A novel adenosine analog, thio-Cl-IB-MECA, induces G0/G1 cell cycle arrest and apoptosis in human promyelocytic leukemia HL-60 cells

Human A3 adenosine receptor (A3AR) agonists have been shown to play important roles in several physiological and pathological processes, including growth inhibition of human cancer cells. On this line, we recently found that a novel adenosine analog, 2-chloro-N6-(3-iodobenzyl)-4'-thioadenosine-5'-N-methyluronamide (thio-Cl-IB-MECA) was a potent human A3AR agonist, and is superior to a known agonist Cl-IB-MECA Jeong LS, Jin DZ, Kim HO, Shin DH, Moon HR, Gunaga P, et al. J Med Chem 2003;46:3775]. Here, we report that a novel A3AR agonist, thio-Cl-IB-MECA inhibited the growth of human promyelocytic leukemia HL-60 cells by arresting cell cycle and induction of apoptosis. Thio-Cl-IB-MECA induced the cell cycle arrest of G0/G1 in the early time and at lower concentration (up to 25 microM). At higher concentration (50 microM), the apoptotic cell deaths were manifested by observation of the increase of sub-G0 phase of cell cycle distribution, DNA fragmentation and poly(ADP-ribose) polymerase (PARP) cleavage. In addition, the down-regulation of checkpoint protein cyclin D1 and c-myc by thio-Cl-IB-MECA was well correlated with the arrest of cell cycle transition of G1 to S phase. Further study revealed that the growth inhibitory activity of thio-Cl-IB-MECA is also related with the modulation of Wnt signaling pathway. The levels of beta-catenin, phosphorylated forms of GSK-beta and Akt were down-regulated by the treatment of thio-Cl-IB-MECA (10 nM) in a time-dependent manner, providing one of plausible mechanistic evidence for the involvement of the Wnt signaling pathway in the HL-60 cell growth inhibitory effects by thio-Cl-IB-MECA. These results suggest that a novel A3AR agonist, thio-Cl-IB-MECA can down-regulate Wnt signaling, inhibit proliferation and induce apoptosis in HL-60 leukemia cells, and thus provide the possibility of this compound in the potential therapeutic value of the treatment of leukemia.