3-Methyl-PCP–in vitro and in vivo metabolism in humans and post-mortem investigation of a fatal intoxication

Abstract

Arylcyclohexylamine analogs of phencyclidine (PCP) increasingly emerged on the novel psychoactive substance market over the last few years. Recently, 3-Me-PCP appeared on the market and, like many PCP analogs, is considered to be an equally or even more potent dissociative drug as compared to PCP. However, there is a significant lack of scientific data on this compound, as neither fatal nor non-fatal intoxications involving 3-Me-PCP have been reported. Therefore, we investigated the in vivo and in vitro metabolism of 3-Me-PCP and present the findings from a fatal intoxication case involving 3-Me-PCP. For tentative identification of phase-I metabolites, 3-Me-PCP was incubated with pooled human liver microsomes (pHLM). In addition, an authentic urine sample was worked up using protein precipitation with and without prior glucuronide cleavage. Analyses for metabolite identification were carried out using liquid chromatography coupled to time-of-flight mass spectrometry in positive ionization mode (LC-ESI-QTOF-MS). Chromatographic separation was achieved on a Kinetex® Biphenyl column (100 × 2.1 mm, 2.6 μm). For the post-mortem investigation of the fatal intoxication, a standard addition approach using automated SPE for sample workup was performed to quantify 3-Me-PCP in heart blood and urine with LC-MS/MS. 3-Me-PCP was extensively metabolized by hepatic enzymes in the pHLM assay. Altogether, ten in vitro phase-I metabolites of 3-Me-PCP were identified using LC − ESI-QTOF − MS, with hydroxylations, oxidations, and N-dealkylations being the observed reactions. All of these phase-I metabolites could be confirmed in the authentic urine sample. In both experimental settings, the 3-hydroxymethyl-PCP metabolite was detected with the highest abundance, followed by cyclohexyl-hydroxy-3-Me-PCP and the ω-carboxylic acid metabolite formed after ring-opening N-dealkylation at the piperidine moiety. The concentrations of 3-Me-PCP in heart blood and urine of the fatal intoxication case were 510 ± 35 ng/mL and 600 ± 72 ng/mL, respectively. The in vitro pHLM assay was suitable to identify and predict the main metabolites of 3-Me-PCP in the available real case sample. Suggested biomarkers for 3-Me-PCP consumption are 3-hydroxymethyl-PCP, cyclohexyl-hydroxy-3-Me-PCP, and the ω-carboxylic acid metabolite formed after ring-opening N-dealkylation at the piperidine moiety. The chemical structures of the detected metabolites remain tentative until structure elucidation, e.g., by NMR after isolation or the synthesis of reference material was performed. However, this does not preclude their use as valid biomarkers. Furthermore, even in the context of a multidrug intake, the 3-Me-PCP intoxication was confirmed during post-mortem investigations and the determined concentrations of 3-Me-PCP were considered likely to have contributed to toxicity/death (Toxicological Significance Score of 3). This represents the first documented fatal case involving 3-Me-PCP.