NO-aspirin (
NO-ASA), consisting of
aspirin and a
nitric oxide-releasing group, is safer than
aspirin and effective in
colon cancer prevention. Here, we examined the mechanism of action of
NO-ASA by focusing primarily on its effects on the cell cycle.
NO-ASA reduced the growth of several cell lines from colon, pancreas, skin, cervix and
breast cancer much more potently than
aspirin, with 24-h IC(50) values of 133-268 µM, while those of ASA were >1,000 µM.
NO-ASA elevated the intracellular levels of
reactive oxygen species, generating a state of oxidative stress. In all cell lines examined,
NO-ASA induced cell cycle arrest in the G(2)/M phase transition accompanied by altered expression of G(2)/M transition-related
proteins. In SW480
colon cancer cells
NO-ASA modulated
proteins controlling this transition. Thus, it markedly increased the levels of
cyclin B1, decreased the expression of
cyclin D1 and Cdc25C, and increased the Thr14/Tyr15-phosphorylation of Cdk1 while leaving unchanged its
protein levels. These changes, including the G2/M arrest, were prevented by pretreating the cells with the
anti-oxidant N-acetyl-
cysteine, indicating that redox signaling is likely responsible for the cell cycle changes, a conclusion consistent with the known redox regulation of these
proteins. Collectively, these results confirm the profound cytokinetic effect of
NO-ASA and provide strong evidence that it regulates cell cycle transitions through its ability to induce oxidative stress, which activates redox signaling in the target cell.