Combined in vitro and in silico approaches to the assessment of stimulant properties of novel psychoactive substances – The case of the benzofuran 5-MAPB
Novel psychoactive substances (NPS) are increasingly prevalent world-wide although their pharmacological characteristics are largely unknown; those with stimulant properties, due to interactions with the dopamine transporter (DAT), have addictive potential which their users may not realise.
We evaluated the binding of 1-(1-benzofuran-5-yl)-N-methylpropan-2-amine (5-MAPB) to rat striatal DAT by means of quantitative autoradiography with [125I]RTI-121, and the effects of 5-MAPB on electrically-evoked dopamine efflux by fast-cyclic voltammetry in rat brain slices. 5-MAPB displaced [125I]RTI-121 in a concentration-dependent manner, with significant effects at 10 and 30 μM. The voltammetry data suggest that 5-MAPB reduces the rate of dopamine reuptake; while the peak dopamine efflux was not increased, the area under the curve was augmented. 5-MAPB can also cause reverse dopamine transport consistent with stimulant properties, more similar to amphetamine than cocaine. Molecular modelling and docking studies compared the binding site of DAT in complex with 5-MAPB to dopamine, amphetamine, 5-APB, MDMA, cocaine and RTI-121. This structural comparison reveals a binding mode for 5-MAPB found in the primary binding (S1) site, central to transmembrane domains 1, 3, 6 and 8, which overlaps with the binding modes of dopamine, cocaine and its analogues. Atomistic molecular dynamics simulations further show that, when in complex with 5-MAPB, DAT can exhibit conformational transitions that spontaneously isomerize the transporter into inward-facing state, similarly to that observed in dopamine-bound DAT.
These novel insights, offered by the combination of computational methods of biophysics with neurobiological procedures, provide structural context for NPS at DAT and relate them with their functional properties at DAT as the molecular target of stimulants.