A Systematic Study of the In Vitro Pharmacokinetics and Estimated Human In Vivo Clearance of Indole and Indazole-3-Carboxamide Synthetic Cannabinoid Receptor Agonists Detected on the Illicit Drug Market

Abstract

In vitro pharmacokinetic studies were conducted on enantiomer pairs of twelve valinate or tert-leucinate indole and indazole-3-carboxamide synthetic cannabinoid receptor agonists (SCRAs) detected on the illicit drug market to investigate their physicochemical parameters and structure-metabolism relationships (SMRs). Experimentally derived Log D7.4 ranged from 2.81 (AB-FUBINACA) to 4.95 (MDMB-4en-PINACA) and all SCRAs tested were highly protein bound, ranging from 88.9 ± 0.49% ((R)-4F-MDMB-BINACA) to 99.5 ± 0.08% ((S)-MDMB-FUBINACA). Most tested SCRAs were cleared rapidly in vitro in pooled human liver microsomes (pHLM) and pooled cryopreserved human hepatocytes (pHHeps). Intrinsic clearance (CLint) ranged from 13.7 ± 4.06 ((R)-AB-FUBINACA) to 2944 ± 95.9 mL min−1 kg−1 ((S)-AMB-FUBINACA) in pHLM, and from 110 ± 34.5 ((S)-AB-FUBINACA) to 3216 ± 607 mL min−1 kg−1 ((S)-AMB-FUBINACA) in pHHeps. Predicted Human in vivo hepatic clearance (CLH) ranged from 0.34 ± 0.09 ((S)-AB-FUBINACA) to 17.79 ± 0.20 mL min−1 kg−1 ((S)-5F-AMB-PINACA) in pHLM and 1.39 ± 0.27 ((S)-MDMB-FUBINACA) to 18.25 ± 0.12 mL min−1 kg−1 ((S)-5F-AMB-PINACA) in pHHeps. Valinate and tert-leucinate indole and indazole-3-carboxamide SCRAs are often rapidly metabolised in vitro but are highly protein bound in vivo and therefore predicted in vivo CLH is much slower than CLint. This is likely to give rise to longer detection windows of these substances and their metabolites in urine, possibly as a result of accumulation of parent drug in lipid-rich tissues, with redistribution into the circulatory system and subsequent metabolism.

Defining Steric Requirements at CB1 and CB2 Cannabinoid Receptors Using Synthetic Cannabinoid Receptor Agonists 5F-AB-PINACA, 5F-ADB-PINACA, PX-1, PX-2, NNL-1, and Their Analogues

“…The low in vivo potencies of 15 (PX-1) and 19 (PX-2) relative to their moderate CB 1 affinities and potencies in vitro might be attributed to suboptimal DMPK profiles. Although cannabinoids (including SCRAs) typically possess greater lipophilicity than other oral central nervous system drugs, the compound Log P ( C Log P ) prediction for 15 (PX-1; C Log P = 3.59) suggests greater lipophilicity than other indole analogues with confirmed potency in mice, such as 12 ( C Log P = 2.11) and 13 ( C Log P = 2.55) . However, 19 (PX-2; C Log P = 2.78) has a similar predicted partition coefficient when compared to indazoles 17 ( C Log P = 2.29) and 18 ( C Log P = 2.69), both of which are highly potent cannabimimetic agents in mice .…”

“…To the best of our knowledge, no pharmacokinetic data for 15 (PX-1) or 19 (PX-2) in mammalian species have been reported to date. SCRAs featuring amino acid amides are subject to extensive metabolic biotransformation, ,, and it is possible that the low in vivo potency of 15 (PX-1) and 19 (PX-2) may be attributed to the rapid biotransformation of these compounds to inactive metabolites. Although 15 (PX-1) and 19 (PX-2) are closely related to several SCRAs that are potent CB 1 receptor agonists in vivo, even small changes in the molecular structure can produce vastly different metabolic profiles and clearance rates. − Species differences may also play a role in observed differences because in vitro potencies for the parent compounds at the human CB 1 receptor may not be reflected in mice given the highly idiosyncratic nature of structure–metabolism relationships for this class.…”

Advances on Bioanalysis: Recent Approaches in the Determination of Biomarkers, Drugs of Abuse and Medicines

“…Brandon et al [ 8 ] conducted an interesting study concerning the factors that influence the metabolism and pharmacokinetics of different synthetic cannabinoid receptor agonists. The authors have used both in silico and experimental methods to determine a number of parameters such as lipophilicity, short-term stability in plasma, plasma protein binding, in vitro intrinsic clearance, the structural and conformational features influencing their interaction with metabolic enzymes and their metabolic clearance rates.…”

Characterisation of AMB-FUBINACA metabolism and CB1-mediated activity of its acid metabolite

“…AMB-FUBINACA is largely stable in human plasma with ~ 86% of the original concentration remaining intact following a five-hour in vitro incubation. Notably, 94% remained in the presence of esterase inhibitors [ 26 ]. The absence of CESs in human blood may explain why in vitro plasma studies demonstrate AMB-FUBINACA to be very stable, despite the metabolism being classified as rapid [ 20 , 26 , 27 ].…”

“…Notably, 94% remained in the presence of esterase inhibitors [ 26 ]. The absence of CESs in human blood may explain why in vitro plasma studies demonstrate AMB-FUBINACA to be very stable, despite the metabolism being classified as rapid [ 20 , 26 , 27 ]. No AMB-FUBINACA was detected in the whole blood or urine of non-fatal poisonings with AMB-FUBINACA [ 28 ], and only 26% of AMB-FUBINACA fatalities in New Zealand had AMB-FUBINACA present in their blood [ 1 ].…”