Therapeutic potential of A2 and A3 adenosine receptor: a review of novel patented ligands.

Introduction: Adenosine exerts its effects by interacting with G-protein coupled receptors (GPCR) namely A1, A2A, A2B and A3, respectively. These are involved in several diseases, for example and most importantly, Parkinson’s disease, ischemia and inflammation. There is high interest in the development of potent and selective ligands for these adenosine receptor (AR) subtypes, primarily for their therapeutic potential but also as pharmacological tools in receptor studies. Areas covered: This paper concentrates on reviewing the therapeutic potential of A2 and A3 ARs, which represent the most interesting subtypes of recent years. A general description of each receptor is reported with novel agonist and antagonist structures, patented in 2008 -- 2011. PubMed and Free Patents Online databases were principally used to collect all the material. Expert opinion: In the past years, by modulating A2 and A3ARs, several new possible therapeutic applications were discovered. For this reason, research concerning AR ligands is still of great interest. In particular, few potent and selective A2B agonists and antagonists are actually reported and a clear SAR (structure--activity relationship) profile lacks for this AR subtype. At the A3AR, allosteric modulation may prevent problems related to the high difference between rat and human orthosteric sites and simplify the preclinical studies on A3AR.