Long term kinetic measurements revealing precision and general performance of surface plasmon resonance biosensors

Effects of Chemical Fixatives on Kinetic Measurements of Biomolecular Interaction on Cell Membrane

Understanding the interaction between ligands and membrane proteins is important for drug design and optimization. Although investigation using live cells is desirable, it is not feasible in some circumstances and cell fixation is performed to reduce cell motion and degradation. This study compared the effects of five fixatives, i.e., formaldehyde vapor (FV), paraformaldehyde (PFA), acetone, methanol, and ethanol, on kinetic measurements via the LigandTracer method. We found that all five fixatives exerted insignificant effects on lectin-glycan interaction. However, antibody-receptor interaction is markedly perturbed by coagulant fixatives. The acetone fixation changed the binding of the anti-human epidermal growth factor receptor 2 (HER2) antibody to HER2 on the cell membrane from a 1:2 to a 1:1 binding model, while methanol and ethanol abolished the antibody binding possibly by removal of the HER2 receptors on the cell membrane. The capability of binding was retained when methanol fixation was performed at lower temperatures, albeit with a binding model of 1:1 instead. Moreover, whereas cell morphology does not exert a substantial impact on lectin-glycan interaction, it can indeed modify the binding model of antibody-receptor interaction. Our results provided insights into the selection of fixatives for cell-based kinetic studies.

Live Cells versus Fixated Cells: Kinetic Measurements of Biomolecular Interactions with the LigandTracer Method and Surface Plasmon Resonance Microscopy

Cell-based kinetic studies of ligand or candidate drug binding to membrane proteins have produced affinity and kinetic values that are different from measurements using purified proteins. However, ligand binding to fixated cells whose membrane constituents (e.g., proteins and their glycosylated forms) are partially connected by a cross-linking reagent has not been compared to that to live cells. Under the same experimental conditions for the LigandTracer method, we measured the interactions of fluorophore-labeled lectins and antibody molecules with glycans at HFF cells and the human epithelial growth receptor 2 at SKBR3 cells, respectively. In conjunction with surface plasmon resonance microscopy, the effects of labels and cell/sub-cell heterogeneity on binding kinetics were investigated. Our results revealed that, for cell constituents whose structures and functions are not closely dependent on cell viability, the ligand binding kinetics at fixated cells is only slightly different from that at live cells. The altered kinetics is explained on the basis of a less mobile receptor confined in a local environment created by partially interconnected protein molecules. We show that cell/sub-cell heterogeneity and labels on the ligands can alter the binding reaction more significantly. Thus, fixating cells not only simplifies experimental procedures for drug screening and renders assays more robust but also provides reliable kinetic information about drug binding to cell constituents whose structures are not changed by chemical fixation.

Efficacy, Pharmacokinetics, Biodistribution and Excretion of a Novel Acylated Long-Acting Insulin Analogue INS061 in Rats

Purpose

Long-acting insulin analogues are known to be a major player in the management of glucose levels in type I diabetic patients. However, highly frequent hypo- and hyperglycemic incidences of current long-acting insulins are the important factor to limit stable management of glucose level for clinical benefits. To further optimize the properties for steadily controlling glucose level, a novel long-acting insulin INS061 was designed and its efficacy, pharmacokinetics, biodistribution and excretion profiles were investigated in rats.

Methods

The glucose-lowering effects were evaluated in a streptozocin-induced diabetic rats compared to commercial insulins via subcutaneous administration. The pharmacokinetics, biodistribution, and excretion were examined by validated analytical methods including radioactivity assay and radioactivity assay after the precipitation with TCA and the separation by HPLC.

Results

INS061 exhibited favorable blood glucose lowering effects up to 24 h compared to Degludec. Pharmacokinetic study revealed that the concentration-time curves of INS061 between two administration routes were remarkably different. Following intravenous administration, INS061 was quickly distributed to various organs and tissues and slowly eliminated over time with urinary excretion being the major route for elimination, and the maximum plasma concentrations (Cmax) and systemic exposures (AUC) increased in a linear manner.

Conclusion

The present structural modifications of human insulin possessed a long-acting profile and glucose-lowering function along with favorable in vivo properties in rats, which establish a foundation for further preclinical and clinical evaluation.

Beyond conventional dose-response curves: Sensorgram comparison in SPR allows single concentration activity and similarity assessment

Previously we have introduced two SPR-based assay principles (dual-binding assay and bridging assay), which allow the determination of two out of three possible interaction parameters for bispecific molecules within one assay setup: two individual interactions to both targets, and/or one simultaneous/overall interaction, which potentially reflects the inter-dependency of both individual binding events. However, activity and similarity are determined by comparing report points over a concentration range, which also mirrors the way data is generated by conventional ELISA-based methods So far, binding kinetics have not been specifically considered in generic approaches for activity assessment. Here, we introduce an improved slope-ratio model which, together with a sensorgram comparison based similarity assessment, allows the development of a detailed, USP-conformal ligand binding assay using only a single sample concentration. We compare this novel analysis method to the usual concentration-range approach for both SPR-based assay principles and discuss its impact on data quality and increased sample throughput.

Aptamer-Templated Silver Nanoclusters Embedded in Zirconium Metal-Organic Framework for Bifunctional Electrochemical and SPR Aptasensors toward Carcinoembryonic Antigen

This study reported a novel biosensor based on the nanocomposite of zirconium metal-organic framework (Zr-MOF, UiO-66) embedded with silver nanoclusters (Ag NCs) using the carcinoembryonic antigen (CEA)-targeted aptamer as template (AgNCs@Apt@UiO-66). The synthesized AgNCs@Apt@UiO-66 nanocomposite not only possesses good biocompatibility, active electrochemical performance, and strong bioaffinity, but also can be dispersed to form two-dimensional nanocomposite with nanoscale thickness. As such, the use of the AgNCs@CEA-aptamer enables AgNC@Apt@UiO-66 with sensitive and selective detection capacity of trace CEA, further concurrently being exploited as scaffold for surface plasmon resonance spectroscopy (SPR) and electrochemical biosensors. The results showed that the proposed electrochemical AgNC@Apt@UiO-66-based aptasensor exhibits high sensitivity with a low detection limit (LOD) of 8.88 and 4.93 pg·mL^-1 deduced from electrochemical impedance spectroscopy and differential pulse voltammetry, respectively, within a broad linear range of the CEA concentration (0.01-10 ng·mL^-1). Meanwhile, the developed SPR biosensor exhibited a slightly high LOD of 0.3 ng·mL^-1 within the CEA concentration of 1.0-250 ng·mL^-1. Both the electrochemical and SPR aptasensors displayed high selectivity, good reproducibility, stability, acceptable regenerability, and applicability in real human serum samples. These results proved that the proposed aptamer-targeted Zr-MOF nanocomposite can be utilized in multiple-functionally biosensing, further promoting the potential application of Zr-MOF-related nanomaterials in clinical diagnosis.