Design, Synthesis,\nand <i>In Vitro</i> Characterization\nof Proteolytically-Stable Opioid-Neurotensin Hybrid Peptidomimetics

Linking\nan opioid to a nonopioid pharmacophore represents a promising\napproach for reducing opioid-induced side effects during pain management.\nHerein, we describe the optimization of the previously reported opioid-neurotensin\nhybrids (OPNT-hybrids), <b>SBL-OPNT-05</b> & <b>-10</b>, containing the μ-/δ-opioid agonist H-Dmt-d-Arg-Aba-β-Ala-NH<sub>2</sub> and NT(8–13) analogs optimized\nfor NTS2 affinity. In the present work, the constrained dipeptide\nAba-β-Ala was modified to investigate the optimal linker length\nbetween the two pharmacophores, as well as the effect of expanding\nthe aromatic moiety within constrained dipeptide analogs, via the\ninclusion of a naphthyl moiety. Additionally, the <i>N</i>-terminal Arg residue of the NT(8–13) pharmacophore was substituted\nwith β<sup>3</sup><i>h</i>Arg. For all analogs, affinity\nwas determined at the MOP, DOP, NTS1, and NTS2 receptors. Several\nof the hybrid ligands showed a subnanomolar affinity for MOP, improved\nbinding for DOP compared to <b>SBL-OPNT-05</b> & <b>-10</b>, as well as an excellent NTS2-affinity with high selectivity over\nNTS1. Subsequently, the G<sub>αi1</sub> and β-arrestin-2\npathways were evaluated for all hybrids, along with their stability\nin rat plasma. Upon MOP activation, <b>SBL-OPNT-13</b> and <b>-18</b> were the least effective at recruiting β-arrestin-2\n(<i>E</i><sub>max</sub> = 17 and 12%, respectively), while\nboth compounds were also found to be partial agonists at the G<sub>αi1</sub> pathway, despite improved potency compared to DAMGO.\nImportantly, these analogs also showed a half-life in rat plasma in\nexcess of 48 h, making them valuable tools for future <i>in vivo</i> investigations.