Discovery of the First Environment-Sensitive Fluorescent Probe for GPR120 (FFA4) Imaging

Fluorescent Ligand-Based Discovery of Small-Molecule Sulfonamide Agonists for GPR120

As a critical member of G protein-coupled receptors (GPCRs), G protein-coupled receptor 120 (GPR120) is a potential target for many physiological diseases, such as type 2 diabetes mellitus, inflammation, and obesity. Considering that small-molecule fluorescent ligands can combine the advantages of visualization, high sensitivity and selectivity, we initially undertook an effort to develop a series of fluorescent ligands to track GPR120 and establish a method to screen GPR120 agonists. The representative fluorescent ligand N1 possesses suitable optical property, equitable biological activity, and high fluorescence imaging feasibility, therefore, based on compound N1, we subsequently founded a bioluminescence resonance energy transfer (BRET) competition binding assay to screen three series of sulfonamide GPR120 agonists we developed herein. The activity evaluation results revealed that compound D5 was a potent GPR120 agonist with high activity and selectivity. Moreover, compound D5 exhibited a significant glucose-lowering effect in db/db mice, which indicates its potential application in the treatment of type 2 diabetes mellitus in vivo. It is anticipated that our fluorescent ligand-based method is a useful toolbox and will find broad applications in the discovery of small-molecule agonists for GPR120.

Design and Application of Receptor-Targeted Fluorescent Probes Based on Small Molecular Fluorescent Dyes

In recent years, a variety of receptor-targeted fluorescent probes have been developed and widely used to realize the visualization of certain receptors, which facilitates the early diagnosis and treatment of diseases. In this Review, we focus on the recent achievements in design, chemical structure, imaging characterization, and potential applications of receptor-targeted fluorescent probes from the past 10 years. The development and application of receptor-targeted fluorescent probes will expand our knowledge of the distribution and function of disease-related receptors, shed light on the drug discovery for clinical diseases where receptors are implicated, and feed into the diagnosis and treatment of a plethora of diseases, including tumors.

Discovery of the Environment-Sensitive Near-Infrared (NIR) Fluorogenic Ligand for α1-Adrenergic Receptors Imaging In Vivo

Fluorescent ligands have emerged as powerful tools for noninvasive research of G protein-coupled receptors (GPCRs), since they could provide the invaluable information regarding GPCRs' structure and function in vitro. However, the in vivo applications of thus tools are hampered owing to their short-wavelength spectra and lack of fluorogenic switch. Here, we describe the experimental details of discovery of the environment-sensitive near-infrared (NIR) fluorogenic ligand for in vivo imaging of α1-adrenergic receptor (α1-AR).

New small molecule fluorescent probes for G protein-coupled receptors: valuable tools for drug discovery

G protein-coupled receptors (GPCRs) are essential signaling proteins and tractable therapeutic targets. To develop new drug candidates, GPCR drug discovery programs require versatile, sensitive pharmacological tools for ligand binding and compound screening. With the availability of new imaging modalities and proximity-based ligand binding technologies, fluorescent ligands offer many advantages and are increasingly being used, yet labeling small molecules remains considerably more challenging relative to peptides. Focusing on recent fluorescent small molecule studies for family A GPCRs, this review addresses some of the key challenges, synthesis approaches and structure-activity relationship considerations, and discusses advantages of using high-resolution GPCR structures to inform conjugation strategies. While no single approach guarantees successful labeling without loss of affinity or selectivity, the choice of fluorophore, linker type and site of attachment have proved to be critical factors that can significantly affect their utility in drug discovery programs, and as discussed, can sometimes lead to very unexpected results.

Discovery of Turn-On Fluorescent Probes for Detecting PDEδ Protein in Living Cells and Tumor Slices

The first small-molecule fluorescent turn-on probes for detecting PDEδ protein were rationally designed, showing reasonable fluorescent properties and the fluorescent ability has been applied for visualization of the PDEδ protein in living cells and at tissue levels. The qPCR results showed that the mRNA expression of KRAS, PDEδ, AKT1, MAPK1, MEK7, RAF1, and mTOR were downregulated by probes 1-3 through PI3K/AKT/mTOR and MAPK signal pathways. The probes also can downregulate the protein level of pErk and tErk. Therefore, these small-molecule fluorescent probes are expected to be used in the screening of antipancreatic cancer drugs targeting the PDEδ protein, as well as in obtaining a better understanding of the pathological and physiological roles of PDEδ protein.

Discovery of Nonpeptide, Environmentally Sensitive Fluorescent Probes for Imaging p53-MDM2 Interactions in Living Cell Lines and Tissue Slice

Based on structural optimization work, probes 9-11 with practical activity and selectivity in tissue as well as living cell lines are well designed and synthesized. All the probes showed potent inhibitory and acceptable cell toxicity compared with the commercially available p53-MDM2 inhibitor Nutlin-3, and can increase the protein expression level of p53 and MDM2 in the A549 cell line; in particular, probes 10 and 11 can increase the protein expression level of p53 better than Nutlin-3. Moreover, their application in imaging and detecting wild-type p53-MDM2 protein-protein interactions have been well demonstrated in at the cell and tissue levels. Overall, these environmentally sensitive fluorescent turn-on probes are affordable and rapid for imaging, which is expected for applications in target drug screening as well as in pathologic diagnosis.

pH-Responsive Nanofibers for Precise and Sequential Delivery of Multiple Payloads

Effective combination therapies can be achieved by programming materials for controlling release sequence, timing, and dose of multiple payloads. Herein, we synthesize dextran esters by coesterification of dextran, which display responsive properties at a precise pH threshold between 5.0 and 7.0. Multilayers electrospun nanofibers are prepared so that three different payloads are entrapped in three different dextran esters. The release of the three drugs can be sequentially and independently activated by a gradual increase of pH value. Because both pH threshold and release kinetics are matching conditions encountered by aliments along the gastrointestinal tract, these dextran ester multilayer nanofibers are promising for oral drug delivery.

Environment-sensitive turn-on fluorescent probes for p53-MDM2 protein-protein interaction

A series of probes with a turn-on switch for the p53-MDM2 protein-protein interaction were developed. After careful evaluation, these small molecule fluorescent probes exhibited high practical activity and selectivity in vitro and in cellulo. In particular probe 10, which had a K_i value of 0.03 μM, displayed much better binding affinity compared to the positive control Nutlin-3, which had a K_i value of 0.23 μM. These no-wash environment-sensitive turn-on fluorescent probes have been successfully applied to imaging p53-MDM2 interaction in the human lung cancer cell line A549 (wild-type p53) at the micromolar level. Therefore, these fluorescent probes are expected to be used in drug screening and cell staining in p53-MDM2 fields, as well as in pathological and physiological studies of the p53-MDM2 interaction.