Rigid Adenine Nucleoside Derivatives as Novel Modulators of the Human Sodium Symporters for Dopamine and Norepinephrine

Abstract

Thirty-two congeneric rigid adenine nucleoside derivatives containing a North (N)-methanocarba ribose substitution and a 2-arylethynyl group either enhanced (up to 760% of control) or inhibited [ potent DA uptake inhibitor (compound 6) with an IC 50 value of 92 nM (3-fold more potent than cocaine), but not nitrogen heterocycles. Several compounds inhibited or enhanced binding at the norepinephrine transporter (NET) and serotonin transporter (SERT) and inhibited function in the micromolar range; truncation at the 49-position in compound 23 allowed for weak inhibition of the SERT. We have not yet eliminated adenosine receptor affinity from this class of DAT modulators, but we identified modifications that remove DAT inhibition as an off-target effect of potent adenosine receptor agonists. Thus, we have identified a new class of allosteric DAT ligands, rigidified adenosine derivatives, and explored their initial structural requirements. They display a very atypical pharmacological profile, i.e., either enhancement by increasing affinity or inhibition of radioligand binding at the DAT, and in some cases the NET and SERT, and inhibition of neurotransmitter uptake.

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

“…Thus, 5-bromo is a suitable substitution for 5-chloro with respect to hDAT interaction (also evident in 2 compared to 1 ). 3 Curiously, benzyl ester 19 inhibited binding at SERT with a K i value of 5.6 μM, and 28 inhibited NET binding with a K i of 3.1 μM, and none of the other newly synthesized nucleosides inhibited binding at these two transporters with K i < 10 μM.…”

“…3 Compounds 4 , 3 6 and 8 - 16 , 22 , and 27 - 29 were synthesized by the routes shown in Schemes 1 - 3. Known nucleosides 1 - 3 , 5 and 7 were prepared as reported.…”

“…23 A fixed concentration of 10 μM was used in the primary screen for inhibition of radioligand binding at the hDAT. Because (N)-methanocarba nucleosides may enhance binding of a high affinity tropane derivative, [ 3 H]methyl (1 R ,2 S ,3 S )-3-(4-fluorophenyl)-8-methyl-8-azabicyclo[3.2.1]octane-2-carboxylate (WIN35,428, 24 ), at hDAT, 3 a significant negative value for % inhibition of radioligand binding, i.e. greater binding than control, was also interpreted as a hit.…”

“…3,4 DAT function is inhibited by cocaine, which increases the levels of DA at the synapse by a combination of mechanisms. 5 Micromolar activity of the same substituted nucleosides at the structurally related norepinephrine transporter (NET, SLC6A2) and weaker interactions with the serotonin transporter (SERT, SLC6A4) were also noted.…”

“…3,20 For example, ( 1S,2R,3S,4R,5S )-4-(2-((5-chlorothiophen-2-yl)ethynyl)-6-(methylamino)-9 H -purin-9-yl)-2,3-dihydroxy- N -methylbicyclo[3.1.0]hexane-1-carboxamide (MRS5980, 1 , Chart 1), which displays >10,000-fold greater affinity for the hA 3 AR (K i = 0.70 nM) than at other ARs, also inhibited DA uptake with an IC 50 of 253 nM. 3 Contrary to effects on uptake, however, 1 enhanced the binding of a tropane radioligand [ 125 I]methyl (1 R ,2 S ,3 S )-3-(4-iodophenyl)-8-methyl-8-azabicyclo[3.2.1]octane-2-carboxylate (RTI-55, 23 ) 3 to hDAT with an EC 50 of 35 nM. The closely related derivatives 2 and 3 differing only in the terminal aryl group enhanced binding of [ 125 I] 23 with EC 50 values of 9.1 and 70 nM, respectively.…”