NovelN²-Substituted Pyrazolo[3,4-d]pyrimidine Adenosine A₃Receptor Antagonists: Inhibition of A₃-Mediated Human Glioblastoma Cell Proliferation^†

Abstract

Adenosine induces glioma cell proliferation by means of an antiapoptotic effect, which is blocked by cotreatment with selective A(3) AR antagonists. In this study, a novel series of N(2)-substituted pyrazolo[3,4-d]pyrimidines 2a-u was developed as highly potent and selective A(3) AR antagonists. The most performing compounds were derivatives 2a (R(1) = CH(3) and R(2) = COC(6)H(5); K(i) 334, 728, and 0.60 nM at the human A(1), A(2A), and A(3) ARs, respectively) and 2b (R(1) = CH(3) and R(2) = COC(6)H(4)-4-OCH(3); K(i) 1037, 3179, and 0.18 nM at the human A(1), A(2A), and A(3) ARs, respectively), which counteracted the effect of the A(3) 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 A(3) 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 A(3) AR agonist activation of intracellular kinases ERK 1/2.

The A3 adenosine receptor as multifaceted therapeutic target: pharmacology, medicinal chemistry, and in silico approaches

“…Very recently, a newly synthesized A 3 AR antagonist (pyrazolo[3,4‐ d ]pyrimidine, see compound 133 in Fig. ) was demonstrated to counteract the A 3 AR agonists Cl‐IB‐MECA‐ and IB‐MECA‐mediated proliferation of human glioma U87MG cells through the inhibition of A 3 AR agonist‐mediated ERK 1/2 activation . This observation was consistent with the studies that demonstrated that ERK 1/2, p38, and Akt could be the phosphorylative pathways responsible for A 3 AR‐mediated cell proliferation in glioblastoma.…”

“…Compound 133 was subsequently tested on human glioma U87MG cells, and it was shown to counteract the A 3 AR agonist‐mediated proliferation of the glioma cells through the inhibition of ERK 1/2 activation. Therefore, it might represent a promising lead compound for the development of adjuvant agents in the glioma chemotherapy …”

The A3Adenosine Receptor: History and Perspectives

“…Both pro-and antiapoptotic as well as pro-and antiproliferative effects have been reported depending on the level of receptor activation (Jacobson, 1998;Merighi et al, 2005b;Gessi et al, 2007;Kim et al, 2010;Taliani et al, 2010;Varani et al, 2011a;Sakowicz-Burkiewicz et al, 2013). At first, telomerase activity inhibition and cytostatic effects were observed in tumor cells (Fishman et al, 2000(Fishman et al, , 2001.…”

Antiproliferative effects of selective adenosine receptor agonists and antagonists on human lymphocytes: evidence for receptor-independent mechanisms

“…Part of this effect may be attributed to adenosine via the activation of ARs and sustained increase in cAMP levels [5]. Besides the activation of extracellular receptors [11,[15][16][17], direct intracellular toxicity (also by adenosine metabolites) has been described [18][19][20][21]. Furthermore, adenosine is able to stimulate cell growth and proliferation and/or to induce apoptosis in various normal and tumor cell lines.…”