A comprehensive evaluation of the potential binding poses of fentanyl and its analogs at the µ-opioid receptor

Fentanyl and its analogs are selective agonists of the µ-opioid receptor (MOR). Among novel synthetic opioids (NSOs), they dominate the recreational drug market and are the main culprits for the opioid crisis, which has been exacerbated by the COVID-19 pandemic. By taking advantage of the crystal structures of the MOR, several groups have investigated the binding mechanism of fentanyl, but have not reached a consensus, in terms of both the binding orientation and the fentanyl conformation. Thus, the binding mechanism of fentanyl at the MOR remains an unsolved and challenging question. Here, we carried out a systematic computational study to investigate the preferred fentanyl conformations, and how these conformations are being accommodated in the MOR binding pocket. We characterized the free energy landscape of fentanyl conformations with metadynamics simulations, as well as performed long-timescale molecular dynamics simulations to compare and evaluate several possible fentanyl binding conditions. Our results indicate that the most preferred binding pose in the MOR binding pocket corresponds well with the minima on the energy landscape of fentanyl in the absence of the receptor, while the energy landscape can be reconfigured by modifying the fentanyl scaffold. The interactions with the receptor may stabilize a slightly unfavored fentanyl conformation in an alternative binding pose. By extending similar investigations to fentanyl analogs, our findings establish a structure-activity relationship of fentanyl binding at the MOR. In addition to providing a structural basis to understand the potential toxicity of the emerging NSOs, such insights will contribute to developing new, safer analgesics.

Improvements in Toxicology Testing to Identify Fentanyl Analogs and Other Novel Synthetic Opioids in Fatal Drug Overdoses, Connecticut, January 2016–June 2019

Objectives Drug overdose deaths in Connecticut increasingly involve a growing number of fentanyl analogs and other novel nonfentanyl synthetic opioids (ie, novel synthetics). Current postmortem toxicology testing methods often lack the sophistication needed to detect these compounds. We examined how improved toxicology testing of fatal drug overdoses can determine the prevalence and rapidly evolving trends of novel synthetics. Methods From 2016 to June 2019, the Connecticut Office of the Chief Medical Examiner increased its scope of toxicology testing of suspected drug overdose deaths in Connecticut from basic to enhanced toxicology testing to detect novel synthetics. The toxicology laboratory also expanded its testing panels during this time. We analyzed toxicology results to identify and quantify the involvement of novel synthetics over time. Results From 2016 to June 2019, 3204 drug overdose deaths received enhanced toxicology testing; novel synthetics were detected in 174 (5.4%) instances. Ten different novel synthetics were detected with 205 total occurrences. Of 174 overdose deaths with a novel synthetic detected, most had 1 (n = 146, 83.9%) or 2 (n = 26, 14.9%) novel synthetics detected, with a maximum of 4 novel synthetics detected. Para-fluorobutyrylfentanyl/FIBF, furanylfentanyl, and U-47700 were most identified overall, but specific novel synthetics came in and out of prominence during the study period, and the variety of novel synthetics detected changed from year to year. Conclusions Enhanced toxicology testing for drug overdose deaths is effective in detecting novel synthetics that are not identified through basic toxicology testing. Identifying emerging novel synthetics allows for a timely and focused response to potential drug outbreaks and illustrates the changing drug market.

Fentanyl, Acetylfentanyl, and Carfentanil in Impaired Driving Cases: A Review of 270 Cases

The detection of fentanyl and fentanyl analogs has been widely communicated throughout the scientific community. While most of the reporting has been in relation to overdose deaths, these drugs are commonly detected in impaired driving cases. A retrospective study of impaired driving cases analyzed between 2017 and 2019 produced 270 cases positive for fentanyl, carfentanil, and/or acetylfentanyl. Fentanyl was the predominant drug found in these 270 cases (65.5%) with concentrations ranging from less than 1.0 ng/mL to 64 ng/mL. Carfentanil was found alone in 6.6% cases with three concentrations above 1.0 ng/mL. Acetylfentanyl was always found when fentanyl was positive with concentrations ranging from less than 1.0 ng/mL to 9.2 ng/mL. Detailed case histories are provided with corresponding toxicology results. Toxicology results show impaired drivers using multiple drugs with a wide range of observed behaviors. The inclusion of these drugs in routine impaired driver toxicology testing is extremely important when attempting to determine their overall prevalence.