Structure-Activity Relationship of Truncated 2,8-Disubstituted-Adenosine Derivatives as Dual A/A Adenosine Receptor Antagonists and Their Cancer Immunotherapeutic Activity.

Based on hAAR structures, a hydrophobic C8-heteroaromatic ring in 5'-truncated adenosine analogues occupies the subpocket tightly, converting hAAR agonists into antagonists while maintaining affinity toward hAAR. The final compounds of 2,8-disubstituted--substituted 4'-thionucleosides, or 4'-oxo, were synthesized from d-mannose and d-erythrono-1,4-lactone, respectively, using a Pd-catalyst-controlled regioselective cross-coupling reaction. All tested compounds completely antagonized hAAR, including with the highest affinity ( = 7.7 ± 0.5 nM). The hAAR- X-ray structure revealed that C8-heteroaromatic rings prevented receptor activation-associated conformational changes. However, the C8-substituted compounds still antagonized hAAR. Structural SAR features and docking studies supported different binding modes at AAR and AAR, elucidating pharmacophores for receptor activation and selectivity. Favorable pharmacokinetics were demonstrated, in which displayed high oral absorption, moderate half-life, and bioavailability. Also, significantly improved the antitumor effect of anti-PD-L1 . Overall, this study suggests that the novel dual AAR/AAR nucleoside antagonists would be promising drug candidates for immune-oncology.