Study of A2A adenosine receptor gene deficient mice reveals that adenosine analogue CGS 21680 possesses no A2A receptor-unrelated lymphotoxicity

1 Cell surface A(2A) adenosine receptor (A(2A)R) mediated signalling affects a variety of important processes and adenosine analogues possess promising pharmacological properties. 2 Demonstrating the receptor specificity of potentially lymphotoxic adenosine-based drugs facilitates their development for clinical applications. 3 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. 4 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. 5 Incubation of A2AR-expressing thymocytes with extracellular adenosine or CGS 21680 bz 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. 6 The A(2A) receptor-specific lymphotoxicity of CGS 21650 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. 7 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.