Relationship between receptor/ligand binding affinity and adhesion strength

Neutrophils exhibit flexible migration strategies and trail formation mechanisms on varying adhesive substrates

Substrate anchorage is essential for cell migration, and actin polymerization at cell front and myosin contractility at cell rear are known to govern cell forward movement. Yet their differential driving strategies for neutrophil migration on distinct adhesiveness substrates and their contributions to the migration-induced trail formation remain unclear. Here we explore the morphological changes, migration dynamics, and trail formation of neutrophils on ICAM-1 and PLL substrates, with a focus on the relationships among adhesive forces, traction forces, and out-of-plane forces. Results indicate that, on ICAM-1, neutrophil migration and trail formation rely on the coordinated interactions of Arp2/3 and myosin, along with biochemical regulation (via Syk and calpain) of adhesion and de-adhesion. This pattern leads to traction forces being concentrated at relatively fewer adhesive sites, facilitating cell forward migration. On PLL, however, neutrophils primarily depend on Arp2/3-mediated actin polymerization, resulting in a broader distribution of traction forces and weaker adhesions, which allows for higher leading-edge migrating velocities. Elevated membrane tension and out-of-plane forces generated by bleb protrusions on PLL reduce the reliance on myosin-driven contraction at the trailing edge, enabling easier tail detachment through elastic recoil. This work highlights the differential impact of substrate adhesiveness on neutrophil migration and trail formation and dynamics, providing new insights into cell migration mechanisms and potential therapeutic targets for inflammatory and immune-related disorders.

Reversible Self-Assembled Monolayers with Tunable Surface Dynamics for Controlling Cell Adhesion Behavior

Cells adhering onto surfaces sense and respond to chemical and physical surface features. The control over cell adhesion behavior influences cell migration, proliferation, and differentiation, which are important considerations in biomaterial design for cell culture, tissue engineering, and regenerative medicine. Here, we report on a supramolecular-based approach to prepare reversible self-assembled monolayers (rSAMs) with tunable lateral mobility and dynamic control over surface composition to regulate cell adhesion behavior. These layers were prepared by incubating oxoacid-terminated thiol SAMs on gold in a pH 8 HEPES buffer solution containing different mole fractions of ω-(ethylene glycol)2-4- and ω-(GRGDS)-, α-benzamidino bolaamphiphiles. Cell shape and morphology were influenced by the strength of the interactions between the amidine-functionalized amphiphiles and the oxoacid of the underlying SAMs. Dynamic control over surface composition, achieved by the addition of inert filler amphiphiles to the RGD-functionalized rSAMs, reversed the cell adhesion process. In summary, rSAMs featuring mobile bioactive ligands offer unique capabilities to influence and control cell adhesion behavior, suggesting a broad use in biomaterial design, tissue engineering, and regenerative medicine.

Ultrafast Electrothermal Flow-Enhanced Magneto Biosensor for Highly Sensitive Protein Detection in Whole Blood

Current diagnostic tests for sensitive protein detection rely on immunological techniques, such as ELISA, which require sample purification, multiple washing steps and lengthy incubation, hindering their use for rapid testing. Here, we report a simple electrothermal flow-enhanced biosensor for ultrafast, high sensitivity measurements of protein biomarkers in whole blood. Magnetic nanobeads dually-labeled with a detection antibody and enzyme reporter are used to form immunocomplexes with the target protein, which are readily transported to the sensor via magnetic concentration. The incorporation of electrothermal flows enhances immunocomplex formation, allowing for rapid and sensitive detection without requiring blood purification or lengthy incubation. Proof of concept was carried out using Plasmodium falciparum histidine-rich protein 2 (PfHRP2), a malaria parasite biomarker, which could be detected at concentrations as low as 5.7 pg mL-1 (95 fM) in whole blood in 7 min. The speed, sensitivity and simplicity of this device make it attractive for rapid diagnostic testing.

Microsphere sensors for characterizing stress fields within three-dimensional extracellular matrix

Stress in the three-dimensional extracellular matrix is one of the key cues in regulating multiscale biological processes. Thus far, noticeable progress in methods and techniques (e.g., micropipette aspiration, AFM, and molecule probes) has been made to quantify stress in cell microenvironment at different length scales. Among them, the microsphere sensor-based method (MSS-based method) has emerged as an advantageous approach over conventional techniques in quantifying stress in situ and in vivo at cellular and supra-cellular scales. This method is implemented by seven sequential steps, including fabrication, modification, characterization, cell adhesion, imaging, displacement field extraction and stress calculation. Precise control of each step and inter-tunning between steps can provide quantitative characterization of stress field. However, detailed procedural information associated with each step and process has been scattered. This review aims to provide a comprehensive overview of MSS-based method, systematically summarizing the principles and research progresses. Firstly, the basic principles are introduced, and the specific experiment and calculation processes of MSS-based method are presented in detail. Then, recent advances and applications of this method are summarized. Finally, perspectives of the limitations and development trends of MSS-based method are discussed. This specific and comprehensive review would provide a guideline for the widespread application of MSS-based method as an advantageous method for in situ and in vivo stress characterization at cellular and supra-cellular scale within three-dimensional extracellular matrix. STATEMENT OF SIGNIFICANCE: In this review, a method based on a microsphere sensor (MSS-based method) as an advantageous approach over conventional techniques in quantifying stress in situ and in vivo at cellular and supra-cellular scales is introduced and discussed. This technique is implemented by seven sequential steps, including fabrication, modification, characterization, cell junction, imaging, displacement field extraction, and stress calculation. Precise control of each step and inter-tunning between steps can provide quantitative stress field. However, detailed procedural information associated with each step has been scattered. Thus, a comprehensive review collating recent advances and perspective discussions is a necessity to introduce a better option for quantifying the stress field in biological processes at the cellular and supra-cellular scales.

Next-Generation Molecular Discovery: From Bottom-Up In Vivo and In Vitro Approaches to In Silico Top-Down Approaches for Therapeutics Neogenesis

Protein and drug engineering comprises a major part of the medical and research industries, and yet approaches to discovering and understanding therapeutic molecular interactions in biological systems rely on trial and error. The general approach to molecular discovery involves screening large libraries of compounds, proteins, or antibodies, or in vivo antibody generation, which could be considered "bottom-up" approaches to therapeutic discovery. In these bottom-up approaches, a minimal amount is known about the therapeutics at the start of the process, but through meticulous and exhaustive laboratory work, the molecule is characterised in detail. In contrast, the advent of "big data" and access to extensive online databases and machine learning technologies offers promising new avenues to understanding molecular interactions. Artificial intelligence (AI) now has the potential to predict protein structure at an unprecedented accuracy using only the genetic sequence. This predictive approach to characterising molecular structure-when accompanied by high-quality experimental data for model training-has the capacity to invert the process of molecular discovery and characterisation. The process has potential to be transformed into a top-down approach, where new molecules can be designed directly based on the structure of a target and the desired function, rather than performing screening of large libraries of molecular variants. This paper will provide a brief evaluation of bottom-up approaches to discovering and characterising biological molecules and will discuss recent advances towards developing top-down approaches and the prospects of this.

Screening tumor specificity targeted by arnicolide D, the active compound of Centipeda minima and molecular mechanism underlying by integrative pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Herb-derived anti-tumor agents, such as paclitaxel and vincristine, exert significant but varied effectivenesses towards different cancer types. Similarly, Centipeda minima (CM) is a well-known traditional Chinese medicine that has been used to treat rhinitis, relieve pain and reduce swelling, and recently found to exert overwhelming anti-tumor effects against breast cancer, colon cancer, and nasopharyngeal carcinoma with different response rates. However, what is the optimizing cancer model that benefits most from CM, and what is the specific target underlying still require more exclusive and profound investigations.

AIMS OF THE STUDY

This study aimed to explore the dominant tumor model and specific target of CM by integrative pharmacology and biological experiments.

MATERIALS AND METHODS

The most predominant and specific cancer types that are sensitive to CM were screened and identified based on a combination network pharmacology and bioinformatics analysis. Compound-target network and protein-protein interaction of CM-related cancer targets were carried out to determine the most abundant active compound. Simultaneously, the priority target responsible for CM-related anti-tumor efficacy was further validated by molecular docking and in vitro experiments.

RESULTS

In total, approximately 42% (8/19) of the targets were enriched in prostate cancer (p = 1.25E-09), suggesting prostate cancer would be the most sensitive tumor response to CM-related efficacy. Furthermore, we found that arnicolide D (ARD), the most abundant and representative active compound of CM, could directly bind to Src with binding energy of -7.3 kcal/mol, implying Src would be the priority target responsible for CM-related anti-tumor efficacy. Meanwhile, the results were further validated by solvent-induced protein precipitation (SIP) assay. In addition, PCR and WB results also revealed that either CM or ARD could not influence the gene expression of Src, while significantly decreased its protein expression instead, which further suggested that ARD might markedly shortene the Src protein half-life to promote Src protein degradation, thereby achieving significant anti-prostate cancer efficacy.

CONCLUSION

Our findings not only suggest CM as a promising Src-targeting candidate for prostate cancer treatment, but also bring up a strategy for understanding the personalization of herbal medicines by using integrative pharmacology.

Exploring the Potential Mechanism of Chuanxiong Rhizoma Treatment for Migraine Based on Systems Pharmacology

Migraine is a disease whose aetiology and mechanism are not yet clear. Chuanxiong Rhizoma (CR) is employed in traditional Chinese medicine (TCM) to treat various disorders. CR is effective for migraine, but its active compounds, drug targets, and exact molecular mechanism remain unclear. In this study, we used the method of systems pharmacology to address the above issues. We first established the drug-compound-target-disease (D-C-T-D) network and protein-protein interaction (PPI) network related to the treatment of migraine with CR and then established gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. The results suggest that the treatment process may be related to the regulation of inflammation and neural activity. The docking results also revealed that PTGS2 and TRPV1 could directly bind to the active compounds that could regulate them. In addition, we found that CR affected 11 targets that were more highly expressed in the liver or heart but were the lowest in the whole brain. It also expounds the description of CR channel tropism in TCM theory from these angles. These findings not only indicate that CR can be developed as a potential effective drug for the treatment of migraine but also demonstrate the application of systems pharmacology in the discovery of herbal-based disease therapies.

Imparting Immunomodulatory Activity to Scaffolds via Biotin-Avidin Interactions

Biotin-avidin interactions have been explored for decades as a technique to functionalize biomaterials, as well as for in vivo targeting, but whether changes in these interactions can be leveraged for immunomodulation remain unknown. The goal of this study was to investigate how biotin density and avidin variant can be used to deliver the immunomodulatory cytokine, interleukin 4 (IL4), from a porous gelatin scaffold, Gelfoam, to primary human macrophages in vitro. Here, we demonstrate that the degree of scaffold biotinylation controlled the binding of two different avidin variants, streptavidin and CaptAvidin. Biotinylated scaffolds were also loaded with streptavidin and biotinylated IL4 under flow, suggesting a potential use for targeting this biomaterial in vivo. While biotin-avidin interactions did not appear to influence the protein release in this system, increasing degrees of biotinylation did lead to increased M2-like polarization of primary human macrophages over time in vitro, highlighting the capability to leverage biotin-avidin interactions to modulate the macrophage phenotype. These results demonstrate a versatile and modular strategy to impart immunomodulatory activity to biomaterials.

Shear-Resistant, Biological Tethering of Nanostimulators for Enhanced Therapeutic Cell Paracrine Factor Secretion

Mesenchymal stromal cells (MSCs) secreting multiple growth factors and immunomodulatory cytokines are promising for regenerative medicine. To further enhance their secretory activity, efforts have emerged to tether nanosized carriers of secretory stimuli, named nanostimulators, to the MSC surface by forming nonchemical bonds. Despite some successes, there is a great need to improve the retention of nanostimulators during transport through a syringe needle, where high shear stress exerted on the cell surface separates them. To this end, we hypothesize that poly(lactic-co-glycolic acid)-block-hyaluronic acid (PLGA-HA) conjugated with integrin-binding RGD peptides, denoted PLGA-HA-RGD, can form nanostimulators that remain on the cell surface stably during the injection. The resulting HA-CD44 and RGD-integrin bonds would synergistically increase the adhesion strength of nanostimulators. Interestingly, nanostimulators prepared with PLGA-HA-RGD show 3- to 6-fold higher retention than those made with PLGA-HA. Therefore, the PLGA-HA-RGD nanostimulators induced MSCs to secrete 1.5-fold higher vascular endothelial growth factors and a 1.2-fold higher tissue inhibitor of matrix metalloproteinase-1 as compared to PLGA-HA nanostimulators. Consequently, MSCs tethered with PLGA-HA-RGD nanostimulators served to stimulate endothelial cell activities to form a blood vessel-like endothelial lumen with increased length and number of junctions. The nanostimulator design strategy would also be broadly applicable to regulate, protect, and home a broad array of therapeutic or immune cells by tethering carriers with bioactive molecules of interest.

Network Pharmacology-Based Strategy for the Investigation of the Anti-Obesity Effects of an Ethanolic Extract of Zanthoxylum bungeanum Maxim

Network pharmacology is considered as the next paradigm in drug discovery. In an era when obesity has become global epidemic, network pharmacology becomes an ideal tool to discover novel herbal-based therapeutics with effective anti-obesity effects. Zanthoxylum bungeanum Maxim (ZBM) is a medicinal herb. The mature pericarp of ZBM is used for disease treatments and as spice for cooking. Here, we used the network pharmacology approach to investigate whether ZBM possesses anti-obesity effects and reveal the underlying mechanism of action. We first built up drug–ingredient–gene symbol–disease network and protein–protein interaction network of the ZBM-related obesity targets, followed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. The results highlight apoptosis as a promising signaling pathway that mediates the anti-obesity effects of ZBM. Molecular docking also reveals quercetin, a compound in ZBM has the highest degree of connections in the compound-target network and has direct bindings with the apoptotic markers. Furthermore, the apoptotic effects of ZBM are further validated in 3T3-L1 adipocytes and in the high-fat diet–induced obesity mouse model. These findings not only suggest ZBM can be developed as potential anti-obesity therapeutics but also demonstrate the application of network pharmacology for the discovery of herbal-based therapeutics for disease treatments.

The GDP-Bound State of Mitochondrial Mfn1 Induces Membrane Adhesion of Apposing Lipid Vesicles through a Cooperative Binding Mechanism

Mitochondria are double-membrane organelles that continuously undergo fission and fusion. Outer mitochondrial membrane fusion is mediated by the membrane proteins mitofusin 1 (Mfn1) and mitofusin 2 (Mfn2), carrying a GTP hydrolyzing domain (GTPase) and two coiled-coil repeats. The detailed mechanism on how the GTP hydrolysis allows Mfns to approach adjacent membranes into proximity and promote their fusion is currently under debate. Using model membranes built up as giant unilamellar vesicles (GUVs), we show here that Mfn1 promotes membrane adhesion of apposing lipid vesicles. The adhesion forces were sustained by the GDP-bound state of Mfn1 after GTP hydrolysis. In contrast, the incubation with the GDP:AlF4−, which mimics the GTP transition state, did not induce membrane adhesion. Due to the flexible nature of lipid membranes, the adhesion strength depended on the surface concentration of Mfn1 through a cooperative binding mechanism. We discuss a possible scenario for the outer mitochondrial membrane fusion based on the modulated action of Mfn1.

Magnetic-Based Enrichment of Rare Cells from High Concentrated Blood Samples

Here, we tested two magnetic-bead based systems for the enrichment and detection of rare tumor cells in concentrated blood products. For that, the defined numbers of cells from three pancreatic cancer cell lines were spiked in 108 peripheral blood mononuclear cells (PBMNCs) concentrated in 1 mL, mimicking diagnostic leukapheresis (DLA) samples, and samples were processed for circulating tumor cells (CTC) enrichment with the IsoFlux or the KingFisher systems, using different types of magnetic beads from the respective technology providers. Beads were conjugated with different anti-EpCAM and MUC-1 antibodies. Recovered cells were enumerated and documented by fluorescent microscopy. For the IsoFlux system, best performance was obtained with IsoFlux CTC enrichment kit, but these beads compromised the subsequent immunofluorescence staining. For the KingFisher system, best recoveries were obtained using Dynabeads Biotin Binder beads. These beads also allowed one to capture CTCs with different antibodies and the subsequent immunofluorescence staining. KingFisher instrument allowed a single and streamlined protocol for the enrichment and staining of CTCs that further prevented cell loss at the enrichment/staining interface. Both IsoFlux and KingFisher systems allowed the enrichment of cell line cells from the mimicked-DLA samples. However, in this particular experimental setting, the recovery rates obtained with the KingFisher system were globally higher, the system was more cost-effective, and it allowed higher throughput.

Guided mode resonance sensor for the parallel detection of multiple protein biomarkers in human urine with high sensitivity

The rising cost of global healthcare provision and new approaches to managing disease are driving the development of low-cost biosensing modalities, such as label-free photonic methods based on dielectric resonances. Here, we use the combined sensing and imaging capability of a guided mode resonance (GMR) sensor to detect multiple biomarkers (troponin, procalcitonin and C-Reactive Protein) in parallel in undiluted urine samples. A key requirement of such a biosensor is the simple and direct functionalization with suitable antibodies to ensure the disease-specific detection of protein biomarkers. Here, antibodies were immobilized using a succinimidyl-[(N-maleimidopropionamido)-hexaethyleneglycol] ester (SM(PEG)6) spacer. The polyethylene glycol (PEG) chemistry enables low detection limits of 10 pg mL-1 or better for all protein biomarkers, while minimizing non-specific binding compared to more commonly used strategies such as (3-Aminopropyl)triethoxysilane (APTES) or dextran. Our approach supports the vision of a simple yet highly sensitive diagnostic platform that could be used for pre-screening patients for a wide range of diseases at point-of-care, thereby relieving the pressure on overstretched healthcare services.

A two-dimensional immunomagnetic nano-net for the efficient isolation of circulating tumor cells in whole blood

An immunomagnetic "nano-net" was designed and synthesized for specifically capturing rare cells of interest from mixtures. The nano-net, Ab@Lipo-MNP-GO, consists of conjugated antibody molecules on a lipid coated magnetic nanoparticle-graphene oxide sheet complex. The magnetism, chemical composition, and the morphology of the construct and its precursors were characterized by SQUID, FTIR, TGA, DLS and SEM, to confirm the feasibility of the synthetic steps and the resulting properties suitable for solution phase immuno-recognition for cell capture. When applied to capturing circulating tumor cells (CTCs) in oral, colon and lung cancer clinical patients' blood samples, the nano-net construct exhibited far superior ability whereas conventional immunomagnetic beads in some cases were unable to capture any CTCs, even by increasing the bead concentration. Confocal images showed that the nano-net wrapped around the CTCs while the immunomagnetic beads attached them with point contacts. A stable, patch-like multivalent matrix nano-net was demonstrated to tackle the shortcomings of single point contact of immunomagnetic beads to the target cell. This strategy is universal for any cell separation in complex fluids.

Fiber optic plasmonic sensors: Providing sensitive biosensor platforms with minimal lab equipment

A simple, convenient, and inexpensive method to fabricate optical fiber based biosensors which utilize periodic hole arrays in gold films for signal transduction is reported. The process of hole array formation mainly relies on self-assembly of hydrogel microgels in combination with chemical gold film deposition and subsequent transfer of the perforated film onto an optical fiber tip. In the fabrication process solely chemical wet lab techniques are used, avoiding cost-intensive instrumentation or clean room facilities. The presented method for preparing fiber optic plasmonic sensors provides high throughput and is perfectly suited for commercialization using batch processing. The transfer of the perforated gold film onto an optical fiber tip does not affect the sensitivity of the biosensor ((420 ± 83) nm/refractive index unit (RIU)), which is comparable to sensitivities of sensor platforms based on periodic hole arrays in gold films prepared by significantly more complex methods. Furthermore, real-time and in-line immunoassay studies with a specially designed 3D printed flow cell are presented exploiting the presented optical fiber based biosensors.

Flow induced HeLa cell detachment kinetics show that oxygen-containing functional groups in graphene oxide are potent cell adhesion enhancers

A broader and quantitative understanding of cell adhesion to two-dimensional carbon-based materials is needed to expand the applications of graphene and graphene oxide (GO) in tissue engineering, prosthetics, biosensing, detection of circulating cancer cells, and (photo)thermal therapy. We therefore studied the detachment kinetics of human cancer cells HeLa adhered on graphene, GO, and glass substrates using stagnation point flow on an impinging jet apparatus. HeLa cells detached easily from graphene at a force of 9.4 nN but adhered very strongly to GO. The presence of hydrophilic functional groups thus apparently enhanced the HeLa cells' adherence to the GO surface. On graphene, smaller HeLa cells adhered more strongly and detached later than cells with larger projected areas, but the opposite behavior was observed on GO. These findings reveal GO to be a suitable platform for detecting cells or establishing contacts, e.g. between graphene-based circuits/electrodes and tissues. Our experiments also show that the impinging jet method is a powerful tool for studying cellular detachment mechanisms and adhesion strength, and could therefore be very useful for investigating interactions between cells and graphene-based materials.

Gold Binding Peptide Identified from Microfluidic Biopanning: An Experimental and Molecular Dynamics Study

Biopanning refers to the processes of screening peptides with a high affinity to a target material. Microfluidic biopanning has advantages compared to conventional biopanning which requires large amounts of the target material and involves inefficient multiple pipetting steps to remove nonspecific or low-affinity peptides. Here, we fabricate a microfluidic biopanning system to identify a new gold-binding peptide (GBP). A polydimethylsiloxane microfluidic device is fabricated and bonded to a glass slide with a gold pattern that is deposited by electron-beam evaporation. The microfluidic biopanning system can provide high adjustability in the washing step during the biopanning process because the liquid flow rate and the resulting shear stress can be precisely controlled. The surface plasmon resonance analysis shows that the binding affinity of the identified GBP is comparable to previously reported GBPs. Moreover, molecular dynamics simulations are performed to understand its binding affinity against the gold surface in detail. Theoretical calculations suggest that the association and dissociation rates of the GBPs depend on their sequence-dependent conformations and interactions with the gold surface. These findings provide insight into designing efficient biopanning tools and peptides with a high affinity for various target materials.

Febrile Temperature Elevates the Expression of Phosphatidylserine on Plasmodium falciparum (FCR3CSA) Infected Red Blood Cell Surface Leading to Increased Cytoadhesion

During the asexual intra-erythrocytic cycle, Plasmodium (P.) falciparum exports parasitic proteins to the surface of infected red blood cells (iRBCs) facilitating its cytoadhesion to various endothelial host receptors. This adhesive behavior is a critical contributor towards disease manifestation. However, little is known about the influence of recurring elevated temperature – a common symptom of the malaria infection – on the adhesive properties of iRBCs to endothelial receptors. To address this, we performed dual-micropipette step-pressure technique between P. falciparum (strain FCR3CSA) iRBCs and Chinese Hamster Ovary cells expressing Chondroitin sulfate A (CHO-CSA) after transient iRBCs incubation at febrile temperatures which revealed increase in adhesion parameters. Furthermore, flow cytometry analysis revealed an increase in phosphatidylserine (PS) expression on the iRBC surface following exposure to febrile temperature. The adhesion between iRBCs and CHO-CSA cells was remarkably reduced in presence of soluble Annexin V, indicating the mediation of PS on the adhesion events. Our results suggest that elevated PS recruitment on iRBC under thermally stressed conditions contributes to the increased adhesive behavior of iRBCs CSA-binding phenotype to CHO-CSA.

An Effective Way of Producing Fully Assembled Antibody in Transgenic Tobacco Plants by Linking Heavy and Light Chains via a Self-Cleaving 2A Peptide

Therapeutic monoclonal antibodies (mAbs) have evolved into an important class of effective medicine in treatment of various diseases. Since the antibody molecule consists of two identical heavy chains (HC) and two light chains (LC), each chain encoded by two different genes, their expressions at similar levels are critical for efficient assembly of functional recombinant mAbs. Although the plant-based expression system has been tested to produce fully assembled recombinant mAbs, coordinately expressing HC and LC at similar levels in a transgenic plant remains a challenge. A sequence coding for a foot-and-mouth disease virus (FMDV) 2A peptide has been successfully used to link two or more genes, which enable the translated polyprotein to be "self-cleaved" into individual protein in various genetically modified organisms. In the present study, we exploited the usage of F2A in Ebola virus monoclonal antibody (EBOV mAb) production. We found that transgenic tobacco plants carrying a transcription unit containing HC and LC linked by 2A not only produced similar levels of HC and LC but also rendered a higher yield of fully assembled EBOV mAb compared to those expressing HC and LC in two independent transcription units. Purified EBOV mAb bound to an Ebola epitope peptide with apparent K_d -values of 90.13-149.2 nM, indicating its proper assembly and high affinity binding to Ebola epitope peptide. To our knowledge, this is the first report showing mAb production by overexpressing a single transcription unit consisting of HC, LC and 2A in stable transformed tobacco plants.

Fundamentals of affinity cell separations

Cell separations using affinity methods continue to be an enabling science for a wide variety of applications. In this review, we discuss the fundamental aspects of affinity separation, including the competing forces for cell capture and elution, cell-surface interactions, and models for cell adhesion. Factors affecting separation performance such as bond affinity, contact area, and temperature are presented. We also discuss and demonstrate the effects of nonspecific binding on separation performance. Metrics for evaluating cell separations are presented, along with methods of comparing separation techniques for cell isolation using affinity capture.

Label-free and real-time monitoring of single cell attachment on template-stripped plasmonic nano-holes

Leveraging microfluidics and nano-plasmonics, we present in this paper a new method employing a micro-nano-device that is capable of monitoring the dynamic cell-substrate attachment process at single cell level in real time without labeling. The micro-nano-device essentially has a gold thin film as the substrate perforated with periodic, near-cm2-area, template-stripped nano-holes, which generate plasmonic extraordinary optical transmission (EOT) with a high sensitivity to refractive index changes at the metal-dielectric interface. Using this device, we successfully demonstrated label-free and real-time monitoring of the dynamic cell attachment process for single mouse embryonic stem cell (C3H10) and human tumor cell (HeLa) by collecting EOT spectrum data during 3-hour on-chip culture. We further collected the EOT spectral shift data at the start and end points of measurement during 3-hour on-chip culture for 50 C3H10 and 50 HeLa cells, respectively. The experiment results show that the single cell attachment process of both HeLa and C3H10 cells follow the logistic retarded growth model, but with different kinetic parameters. Variations in spectral shift during the same culture period across single cells present new evidence for cell heterogeneity. The micro-nano-device provides a new, label-free, real-time, and sensitive, platform to investigate the cell adhesion kinetics at single cell level.

Tumor-targeting domains for chimeric antigen receptor T cells

Immunotherapy with chimeric antigen receptor (CAR) T cells has been advancing steadily in clinical trials. Since the ability of engineered T cells to recognize intended tumor-associated targets is crucial for the therapeutic success, antigen-binding domains play an important role in shaping T-cell responses. Single-chain antibody and T-cell receptor fragments, natural ligands, repeat proteins, combinations of the above and universal tag-specific domains have all been used in the antigen-binding moiety of chimeric receptors. Here we outline the advantages and disadvantages of different domains, discuss the concepts of affinity and specificity, and highlight the recent progress of each targeting strategy.

The principles and applications of avidin-based nanoparticles in drug delivery and diagnosis

Avidin-biotin interaction is one of the strongest non-covalent interactions in the nature. Avidin and its analogues have therefore been extensively utilized as probes and affinity matrices for a wide variety of applications in biochemical assays, diagnosis, affinity purification, and drug delivery. Recently, there has been a growing interest in exploring this non-covalent interaction in nanoscale drug delivery systems for pharmaceutical agents, including small molecules, proteins, vaccines, monoclonal antibodies, and nucleic acids. Particularly, the ease of fabrication without losing the chemical and biological properties of the coupled moieties makes the avidin-biotin system a versatile platform for nanotechnology. In addition, avidin-based nanoparticles have been investigated as diagnostic systems for various tumors and surface antigens. In this review, we will highlight the various fabrication principles and biomedical applications of avidin-based nanoparticles in drug delivery and diagnosis. The structures and biochemical properties of avidin, biotin and their respective analogues will also be discussed.

Biaxial Dielectrophoresis Force Spectroscopy: A Stoichiometric Approach for Examining Intermolecular Weak Binding Interactions

The direct quantification of weak intermolecular binding interactions is very important for many applications in biology and medicine. Techniques that can be used to investigate such interactions under a controlled environment, while varying different parameters such as loading rate, pulling direction, rupture event measurements, and the use of different functionalized probes, are still lacking. Herein, we demonstrate a biaxial dielectrophoresis force spectroscopy (BDFS) method that can be used to investigate weak unbinding events in a high-throughput manner under controlled environments and by varying the pulling direction (i.e., transverse and/or vertical axes) as well as the loading rate. With the BDFS system, we can quantitatively analyze binding interactions related to hydrogen bonding or ionic attractions between functionalized microbeads and a surface within a microfluidic device. Our BDFS system allowed for the characterization of the number of bonds involved in an interaction, bond affinity, kinetic rates, and energy barrier heights and widths from different regimes of the energy landscape.

Lower Affinity T Cells are Critical Components and Active Participants of the Immune Response

Kinetic and biophysical parameters of T cell receptor (TCR) and peptide:MHC (pMHC) interaction define intrinsic factors required for T cell activation and differentiation. Although receptor ligand kinetics are somewhat cumbersome to assess experimentally, TCR:pMHC affinity has been shown to predict peripheral T cell functionality and potential for forming memory. Multimeric forms of pMHC monomers have often been used to provide an indirect readout of higher affinity T cells due to their availability and ease of use while allowing simultaneous definition of other functional and phenotypic characteristics. However, multimeric pMHC reagents have introduced a bias that underestimates the lower affinity components contained in the highly diverse TCR repertoires of all polyclonal T cell responses. Advances in the identification of lower affinity cells have led to the examination of these cells and their contribution to the immune response. In this review, we discuss the identification of high- vs. low-affinity T cells as well as their attributed signaling and functional differences. Lastly, mechanisms are discussed that maintain a diverse range of low- and high-affinity T cells.

Application of avidin-biotin technology to improve cell adhesion on nanofibrous matrices

BACKGROUND

Electrospinning is an easy and effective technique to produce submicron fibers possessing a range of attractive characteristics such as interconnected porous structures similar to natural ECM and good resilience to movement. Rapid and efficient cell attachment to nanofibrous matrices is a necessary prerequisite in tissue engineering. Thus, the aim of this study is to evaluate poly(ε-caprolactone-co-lactide)/Pluronic (PLCL/Pluronic) nanofibrous matrices with avidin-biotin technology for improving cell adhesion for the first time.

RESULTS

PLCL/Pluronic nanofibers had relatively homogeneous fibers and interconnected porous structures. Pluronic significantly modified the hydrophilicity of nanofibrous matrices and PLCL/Pluronic nanofibrous matrices had better performance on maintaining cell proliferation. Avidin-biotin technology had no negative effect on the hydrophilic property, mechanical property and cell proliferation. Meanwhile, the attachment and spreading of adipose-derived stem cells (ADSCs) onto PLCL/Pluronic nanofibrous matrices with avidin-biotin technology was promoted obviously.

CONCLUSIONS

PLCL/Pluronic nanofibrous matrices inheriting the excellent characteristics of both PLCL and Pluronic have the better cell adhesion ability through avidin-biotin technology, implying a promising application in skin care, tissue regeneration and other related area.

Perspective on microfluidic cell separation: a solved problem?

The purification and sorting of cells using microfluidic methodologies has been a remarkably active area of research over the past decade. Much of the scientific and technological work associated with microfluidic cell separation has been driven by needs in clinical diagnostics and therapeutic monitoring, most notably in the context of circulating tumor cells. The last several years have seen advances in a broad range of separation modalities ranging from miniaturized analogs of established techniques such as fluorescence- and magnetic-activated cell sorting (FACS and MACS, respectively), to more specialized approaches based on affinity, dielectrophoretic mobility, and inertial properties of cells. With several of these technologies nearing commercialization, there is a sense that the field of microfluidic cell separation has achieved a high level of maturity over an unusually short span of time. In this Perspective, we set the stage by describing major scientific and technological advances in this field and ask what the future holds. While many scientific questions remain unanswered and new compelling questions will undoubtedly arise, the relative maturity of this field poses some unique challenges.

Bond elasticity controls molecular recognition specificity in antibody-antigen binding

Force-spectroscopy experiments make it possible to characterize single ligand-receptor pairs. Here we measure the spectrum of bond strengths and flexibilities in antibody-antigen interactions using optical tweezers. We characterize the mechanical evolution of polyclonal antibodies generated under infection and the ability of a monoclonal antibody to cross-react against different antigens. Our results suggest that bond flexibility plays a major role in remodeling antibody-antigen bonds in order to improve recognition during the maturation of the humoral immune system.

Glycated collagen and altered glucose increase endothelial cell adhesion strength

Cell adhesion strength is important to cell survival, proliferation, migration, and mechanotransduction, yet changes in endothelial cell adhesion strength have not yet been examined in diseases such as diabetes with high rates of cardiovascular complications. We therefore investigated porcine aortic endothelial cell adhesion strength on native and glycated collagen-coated substrates and in low, normal, and high glucose culture using a spinning disc apparatus. Adhesion strength increased by 30 dynes/cm(2) in cells on glycated collagen as compared to native collagen. Attachment studies revealed that cells use higher adhesion strength αv β3 integrins to bind to glycated collagen instead of the typical α2 β1 integrins used to bind to native collagen. Similarly, endothelial cells cultured in low and high glucose had 15 dynes/cm(2) higher adhesion strength than cells in normal glucose after 2 days. Increased adhesion strength was due to elevated VEGF release and intracellular PKC in low and high glucose cells, respectively. Thus glucose increased endothelial cell adhesion strength via different underlying mechanisms. These adhesion strength changes could contribute to diabetic vascular disease, including accelerated atherosclerosis and disordered angiogenesis.

Zebrafish keratocyte explant cultures as a wound healing model system: differential gene expression & morphological changes support epithelial-mesenchymal transition

The control of collective cell migration of zebrafish keratocyte sheets in explant culture is of interest for cell migration and epithelial wound healing and depends on the gene expression profile. In a zebrafish genome array, ∼17.5% of the probe sets were differentially expressed greater than two-fold (p≤0.003) between 1 and 7 days of explant culture. Among the differentially expressed genes were a variety of wound healing-related genes and many of the biomarkers for epithelial-mesenchymal transition (EMT), including a switch from keratin and E-cadherin to vimentin and N-cadherin expression and several EMT-related transcription factors were found to be differentially expressed. Supporting evidence for EMT is seen in both morphological change and rearrangement of the actin cytoskeleton and in expression of cadherins during explant culture with a visible disassembly of the cell sheet. TGFβ1 and TNFα expression were analyzed by qPCR at various time points and peak differential expression of both cytokines occurred at 3 days, indicating that the EMT process is ongoing under conditions routinely used in the study of fish keratocyte motility. These data establish that an EMT process is occurring during zebrafish keratocyte explant culture and support the use of this system as a wound healing model.

Attomolar protein detection using a magnetic bead surface coverage assay

We demonstrate a microfluidic method for ultra-sensitive protein detection in serum. First, 'large' (2.8 μm) antibody-functionalized magnetic beads specifically capture antigen from a serum matrix under active microfluidic mixing. Subsequently, the large beads loaded with the antigens are gently exposed to a surface pattern of fixed 'small' (1.0 μm) antibody-coated magnetic beads. During the exposure, attractive magnetic bead dipole-dipole interactions improve the contact between the two bead types and help the antigen-antibody immunocomplex formation, while non-specific large bead adsorption is limited by exploiting viscous drag forces in the microfluidic channel on the small-bead pattern. This efficient antigen-antibody recognition and binding mechanism mimics a biological process of selective recognition of tissue molecules, like is the case when leukocytes roll and slow down on blood vessel walls by selectin-mediated adhesion. After exposure of the large beads to the pattern of small beads, the antigen concentration is detected by simply counting the number of surface pattern-bound large magnetic beads. The new technique allows detection of proteins down to the sub-zeptomole range. In particular, we demonstrate detection of only 200 molecules of Tumor Necrosis Factor-α (TNF-α) in a serum sample volume of 5 μL, corresponding to a concentration of 60 attomolar or 1 fg mL(-1).

A spatial model for integrin clustering as a result of feedback between integrin activation and integrin binding

Integrins are transmembrane adhesion receptors that bind extracellular matrix (ECM) proteins and signal bidirectionally to regulate cell adhesion and migration. In many cell types, integrins cluster at cell-ECM contacts to create the foundation for adhesion complexes that transfer force between the cell and the ECM. Even though the temporal and spatial regulation of these integrin clusters is essential for cell migration, how cells regulate their formation is currently unknown. It has been shown that integrin cluster formation is independent of actin stress fiber formation, but requires active (high-affinity) integrins, phosphoinositol-4,5-bisphosphate (PIP2), talin, and immobile ECM ligand. Based on these observations, we propose a minimal model for initial formation of integrin clusters, facilitated by localized activation and binding of integrins to ECM ligands as a result of biochemical feedback between integrin binding and integrin activation. By employing a diffusion-reaction framework for modeling these reactions, we show how spatial organization of bound integrins into clusters may be achieved by a local source of active integrins, namely protein complexes formed on the cytoplasmic tails of bound integrins. Further, we show how such a mechanism can turn small local increases in the concentration of active talin or active integrin into integrin clusters via positive feedback. Our results suggest that the formation of integrin clusters by the proposed mechanism depends on the relationships between production and diffusion of integrin-activating species, and that changes to the relative rates of these processes may affect the resulting properties of integrin clusters.

Slow light engineering for high Q high sensitivity photonic crystal microcavity biosensors in silicon

Current trends in photonic crystal microcavity biosensors in silicon-on-insulator (SOI), that focus on small and smaller sensors have faced a bottleneck trying to balance two contradictory requirements of resonance quality factor and sensitivity. By simultaneous control of the radiation loss and optical mode volumes, we show that both requirements can be satisfied simultaneously. Microcavity sensors are designed in which resonances show highest Q ≈ 9300 in the bio-ambient phosphate buffered saline (PBS) as well as highest sensitivity among photonic crystal biosensors. We experimentally demonstrated mass sensitivity 8.8 atto-grams with sensitivity per unit area of 0.8 pg/mm(2). Highest sensitivity, irrespective of the dissociation constant K(d), is demonstrated among all existing label-free optical biosensors in silicon at the concentration of 0.1 μg/ml.

Microfluidic system for facilitated quantification of nanoparticle accumulation to cells under laminar flow

The identification of novel, synthetic targeting ligands to endothelial receptors has led to the rapid development of targeted nanoparticles for drug, gene and imaging probe delivery. Central to development and optimization are effective models for assessing particle binding in vitro. Here, we developed a simple and cost effective method to quantitatively assess nanoparticle accumulation under physiologically-relevant laminar flow. We designed reversibly vacuum-sealed PDMS microfluidic chambers compatible with 35 mm petri dishes, which deliver uniform or gradient shear stress. These chambers have sufficient surface area for facile cell collection for particle accumulation quantitation through FACS. We tested this model by synthesizing and flowing liposomes coated with APN (K (D) ~ 300 μM) and VCAM-1-targeting (K (D) ~ 30 μM) peptides over HUVEC. Particle binding significantly increased with ligand concentration (up to 6 mol%) and decreased with excess PEG. While the accumulation of particles with the lower affinity ligand decreased with shear, accumulation of those with the higher affinity ligand was highest in a low shear environment (2.4 dyne/cm(2)), as compared with greater shear or the absence of shear. We describe here a robust flow chamber model that is applied to optimize the properties of 100 nm liposomes targeted to inflamed endothelium.

TGFβ (transforming growth factor β) and keratocyte motility in 24 h zebrafish explant cultures

Fish keratocytes are used as a model system for the study of the mechanics of cell motility because of their characteristic rapid, smooth gliding motion, but little work has been done on the regulation of fish keratocyte movement. As TGFβ (transforming growth factor β) plays multiple roles in primary human keratinocyte cell migration, we investigated the possible involvement of TGFβ in fish keratocyte migration. Studying the involvement of TGFβ1 in 24 h keratocyte explant allows the examination of the cells before alterations in cellular physiology occur due to extended culture times. During this initial period, TGFβ levels increase 6.2-fold in SFM (serum-free medium) and 2.4-fold in SFM+2% FBS (fetal bovine serum), while TGFβ1 and TGFβRII (TGFβ receptor II) mRNA levels increase ∼3- and ∼5-fold respectively in each culture condition. Two measures of motility, cell sheet area and migration distance, vary with the amount of exogenous TGFβ1 and culture media. The addition of 100 ng/ml exogenous TGFβ1 in SFM increases both measures [3.3-fold (P = 4.5×10-5) and 26% (P = 2.1×10-2) respectively]. In contrast, 100 ng/ml of exogenous TGFβ1 in medium containing 2% FBS decreases migration distance by 2.1-fold (P = 1.7×10-7), but does not affect sheet area. TGFβ1 (10 ng/ml) has little effect on cell sheet area in SFM cultures, but leads to a 1.8-fold increase (P = 1.5×10-2) with 2% FBS. The variable response to TGFβ1 may be, at least in part, explained by the effect of 2% FBS on cell morphology, mode of motility and expression of endogenous TGFβ1 and TGFβRII. Together, these results suggest that expression of TGFβ and its receptor are up-regulated during zebrafish keratocyte explant culture and that TGFβ promotes fish keratocyte migration.

Using engineered single-chain antibodies to correlate molecular binding properties and nanoparticle adhesion dynamics

Elucidation of the relationship between targeting molecule binding properties and the adhesive behavior of therapeutic or diagnostic nanocarriers would aid in the design of optimized vectors and lead to improved efficacy. We measured the adhesion of 200-nm-diameter particles under fluid flow that was mediated by a diverse array of molecular interactions, including recombinant single-chain antibodies (scFvs), full antibodies, and the avidin/biotin interaction. Within the panel of scFvs, we used a family of mutants that display a spectrum of binding kinetics, allowing us to compare nanoparticle adhesion to bond chemistry. In addition, we explored the effect of molecular size by inserting a protein linker into the scFv fusion construct and by employing scFvs that are specific for targets with vastly different sizes. Using computational models, we extracted multivalent kinetic rate constants for particle attachment and detachment from the adhesion data and correlated the results to molecular binding properties. Our results indicate that the factors that increase encounter probability, such as adhesion molecule valency and size, directly enhance the rate of nanoparticle attachment. Bond kinetics had no influence on scFv-mediated nanoparticle attachment within the kinetic range tested, however, but did appear to affect antibody/antigen and avidin/biotin mediated adhesion. We attribute this finding to a combination of multivalent binding and differences in bond mechanical strength between recombinant scFvs and the other adhesion molecules. Nanoparticle detachment probability correlated directly with adhesion molecule valency and size, as well as the logarithm of the affinity for all molecules tested. On the basis of this work, scFvs can serve as viable targeting receptors for nanoparticles, but improvements to their bond mechanical strength would likely be required to fully exploit their tunable kinetic properties and maximize the adhesion efficiency of nanoparticles that bear them.

Velocity effect on aptamer-based circulating tumor cell isolation in microfluidic devices

The isolation and detection of rare circulating tumor cells (CTCs) has been one of the focuses of intense research recently. In a microfluidic device, a number of factors can influence the enrichment capability of surface-bound probe molecules. This article analyzes the important factor of flow velocity in a microfluidic channel. The competition of surface-grafted anti-EGFR aptamers to bind the overexpressed EGFR on cell membranes against the drag force from the fluid flow is an important efficiency determining factor. The flow rate variations are applied both in experiments and in simulation models to study their effects on CTC capture efficiency. A mixture of mononuclear cells and human Glioblastoma cells is used to isolate cancer cells from the cellular flow. The results show interdependence between the adhesion probability, isolation efficiency, and flow rate. This work can help in designing flow-through lab-on-chip devices that use surface-bound probe affinities against overexpressed biomarkers for cell isolation. This work demonstrates that microfluidic based approaches have strong potential applications in CTC detection and isolation.

A biological breadboard platform for cell adhesion and detachment studies

The dynamic nature of cell adhesion and detachment, which plays a critical role in a variety of physiological and pathological phenomena, still remains unclear. This motivates the pursuit of controllable manipulation of cell adhesion and detachment for a better understanding of cellular dynamics. Here we present an addressable, multifunctional, and reusable platform, termed the biological breadboard (BBB), for spatiotemporal manipulation of cell adhesion and detachment at cellular and subcellular levels. The BBB, composed of multiple gold electrodes patterned on a Pyrex substrate, is surface-modified with arginine-glycine-aspartic acid terminated thiol (RTT) and polyethylene glycol (PEG) to achieve a cell-adhesive surface on the gold electrodes and a cell-resistive surface on the Pyrex substrate, respectively. Cell adhesion is regulated by the steric repulsion of PEG chains, while cell detachment is controlled by the reductive desorption of a gold-thiol self-assembled monolayer (SAM) at an activation potential of -0.90 to -1.65 V. Experimental characterizations using NIH 3T3 fibroblasts are presented to demonstrate the utility of our device.

Orientation and detachment dynamics of Bacillus spores from stainless steel under controlled shear flow: modelling of the adhesion force

Shear-flow induced spore detachment was performed under well-controlled laminar flow conditions, in a specially-designed shear stress flow chamber. By comparing detachment profiles of a panel of four strains, belonging to the B. cereus group (B. cereus and B. thuringiensis) and to less related Bacillus species (B. pumilus), it was shown that the spore ability of attaching to stainless steel, probed under dynamic conditions, was mainly affected by the presence (and number) of appendages. Adhesion force between the B. cereus 98/4 strain and stainless steel was quantified at nanoscale. To this aim, detachment results were combined with a theoretical modelling, based on the balance of hydrodynamic forces and torque exerted over a simplified spore model with a spherical form. The wall shear stress, required to remove 50% of the spores initially attached to stainless steel, was determined. On this basis, an adhesion force of 930 ± 390 pN was obtained. Real-time re-orientation of B. cereus 98/4 spores was experimentally established, by using a high-speed camera for tracking the motions of individual spores with high temporal and spatial resolution. Even though tethered to stainless steel without any detachment occurring, spores kept mobile on the substratum, probably due to the existence of discrete bonds or local clusters of anchoring sites, and tended to re-orientate in the flow direction, for minimizing hydrodynamic forces and torque exerted by fluid flow. A significant heterogeneity within the population was also observed, with the co-existence of both moving and immobile spores.

Diffusion-dependent mechanisms of receptor engagement and viral entry

Enveloped viruses attach to host cells by binding to receptors on the cell surface. For many viruses, entry occurs via membrane fusion after a sufficient number of receptors have engaged ligand proteins on the virion. Under conditions where the cell surface receptor densities are low, recruitment of receptors may be limited by diffusion rather than by receptor-ligand interactions. We present a receptor-binding model that includes the effects of receptor availability at the viral binding site. The receptor binding and unbinding kinetics are coupled to receptor diffusion across the cell membrane. We find numerical solutions to our model and analyze the viral entry probabilities and the mean times to entry as functions of receptor concentration, receptor diffusivity, receptor binding stoichiometry, receptor detachment rates, and virus degradation/detachment rates. We also show how entry probabilities and times differ when receptors bind randomly or sequentially to the binding sites on the viral glycoprotein spikes. Our results provide general insight into the biophysical transport mechanisms that may arise in viral attachment and entry.

Modeling cytoskeletal flow over adhesion sites: competition between stochastic bond dynamics and intracellular relaxation

In migrating cells, retrograde flow of the actin cytoskeleton is related to traction at adhesion sites located at the base of the lamellipodium. The coupling between the moving cytoskeleton and the stationary adhesions is mediated by the continuous association and dissociation of molecular bonds. We introduce a simple model for the competition between the stochastic dynamics of elastic bonds at the moving interface and relaxation within the moving actin cytoskeleton represented by an internal viscous friction coefficient. Using exact stochastic simulations and an analytical mean field theory, we show that the stochastic bond dynamics lead to biphasic friction laws as observed experimentally. At low internal dissipation, stochastic bond dynamics lead to a regime of irregular stick-and-slip motion. High internal dissipation effectively suppresses cooperative effects among bonds and hence stabilizes the adhesion.