited. This study introduces a novel PET tracer, offering improved imaging of PD-L1 heterogeneity in GBM xenografts, with a comparative analysis to [18F]AlF-NOTA-WL12. [18F]AlF-NOTA-PCP2 was synthesized with high purity and its affinity for PD-L1 was characterized using surface plasmon resonance (SPR) and cell binding assays. Its specificity for PD-L1 was evaluated both in vitro using various cell lines and in vivo with GBM xenograft models in NOD/SCID mice. PET/CT imaging was conducted to evaluate the tracer's biodistribution, pharmacokinetics, and ability to quantify tumoral spatial heterogeneity of PD-L1 expression. A focused comparative analysis between [18F]AlF-NOTA-PCP2 and [18F]AlF-NOTA-WL12 was conducted, examining binding affinity, biodistribution, pharmacokinetics, and imaging effectiveness in GBM xenografts. Additionally, human radiation dosimetry estimates compared the safety profiles of both tracers. [18F]AlF-NOTA-PCP2 demonstrated high radiochemical purity (> 95%) and a strong affinity for PD-L1, comparable to [18F]AlF-NOTA-WL12. In vitro and in vivo studies confirmed its specificity for PD-L1, with increased uptake in PD-L1 expressing cells and tumors. Toxicological profiles indicated no significant abnormalities in serum biochemical indicators or major organ tissues. MicroPET/CT imaging showed [18F]AlF-NOTA-PCP2's effectiveness in visualizing PD-L1 expression levels and spatial heterogeneity in GBM xenografts. Comparative studies revealed [18F]AlF-NOTA-PCP2's improved pharmacokinetic properties, including higher tumor-to-blood ratios and lower nonspecific liver uptake, as well as reduced radiation exposure compared to [18F]AlF-NOTA-WL12. [18F]AlF-NOTA-PCP2 distinguishes itself as an exceptionally sensitive PET/CT tracer, adept at non-invasively and accurately quantifying PD-L1 expression and its spatial heterogeneity in tumors, especially in GBM. Its favorable pharmacokinetic properties, safety profile, and high affinity for PD-L1 highlight its potential for enhancing the precision of cancer immunotherapy and guiding individualized treatment strategies. While promising, its clinical translation, especially in brain imaging, necessitates further validation in clinical trials.

The Dual-Targeted Fusion Inhibitor Clofazimine Binds to the S2 Segment of the SARS-CoV-2 Spike Protein.

Clofazimine and Arbidol have both been reported to be effective in vitro SARS-CoV-2 fusion inhibitors. Both are promising drugs that have been repurposed for the treatment of COVID-19 and have been used in several previous and ongoing clinical trials. Small-molecule bindings to expressed constructs of the trimeric S2 segment of Spike and the full-length SARS-CoV-2 Spike protein were measured using a Surface Plasmon Resonance (SPR) binding assay. We demonstrate that Clofazimine, Toremifene, Arbidol and its derivatives bind to the S2 segment of the Spike protein. Clofazimine provided the most reliable and highest-quality SPR data for binding with S2 over the conditions explored. A molecular docking approach was used to identify the most favorable binding sites on the S2 segment in the prefusion conformation, highlighting two possible small-molecule binding sites for fusion inhibitors. Results related to molecular docking and modeling of the structure-activity relationship (SAR) of a newly reported series of Clofazimine derivatives support the proposed Clofazimine binding site on the S2 segment. When the proposed Clofazimine binding site is superimposed with other experimentally determined coronavirus structures in structure-sequence alignments, the changes in sequence and structure may rationalize the broad-spectrum antiviral activity of Clofazimine in closely related coronaviruses such as SARS-CoV, MERS, hCoV-229E, and hCoV-OC43.

Ethyl vinyl ketone activates oxidative and calcium burst and CML8-ACA8 participates in calcium recovery in Arabidopsis leaves

Plants produce ethyl vinyl ketone (evk) in response to biotic stress, but the evk's identification and downstream defense response remain unclear. In this paper, it is predicted by docking for the first time that evk can be recognized by RBOH protein and assist the electron transfer of RBOHD/RBOHF by binding to its FAD or NADPH binding site. Surface plasmon resonance (SPR) binding assay shows that evk indeed bind to RBOHD. Here, we show that evk treatment increased H2O2 and intracellular calcium concentrations in Arabidopsis thaliana mesophyll cells, as observed by confocal laser scanning microscopy and non-invasive micro-test technology, and that H2O2 signaling functioned upstream of Ca2+ signaling. Yeast two-hybrid, firefly luciferase complementation imaging, and in vitro pull-down assays demonstrated that the ACA8 (AUTOINHIBITED Ca2+-ATPASE, ISOFORM 8)–CML8 (CALMODULIN-LIKE 8) interaction promoted Ca2+ efflux to return Ca2+ levels to the resting state.

Investigating membrane-binding properties of lipoxygenases using surface plasmon resonance

Lipoxygenases (LOXs) catalyze the oxidation of polyunsaturated fatty acids and synthesize oxylipin products that drive important cellular signaling processes in plants and animals. While there has been indirect evidence presented for the interaction of mammalian LOXs with membranes, a quantitative study of the molecular details of LOX-membrane interactions is lacking. Here, we mimicked biological membranes using surface plasmon resonance (SPR) sensor chips derivatized with 2-D planar lipophilic anchors (2D LP) to capture liposomes of varying phospholipid compositions that self-assemble into lipid bilayers on the SPR chip. The sensor chip surfaces were then used to investigate the membrane-binding properties of model LOX enzymes. SPR binding assays displayed reproducible and stable liposome capture to the sensor chip surface that allowed for the detailed characterization of LOX-membrane interactions. Our studies demonstrate a calcium-dependence for the membrane binding activities of coral 8R-LOX and human 15-LOX-2. Furthermore, our data confirm the importance of key membrane insertion loop residues in each of these LOX enzymes for membrane binding activity. Experiments utilizing model plant and human LOXs reveal differences in membrane-binding specificities. Our study establishes and validates a robust SPR-based platform using 2D LP sensor chips that allows for the detailed study of LOX-membrane interactions under different experimental conditions, including altered membrane compositions. Collectively, this investigation improves our overall understanding of LOX-membrane interaction properties, and our SPR-based approach holds potential for future use in the development of LOX-based therapeutics.

Abstract 6172: Characterization of a novel series of highly selective PARP1 inhibitors

Abstract First-generation PARP1 inhibitors have provided significant therapeutic benefit to patients whose tumors exhibit homologous repair deficiencies, including BRCA mutations, however their use has been associated with hematological toxicities that have restricted their application, particularly in combination with standard-of-care chemotherapy. All four FDA-approved PARP1 inhibitors are largely non-selective for the closely related enzyme PARP2, inhibition of which has been shown to drive hematotoxicity. Hence, the development of second-generation molecules highly selective for PARP1 over PARP2 offers a significant opportunity to 1) dramatically enhance therapeutic index, 2) enable additional precision medicine/combination approaches with chemotherapy, radiotherapy, immunotherapy and targeted agents and 3) expand the addressable patient population to those whose tumors harbor additional DDR defects. Utilizing X-ray crystallography and structure-based drug design, we describe the characterization of a novel chemical series of highly selective PARP1 inhibitors. These molecules demonstrate high potency in multiple biochemical and cell-based assays, including viability and colony forming unit read-outs in BRCA-deficient cancer cells, whilst sparing isogenically-paired BRCA wild-type cells and non-transformed primary cell lines. The molecules are potent PARP1-DNA trappers and exhibit high affinity, high selectivity and prolonged residence time in biophysical surface plasmon resonance (SPR) binding assays. The molecules also demonstrate exceptionally high selectivity for PARP1 over PARP2, and across the mono and polyPARP family, using a cell-based NanoBRET target engagement assay. This chemical series generally exhibits highly desirable physico-chemical and in vitro ADME properties, coupled with an excellent in vitro safety profile, which translate to high oral bioavailability and low clearance in rodent PK studies. Lead molecules yield deep and durable anti-tumor efficacy in a BRCA1m MDA-MB-436 breast cancer xenograft model with responses continuing after cessation of treatment. Percent tumor regression and post-dose tumor control was superior to olaparib at 1/10th of the dose. Importantly, our molecules demonstrate prolonged tumor residence time and a markedly superior tumor:plasma ratio compared to competitor PARP1-selective inhibitors. Taken together, these data predict low therapeutic dosing with the potential to demonstrate improved efficacy and tolerability compared to marketed PARP inhibitors. In summary, we describe the characterization of novel potent and selective PARP1 inhibitors. These molecules demonstrate excellent in vitro ADMET and in vivo PK, coupled with profound anti-tumor efficacy and tumor-targeting properties in a genetically-defined mouse model, supporting their progression into clinical studies. Citation Format: Phillip M. Cowley, Barry E. McGuinness, Gillian M. Campbell, Alan Wise. Characterization of a novel series of highly selective PARP1 inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6172.

Imaging of Indocyanine Green-Human Serum Albumin (ICG-HSA) Complex in Secreted Protein Acidic and Rich in Cysteine (SPARC)-Expressing Glioblastoma.

Glioblastoma is the most common and fatal primary glioma and has a severe prognosis. It is a challenge for neurosurgeons to remove brain tumor tissues completely by resection. Meanwhile, fluorescence-guided surgery (FGS) is a technique used in glioma surgery to enhance the visualization of tumor edges to clarify the extent of tumor resection. Indocyanine green (ICG) is the only FDA-approved NIR fluorescent agent. It non-covalently binds to human serum albumin (HSA). Secreted protein acidic and rich in cysteine (SPARC) is an extracellular glycoprotein expressed in gliomas and binds to albumin, suggesting that it plays an important role in tumor uptake of the ICG-HSA complex. Here we demonstrate the binding properties of HSA or SPARC to ICG using surface plasmon resonance and saturation binding assay. According to in vitro and in vivo studies, the results showed that the uptake of ICG-HSA complex was higher in SPARC-expressing glioblastoma cell line and tumor region compared with the uptake of free ICG. Here, we visualized the SPARC-dependent uptake of ICG and ICG-HSA complex in U87MG. Our results demonstrated that the ICG-HSA complex is likely to be used as an efficient imaging agent targeting SPARC-expressing tumors, especially glioblastoma.

Heparan sulfate glycomimetics via iterative assembly of "clickable" disaccharides.

Heparan sulfate (HS) glycosaminoglycans are widely expressed on the mammalian cell surfaces and extracellular matrices and play important roles in a variety of cell functions. Studies on the structure-activity relationships of HS have long been hampered by the challenges in obtaining chemically defined HS structures with unique sulfation patterns. Here, we report a new approach to HS glycomimetics based on iterative assembly of clickable disaccharide building blocks that mimic the disaccharide repeating units of native HS. Variably sulfated clickable disaccharides were facilely assembled into a library of mass spec-sequenceable HS-mimetic oligomers with defined sulfation patterns by solution-phase iterative syntheses. Microarray and surface plasmon resonance (SPR) binding assays corroborated molecular dynamics (MD) simulations and confirmed that these HS-mimetic oligomers bind protein fibroblast growth factor 2 (FGF2) in a sulfation-dependent manner consistent with that of the native HS. This work established a general approach to HS glycomimetics that can potentially serve as alternatives to native HS in both fundamental research and disease models.

Improving Stability Enhances In Vivo Efficacy of a PCSK9 Inhibitory Peptide.

Optimization of peptide stability is essential for the development of peptides as bona fide alternatives to approved monoclonal antibodies. This is clearly the case for the many peptides reported to antagonize proprotein convertase subtilisin-like/kexin type 9 (PCSK9), a clinically validated target for lowering cholesterol. However, the effects of optimization of stability on in vivo activity and particularly the effects of binding to albumin, an emerging drug design paradigm, have not been studied for such peptide leads. In this study, we optimized a PCSK9 inhibitory peptide by mutagenesis and then by conjugation to a short lipidated tag to design P9-alb fusion peptides that have strong affinity to human serum albumin. Although attachment of the tag reduced activity against PCSK9, which was more evident in surface plasmon resonance binding and enzyme-linked immunosorbent competition assays than in cellular assays of activity, activity remained in the nanomolar range (∼40 nM). P9-alb peptides were exceptionally stable in human serum and had half-lives exceeding 48 h, correlating with longer half-lives in mice (40.8 min) compared to the unconjugated peptide. Furthermore, the decrease in in vitro binding was not deleterious to in vivo function, showing that engendering albumin binding improved low-density lipoprotein receptor recovery and cholesterol-lowering activity. Indeed, the peptide P9-albN2 achieved similar functional endpoints as the approved anti-PCSK9 antibody evolocumab, albeit at higher doses. Our study illustrates that optimization of stability instead of binding affinity is an effective way to improve in vivo function.

Identification of orphan ligand-receptor relationships using a cell-based CRISPRa enrichment screening platform.

Secreted proteins, which include cytokines, hormones, and growth factors, are extracellular ligands that control key signaling pathways mediating cell-cell communication within and between tissues and organs. Many drugs target secreted ligands and their cell surface receptors. Still, there are hundreds of secreted human proteins that either have no identified receptors ('orphans') or are likely to act through cell surface receptors that have not yet been characterized. Discovery of secreted ligand-receptor interactions by high-throughput screening has been problematic, because the most commonly used high-throughput methods for protein-protein interaction (PPI) screening are not optimized for extracellular interactions. Cell-based screening is a promising technology for the deorphanization of ligand-receptor interactions, because multimerized ligands can enrich for cells expressing low affinity cell surface receptors, and such methods do not require purification of receptor extracellular domains. Here, we present a proteo-genomic cell-based CRISPR activation (CRISPRa) enrichment screening platform employing customized pooled cell surface receptor sgRNA libraries in combination with a magnetic bead selection-based enrichment workflow for rapid, parallel ligand-receptor deorphanization. We curated 80 potentially high-value orphan secreted proteins and ultimately screened 20 secreted ligands against two cell sgRNA libraries with targeted expression of all single-pass (TM1) or multi-pass transmembrane (TM2+) receptors by CRISPRa. We identified previously unknown interactions in 12 of these screens, and validated several of them using surface plasmon resonance and/or cell binding assays. The newly deorphanized ligands include three receptor protein tyrosine phosphatase (RPTP) ligands and a chemokine-like protein that binds to killer immunoglobulin-like receptors (KIRs). These new interactions provide a resource for future investigations of interactions between the human-secreted and membrane proteomes.

Design, Synthesis and Structure-Activity Relationships of Phenylalanine-Containing Peptidomimetics as Novel HIV-1 Capsid Binders Based on Ugi Four-Component Reaction.

As a key structural protein, HIV capsid (CA) protein plays multiple roles in the HIV life cycle, and is considered a promising target for anti-HIV treatment. Based on the structural information of CA modulator PF-74 bound to HIV-1 CA hexamer, 18 novel phenylalanine derivatives were synthesized via the Ugi four-component reaction. In vitro anti-HIV activity assays showed that most compounds exhibited low-micromolar-inhibitory potency against HIV. Among them, compound I-19 exhibited the best anti-HIV-1 activity (EC50 = 2.53 ± 0.84 μM, CC50 = 107.61 ± 27.43 μM). In addition, I-14 displayed excellent HIV-2 inhibitory activity (EC50 = 2.30 ± 0.11 μM, CC50 > 189.32 μM) with relatively low cytotoxicity, being more potent than that of the approved drug nevirapine (EC50 > 15.02 μM, CC50 > 15.2 μM). Additionally, surface plasmon resonance (SPR) binding assays demonstrated direct binding to the HIV CA protein. Moreover, molecular docking and molecular dynamics simulations provided additional information on the binding mode of I-19 to HIV-1 CA. In summary, we further explored the structure—activity relationships (SARs) and selectivity of anti-HIV-1/HIV-2 of PF-74 derivatives, which is conducive to discovering efficient anti-HIV drugs.

Characterization of molecular interactions between cannabidiol and human plasma proteins (serum albumin and γ-globulin) by surface plasmon resonance, microcalorimetry, and molecular docking

A cannabidiol (CBD) oral solution (Epidiolex®) has been approved by the United States Food and Drug Administration to treat seizure conditions. However, the biomedical and pharmaceutical applications of CBD are hindered partially due to a limited understanding of CBD’s pharmacokinetic behaviors, such as its interactions with plasma proteins. Herein, we investigated the molecular interactions between CBD and two plasma proteins, namely, human serum albumin (HSA) and γ-globulin, using biophysical techniques including surface plasmon resonance (SPR), isothermal titration calorimetry, and differential scanning calorimetry, as well as molecular docking. CBD bound to HSA and γ-globulin in an exothermic manner (enthalpy: −9.3 ×104 and −3.7 ×104 kcal/mol, respectively) with a binding affinity of 1.8 × 10−5 and 1.3 × 10−5 M, respectively. The binding ratio between CBD and HSA or γ-globulin was approximately 1:1 and 3:1, respectively. Furthermore, computational modeling suggested that CBD and warfarin may bind to HSA independently, supported by data from a competitive SPR binding assay. Findings from the current study elucidate CBD’s plasma protein binding characteristics and shed light on their impact on CBD’s pharmacokinetic property.

A Series of Substituted Bis-Aminotriazines Are Activators of the Natriuretic Peptide Receptor C.

C-type natriuretic peptide (CNP) is involved in the regulation of vascular homeostasis, which is at least partly mediated through agonism of natriuretic peptide receptor C (NPR-C), and loss of this signaling has been associated with vascular dysfunction. As such, NPR-C is a novel therapeutic target to treat cardiovascular diseases. A series of novel small molecules have been designed and synthesized, and their structure-activity relationships were evaluated by a surface plasmon resonance binding assay. The biological activity of hit compounds was confirmed through organ bath assays measuring vascular relaxation and inhibition of cAMP production, which was shown to be linked to its NPR-C activity. Lead compound 1 was identified as a potent agonist (EC50 ∼ 1 μM) with promising in vivo pharmacokinetic properties.

Spiroarborin, an ent-Clerodane Homodimer from Callicarpa arborea as an Inhibitor of the Eleven-Nineteen Leukemia (ENL) Protein by Targeting the YEATS Domain.

A spiro ent-clerodane homodimer with a rare 6/6/6/6/6-fused pentacyclic scaffold, spiroarborin (1), together with four new monomeric analogues (2-5), were isolated from Callicarpa arborea. Their structures were elucidated by comprehensive spectroscopic data analysis, quantum-chemical calculations, and X-ray diffraction. A plausible biosynthetic pathway of 1 was proposed, and a biomimetic synthesis of its derivative was accomplished. Compound 1 showed a potent inhibitory effect by directly binding to the YEATS domain of the 11-19 leukemia (ENL) protein with an IC50 value of 7.3 μM. This gave a KD value of 5.0 μM, as recorded by a surface plasmon resonance binding assay.

A Structural Basis for Inhibition of the Complement Initiator Protease C1r by Lyme Disease Spirochetes.

Complement evasion is a hallmark of extracellular microbial pathogens such as Borrelia burgdorferi, the causative agent of Lyme disease. Lyme disease spirochetes express nearly a dozen outer surface lipoproteins that bind complement components and interfere with their native activities. Among these, BBK32 is unique in its selective inhibition of the classical pathway. BBK32 blocks activation of this pathway by selectively binding and inhibiting the C1r serine protease of the first component of complement, C1. To understand the structural basis for BBK32-mediated C1r inhibition, we performed crystallography and size-exclusion chromatography-coupled small angle X-ray scattering experiments, which revealed a molecular model of BBK32-C in complex with activated human C1r. Structure-guided site-directed mutagenesis was combined with surface plasmon resonance binding experiments and assays of complement function to validate the predicted molecular interface. Analysis of the structures shows that BBK32 inhibits activated forms of C1r by occluding substrate interaction subsites (i.e., S1 and S1') and reveals a surprising role for C1r B loop-interacting residues for full inhibitory activity of BBK32. The studies reported in this article provide for the first time (to our knowledge) a structural basis for classical pathway-specific inhibition by a human pathogen.

Design and Synthesis of Oleanolic Acid Trimers to Enhance Inhibition of Influenza Virus Entry.

Influenza is a major threat to millions of people worldwide. Entry inhibitors are of particular interest for the development of novel therapeutic strategies for influenza. We have previously discovered oleanolic acid (OA) to be a mild influenza hemagglutinin (HA) inhibitor. In this work, inspired by the 3D structure of HA as a homotrimeric receptor, we designed and synthesized 15 OA trimers with different linkers and central region via the copper-catalyzed azide-alkyne cycloaddition reaction. All of the OA trimers were evaluated for their antiviral activities in vitro, and 12c, 12e, 13c, and 13d were observed to exhibit robust potency (IC50 in the submicromolar range) against influenza A/WSN/33 (H1N1) virus that was stronger than that observed with oseltamivir. In addition, these compounds also displayed strong biological activity against A/Hong Kong/4801/2014 and B/Sichuan/531/2018 (BV). The results of hemagglutination inhibition assays and surface plasmon resonance binding assays suggest that these OA trimers may interrupt the interaction between the HA protein of influenza virus and the host cell sialic acid receptor, thus blocking viral entry. These findings highlight the utility of multivalent OA conjugates to enhance the ligand-target interactions in anti-influenza virus drug design and are also helpful for studying antiviral drugs derived from natural products.

Design, synthesis, and antiviral activity of phenylalanine derivatives as HIV-1 capsid inhibitors

The HIV-1 Capsid (CA) is considered as a promising target for the development of potent antiviral drugs, due to its multiple roles during the viral life cycle. Herein, we report the design, synthesis, and antiviral activity evaluation of series of novel phenylalanine derivatives as HIV-1 CA protein inhibitors. Among them, 4-methoxy-N-methylaniline substituted phenylalanine (II-13c) and indolin-5-amine substituted phenylalanine (V-25i) displayed exceptional anti-HIV-1 activity with the EC50 value of 5.14 and 2.57 μM respectively, which is slightly weaker than that of lead compound PF-74 (EC50 = 0.42 μM). Besides, surface plasmon resonance (SPR) binding assay demonstrated II-13c and V-25i prefer to combine with CA hexamer rather than monomer, which is similar to PF-74. Subsequently, molecular dynamics simulation (MD) revealed potential interactions between representative compounds with HIV-1 CA hexamer. Overall, this work laid a solid foundation for further structural optimization to discover novel promising HIV-1 CA inhibitors.

SAR442085, a novel anti-CD38 antibody with enhanced antitumor activity against multiple myeloma

Anti-CD38 monoclonal antibodies (mAbs) represent a breakthrough in the treatment of multiple myeloma (MM), yet some patients fail to respond or progress quickly with this therapy, highlighting the need for novel approaches. In this study we compared the preclinical efficacy of SAR442085, a next-generation anti-CD38 mAb with enhanced affinity for activating Fcγ receptors (FcγR), with first-generation anti-CD38 mAb daratumumab and isatuximab. In surface plasmon resonance and cellular binding assays, we found that SAR442085 had higher binding affinity than daratumumab and isatuximab for FcγRIIa (CD32a) and FcγRIIIa (CD16a). SAR442085 also exhibited better in vitro antibody-dependent cellular cytotoxicity (ADCC) against a panel of MM cells expressing variable CD38 receptor densities including MM patients' primary plasma cells. The enhanced ADCC of SAR442085 was confirmed using NK-92 cells bearing low and high affinity FcγRIIIa (CD16a)-158F/V variants. Using MM patients' primary bone marrow cells, we confirmed that SAR442085 had an increased ability to engage FcγRIIIa, resulting in higher natural killer (NK) cell activation and degranulation against primary plasma cells than preexisting Fc wild-type anti-CD38 mAbs. Finally, using huFcgR transgenic mice that express human Fcγ receptors under the control of their human regulatory elements, we demonstrated that SAR442085 had higher NK cell-dependent in vivo antitumor efficacy and better survival than daratumumab and isatuximab against EL4 thymoma or VK*MYC myeloma cells overexpressing human CD38. These results highlight the preclinical efficacy of SAR442085 and support the current evaluation of this next-generation anti-CD38 antibody in phase I clinical development in patients with relapsed/refractory MM.