Nitric oxide-donating
aspirin (
NO-aspirin), representing a new concept in the development of more efficacious nonsteroidal anti-inflammatory drugs, consists of traditional
aspirin bearing -ONO(2), which releases NO. Conventional
aspirin prevents human
colon cancer, but its toxicity precludes its application as a chemopreventive agent.
NO-aspirin seems safer and in cultured
cancer cells it is >1000-fold more potent than
aspirin. To determine the mechanism by which
NO-aspirin inhibits cell growth, we studied its effect on
mitogen-activated protein kinase (MAPK) signaling in HT-29 human
colon cancer cells.
NO-aspirin stimulated the phosphorylation of
extracellular signal-regulated kinase 1/2 and Akt only marginally. The greatest increases in phosphorylation were seen in cJun NH(2)-terminal
kinase (JNK) and p38 MAP
kinases, which were observed as early as 5 min and after 1 h of treatment, averaged more than 10-fold over control. The activation of JNK and p38 was accompanied by large increases in the phosphorylation of the downstream
transcription factors cJun and
activating transcription factor 2 (ATF-2). We used specific MAPK inhibitors, small interfering (
siRNA) gene silencing methods, and dominant-negative cJun to determine the relevance of these phosphorylation events to the ability of
NO-aspirin to inhibit
colon cancer cell growth. Only the dual inhibitor of p38 and JNK and the use of combined
siRNA silencing of p38 and cJun abrogated the ability of
NO-aspirin to block cell growth. Our data indicate that
NO-aspirin is dependent on both the p38 and the JNK MAP
kinase pathways for its ability to inhibit the growth of
colon cancer cells.