pH-dependent opioid ligands - structural features and mechanisms underlying analgesic effects

• Applicant: Professor Dr. Christoph Stein
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Anaesthesiology ; Pharmacology
• Term: from 2020 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434131077

• Final Report Year: 2023

Final Report Abstract

This project, together with other grants, was designed to elucidate the detailed structural characteristics and the cellular mechanisms (ligand binding, G-protein activation, signaling components, modulation of membrane ion channels) underlying the actions of pH (acidosis)-dependent opioid painkillers (analgesics). This is a significant knowledge gap because many failures and unethical risks imposed upon trial participants in drug development have been ascribed to a lack of insight into mechanisms of action. Pain is a sensory and emotional experience which can be comprehensively studied only in humans, but it is necessary to revert to cellular (in vitro) and animal (in vivo) models to investigate mechanisms underlying opioid receptor (OR) signaling. The present project proposed to examine the chemical characteristics determining the interactions between ORs and opioid analgesics in normal compared to injured (acidotic) environments in vitro, and whether pH-dependent opioid compounds induce adverse side effects in animal models of persistent pain in vivo. This required the setup of elaborate methodology (e.g. Förster-Resonance-Energy-Transfer; FRET). Due to institutional factors, the setup was halted without tangible results for most of the proposed in vitro experiments. However, some in vivo investigations were completed, demonstrating that a pH-dependent opioid agonist (NFEPP) produced pain relief and associated rewarding effects via peripheral OR, but did not elicit typical adverse side effects of conventional opioids.

Publications

• Uncovering the analgesic effects of a pH-dependent mu-opioid receptor agonist using a model of nonevoked ongoing pain. Pain, 161(12), 2798-2804.
  Massaly, Nicolas; Temp, Julia; Machelska, Halina & Stein, Christoph
  
• Modulation of G-protein activation, calcium currents and opioid receptor phosphorylation by the pH-dependent antinociceptive agonist NFEPP. Frontiers in Molecular Neuroscience, 16.
  Celik, Melih Özgür; Seitz, Viola; Yergöz, Fatih; Dembla, Sandeep; Blum, Nina Kathleen; Schulz, Stefan & Stein, Christoph