Therapeutic hypothermia represents a brain-protective strategy for multiple emergency situations, such as
stroke or traumatic injury.
Neurotensin (NT), which exerts its effects through activation of two
G protein-coupled receptors, namely NTS1 and NTS2, induces a strong and long-lasting decrease in core body temperature after its central administration. Growing evidence demonstrates that NTS1 is the receptor subtype mediating the hypothermic action of NT. As such, potent NTS1 agonists designed on the basis of the minimal C-terminal
NT(8-13) bioactive fragment have been shown to produce mild
hypothermia and exert
neuroprotective effects under various clinically relevant conditions. The high susceptibility of
NT(8-13) to
protease degradation (half-life <2 min) represents, however, a serious limitation for its use in pharmacological
therapy. In light of this, we report here a structure-activity relationship study in which pairs of
NT(8-13) analogs have been developed, based on the incorporation of a reduced Lys8-Lys9 bond. To further stabilize the
peptide bonds, a panel of backbone modifications was also inserted along the
peptide sequence, including Sip10, D-Trp11, Dmt11, Tle12, and TMSAla13. Our results revealed that the combination of appropriate chemical modifications leads to compounds exhibiting improved resistance to proteolytic cleavages (>24 h; 16). Among them, the
NT(8-13) analogs harboring the reduced
amine bond combined with the unnatural
amino acids TMSAla13 (4) and Sip10 (6) or the di-substitution Lys11 - TMSAla13 (12), D-Trp11-TMSAla13 (14), and Dmt11-Tle12 (16) produced sustained hypothermic effects (-3°C for at least 1 h). Importantly, we observed that
hypothermia was mainly driven by the increased stability of the
NT(8-13) derivatives, instead of the high binding-affinity at NTS1. Altogether, these results reveal the importance of the reduced
amine bond in optimizing the metabolic properties of the
NT(8-13) peptide and support the development of stable NTS1 agonists as first
drug candidate in neuroprotective
hypothermia.