Jason Wallach

From PCP to MXE: a comprehensive review of the non-medical use of dissociative drugs.

PCP or phencyclidine was discovered in 1956 and soon became a popular street drug. Dissociatives including PCP, ketamine, and dextromethorphan have been used non-medically for their mind-altering effects for over 60 years. Many of these compounds have also been used clinically and in legitimate research. At least 14 derivatives of PCP were sold for non-medical and illict use from the late 1960s until the 1990s. With the advent of the Internet, the drug market underwent a dramatic evolution. While initially gray-market chemical vendors offering dextromethorphan and ketamine thrived, most recently the market has shifted to legal high and online-based research chemical vendors. Starting with the first dissociative research chemical, 4-MeO-PCP in 2008, the dissociative research chemical market has rapidly evolved and currently comprises at least 12 dissociatives, almost half of which were unknown in the scientific literature prior to their introduction. Several of these, including methoxetamine, have reached widespread use internationally. A historical account of non-medical use of over 30 dissociative compounds was compiled from a diverse collection of sources. The first complete portrait of this underground market is presented along with the relevant legal, technological, and scientific developments which have driven its evolution.

Pharmacological Investigations of the Dissociative ‘Legal Highs’ Diphenidine, Methoxphenidine and Analogues

1,2-Diarylethylamines including lanicemine, lefetamine, and remacemide have clinical relevance in a range of therapeutic areas including pain management, epilepsy, neurodegenerative disease and depression. More recently 1,2-diarylethylamines have been sold as ‘legal highs’ in a number of different forms including powders and tablets. These compounds are sold to circumvent governmental legislation regulating psychoactive drugs. Examples include the opioid MT-45 and the dissociative agents diphenidine (DPH) and 2-methoxy-diphenidine (2-MXP). A number of fatal and non-fatal overdoses have been linked to abuse of these compounds. As with many ‘legal highs’, little is known about their pharmacology. To obtain a better understanding, the effects of DPH, 2-MXP and its 3- and 4-MeO- isomers, and 2-Cl-diphenidine (2-Cl-DPH) were investigated using binding studies at 46 central nervous system receptors including the N-methyl-D-aspartate receptor (NMDAR), serotonin, dopamine, norepinephrine, histamine, and sigma receptors as well as the reuptake transporters for serotonin, dopamine and norepinephrine. Reuptake inhibition potencies were measured at serotonin, norepinephrine and dopamine transporters. NMDAR antagonism was established in vitro using NMDAR-induced field excitatory postsynaptic potential (fEPSP) experiments. Finally, DPH and 2-MXP were investigated using tests of pre-pulse inhibition of startle (PPI) in rats to determine whether they reduce sensorimotor gating, an effect observed with known dissociative drugs such as phencyclidine (PCP) and ketamine. The results suggest that these 1,2-diarylethylamines are relatively selective NMDAR antagonists with weak off-target inhibitory effects on dopamine and norepinephrine reuptake. DPH and 2-MXP significantly inhibited PPI. DPH showed greater potency than 2-MXP, acting with a median effective dose (ED50) of 9.5 mg/kg, which is less potent than values reported for other commonly abused dissociative drugs such as PCP and ketamine.

Preparation and analytical characterization of 1-(1-phenylcyclohexyl)piperidine (PCP) and 1-(1-phenylcyclohexyl)pyrrolidine (PCPy) analogues

Classic examples of psychoactive arylcycloalkylamines include ketamine and 1-(1-phenylcyclohexyl)piperidine (PCP) and many others serve as important structural templates for neuropharmacological research. The recent emergence of PCP analogues that can be obtained from internet retailers requires the implementation of appropriate monitoring strategies for harm reduction purposes. Access to analytical data plays a key part when encountering these substances, especially if reference material is not available. The present study describes the synthesis of three substituted 1-(1-phenylcyclohexyl)piperidines, (3-MeO-, 4-MeO- and 3-Me-PCP) and three substituted 1-(1-phenylcyclohexyl)pyrrolidine analogues (3-MeO-, 4-MeO- and 3-Me-PCPy). Analytical characterizations of all six arylcyclohexylamines and their primary 1-phenylcyclohexanamine intermediates included gas chromatography ion trap electron- and chemical ionization and high resolution mass spectrometry, liquid chromatography electrospray hybrid triple-quadrupole linear ion trap tandem mass spectrometry, infrared, diode array detection and (1) H and (13) C nuclear magnetic resonance (NMR) spectroscopy. Solvent (CDCl3 vs. d6 -DMSO) and protonation effects (free bases vs hydrochloride salts) were studied in order to investigate the impact on shifts and splitting patterns, for example, when attempting to assign separate axial and equatorial proton chemical shifts of NMR spectra. Differentiation between the isomeric 3-MeO-/4-MeO-PCP and PCPy analogues was feasible under mass spectral conditions. Gas chromatography analysis appeared to induce notable degradation of the 4-MeO-substituted analytes, especially when dealing with the HCl salts which led to the detection of the substituted 1-phenylcyclohex-1-ene nucleus. This phenomenon was observed to be less pronounced with the 3-MeO isomers, possibly due to the resonance properties of the para-methoxy group followed by more facile elimination of the amine.

Ephenidine: A new psychoactive agent with ketamine-like NMDA receptor antagonist properties

ABSTRACT To avoid legislation based on chemical structure, research chemicals, frequently used for recreational purposes, are continually being synthesized. N‐Ethyl‐1,2‐diphenylethanamine (ephenidine) is a diarylethylamine that has recently become popular with recreational users searching for dissociative hallucinogenic effects. In the present study, the pharmacological basis of its neural actions has been investigated, initially by assessing its profile in central nervous system receptor binding assays and subsequently in targeted electrophysiological studies. Ephenidine was a potent inhibitor of 3H‐MK‐801 binding (Ki: 66 nM), implying that it acts at the PCP site of the N‐methyl‐d‐aspartate (NMDA) receptor. It also showed modest activity at dopamine (379 nM) and noradrenaline (841 nM) transporters and at sigma 1 (629 nM) and sigma 2 (722 nM) binding sites. In experiments of extracellular recording of field excitatory postsynaptic potentials (fEPSPs) from area CA1 of rat hippocampal slices, ephenidine, 1 and 10 &mgr;M, respectively, produced a 25% and a near maximal inhibition of the NMDA receptor mediated fEPSP after 4 h superfusion. By contrast, ephenidine (50 &mgr;M) did not affect the AMPA receptor mediated fEPSPs. In whole cell patch clamp recordings, from hippocampal pyramidal cells, ephenidine (10 &mgr;M) blocked NMDA receptor‐mediated EPSCs in a highly voltage‐dependent manner. Additionally, ephenidine, 10 &mgr;M, blocked the induction of long term potentiation (LTP) in CA1 induced by theta burst stimulation. The present data show that the new psychoactive substance, ephenidine, is a selective NMDA receptor antagonist with a voltage‐dependent profile similar to ketamine. Such properties help explain the dissociative, cognitive and hallucinogenic effects in man. This article is part of the Special Issue entitled ‘Ionotropic glutamate receptors’. HIGHLIGHTSNew ‘legal high’, the dissociative ephenidine, displaces MK‐801 binding.Ephenidine, like ketamine, blocks NMDA receptor mediated synaptic potentials and plasticity.Ephenidine, like ketamine, blocks the NMDA receptor in a highly voltage‐dependent manner.Ephenidine blocks long‐term potentiation, LTP.NMDA receptor antagonism likely underlies the psychoactive effects of ephenidine.

New psychoactive substances 3-methoxyphencyclidine (3-MeO-PCP) and 3-methoxyrolicyclidine (3-MeO-PCPy): metabolic fate elucidated with rat urine and human liver preparations and their detectability in urine by GC-MS, LC-(high resolution)-MSn, and LC-high resolution-MS/MS.

Background: 3-Methoxyphencyclidine (3-MeO-PCP) and 3-methoxyrolicyclidine (3-MeO-PCPy) are two new psychoactive substances (NPS). The aims of the present study were the elucidation of their metabolic fate in rat and pooled human liver microsomes (pHLM) the identification of the cytochrome P450 (CYP) isoenzymes involved and the detectability using standard urine screening approaches (SUSA) after intake of common users’ doses using gas chromatography-mass spectrometry (GC-MS) liquid chromatography-multi-stage mass spectrometry (LC-MSn) and liquid chromatography-high-resolution tandem mass spectrometry (LC-HR-MS/MS) Methods: For metabolism studies rat urine samples were treated by solid phase extraction or simple precipitation with or without previous enzymatic conjugate cleavage. After analyses via LC-HR-MSn the phase I and II metabolites were identified Results: Both drugs showed multiple aliphatic hydroxylations at the cyclohexyl ring and the heterocyclic ring single aromatic hydroxylation carboxylation after ring opening O-demethylation and glucuronidation. The transferability from rat to human was investigated by pHLM incubations where O-demethylation and hydroxylation were observed. The involvement of the individual CYP enzymes in the initial metabolic steps was investigated after single CYP incubations. For 3-MeO-PCP CYP 2B6 was responsible for aliphatic hydroxylations and CYP 2C19 and CYP 2D6 for O-demethylation. For 3-MeO-PCPy aliphatic hydroxylation was again catalyzed by CYP 2B6 and O-demethylation by CYP 2C9 and CYP 2D6 Conclusions: As only polymorphically expressed enzymes were involved pharmacogenomic variations might occur but clinical data are needed to confirm the relevance. The detectability studies showed that the authors’ SUSAs were suitable for monitoring the intake of both drugs using the identified metabolites

Developing selective histone deacetylases (HDACs) inhibitors through ebselen and analogs

Histone deacetylases (HDACs) are key regulators of gene expression in cells and have been investigated as important therapeutic targets for cancer and other diseases. Different subtypes of HDACs appear to play disparate roles in the cells and are associated with specific diseases. Therefore, substantial effort has been made to develop subtype-selective HDAC inhibitors. In an effort to discover existing scaffolds with HDAC inhibitory activity, we screened a drug library approved by the US Food and Drug Administration and a National Institutes of Health Clinical Collection compound library in HDAC enzymatic assays. Ebselen, a clinical safe compound, was identified as a weak inhibitor of several HDACs, including HDAC1, HDAC3, HDAC4, HDAC5, HDAC6, HDAC7, HDAC8, and HDAC9 with half maximal inhibitory concentrations approximately single digit of µM. Two ebselen analogs, ebselen oxide and ebsulfur (a diselenide analog of ebselen), also inhibited these HDACs, however with improved potencies on HDAC8. Benzisothiazol, the core structure of ebsulfur, specifically inhibited HDAC6 at a single digit of µM but had no inhibition on other HDACs. Further efforts on structure–activity relationship based on the core structure of ebsulfur led to the discovery of a novel class of potent and selective HDAC6 inhibitors with RBC-2008 as the lead compound with single-digit nM potency. This class of histone deacetylase inhibitor features a novel pharmacophore with an ebsulfur scaffold selectively targeting HDAC6. Consistent with its inhibition on HDAC6, RBC-2008 significantly increased the acetylation levels of α-tubulin in PC-3 cells. Furthermore, treatment with these compounds led to cell death of multiple tumor cell lines in a dose-dependent manner. These results demonstrated that ebselen and ebsulfur analogs are inhibitors of HDACs, supporting further preclinical development of this class of compounds for potential therapeutic applications.

Is nitrogen mustard contamination responsible for the reported MT-45 toxicity?

Helander et al. are commended for disseminating their case reports in the recent publication entitled “Acute skin and hair symptoms followed by severe, delayed eye complications in subjects using the synthetic opioid MT-45″.1 We have followed reports of side effects associated with MT-45 use for several years and the above publication serves as an important reminder of the risks of harm involved in the unregulated use of new psychoactive substances.

Receptor Targets in Alzheimer’s Disease Drug Discovery

A high number of receptor targets have been investigated as potential therapeutic targets in Alzheimer’s disease (AD) treatment. These include binding sites of G protein-coupled receptors, enzymes, ionotropic receptors, and hormonal receptors. This chapter presents a brief overview of some of these receptor sites with respect to drug discovery in AD as well as some of the most recent drugs that target them. Priority was given to receptors investigated within the last decade that have advanced to high preclinical or clinical status in the drug discovery and development continuum. In addition, newer receptor-based strategies such as polypharmacological approaches are briefly discussed.

Syntheses and pharmacological evaluations of novel N-substituted bicyclo-heptane-2-amines at N-methyl-D-aspartate receptors.

Several novel norcamphor (bicycloheptane)‐based compounds were designed and synthesized as non‐competitive N‐methyl‐d‐aspartate receptor antagonists at the phencyclidine binding sites. The heterocyclic ring was also varied to examine piperidine, pyrrolidine, and morpholine groups. We examined pharmacological activities of these compounds in vitro (binding studies) and in vivo (maximal electroshock test). Pharmacological evaluations revealed one of the compounds, 5a, to be a good lead, exhibiting moderate binding at N‐methyl‐d‐aspartate receptors (IC50 = 7.86 μm; Ki = 5.28 μm), maximal electroshock neuroprotection activity at 100 mg/kg and acceptable toxicity profile.

Syntheses and Pharmacological Evaluations of Novel N-substituted Bicyclo-heptan-2-amines at NMDA Receptors

Several novel norcamphor (bicycloheptane)‐based compounds were designed and synthesized as non‐competitive N‐methyl‐d‐aspartate receptor antagonists at the phencyclidine binding sites. The heterocyclic ring was also varied to examine piperidine, pyrrolidine, and morpholine groups. We examined pharmacological activities of these compounds in vitro (binding studies) and in vivo (maximal electroshock test). Pharmacological evaluations revealed one of the compounds, 5a, to be a good lead, exhibiting moderate binding at N‐methyl‐d‐aspartate receptors (IC50 = 7.86 μm; Ki = 5.28 μm), maximal electroshock neuroprotection activity at 100 mg/kg and acceptable toxicity profile.