# Negative allosteric modulation of mu opioid receptors to reverse fentanyl overdose

> **NIH NIH R21** · TRUSTEES OF INDIANA UNIVERSITY · 2024 · $237,750

## Abstract

Abstract
Fentanyl’s high potency, facile synthesis, abuse liability, and propensity to cause profound respiratory
depression via the mu opioid receptor (MOR) have combined to create the opioid epidemic. Fentanyl now
accounts for ~80% of opioid overdose deaths and is predicted to contribute to more than 1.2 million deaths
during the current decade. The rapid onset of fentanyl-induced respiratory depression requires a fast-acting
therapy. For practical purposes, this needs to be a pharmacological treatment. The primary pharmacological
treatment for opioid overdose is naloxone. Naloxone is a competitive orthosteric antagonist of MOR and thus
its effectiveness depends on the dose of naloxone given, naloxone’s affinity for MOR compared to the opioid,
and the rate at which the opioid leaves the receptor. While naloxone can be lifesaving, there are numerous
examples of naloxone failing to reverse an opioid overdose, emphasizing the importance of improving the
pharmacological treatment of opioid overdose.
One way to improve naloxone’s efficacy at MOR is by using a negative allosteric modulator (NAM) of MOR.
NAMs decrease agonist signaling by either increasing the rate at which the agonist leaves the receptor or by
decreasing the efficiency of signaling. Either could be beneficial combined with naloxone to reverse an opioid
overdose. Interestingly, cannabidiol (CBD) is a low potency MOR NAM. In preliminary experiments, we
screened a CBD analog library for their ability to reverse fentanyl-mediated inhibition of adenylyl cyclase (AC).
We identified potent NAMs that reversed fentanyl inhibition of AC and fentanyl analgesia, but they failed to
prevent fentanyl induced respiratory depression or enhance naloxone reversal of respiratory depression.
These results suggest that pathways other than MOR inhibition of AC mediate fentanyl-induced respiratory
depression. Thus, in the proposed work, our first goal is to screen our candidate NAMs for attenuation of
fentanyl/MOR signaling across a broad range of signaling pathways with the goal of identifying CBD analogs
that inhibit MOR signaling pathways in addition to AC. Even though our potent MOR NAMs didn’t decrease
respiratory depression, an important second goal is to determine if they affect other key behaviors mediated by
fentanyl/MOR: reward, dependence, and tolerance. We will address these two goals with two specific aims.
Specific Aim 1. Screen the CBD analog library for attenuation of fentanyl/MOR modulation of the following
pathways: adenylyl cyclase, GIRK, MOR internalization, ERK1/2, phospholipase C, and arrestin.
Specific Aim 2. Determine the ability of the novel MOR NAM, JGC8, to attenuate key fentanyl/MOR-mediated
behaviors: reward, dependence, alleviation of neuropathic pain, and tolerance.
We feel Aim 1 will likely identify compounds with unique signaling profiles. Aim 2 will determine if the already
identified MOR NAM, JGC8, affects therapeutically important fentanyl-elicited behaviors and, combined...

## Key facts

- **NIH application ID:** 10952479
- **Project number:** 1R21DA061122-01
- **Recipient organization:** TRUSTEES OF INDIANA UNIVERSITY
- **Principal Investigator:** Kenneth Mackie
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $237,750
- **Award type:** 1
- **Project period:** 2024-09-15 → 2026-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10952479

## Citation

> US National Institutes of Health, RePORTER application 10952479, Negative allosteric modulation of mu opioid receptors to reverse fentanyl overdose (1R21DA061122-01). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10952479. Licensed CC0.

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