Decoding the Signaling of a GPCR Heteromeric Complex Reveals a Unifying Mechanism of Action of Antipsychotic Drugs

Introduction. Novel synthetic ‘designer’ drugs with stimulant, ecstasy-like (entactogenic) and/or hallucinogenic properties have become increasingly popular among recreational drug users in recent years. The substances used change frequently in response to market trends and legislative controls and it is an important challenge for poisons centres and clinical toxicologists to remain updated on the pharmacological and toxicological effects of these emerging agents. Aims. To review the available information on newer synthetic stimulant, entactogenic and hallucinogenic drugs, provide a framework for classification of these drugs based on chemical structure and describe their pharmacology and clinical toxicology. Methods. A comprehensive review of the published literature was performed using PUBMED and Medline databases, together with additional non-peer reviewed information sources, including books, media reports, government publications and internet resources, including drug user web forums. Epidemiology. N...

Clinical toxicology of newer recreational drugs.

Recent Advances in the Neuropsychopharmacology of Serotonergic Hallucinogens

Receptor interaction profiles of novel psychoactive tryptamines compared with classic hallucinogens

Novel psychoactive substances are newly used designer drugs ("internet drugs", "research chemicals", "legal highs") potentially posing similar health risks to classic illicit substances. Chemically, many novel psychoactive substances can be classified as phenethylamines, amphetamines, synthetic cathinones, piperazines, pipradrols/piperidines, aminoindanes benzofurans, and tryptamines. Pharmacologically, these substances interact with various monoaminergic targets. Typically, stimulants inhibit the transport of dopamine and noradrenaline (pipradrols, pyrovalerone cathinones) or induce the release of these monoamines (amphetamines and methamphetamine-like cathinones), entactogens predominantly enhance serotonin release (phenylpiperazines, aminoindanes, para-substituted amphetamines, and MDMA-like cathinones) similar to MDMA (ecstasy), and hallucinogens (tryptamines, hallucinogenic phenethylamines) are direct agonists at serotonergic 5-HT2A receptors. Synthetic cannabinoids are another group of novel substances which all act as agonists at the cannabinoid CB1 receptor similar to THC but are chemically diverse. In particular, the relative serotonergic vs dopaminergic activity (determined by the dopamine/serotonin transporter inhibition ratio in vitro) can be helpful to predict the desired psychotropic but also the toxic effects of novel substances as well as their potential for addiction. Although the use of novel psychoactive substances mostly produces minor or moderate poisonings, serious complications occur. Serotonergic drugs (entactogens and hallucinogens) are associated with acute serotonin syndrome, hyperthermia, seizures, and hyponatremia. Dopaminergic drugs are highly addictive and acute toxicity includes prolonged stimulation, insomnia, agitation, and psychosis. Agitation, anxiety, paranoia, hypertension, and rarely myocardial infarction and renal failure are seen with synthetic cannabinoids. Treatment is supportive.

Novel psychoactive substances (designer drugs): overview and pharmacology of modulators of monoamine signaling.

Experiments were conducted to examine the molecular basis for the high affinity and potency of a new class of 5-HT(2A) receptor agonists, N-benzyl phenethylamines. Competition binding assays at several serotonin receptors confirmed that an N-arylmethyl substitution was necessary for affinity increases up to 300-fold over simple N-alkyl homologs, as well as enhanced selectivity for 5-HT(2A) versus 5-HT(2C) and 5-HT(1A) receptors. PI hydrolysis functional assays confirmed that these N-benzyl phenethylamines are potent and highly efficacious agonists at the rat 5-HT(2A) receptor. Virtual docking of these compounds into a human 5-HT(2A) receptor homology model indicated that the N-benzyl moiety might be interacting with Phe339((6.51)), whereas the phenethylamine portion was likely to be interacting with Phe340((6.52)). Experiments in h5-HT(2A) receptors with Phe339((6.51))L and Phe340((6.52))L mutations seem to support this hypothesis. Dramatic detrimental effects on affinity, potency, and intrinsic activity were observed with the Phe339((6.51))L mutation for all N-benzyl analogs, whereas most N-unsubstituted phenethylamines and traditional agonists were only weakly affected, if at all. Consistent with other published studies, the Phe340((6.52))L mutation detrimentally affected affinity, potency, and intrinsic activity of nearly all compounds tested, although a strong change in intrinsic activity was not seen with most N-aryl analogs. These data further validate the topology of our h5-HT(2A) receptor homology model. It is noteworthy that this study is the first to identify a hitherto unrecognized role for residue 6.51 in agonist activation of a serotonin G protein-coupled receptor (GPCR), whereas most previous reports have suggested a varied and sometimes contradictory role in homologous GPCRs.

John C. Naylor

Papers

Molecular interaction of serotonin 5-HT2A receptor residues Phe339(6.51) and Phe340(6.52) with superpotent N-benzyl phenethylamine agonists.