Effect fingerprinting of new psychoactive substances (NPS): What can we learn from in vitro data?

The use of new psychoactive substances (NPS) is increasing and currently > 600 NPS have been reported. However, limited information on neuropharmacological and toxicological effects of NPS is available, hampering risk characterization. We reviewed the literature on the in vitro neuronal modes of action to obtain effect fingerprints of different classes of illicit drugs and NPS. The most frequently reported NPS were selected for review: cathinones (MDPV, alpha-PVP, mephedrone, 4-MEC, pentedrone, methylone), cannabinoids (JWH-018), (hallucinogenic) phenethylamines (4-fluoroamphetamine, benzofurans (5-APB, 6-APB), 2C-B, NBOMes (25B-NBOMe, 25C-NBOMe, 25I-NBOMe)), arylcyclohexylamines (methoxetamine) and piperazine derivatives (mCPP, TFMPP, BZP). Our effect fingerprints highlight the main modes of action for the different NPS studied, including inhibition and/or reversal of monoamine reuptake transporters (cathinones and non-hallucinogenic phenethylamines), activation of 5-HT(2)receptors (hallucinogenic phenethylamines and piperazines), activation of cannabinoid receptors (cannabinoids) and inhibition of NDMA receptors (arylcyclohexylamines). Importantly, we identified additional targets by relating reported effect concentrations to the estimated human brain concentrations during recreational use. These additional targets include dopamine receptors, alpha- and beta-adrenergic receptors, GABA(A)receptors and acetylcholine receptors, which may all contribute to the observed clinical symptoms following exposure. Additional data is needed as the number of NPS continues to increase. Also, the effect fingerprints we have obtained are still incomplete and suffer from a large variation in the reported effects and effect sizes. Dedicated in vitro screening batteries will aid in complementing specific effect fingerprints of NPS. These fingerprints can be implemented in the risk assessments of NPS that are necessary for eventual control measures to reduce Public Health risks.