Human Hepatocyte Metabolism of Novel Synthetic Cannabinoids MN-18 and Its 5-Fluoro Analog 5F-MN-18

BACKGROUND: In 2014, 2 novel synthetic cannabinoids, MN-18 and its 5-fluoro analog, 5F-MN-18, were first identified in an ongoing survey of novel psychoactive substances in Japan. In vitro pharmacological assays revealed that MN-18 and 5F-MN-18 displayed high binding affinities to human CB 1 and CB 2 receptors, with K i being 1.65–3.86 nmol/L. MN-18 and 5F-MN-18 were scheduled in Japan and some other countries in 2014. Despite increasing prevalence, no human metabolism data are currently available, making it challenging for forensic laboratories to confirm intake of MN-18 or 5F-MN-18. METHODS: We incubated 10 μmol/L of MN-18 and 5F-MN-18 in human hepatocytes for 3 h and analyzed the samples on a TripleTOF 5600 + high-resolution mass spectrometer to identify appropriate marker metabolites. Data were acquired via full scan and information-dependent acquisition-triggered product ion scans with mass defect filter. RESULTS: In total, 13 MN-18 metabolites were detected, with the top 3 abundant metabolites being 1-pentyl-1H-indazole-3-carboxylic acid, pentyl-carbonylated MN-18, and naphthalene-hydroxylated MN-18. For 5F-MN-18, 20 metabolites were observed, with the top 3 abundant metabolites being 5′-OH-MN-18, MN-18 pentanoic acid, and 1-(5-fluoropentyl)-1H-indazole-3-carboxylic acid. CONCLUSIONS: We have characterized MN-18 and 5F-MN-18 metabolism with human hepatocytes and high-resolution mass spectrometry, and we recommend characteristic major metabolites for clinical and forensic laboratories to identify MN-18 and 5F-MN-18 intake and link observed adverse events to these novel synthetic cannabinoids.