Squalene-PEG-Exendin as High-Affinity Constructs for Pancreatic Beta-Cells.

Area of Science:

• Bioconjugation Chemistry
• Peptide Engineering
• Drug Delivery Systems

Background:

• Targeting native, transplanted, or cancerous beta-cells is crucial for therapeutic interventions.
• Exendin-4 is a peptide hormone analogue with potential for beta-cell targeting.
• Developing novel drug delivery systems requires precise control over molecular modifications.

Purpose of the Study:

• To synthesize novel exendin-4 derivatives with unnatural amino acids.
• To conjugate these derivatives with imaging agents and amphiphilic squalene-PEG groups.
• To evaluate the targeting specificity and pharmacokinetic properties of the resulting probes.

Main Methods:

• Chemical modification of exendin-4 with unnatural amino acids.
• Orthogonal chemical modifications for attaching imaging agents (Cy5) and squalene-PEG.
• Fluorescence-based binding assays to determine affinity to GLP-1 receptor (GLP-1R).
• In vitro cell targeting studies using MIN6 and CHL-GLP-1R cells.
• In vivo imaging and biodistribution studies in normoglycemic mice.

Main Results:

• Developed SQ-PEG-ExC1-Cy5 and SQ-PEG-ExC40-Cy5 fluorescence probes.
• Probes exhibited low nanomolar affinity to GLP-1R (EC50: 1.1 ± 0.2 nM and 0.8 ± 0.2 nM).
• Specific targeting of GLP-1R-expressing cells (MIN6 and CHL-GLP-1R) in vitro.
• Observed specific islet targeting in vivo after i.v. injection.
• Prolonged blood half-life (3.8 h) for the amphiphilic conjugate.
• Identified liver and pancreas as primary biodistribution organs.

Conclusions:

• Novel exendin-4 derivatives can be effectively modified for targeted beta-cell imaging.
• The developed probes demonstrate high affinity and specificity for GLP-1R.
• These conjugates show potential for in vivo beta-cell visualization and drug delivery applications.