Psychoactive synthetic cathinones (or \u27bath salts\u27): Investigation of mechanisms of action

Synthetic cathinones represent threatening and high abuse-potential designer drugs. These are analogs of cathinone (the b-keto analog of amphetamine (AMPH)) a naturally occurring stimulant found in the plant Catha Edulis. Methcathinone (MCAT) was the first synthetic analog of cathinone to be identified in 1987 by Glennon and co-workers and it exerted its action primarily through the dopamine transporter (DAT). Most central stimulants exert their action via monomaine transporters by causing either the release (e.g. cathinone analogs such as MCAT) or by preventing the reuptake (e.g. cocaine) of the neurotransmitter dopamine (DA) thus increasing the extracellular synaptosomal concentration of this neurotransmitter. In 2010, a new class of designer cathinone-like drugs called ‘bath salts’, initially a combination of methylenedioxypyrovalerone (MDPV), methylone (methylenedioxymethcathione, MDMC) and mephedrone (MEPH), soared to popularity. It caused extremely detrimental side effects; it was exceedingly popular for its recreational use and posed a threat to public health. At the time, their mechanisms of action were unknown. Our group identified that MDPV produced actions distinct from other cathinone analogs (i.e., it was identified as the first cathinone-like compound to act as a reuptake inhibitor at the dopamine transporter (DAT)). These findings suggested that not all cathinone-like compounds act uniformly and this insinuated that unique structural features on the cathinone scaffold might contribute to different effects at the transporter level. The overall goal of this project was to study the mechanisms of action of synthetic cathinones (including ‘bath salts’) at the monoamine transporters. We investigated the contribution of each of various structural features on the cathinone scaffold (i.e, the terminal amine, a and b positions, and the phenyl ring). We also constructed homology models of the human dopamine and serotonin transporters (hDAT and hSERT respectively) to help explain differences in selectivity between the neurochemical and behavioral aspects of DAT and SERT. Overall we found that structural features contributed to similar or distinctive mechanisms of action and also contributed to selectivity at monoamine transporters. Our studies provide information that can be useful to drug and health regulatory agencies to help prevent, treat, or curb the future abuse of such drugs

Ethylenedioxy homologs of N-methyl-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA) and its corresponding cathinone analog methylenedioxymethcathinone: Interactions with transporters for serotonin, dopamine, and norepinephrine

N-Methyl-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA; 'Ecstasy'; 1) and its β-keto analog methylone (MDMC; 2) are popular drugs of abuse. Little is known about their ring-expanded ethylenedioxy homologs. Here, we prepared N-methyl-(3,4-ethylenedioxyphenyl)-2-aminopropane (EDMA; 3), both of its optical isomers, and β-keto EDMA (i.e., EDMC; 4) to examine their effects at transporters for serotonin (SERT), dopamine (DAT), and norepinephrine (NET). In general, ring-expansion of the methylenedioxy group led to a several-fold reduction in potency at all three transporters. With respect to EDMA (3), S(+)3 was 6-fold, 50-fold, and 8-fold more potent than its R(-) enantiomer at SERT, DAT, and NET, respectively. Overall, in the absence of a β-carbonyl group, the ethylenedioxy (i.e., 1,4-dioxane) substituent seems better accommodated at SERT than at DAT and NET

Abuse-Related Neurochemical Effects of Para-Substituted Methcathinone Analogs in Rats: Microdialysis Studies of Nucleus Accumbens Dopamine and Serotonin s

ABSTRACT Methcathinone (MCAT) is a monoamine releaser and parent compound to a new class of designer drugs that includes the synthetic cathinones mephedrone and flephedrone. Using MCAT and a series of para-substituted (or 4-substituted) MCAT analogs, it has been previously shown that expression of abuserelated behavioral effects in rats correlates both with the volume of the para substituent and in vitro neurochemical selectivity to promote monoamine release via the dopamine (DA) versus serotonin (5-HT) transporters in rat brain synaptosomes. The present study used in vivo microdialysis to determine the relationship between these previous measures and the in vivo neurochemical selectivity of these compounds to alter nucleus accumbens (NAc) DA and 5-HT levels. Male Sprague-Dawley rats were implanted with bilateral guide cannulae targeting the NAc. MCAT and five para-substituted analogs (4-F, 4-Cl, 4-Br, 4-CH 3, and 4-OCH 3 ) produced dose-and time-dependent increases in NAc DA and/or 5-HT levels. Selectivity was determined as the dose required to increase peak 5-HT levels by 250% divided by the dose required to increase peak DA levels by 250%. This measure of in vivo neurochemical selectivity varied across compounds and correlated with 1) in vivo expression of abuse-related behavioral effects (r 5 0.89, P 5 0.02); 2) in vitro selectivity to promote monoamine release via DA and 5-HT transporters (r 5 0.95, P , 0.01); and 3) molecular volume of the para substituent (r 5 20.85, P 5 0.03). These results support a relationship between these molecular, neurochemical, and behavioral measures and support a role for molecular structure as a determinant of abuse-related neurochemical and behavioral effects of MCAT analogs

“Deconstruction” of the Abused Synthetic Cathinone Methylenedioxypyrovalerone (MDPV) and an Examination of Effects at the Human Dopamine Transporter

Synthetic cathinones, β-keto analogues of amphetamine (or, more correctly, of phenylalkylamines), represent a new and growing class of abused substances. Several such analogues have been demonstrated to act as dopamine (DA) releasing agents. Methylenedioxypyrovalerone (MDPV) was the first synthetic cathinone shown to act as a cocaine-like DA reuptake inhibitor. MDPV and seven deconstructed analogues were examined to determine which of MDPV’s structural features account(s) for uptake inhibition. In voltage-clamped (−60 mV) Xenopus oocytes transfected with the human DA transporter (hDAT), all analogues elicited inhibitor-like behavior shown as hDAT-mediated outward currents. Using hDAT-expressing mammalian cells we determined the affinities of MDPV and its analogues to inhibit uptake of [³H]­DA by hDAT that varied over a broad range (IC₅₀ values ca. 135 to >25 000 nM). The methylenedioxy group of MDPV made a minimal contribution to affinity, the carbonyl group and a tertiary amine are more important, and the extended α-alkyl group seems most important. Either a tertiary amine, or the extended α-alkyl group (but not both), are required for the potent nature of MDPV as an hDAT inhibitor

Effects of <i>N</i>‑Alkyl-4-Methylamphetamine Optical Isomers on Plasma Membrane Monoamine Transporters and Abuse-Related Behavior

4-Methylamphetamine (4-MA) is an emerging drug of abuse that acts as a substrate at plasma membrane transporters for dopamine (DAT), norepinephrine (NET), and serotonin (SERT), thereby causing nonexocytotic release of monoamine transmitters via reverse transport. Prior studies by us showed that increasing the <i>N</i>-alkyl chain length of N-substituted 4-MA analogues converts 4-MA from a transportable substrate (i.e., releaser) at DAT and NET to a nontransported blocker at these sites. Here, we studied the effects of the individual optical isomers of <i>N</i>-methyl-, <i>N</i>-ethyl-, and <i>N</i>-<i>n</i>-propyl 4-MA on monoamine transporters and abuse-related behavior in rats because action/function might be related to stereochemistry. Uptake inhibition and release assays were conducted in rat brain synaptosomes whereas electrophysiological assessments of drug–transporter interactions were examined using cell-based biosensors. Intracranial-self-stimulation in rats was employed to assess abuse potential in vivo. The experimental evidence demonstrates that <i>S</i>(+)<i>N</i>-methyl 4-MA is a potent and efficacious releaser at DAT, NET, and SERT with the highest abuse potential among the test drugs, whereas <i>R</i>(−)<i>N</i>-methyl 4-MA is a less potent releaser with reduced abuse potential. The <i>S</i>(+)­ethyl analogue has decreased efficacy as a releaser at DAT but retains full release activity at NET and SERT with a reduction in abuse-related effects; the <i>R</i>(−)­ethyl analogue has a similar profile but is less potent. <i>S</i>(+)<i>N</i>-Propyl 4-MA is a nontransported blocker at DAT and NET but an efficacious releaser at SERT, whereas the <i>R</i> enantiomer is almost inactive. In conclusion, the <i>S</i> enantiomers of the <i>N</i>-alkyl 4-MA analogues are most potent. Lengthening the <i>N</i>-alkyl chain converts compounds from potent nonselective releasers showing abuse-related effects to more selective SERT releasers with no apparent abuse potential