Neurotensin

The neurotensin receptor NTSR1 binds the peptide agonist neurotensin (NTS) and signals preferentially via the Gq protein. Recently Grisshammer and coworkers reported the crystal structure of a thermostable mutant NTSR1-GW5 with NTS bound. Understanding how the mutations thermostabilize the structure would allow efficient design of thermostable mutant GPCRs for protein purification, and subsequent biophysical studies. Using microsecond scale molecular dynamics simulations (4 μs) of the thermostable mutant NTSR1-GW5 and wild type NTSR1, we have elucidated the structural and energetic factors that affect the thermostability and dynamics of NTSR1. The thermostable mutant NTSR1-GW5 is found to be less flexible and less dynamic than the wild type NTSR1. The point mutations confer thermostability by improving the inter-helical hydrogen bonds, hydrophobic packing, and the receptor interactions with the lipid bilayer, especially in the intracellular regions. During MD, NTSR1-GW5 becomes more...

The increased expression of the neurotensin (NT) receptor NTS1 by different cancer cells, such as pancreatic adenocarcinoma and ductal breast cancer cells, as compared to normal epithelium, offers the opportunity to target these tumors with radiolabeled neurotensin analogues for diagnostic or therapeutic purposes. The aim of the present study was to design and synthesize new neurotensin radioligands and to select a lead molecule with high in vivo tumor selectivity for further development. Two series of neurotensin analogues bearing DTPA were tested: a series of NT(8-13) analogues, with DTPA coupled to the R-NH 2 , sharing the same peptide sequence with analogues previously developed for radiolabeling with technetium or rhenium, as well as an NT(6-13) series in which DTPA was coupled to the ε-NH 2 of Lys 6. Changes were introduced to stabilize the bonds between Arg 8-Arg 9 , Pro 10-Tyr 11 , and Tyr 11-Ile 12 to provide metabolic stability. Structure-activity studies of NT analogues have shown that the attachment of DTPA induces an important loss of affinity unless the distance between the chelator and the NT(8-13) sequence, which binds to the NTS1 receptor, is increased. The doubly stabilized DTPA-NT-20.3 exhibits a high affinity and an elevated stability to enzymatic degradation. It shows specific tumor uptake and high tumor to blood, to liver, and to intestine activity uptake ratios and affords high-contrast planar and SPECT images in an animal model. The DTPA-NT-20.3 peptide is a promising candidate for imaging neurotensin receptor-positive tumors, such as pancreatic adenocarcinoma and invasive ductal breast cancer. Analogues carrying DOTA are being developed for yttrium-90 or lutetium-177 labeling.