Several new synthetic cathinones, which mimic the effect of classical psychostimulants such as cocaine or MDMA, have appeared in the global illicit drug market in the last decades. In fact, the illicit drug market is continually evolving by constantly adding small modifications to the common chemical structure of synthetic cathinones. Thus, the aim of this study was to investigate the in vitro and in vivo structure–activity relationship (SAR) of six novel synthetic cathinones currently popular as recreational drugs, pentedrone, pentylone, N-ethyl-pentedrone (NEPD), N-ethyl-pentylone (NEP), 4-methyl-pentedrone (4-MPD), and 4-methyl-ethylaminopentedrone (4-MeAP), which structurally differ in the absence or presence of different aromatic substituents and in their amino terminal group. Human embryonic kidney (HEK293) cells expressing the human isoforms of SERT and DAT were used for the uptake inhibition and release assays. Moreover, Swiss CD-1 mice were used to investigate the psychostimulant effect, rewarding properties (3, 10, and 30 mg/kg, i.p.), and the induction of immediate-early genes (IEGs), such as Arc and c-fos in the dorsal striatum (DS) and ventral striatum (VS) as well as bdnf in the medial prefrontal cortex (mPFC), of the test compounds. Our results demonstrated that all tested synthetic cathinones are potent dopamine (DA) uptake inhibitors, especially the N-ethyl analogs, while the ring-substituted cathinones tested showed higher potency as SERT inhibitors than their no ring-substituted analogs. Moreover, unlike NEP, the remaining test compounds showed clear “hybrid” properties, acting as DAT blockers but SERT substrates. Regarding the locomotion, NEP and NEPD were more efficacious (10 mg/kg) than their N-methyl analogs, which correlates with their higher potency inhibiting the DAT and an overexpression of Arc levels in the DS and VS. Furthermore, all compounds tested induced an increase in c-fos expression in the DS, except for 4-MPD, the least effective compound in inducing hyperlocomotion. Moreover, NEP induced an up-regulation of bdnf in the mPFC that correlates with its 5-HTergic properties. Finally, the present study demonstrated for the first time that NEP, 4-MPD, and 4-MeAP induce reward in mice. Altogether, this study provides valuable information about the mechanism of action and psychostimulant and rewarding properties as well as changes in the expression of IEGs related to addiction induced by novel second-generation synthetic cathinones.

The escalating prevalence of new psychoactive substances (NPSs) poses a significant public health challenge, evidenced by the vast chemical diversity, with over 500 substances reported annually to the United Nations Office on Drugs and Crime-Early Warning Advisory (UNODC-EWA) in the past five years. Among NPSs, synthetic cathinones are gaining a lot of popularity among users. Notably, synthetic cathinones accounted for approximately 50% of the total quantity of NPSs reported as seized by EU Member States in 2021. Preliminary data from UNODC indicates that a total of 209 synthetic cathinones have been reported to date. As their popularity grows, studying the structure-activity relationship (SAR) of synthetic cathinones is essential. SAR studies elucidate how structural features impact biological effects, aiding in toxicity prediction, regulatory compliance, and forensic identification. Additionally, SAR studies play a pivotal role in guiding drug policies, aiding authorities in categorizing and regulating newly emerging synthetic cathinones, mitigate public health risks and offer valuable insights into potential therapeutic applications. Thus, our Review consolidates recent findings on the effects of different substitutions in the chemical scaffold of synthetic cathinones on their mechanism of action as well as pharmacological and toxicological effects of synthetic cathinones, thus enhancing understanding of the SAR of synthetic cathinones' pharmacology and potential implications.

Recent studies have sparked renewed interest in the therapeutic potential of psychedelics for treating depression and other mental health conditions. Simultaneously, the novel psychoactive substances (NPS) phenomenon, with a huge number of NPS emerging constantly, has changed remarkably the illicit drug market, being their scientific evaluation an urgent need. Thus, this study aims to elucidate the impact of amino-terminal modifications to the 5-MeO-DMT molecule on its interactions with serotonin receptors and transporters, as well as its psychoactive and thermoregulatory properties. Our findings demonstrated, using radioligand binding methodologies, that all examined 5-MeO-tryptamines exhibited selectivity for 5-HT1AR over 5-HT2AR. In fact, computational docking analyses predicted a better interaction in the 5-HT1AR binding pocket compared to 5-HT2AR. Our investigation also proved the interaction of these compounds with SERT, revealing that the molecular size of the amino group significantly influenced their affinity. Subsequent experiments involving serotonin uptake, electrophysiology, and superfusion release assays confirmed 5-MeO-pyr-T as the most potent partial 5-HT releaser tested. All tested tryptamines elicited, to some degree, the head twitch response (HTR) in mice, indicative of a potential hallucinogenic effect and mainly mediated by 5-HT2AR activation. However, 5-HT1AR was also shown to be implicated in the hallucinogenic effect, and its activation attenuated the HTR. In fact, tryptamines that produced a higher hypothermic response, mediated by 5-HT1AR, tended to exhibit a lower hallucinogenic effect, highlighting the opposite role of both 5-HT receptors. Moreover, although some 5-MeO-tryptamines elicited very low HTR, they still act as potent 5-HT2AR agonists. In summary, this research offers a comprehensive understanding of the psychopharmacological profile of various amino-substituted 5-MeO-tryptamines, keeping structural aspects in focus and accumulating valuable data in the frame of NPS. Moreover, the unique characteristics of some 5-MeO-tryptamines render them intriguing molecules as mixed-action drugs and provide insight within the search of non-hallucinogenic but 5-HT2AR ligands as therapeutical agents.

Changes in the molecular structure of synthetic cathinones has led to an increase in the number of novel emerging drugs in the illicit drug market at an unprecedented rate. Unfortunately, little is known about the neuropsychopharmacology of recently emerged halogen-substituted α-PVP derivatives. Thus, the aim of this study was to investigate the role of para- and meta-halogen (F-, Cl-, and Br-) substitutions on the in vitro, in silico, and in vivo effects of α-pyrrolidinopentiophenone (α-PVP) derivatives. HEK293 cells expressing the human dopamine or serotonin transporter (hDAT and hSERT) were used for the uptake inhibition and transporter affinity assays. Molecular docking was used to model the interaction mechanism against DAT. Swiss CD-1 mice were used for the horizontal locomotor activity, open field test, and conditioned place preference paradigm. All compounds demonstrated potent DA uptake inhibition and higher DAT selectivity than cocaine. Meta-substituted cathinones showed higher DAT/SERT ratios than their para- analogs, which correlates with an increased psychostimulant effect in vivo and with different meta- and para-in silico interactions at DAT. Moreover, all compounds induced rewarding and acute anxiogenic effects in mice. In conclusion, the present study demonstrates the role of meta- and para-halogen substitutions in the mechanism of action and provides the first evidence of the rewarding and anxiety-like properties of halogenated α-PVP derivatives.

Synthetic cathinones are emerging psychoactive substances designed to mimic the effects of classical psychostimulants. Among them, α-D2PV, a novel pyrrolidine-containing cathinone characterized by a phenyl group on the α-carbon atom, has gained significant attention. This study investigates the in vitro and in silico mechanism of action as well as the abuse liability of α-D2PV using rodent models. Dopamine (DA), noradrenaline (NE), and serotonin (5-HT) uptake inhibition assays were conducted in HEK293 cells expressing the corresponding human monoamine transporter, complemented by molecular docking studies at the DA transporter (DAT). Behavioral studies in male Swiss CD-1 mice assessed locomotor activity and conditioned place preference, while microdialysis and self-administration experiments were performed in male Sprague-Dawley rats. The findings reveal that α-D2PV is a potent DA and NE uptake inhibitor, with minimal activity at the 5-HT transporter (SERT). Docking studies showed that the benzene rings of α-PVP and α-D2PV align precisely in their most stable conformations at DAT. In vivo, α-D2PV elicited dose-dependent hyperlocomotion, thigmotaxis, and rewarding effects in mice, alongside increased extracellular DA levels in the nucleus accumbens of awake rats. Self-administration experiments confirmed α-D2PV's high reinforcing efficacy, indicating a significant risk of abuse in humans. Finally, these results underscore the necessity for continued surveillance of α-D2PV within the illicit drug market. Furthermore, novel synthetic cathinones incorporating a phenyl ring at the α-carbon side chain warrant proactive monitoring due to their potential to retain dopaminergic activity and evade initial legal controls.

Current first-line antidepressants, such as selective serotonin reuptake inhibitors (SSRI), often present a delayed onset of action and fail to effectively treat a large proportion of patients, leaving a gap in the treatment of mood disorders. Psychedelics have recently emerged as promising alternatives due to their ability to produce fast-acting antidepressant effects through neuroplastic adaptations, but their hallucinogenic properties remain a major obstacle to their widespread therapeutic use. In this study, we characterized a novel class of halogenated DMT derivatives—5-F-DMT, 5-Cl-DMT, and 5-Br-DMT—for their pharmacological activity, behavioral effects, and therapeutic potential. Using a combination of in vitro assays, in silico modeling, and in vivo behavioral and gene expression studies, we found that halogen substitution at the 5-position modulates receptor affinity and selectivity across key serotonin (5-HT) receptors (5-HT1A/2 A/2B/2CR) and transporter (SERT). Notably, 5-Br-DMT was found to activate 5-HT2AR but did not induce the head twitch response (HTR) in mice, suggesting non-hallucinogenic activity. Furthermore, 5-Br-DMT upregulated immediate early genes (IEGs) associated with neuroplasticity in the mouse prefrontal cortex and hippocampus (Arc, Egr-1, -2 and -3) and promoted dendritic growth in cortical neurons. In a mouse model of stress-induced depression, a single administration (10 mg/kg, i.p.) of 5-Br-DMT resulted in a significant reduction in depressive-like behavior, reflecting rapid antidepressant effects. Collectively, our results highlight 5-Br-DMT as a non-hallucinogenic psychoplastogen with antidepressant properties, supporting its potential as a prototypical candidate for further study. Moreover, the evaluation and biological characterization of the halogenated DMT derivatives offers valuable information on structure-activity relationships that may guide the design of future therapeutic compounds.