Ethan Miller
Research Mentor: John Traynor
Mentor Department: Pharmacology, Medicine
Author(s): Ethan Miller, Shawn Flynn
Session: Session 4 (1:00 PM – 1:50 PM)
Presentation Type: Poster 82
Abstract
An ongoing public health crisis in the United States is opioid overdose, driven in part by the increasing prevalence and potency of synthetic opioids. According to the state of Michigan’s Substance Use Disorder Resources, 1938 adults in Michigan died from opioid overdose in 2024. Highlighting the need to understand the mechanisms that influence the effectiveness of opioid antagonists in overdose reversal. Although antagonists such as naloxone are commonly used in overdose reversal, the National Institute of Health reports that, often in fentanyl overdoses, individuals require larger doses of naloxone. These clinical observations underscore a gap in our understanding of the pharmacological mechanisms involving synthetic opioids. This study investigates agonist–antagonist interactions at the µ-opioid receptor (MOR) by quantifying antagonist-induced shifts in agonist concentration–response curves and analyzing these shifts using Schild regression. Agonist–antagonist assays were performed using a luminescence assay to measure MOR-mediated inhibition of adenylyl cyclase. Concentration–response curves were generated for opioid agonists, including DAMGO, fentanyl, carfentanil, and BU72, in the presence of increasing concentrations of the MOR antagonists naltrexone, methylnaltrexone, and CTOP. Dose ratios were calculated from rightward shifts in the curves and plotted to generate Schild plots, from which pA2 values were derived as quantitative measures of antagonist affinity. Consistent with competitive antagonism, increasing antagonist concentrations produced parallel rightward shifts in agonist concentration–response curves without reducing maximal efficacy. Interestingly, pA2 values for all antagonists were lower when determined using carfentanil and BU72 compared with fentanyl and DAMGO. These findings imply that opioids with high affinity and lipophilicity may resist standard antagonism, possibly due to sustained receptor binding or altered binding dynamics. This work emphasizes critical limitations in current overdose reversal strategies and highlights the need for next-generation antagonists with improved effectiveness against ultra-potent synthetic opioids.
