IN VITRO METABOLISM OF THE STRUCTURALLY SIMILAR FENTANYL ANALOGS, 3-PHENYLPROPANOYLFENTANYL AND BENZOYLFENTANYL

Abstract Background Opioid addiction and toxicity due to overdose by fentanyl analogs (FAs) are a serious problem worldwide. Predicting the pharmacological effect of FAs is very difficult because many new FAs with slight structural alterations frequently appear in the market. The investigation of in vitro metabolism of FAs is an easy and quick method to predict their pharmacological effects. Aims and Objectives In this study, we examined the in vitro metabolism of structurally similar FAs with N-acyl group modification, N-phenyl-N-[1-(2-phenylethyl)-4-piperidyl]-3-phenylpropanamide (3- phenylpropanoylfentanyl, 3-PPF) and N-phenyl-N-[1-(2-phenylethyl)-4-piperidyl]benzamide (benzoylfentanyl, BZF), using human liver microsomes (HLMs). Methods 3-PPF and BZF were incubated with HLMs for 2 and 3 h, respectively (Kadomura et al. 2021). Samples were collected at the designated time points. These FAs and their metabolites were detected by LC-MS/MS and LC-MS IT-TOF. Results The metabolic half-life of 3-PPF was less than 10 min, whereas that of BZF was more than 80 min. Time-course metabolic profiles of these FAs demonstrated that 3-PPF was rapidly metabolized to 3- PPF monohydroxylate, whereas BZF was gradually metabolized into several metabolites. A detailed analysis using LC-MS IT-TOF showed that 3-PPF was primarily monohydroxylated at the N-acyl group. Oxidative N-dealkylated metabolites of 3-PPF and BZF, nor-3-PPF and nor-BZF, were predominantly observed at the end of the experiment, rather than other metabolites. Discussion and Conclusion The relatively longer metabolism of BZF suggests that it may exhibit more significant pharmacological effects than 3-PPF. The rapid metabolism of 3-PPF suggests that FAs with a longer N-acyl group are susceptible to rapid hydroxylation at the N-acyl group. Although various studies have already demonstrated that nor-FAs are inactive metabolites, the detection of nor-3-PPF and nor- BZF may be a useful surrogate for drug intake. References Kadomura N, Ito T, Kawashima H, Matsuhisa T, Kinoshita T, Soda M, Kohyama E, Iwaki T, Nagai H & Kitaichi K (2021) In vitro metabolic profiles of adamantylpositional isomers of synthetic cannabinoids. Forensic Toxicology vol no. 39, pp 26-44.