Structure–Activity Relationship of N-Ethyl-Hexedrone Analogues: Role of the α-Carbon Side-Chain Length in the Mechanism of Action, Cytotoxicity, and Behavioral Effects in Mice

Abstract

Synthetic cathinones are β-keto amphetamine derivatives whose appearance has increased dramatically in the past decades. N-Ethyl substituted cathinones have been proven to potently inhibit dopamine (DA) uptake and induce psychostimulant and rewarding effects in mice. However, little is known about the influence of the alpha-carbon side-chain length of N-ethyl cathinones on their pharmacological and toxicological effects. Thus, the aim of this study was to synthesize and investigate the in vitro and in vivo effects of five N-ethyl substituted cathinones: N-ethyl-cathinone (NEC), N-ethyl-buphedrone (NEB), N-ethyl-pentedrone, N-ethyl-hexedrone (NEH), and N-ethyl-heptedrone. HEK293 cells expressing the human DA or serotonin transporter (hDAT and hSERT) were used for uptake inhibition and binding assays. PC12 cells were used for the cytotoxicity assays. Swiss CD-1 mice were used to study the in vivo psychostimulant, anxiogenic, and rewarding properties. Our results show that all tested cathinones are able to inhibit DA uptake and are DAT-selective. The potency of DA uptake inhibitors increases with the elongation of the aliphatic side chain from methyl to propyl and decreases when increasing from butyl to pentyl, which correlates with an inverted U-shape psychostimulant response in mice at the medium dose tested. On the other hand, an increase in the α-carbon side-chain length correlates with an increase in the cytotoxic properties in PC12 cells, probably due to better membrane penetration. Moreover, all the cathinones tested have shown higher cytotoxicity than methamphetamine. Finally, our study not only demonstrated the rewarding properties of NEC and NEB but also the anxiety-like behavior induced at high doses by all the cathinones tested.

Synthetic Cathinones: Epidemiology, Toxicity, Potential for Abuse, and Current Public Health Perspective

“…Research on N-ethyl-hexedrone analogues has demonstrated that the potency of DA uptake inhibitors increases as the aliphatic side chain extends from methyl to propyl. However, as the chain length increases from butyl to pentyl, the potency decreases [74]. On the other hand, longer α-carbon side chains of SCs resulted in increased cytotoxic properties in PC12 cells, probably due to their enhanced membrane penetration [74].…”

“…However, as the chain length increases from butyl to pentyl, the potency decreases [74]. On the other hand, longer α-carbon side chains of SCs resulted in increased cytotoxic properties in PC12 cells, probably due to their enhanced membrane penetration [74].…”

Structure–Activity Relationship of Synthetic Cathinones: An Updated Review

“…53 Moreover, our group recently showed a correlation of the binding efficacy at DAT with an increase in locomotion at an intermediate dose (10 mg/kg) of N-etlyl-pentedrone (NEPD) analogs. 54 Reward. DA is the primary neurotransmitter associated with reward and pleasure.…”

“…142 Nonetheless, amphetamine-cathinone analogues toxicity studies should be performed in order to confirm this increased toxicity of amphetamines over cathinones is maintained for other substituents, as other studies seem to indicate that cathinones could induce seizures at lower doses than amphetamine or even -with the addition of certain substitutions in their chemical scaffold -cause more cytotoxic effects than methamphetamine. 54,133 Synthetic cathinones can suffer modifications in the aromatic ring (i), in the length of the aliphatic side chain (ii) and in the terminal amino group (iii). Therefore, SARs aim to identify what role do these modifications in the chemical scaffold of the cathinone play in their neuropharmacological and toxicological effects.…”

“…Several authors have studied the effects of prolongation or shortening of the aliphatic side chain of common synthetic cathinones found in the illicit drug market, such as α-PVP, MDPV or NEPD, and in all cases coincide in an increase of the potency at inhibiting DAT when increasing the length of the aliphatic side chain from a methyl to a propyl. 36,54,176 The effect of the length of the aliphatic side chain is also apparent in vivo. For instance, our group recently demonstrated that increasing the length of the aliphatic side chain of N-ethyl substituted cathinones from a methyl to a propyl resulted in an increased locomotor activity, but started to decrease when adding extra carbons.…”