A₃ adenosine receptor agonists containing dopamine moieties for enhanced interspecies affinity

Area of Science:

• Medicinal Chemistry
• Pharmacology
• Computational Chemistry

Background:

• Previous studies identified 4'-truncated (N)-methanocarba-adenosine derivatives with high mouse A3AR affinity.
• Adenosine A3 receptor (A3AR) modulators are of therapeutic interest.

Purpose of the Study:

• To synthesize and evaluate novel 5'-methylamide adenosine derivatives incorporating dopamine-related N6 substituents.
• To investigate the affinity, selectivity, and signaling bias of these new compounds at human and mouse A3ARs.
• To explore the in vivo efficacy and pharmacokinetic properties of selected derivatives.

Main Methods:

• Synthesis of N6-substituted 5'-methylamide adenosine derivatives.
• Radioligand binding assays to determine receptor affinity (Ki) and selectivity.
• Functional assays to assess G protein and beta-arrestin 2 (βarr2) dependent signaling pathways.
• Computational modeling to understand ligand-receptor interactions.
• In vivo hypothermia models to evaluate A3AR activation.

Main Results:

• Derivative MRS7618 (11) exhibited high affinity (Ki 0.563 nM) and selectivity (>20,000-fold) for human A3AR and good affinity (Ki 1.54 nM) for mouse A3AR.
• 2-Alkyl ether derivatives maintained A3AR affinity but showed lower selectivity compared to 2-alkyne analogs.
• Functional assays confirmed these compounds are full agonists without signaling bias.
• Computational modeling suggested interactions between phenyl OH/OMe groups and Gln261 in the mA3AR.
• Despite rapid clearance, parent O-methyl catechol nucleosides showed prolonged mA3AR activation in vivo, possibly via active metabolites.
• Selected analogs induced hypothermia in mice, indicating peripheral A3AR agonism.

Conclusions:

• Novel N6-substituted adenosine derivatives effectively target A3ARs with high affinity and selectivity.
• These compounds act as non-biased full agonists, with potential for therapeutic applications.
• In vivo studies suggest the formation of active metabolites contributing to prolonged receptor activation and observable physiological effects like hypothermia.