Fluorescent-Labeled Selective Adenosine A Receptor Antagonist Enables Competition Binding Assay by Flow Cytometry.

Fluorescent ligands represent powerful tools for biological studies and are considered attractive alternatives to radioligands. In this study, we developed fluorescent antagonists for A adenosine receptors (AARs), which are targeted by antiasthmatic xanthines and were proposed as novel targets in immuno-oncology. Our approach was to merge a small borondipyrromethene (BODIPY) derivative with the pharmacophore of 8-substituted xanthine derivatives. On the basis of the design, synthesis, and evaluation of model compounds, several fluorescent ligands were synthesized. Compound 29 (PSB-12105), which displayed high affinity for human, rat, and mouse AARs ( K = 0.2-2 nM) and high selectivity for this AR subtype, was selected for further studies. A homology model of the human AAR was generated, and docking studies were performed. Moreover, 29 allowed us to establish a homogeneous receptor-ligand binding assay using flow cytometry. These compounds constitute the first potent, selective fluorescent AAR ligands and are anticipated to be useful for a variety of applications.