Structure‐Based Evolution of Subtype‐Selective Neurotensin Receptor Ligands

Abstract

Subtype-selective agonists of the neurotensin receptor NTS2 represent a promising option for the treatment of neuropathic pain, as NTS2 is involved in the mediation of μ-opioid-independent anti-nociceptive effects. Based on the crystal structure of the subtype NTS1 and previous structure–activity relationships (SARs) indicating a potential role for the sub-pocket around Tyr11 of NT(8–13) in subtype-specific ligand recognition, we have developed new NTS2-selective ligands. Starting from NT(8–13), we replaced the tyrosine unit by β2-amino acids (type 1), by heterocyclic tyrosine bioisosteres (type 2) and peptoid analogues (type 3). We were able to evolve an asymmetric synthesis of a 5-substituted azaindolylalanine and its application as a bioisostere of tyrosine capable of enhancing NTS2 selectivity. The S-configured test compound 2 a, [(S)-3-(pyrazolo[1,5-a]pyridine-5-yl)-propionyl11]NT(8–13), exhibits substantial NTS2 affinity (4.8 nm) and has a nearly 30-fold NTS2 selectivity over NTS1. The (R)-epimer 2 b showed lower NTS2 affinity but more than 600-fold selectivity over NTS1.

Development of Covalent Ligand–Receptor Pairs to Study the Binding Properties of Nonpeptidic Neurotensin Receptor 1 Antagonists

“…In those poses, the adamant moiety of 1 occupies a cavity comprised of residues from TM3, TM5 to TM7, and EL2, when its carboxylate is stabilized by hydrogen-bond/ionic interactions to Arg148 3.32 , Arg322 6.54 , and Arg323 6.55 (Figure A,B). It is important to note that the aforementioned interactions represent the only stable hydrogen bonds between 1 and the receptor, which is in contrast to the larger number of hydrogen bonds between NT(8–13) and NTS1 observed within both the crystal structures of NTS1 − and our previous simulations of NT(8–13) coupled to NTS1 . The central pyrazole fragment positions the dimethoxyphenyl substituent in proximity to TM6, TM7, and EL3 and the isopropyl-phenyl residue into the direction of the extracellular entrance of the binding pocket (Figure A,B).…”

“…It is important to note that the aforementioned interactions represent the only stable hydrogen bonds between 1 and the receptor, which is in contrast to the larger number of hydrogen bonds between NT(8−13) and NTS1 observed within both the crystal structures of NTS1 5−7 and our previous simulations of NT (8−13) coupled to NTS1. 29 The central pyrazole fragment positions the dimethoxyphenyl substituent in proximity to TM6, TM7, and EL3 and the isopropyl-phenyl residue into the direction of the extracellular entrance of the binding pocket (Figure 3A,B). The sterically demanding dimethoxyphenyl moiety adopts a position similar to Pro10 of NT (8−13).…”

Emerging role of neurotensin in regulation of the cardiovascular system

“…Importantly, because cardiovascular responses to NT are largely mediated via NTS 1 receptor subtype, they could be minimized by using NT analogues with increased affinity for NTS 2 receptor. One clinical implication wherein these agents are thought to be a promising option, is the treatment of neuropathic pain (Kleczkowska and Lipkowski, 2013;Lafrance et al, 2010;Schaab et al, 2014).…”

Ligand Discovery for a Peptide-Binding GPCR by Structure-Based Screening of Fragment- and Lead-Like Chemical Libraries

“…7,43 Recently, crystal structures of GPCRs that signal in response to peptides and proteins have been determined, in some cases even with peptides bound, 22,44,45 providing opportunities to design novel ligands to targets such as NTSR1. 46,47 Several of the peptidebinding GPCRs have been recognized as attractive but difficult targets for drug development, which is likely due to their large and often solvent exposed binding sites. 11 In the case of NTSR1, the challenges involved in the discovery of small molecule ligands were clearly exemplified by a recent HTS campaign of 332 000 compounds, which resulted in a hit rate of <0.06%, and only one of the discovered ligands was considered suitable for further elaboration.…”

“…These GPCRs have proved to be excellent targets for structure-based methods, and docking screens of fragment libraries have been fruitful. ,− Empirical screens of fragment libraries have also identified very potent ligands of small-molecule binding GPCRs, , but with significantly lower hit rates than molecular docking, demonstrating the potential of structure-based approaches for such targets. The excellent results obtained for small-molecule binding GPCRs can partly be attributed to their binding sites having evolved to recognize fragment-sized compounds and a bias toward ligand-like chemotypes in commercial chemical libraries. , Recently, crystal structures of GPCRs that signal in response to peptides and proteins have been determined, in some cases even with peptides bound, ,, providing opportunities to design novel ligands to targets such as NTSR1. , Several of the peptide-binding GPCRs have been recognized as attractive but difficult targets for drug development, which is likely due to their large and often solvent exposed binding sites . In the case of NTSR1, the challenges involved in the discovery of small molecule ligands were clearly exemplified by a recent HTS campaign of 332 000 compounds, which resulted in a hit rate of <0.06%, and only one of the discovered ligands was considered suitable for further elaboration .…”