Study of A 2A adenosine receptor gene deficient mice reveals that adenosine analogue CGS 21680 possesses no A 2A receptor‐unrelated lymphotoxicity

Cell surface A 2A adenosine receptor (A 2A R) mediated signalling affects a variety of important processes and adenosine analogues possess promising pharmacological properties. Demonstrating the receptor specificity of potentially lymphotoxic adenosine‐based drugs facilitates their development for clinical applications. To distinguish between the receptor‐dependent and ‐independent lymphotoxicity and apoptotic activity of adenosine and its analogues we used lymphocytes from A 2A R‐deficient mice. Comparison of A 2A R‐expressing (+/+) and A 2A R‐deficient (−/−) cells in cyclic AMP accumulation assays confirmed that the A 2A R agonist CGS 21680 is indeed selective for A 2A receptors in T‐lymphocytes. Incubation of A 2A R‐expressing thymocytes with extracellular adenosine or CGS 21680 in vitro results in the death of about 7–15% of thymocytes. In contrast, no death was induced in parallel assays in cells from A 2A R‐deficient mice, providing genetic evidence that CGS 21680 does not display adenosine receptor‐independent intracellular cytotoxicity. The A 2A receptor‐specific lymphotoxicity of CGS 21680 is also demonstrated in a long‐term (6‐day) in vitro model of thymocyte positive selection where addition of A 2A R antagonist ZM 241,385 did block the effects of CGS 21680, allowing the survival of T cells. The use of cells from adenosine receptor‐deficient animals is proposed as a part of the screening process for potential adenosine‐based drugs for their receptor‐independent cytotoxicity and lymphotoxicity. British Journal of Pharmacology (2000) 131 , 43–50; doi: 10.1038/sj.bjp.0703532