Opioids are powerful analgesics acting via the human μ‐opiate receptor (hMOR). Opioid use is associated with adverse effects such as tolerance, addiction, respiratory depression, and constipation. Two synthetic opioids, AH‐7921 and U‐47700 that were developed in the 1970s but never marketed, have recently appeared on the illegal drug market and in forensic toxicology reports. These agents were initially characterized for their analgesic activity in rodents; however, their pharmacology at hMOR has not been delineated. Thus, we synthesized over 50 chemical analogs based on core AH‐7921 and U‐47700 structures to assess for their ability to couple to Gα i signaling and induce hMOR internalization. For both the AH‐7921 and U‐47700 analogs, the 3,4‐dichlorobenzoyl substituents were the most potent with comparable EC 50 values for inhibition of cAMP accumulation; 26.49 ± 11.2 nmol L −1 and 8.8 ± 4.9 nmol L −1 , respectively. Despite similar potencies for Gα i coupling, these two compounds had strikingly different hMOR internalization efficacies: U‐47700 (10 μmol L −1 ) induced ~25% hMOR internalization similar to DAMGO while AH‐7921 (10 μmol L −1 ) induced ~5% hMOR internalization similar to morphine. In addition, the R , R enantiomer of U‐47700 is significantly more potent than the S , S enantiomer at hMOR. In conclusion, these data suggest that U‐47700 and AH‐7921 analogs have high analgesic potential in humans, but with divergent receptor internalization profiles, suggesting that they may exhibit differences in clinical utility or abuse potential.

While important for their antinociceptive properties in medicine, opioids are commonly abused in America due to easily accessible opiate prescription pain medication. Classic opioids can induce adverse side effects such as gastrointestinal dysfunction and fatal respiratory depression, the latter of which is a key underlying factor contributing to the rising rates of lethality of opioid abuse. New synthetic opioids are emerging on the black market, many of which have not been characterized for structure activity relationships at human mu‐opiate receptors (hOPRM1). The rise of new synthetic opioids complicates the opioid crisis in America as they often escape the traditional illicit drug classifications established by law enforcement and may be more potent and lethal than conventional molecules. In this study, we developed a stable amino terminal HA‐tagged hOPRM1 expressing human fibrosarcoma (HT1080) cell line for determining the pharmacology of a panel of opioids analogs derived from synthetic opioids AH‐7921 and U‐47700. Expression of hOPRM1 was verified by Western blot and immunocytochemistry. Assessing the morphine response in this cell line revealed that morphine EC50 (39.3 nM) was comparable to published findings and were naloxone reversible, thereby validating this cell line. The analogs were assessed for their ability to suppress forskolin‐induced cyclic AMP (cAMP) levels in a hOPRM1‐dependent manner revealing a subset of structurally‐related analogs showing functional activity. The preliminary results found in this study indicate that some of the synthetic opioid analogs are likely to have abuse potential based on their ability to bind to and activate the human OPRM1 receptor.Support or Funding InformationThis project was supported by Award No. 2016‐R2‐CX‐0059, awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The opinions, findings, and conclusions or recommendations expressed in this publication/program/exhibition are those of the author(s) and do not necessarily reflect those of the Department of Justice.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.