Scaffold Repurposing of Nucleosides (Adenosine Receptor Agonists): Enhanced Activity at the Human Dopamine and Norepinephrine Sodium Symporters.

We have repurposed (N)-methanocarba adenosine derivatives (A3 adenosine receptor (AR) agonists) to enhance radioligand binding allosterically at the human dopamine (DA) transporter (DAT) and inhibit DA uptake. We extended the structure-activity relationship of this series with small N6-alkyl substitution, 5'-esters, deaza modifications of adenine, and ribose restored in place of methanocarba. C2-(5-Halothien-2-yl)-ethynyl 5'-methyl 9 (MRS7292) and 5'-ethyl 10 (MRS7232) esters enhanced binding at DAT (EC50 ∼ 35 nM) and at the norepinephrine transporter (NET). 9 and 10 were selective for DAT compared to A3AR in the mouse but not in humans. At DAT, the binding of two structurally dissimilar radioligands was enhanced; NET binding of only one radioligand was enhanced; SERT radioligand binding was minimally affected. 10 was more potent than cocaine at inhibiting DA uptake (IC50 = 107 nM). Ribose analogues were weaker in DAT interaction than the corresponding bicyclics. Thus, we enhanced the neurotransmitter transporter activity of rigid nucleosides while reducing A3AR affinity.