High-Affinity and Proteolytically Stable Peptidic Fluorescent NTS₁R Ligands

Area of Science:

• Medicinal Chemistry
• Neuroscience
• Molecular Imaging

Background:

• Neurotensin receptor 1 (NTS₁R) is implicated in CNS disorders, gastrointestinal functions, and cancer.
• Development of high-affinity, stable, and fluorescent ligands is crucial for NTS₁R research.
• Existing ligands often lack sufficient stability or binding characteristics for detailed investigation.

Purpose of the Study:

• To synthesize novel fluorescence-labeled neurotensin(8-13) analogs as high-affinity NTS₁R ligands.
• To enhance proteolytic stability and binding affinity of neurotensin-derived probes.
• To validate the utility of these probes for NTS₁R expression analysis and imaging.

Main Methods:

• Chemical modification of neurotensin(8-13) sequence, including amino-functionalized carbamoylated arginine at position 8, Nα-methylation, and specific amino acid substitutions (Tyr¹¹, Leu¹³).
• Conjugation of fluorophores (5-TAMRA, sulfo-Cy5) to the modified peptide backbone.
• Assessment of binding affinity (K_i), plasma stability (t_1/2), and application in flow cytometry and confocal microscopy for cellular and tissue imaging.

Main Results:

• Synthesized fluorescent NTS₁R ligands (e.g., 5-TAMRA-ligand 19, sulfo-Cy5 probe 21) exhibit unprecedented binding affinity (K_i as low as 0.094 nM).
• Probes demonstrate high stability in human plasma (t_1/2 >> 48 h).
• Successful application in competition binding studies, imaging NTS₁R in living cells, and visualizing NTS₁R in tumor tissue.

Conclusions:

• The developed fluorescent ligands represent a significant advancement for NTS₁R research.
• These probes offer superior affinity and stability, enabling more accurate investigation of NTS₁R.
• The study validates their potential for diagnostic and research applications in oncology and neuroscience.