Discovery of Novel Multifunctional Ligands with μ/δ Opioid Agonist/Neurokinin‑1 (NK1) Antagonist Activities for the Treatment of Pain

Multifunctional ligands with agonist bioactivities at μ/δ opioid receptors (MOR/DOR) and antagonist bioactivity at the neurokinin-1 receptor (NK1R) have been designed and synthesized. These peptide-based ligands are anticipated to produce better biological profiles (e.g., higher analgesic effect with significantly less adverse side effects) compared to those of existing drugs and to deliver better synergistic effects than coadministration of a mixture of multiple drugs. A systematic structure–activity relationship (SAR) study has been conducted to find multifunctional ligands with desired activities at three receptors. It has been found that introduction of Dmt (2,6-dimethyl-tyrosine) at the first position and NMePhe at the fourth position (ligand 3: H-Dmt-d-Ala-Gly-NMePhe-Pro-Leu-Trp-NH-Bn­(3′,5′-(CF3)2)) displays binding as well as functional selectivity for MOR over DOR while maintaining efficacy, potency, and antagonist activity at the NK1R. Dmt at the first position with Phe­(4-F) at the fourth position (ligand 5: H-Dmt-d-Ala-Gly-Phe­(4-F)-Pro-Leu-Trp-NH-Bn­(3′,5′-(CF3)2)) exhibits balanced binding affinities at MOR and DOR though it has higher agonist activity at DOR over MOR. This study has led to the discovery of several novel ligands including 3 and 5 with excellent in vitro biological activity profiles. Metabolic stability studies in rat plasma with ligands 3, 5, and 7 (H-Tyr-d-Ala-Gly-Phe­(4-F)-Pro-Leu-Trp-NH-Bn­(3′,5′-(CF3)2)) showed that their stability depends on modifications at the first and fourth positions (3: T1/2 > 24 h; 5: T1/2 ≈ 6 h; 7: T1/2 > 2 h). Preliminary in vivo studies with these two ligands have shown promising antinociceptive activity.

本研究设计并合成了兼具μ阿片受体（μ opioid receptor, MOR）与δ阿片受体（δ opioid receptor, DOR）激动剂生物活性，同时对神经激肽-1受体（neurokinin-1 receptor, NK1R）具有拮抗剂生物活性的多功能配体。此类肽基配体相较于现有药物，有望展现更优异的生物学特性（如镇痛效应更强且不良反应显著更少），且相较于多药联合给药，可发挥更出色的协同效应。为筛选出在三类受体上均具备预期活性的多功能配体，本研究开展了系统性构效关系（structure–activity relationship, SAR）研究。研究发现，在第1位引入2,6-二甲基酪氨酸（2,6-dimethyl-tyrosine, Dmt）、第4位引入N-甲基苯丙氨酸（NMePhe）的配体3（序列为H-Dmt-d-Ala-Gly-NMePhe-Pro-Leu-Trp-NH-Bn(3′,5′-(CF3)2)），在保留对NK1R的拮抗活性、效价与效能的同时，相较于DOR，对MOR展现出优异的结合与功能选择性。而在第1位引入Dmt、第4位引入4-氟苯丙氨酸（Phe(4-F)）的配体5（序列为H-Dmt-d-Ala-Gly-Phe(4-F)-Pro-Leu-Trp-NH-Bn(3′,5′-(CF3)2)），虽对DOR的激动活性高于MOR，但在MOR与DOR上均展现出均衡的结合亲和力。本研究已发现包括配体3与5在内的多款新型配体，其体外生物学活性表现优异。对配体3、5及7（序列为H-Tyr-d-Ala-Gly-Phe(4-F)-Pro-Leu-Trp-NH-Bn(3′,5′-(CF3)2)）开展的大鼠血浆代谢稳定性研究表明，其代谢稳定性取决于第1位与第4位的修饰：配体3的半衰期T1/2 > 24 h，配体5的T1/2 ≈ 6 h，配体7的T1/2 > 2 h。对上述配体开展的初步体内研究显示，其具备极具潜力的抗伤害感受活性。