Irreversible Antagonists for the Adenosine A 2B Receptor.

Blockade of the adenosine A 2B receptor (A 2B AR) represents a potential novel strategy for the immunotherapy of cancer. In the present study, we designed, synthesized, and characterized irreversible A 2B AR antagonists based on an 8- p -sulfophenylxanthine scaffold. Irreversible binding was confirmed in radioligand binding and bioluminescence resonance energy transfer(BRET)-based Gα 15 protein activation assays by performing ligand wash-out and kinetic experiments. p -(1-Propylxanthin-8-yl)benzene sulfonyl fluoride ( 6a , PSB-21500) was the most potent and selective irreversible A 2B AR antagonist of the present series with an apparent K i value of 10.6 nM at the human A 2B AR and >38-fold selectivity versus the other AR subtypes. The corresponding 3-cyclopropyl-substituted xanthine derivative 6c (PSB-21502) was similarly potent, but was non-selective versus A 1 - and A 2A ARs. Attachment of a reactive sulfonyl fluoride group to an elongated xanthine 8-substituent ( 12 , K i 7.37 nM) resulted in a potent, selective, reversibly binding antagonist. Based on previous docking studies, the lysine residue K269 7.32 was proposed to react with the covalent antagonists. However, the mutant K269L behaved similarly to the wildtype A 2B AR, indicating that 6a and related irreversible A 2B AR antagonists do not interact with K269 7.32 . The new irreversible A 2B AR antagonists will be useful tools and have the potential to be further developed as therapeutic drugs.