Binding Mode Selection Determines the Action of Ecstasy Homologs at Monoamine Transporters

Abstract

Determining the structural elements that define substrates and inhibitors at the monoamine transporters is critical to elucidating the mechanisms underlying these disparate functions. In this study, we addressed this question directly by generating a series of N-substituted 3,4-methylenedioxyamphetamine analogs that differ only in the number of methyl substituents on the terminal amine group. Starting with 3,4-methylenedioxy-N-methylamphetamine, 3,4-methylenedioxy-N,N-dimethylamphetamine (MDDMA) and 3,4-methylenedioxy-N,N,N-trimethylamphetamine (MDTMA) were prepared. We evaluated the functional activities of the compounds at all three monoamine transporters in native brain tissue and cells expressing the transporters. In addition, we used ligand docking to generate models of the respective proteinligand complexes, which allowed us to relate the experimental findings to available structural information. Our results suggest that the 3,4-methylenedioxyamphetamine analogs bind at the monoamine transporter orthosteric binding site by adopting one of two mutually exclusive binding modes. 3,4-methylenedioxyamphetamine and 3,4-methylenedioxy-N-methylamphetamine adopt a high-affinity binding mode consistent with a transportable substrate, whereas MDDMA and MDTMA adopt a lowaffinity binding mode consistent with an inhibitor, in which the ligand orientation is inverted. Importantly, MDDMA can alternate between both binding modes, whereas MDTMA exclusively binds to the low-affinity mode. Our experimental results are consistent with the idea that the initial orientation of bound ligands is critical for subsequent interactions that lead to transporter conformational changes and substrate translocation.

Pharmacokinetic Profiles and Pharmacodynamic Effects for Methylone and Its Metabolites in Rats

“…The data reported here for MDC differ somewhat from findings with 3,4-methylenedioxyamphetamine (MDA), the analogous N-demethylated metabolite of MDMA. We and others have shown that MDA and MDMA display nearly identical potency and selectivity as substrate-type releasers at monoamine transporters in vitro (McKenna et al, 1991;Sandtner et al, 2016;Wichems et al, 1995). Interestingly, HHMC was found to be a potent and selective substrate for DAT and NET, with a DAT/SERT ratio of 155 in vitro.…”

Structure-Activity Relationships of Substituted Cathinones, with Transporter Binding, Uptake, and Release

“…This finding may not apply to all model systems. Sandtner et al (2016) reported higher potencies for release than for uptake for MDMA at the three transporters using rat brain synaptosomes, whereas MDMA was 3-, 3-, and 18-fold less potent for release compared with uptake at hNET, hSERT, and hDAT, respectively (Tables 2 and 3). The release models are quite different, with HEK cells expressing a single transporter with no blocking agents required, and the superfusion assay involved continuous removal of released substrate from the reaction, compared with rat brain synaptosomes that require blockade of VMAT2 as well as blockade of other transporters, and the "static" release assay does not remove released neurotransmitter from the reaction.…”

“…The n-pyrrolidino substituent on 4-MePPP is sterically repulsed by bulky side chains in SERT that are found in the orthosteric binding pocket as delineated by the Leu-T structural model, which may account for the low affinity of this entire series for SERT (Saha et al, 2015). The pure transporter inhibitor activity of this group may be due to the n-pyrrolidino substituent, as Sandtner et al (2016) observed that interactions with critical aspartate residues of DAT and SERT are necessary for substrate activity, and secondary or tertiary substitution on nitrogen inhibits interaction with these residues. The high selectivity for hDAT over hSERT suggests that these compounds may have high abuse liability, consistent with the ability of a-PBP and a-PVP to fully substitute for discriminative stimulus effects of both cocaine and METH and to produce conditioned place preference (Gatch et al, 2015a).…”

From linked open data to molecular interaction: studying selectivity trends for ligands of the human serotonin and dopamine transporter

“…15,16 Structure–activity relationship (SAR) studies as well as docking of selected cathinones into protein homology models of hDAT and hSERT revealed the first insights into the molecular basis of transporter selectivity. 15,17,18 …”