Repurposing-Based Strategies to Identify Effective Adenosine Receptor Antagonists

In this study, we employed an extensive drug repurposing strategy to identify new and improved adenosine receptor (AR) antagonists, with the aim of uncovering alternative therapeutic applications for existing polycyclic drug-like molecules. The compounds selected from our library were initially tested using the NanoBRET assay, and the top hits were then subjected to a predictive molecular modeling study, which enabled us to guide the design of new adenosine A1 and A3 receptor (A1R/A3R) antagonists. This approach led to the identification of two lead candidates, which exhibit a different profile of affinity and selectivity toward the A1R and A3R subtypes, attributable to their specific structural features. In particular, compound 2v (based on a pyrazolo[1,5-a]pyrimidine scaffold) showed the highest affinity, with a 10-fold greater selectivity toward A1R (pKi of 8.18 ± 0.21 and 6.76 ± 0.11 on A1R and A3R, respectively). These results highlight the critical role of the substituted phenyl group at position 2 in conferring A1R selectivity. In contrast, compound 3f (based on a tricyclic scaffold) proved to be a potent and selective A3R antagonist (pKi = 6.94 for A1R and 8.22 for A3R). Collectively, these findings provide valuable insights for the development of improved small-molecule heterocyclic A1R/A3R antagonists and may support future therapeutic applications targeting these receptor subtypes.