Compound C is a cell-permeable pyrazolopyrimidine derivative that is known as an inhibitor of AMP-activated protein kinase (AMPK). Previously, we reported that Compound C reduced the cell viability in human diploid fibroblasts and other platelet-deriv...
Compound C is a cell-permeable pyrazolopyrimidine derivative that is known as an inhibitor of AMP-activated protein kinase (AMPK). Previously, we reported that Compound C reduced the cell viability in human diploid fibroblasts and other platelet-derived growth factor (PDGF) receptor-expressing cells via its inhibitory effects on PDGF-induced signal transduction and cell proliferation in an AMPK-independent manner. We also observed that Compound C reduced the cell viability of Renca murine renal epithelial carcinoma cells, as judged by MTT assay. Therefore, the molecular mechanism of its anti-proliferative effect was investigated in Renca cells. Flow cytometric analysis revealed that Compound C arrested Renca cells in the G2/M phase of the cell cycle. Although Compound C pretreatment reduced serum-dependent phosphorylation of PDGF receptor and Akt, it increased ERK1/2 activation and reactive oxygen species (ROS) production at the early time points. Although pretreatment with N-acetyl cysteine (NAC), one of ROS scavengers, reduced Compound C-induced G2/M cell cycle arrest and recovered cell viability, its effects were very weak. There might be additional factors to explain the mechanism of Compound C-induced G2/M arrest. Although the levels of some cell cycle regulatory proteins, such as phosphorylated pRB, Cdks and cyclins, were not significantly altered by long-term treatment with Compound C, it increased the level of phospho-Tyr15-Cdc2 and decreased the level of phospho-Ser10-histone H3 at 16-24 h. Because activation of Cdc2 and subsequent phosphorylation of histone H3 are obligate steps for entry into mitosis, Compound C-induced increase in inhibitory tyrosine phosphorylation of Cdc2 and decrease in the level of P-Ser10-histone H3 might be responsible, at least in part, for G2/M cell cycle arrest. Compound C also reduced Renca cells adhesion and invasion/migration, as shown in the in vitro cell systems. The effect of Compound C on tumor growth in the syngeneic mouse model was also investigated. As expected, Compound C significantly inhibited the growth of Renca xenografts in the syngeneic Balb/c mice. Inhibition of tumor growth may be attributed mainly to reduced cell proliferation via G2/M cell cycle arrest and in part to decreased cell adhesion and migration/invasion in Compound C-treated mice. These findings suggest the potential use of Compound C against tumor development and progression.