Novel N-2-Substituted Pyrazolo[3,4-d]pyrimidine Adenosine A(3) Receptor Antagonists: Inhibition of A(3)-Mediated Human Glioblastoma Cell Proliferation

Adenosine induces glioma cell proliferation by means of an antiapoptotic effect, which is blocked by cotreatment with selective A3 AR antagonists. In this study, a novel series of N2-substituted pyrazolo[3,4-d]pyrimidines 2a-u was developed as highly potent and selective A3 AR antagonists. The most performing compounds were derivatives 2a (R1 = CH3 and R2 = COC6H 5; Ki 334, 728, and 0.60 nM at the human A1, A2A, and A3 ARs, respectively) and 2b (R1 = CH3 and R2 = COC6H4-4-OCH 3; Ki 1037, 3179, and 0.18 nM at the human A1, A2A, and A3 ARs, respectively), which counteracted the effect of the A3 AR agonists Cl-IB-MECA and IB-MECA on human glioma U87MG cell proliferation. This effect was concentration-dependent, with IC 50 values comparable to A3 AR binding affinity values of 2a and 2b, thereby suggesting that their effects were receptor-mediated. Furthermore, the antiproliferative activity of the new compounds was demonstrated to be mediated by the block of A3 AR agonist activation of intracellular kinases ERK 1/2. © 2010 American Chemical Society.