An AlphaScreen Assay for the Discovery of Synthetic Chemical Inhibitors of Glucagon Production

Small molecule glucagon release inhibitors with activity in human islets

Purpose

Type 1 diabetes (T1D) accounts for an estimated 5% of all diabetes in the United States, afflicting over 1.25 million individuals. Maintaining long-term blood glucose control is the major goal for individuals with T1D. In T1D, insulin-secreting pancreatic islet β-cells are destroyed by the immune system, but glucagon-secreting islet α-cells survive. These remaining α-cells no longer respond properly to fluctuating blood glucose concentrations. Dysregulated α-cell function contributes to hyper- and hypoglycemia which can lead to macrovascular and microvascular complications. To this end, we sought to discover small molecules that suppress α-cell function for their potential as preclinical candidate compounds. Prior high-throughput screening identified a set of glucagon-suppressing compounds using a rodent α-cell line model, but these compounds were not validated in human systems.

Results

Here, we dissociated and replated primary human islet cells and exposed them to 24 h treatment with this set of candidate glucagon-suppressing compounds. Glucagon accumulation in the medium was measured and we determined that compounds SW049164 and SW088799 exhibited significant activity. Candidate compounds were also counter-screened in our InsGLuc-MIN6 β-cell insulin secretion reporter assay. SW049164 and SW088799 had minimal impact on insulin release after a 24 h exposure. To further validate these hits, we treated intact human islets with a selection of the top candidates for 24 h. SW049164 and SW088799 significantly inhibited glucagon release into the medium without significantly altering whole islet glucagon or insulin content. In concentration-response curves SW088799 exhibited significant inhibition of glucagon release with an IC50 of 1.26 µM.

Conclusion

Given the set of tested candidates were all top hits from the primary screen in rodent α-cells, this suggests some conservation of mechanism of action between human and rodents, at least for SW088799. Future structure-activity relationship studies of SW088799 may aid in elucidating its protein target(s) or enable its use as a tool compound to suppress α-cell activity in vitro.

A homogeneous immunoassay for detection of the interaction between two tumor biomarkers of IGF1R-β and SOCS1

The current protein interaction method is time consuming and cumbersome or the instrument is expensive. A new method that is convenient, fast, and high throughput needs to be studied urgently. The purpose of this study was to establish a homogeneous immunoassay to detect the interaction between insulin-like growth factor-1 receptor-β (IGF1R-β) and suppressor of cytokine signaling 1 (SOCS1). The recombinant vectors IGF1R-β/pENTER and SOCS1/pENTER were constructed and transfected into 293T cells. Based on homogeneous immunoassay technology, we established a suitable method. The signal intensity in the 293T lysate that overexpressed IGF1R-β and SOCS1, respectively, was compared with the signal intensity in the simultaneous expression of IGF1R-β and SOCS1. The interaction between IGF1R-β and SOCS1 was verified in vitro. The detection system for the interaction between IGF1R-β and SOCS1 was established. Compared with other methods, homogeneous immunoassay has the advantages of being rapid and sensitive, having higher sensitivity, and easy to operate. The interaction between IGF1R-β and SOCS1 was tested to verify the feasibility of this method and prove its practicability and sensitivity. This new method can be used as a high-throughput platform for protein-protein interaction, with the advantages of trace detection, short detective time, and high detective sensitivity.

Generation of a Monoclonal Antibody against D-Dimer Using HTS-Based LiCA

D-dimer is an essential diagnostic index of thrombotic diseases. Since the existing anti-D-dimer antibodies vary in quality and specificity, a search for alternative anti-D-dimer antibodies is required. The present study aimed to screen a novel monoclonal antibody (mAb) against D-dimer using a light-initiated chemiluminescence assay (LiCA). In this work, mice were immunized with antigen prepared from human plasma by enzyme hydrolysis. After screening, a novel mAb, DD 2G11, was obtained. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis indicated that DD 2G11 could be used as a standard marker for D-dimer. The isotype of DD 2G11 was IgG1, the K_a value was 0.646 nM-1, and the K_d value was 50 nM, indicating that the binding affinity to D-dimer was very high. Furthermore, no cross-reactivity between DD 2G11 and other fibrinogen degradation products (FgDPs) was found. Finally, the correlation between DD 2G11 and the reference antibody (commercial antibody) was investigated by analyzing 56 clinical samples using a latex-enhanced turbidimetric immunoassay (LTIA). The R² value of the linear regression was 0.94538, indicating that DD 2G11 met clinical requirements. In conclusion, the present study provides a more expeditious protocol to screen mAbs and provides a clinically usable mAb against D-dimer.

A Fluorescent Glucose Transport Assay for Screening SGLT2 Inhibitors in Endogenous SGLT2-Expressing HK-2 Cells

The sodium-dependent glucose transporters 2 (SGLT2) plays important role in renal reabsorption of urinal glucose back to plasma for maintaining glucose homeostasis. The approval of SGLT2 inhibitors for treatment of type 2 diabetes highlights the SGLT2 as a feasible and promising drug target in recent years. Current methods for screening SGLT2 inhibitors are complex, expensive and labor intensive. Particularly, these methods cannot directly measure nonradioactive glucose uptake in endogenous SGLT2-expressing kidney cells. In present work, human kidney cells, HK-2, was incubated with a fluorescent D-glucose derivant 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-D-glucose (2-NBDG) and the fluorescent intensity of 2-NBDG was employed to measure the amount of glucose uptake into the cells. By optimizing the passages of HK-2 cells, 2-NBDG concentration and incubation time, and by measuring glucose uptake treated by Dapagliflozin, a clinical drug of SGLT2 inhibitors, we successfully developed a new assay for measuring glucose uptake through SGLT2. The nonradioactive microplate and microscope-based high-throughput screening assay for measuring glucose can be a new method for screening of SGLT2 inhibitors and implied for other cell assays for glucose measurement extensively.

Development and Characterization of Quantitative, High-Throughput-Compatible Assays for Proteolytic Degradation of Glucagon

Glucagon is a vital peptide hormone involved in the regulation of blood sugar under fasting conditions. Although the processes underlying glucagon production and secretion are well understood, far less is known about its degradation, which could conceivably be manipulated pharmacologically for therapeutic benefit. We describe here the development of novel assays for glucagon degradation, based on fluoresceinated and biotinylated glucagon (FBG) labeled at the N- and C-termini, respectively. Proteolysis at any peptide bond within FBG separates the fluorescent label from the biotin tag, which can be quantified in multiple ways. In one method requiring no specialized equipment, intact FBG is separated from the cleaved fluoresceinated fragments using NeutrAvidin agarose beads, and hydrolysis is quantified by fluorescence. In an alternative, high-throughput-compatible method, the degree of hydrolysis is quantified using fluorescence polarization after addition of unmodified avidin. Using a known glucagon protease, we confirm that FBG is cleaved at similar sites as unmodified glucagon and use both methods to quantify the kinetic parameters of FBG degradation. We show further that the fluorescence polarization-based assay performs exceptionally well ( Z'-factor values >0.80) in a high-throughput, mix-and-measure format.

Dapagliflozin suppresses glucagon signaling in rodent models of diabetes

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a class of antidiabetic drug used for the treatment of diabetes. These drugs are thought to lower blood glucose by blocking reabsorption of glucose by SGLT2 in the proximal convoluted tubules of the kidney. To investigate the effect of inhibiting SGLT2 on pancreatic hormones, we treated perfused pancreata from rats with chemically induced diabetes with dapagliflozin and measured the response of glucagon secretion by alpha cells in response to elevated glucose. In these type 1 diabetic rats, glucose stimulated glucagon secretion by alpha cells; this was prevented by dapagliflozin. Two models of type 2 diabetes, severely diabetic Zucker rats and db/db mice fed dapagliflozin, showed significant improvement of blood glucose levels and glucose disposal, with reduced evidence of glucagon signaling in the liver, as exemplified by reduced phosphorylation of hepatic cAMP-responsive element binding protein, reduced expression of phosphoenolpyruvate carboxykinase 2, increased hepatic glycogen, and reduced hepatic glucose production. Plasma glucagon levels did not change significantly. However, dapagliflozin treatment reduced the expression of the liver glucagon receptor. Dapagliflozin in rodents appears to lower blood glucose levels in part by suppressing hepatic glucagon signaling through down-regulation of the hepatic glucagon receptor.