Nitric Oxide-Donating Aspirin Induces Apoptosis in Human Colon Cancer Cells through Induction of Oxidative Stress

Nitric oxide-donating aspirin (NO-ASA) is a promising chemoprevention agent against colon cancer and other cancers. It consists of traditional ASA to which a NO-releasing moiety is bound through a spacer. NO-ASA inhibits colon cancer cell growth several hundred times more potently than does ASA. In Min mice, NO-ASA inhibited intestinal carcinogenesis without affecting cell proliferation. Thus, we examined whether NO-ASA's most important cell kinetic effect is the induction of apoptosis. After confirming induction of apoptosis in Min mice, we studied the underlying mechanism in human colon adenocarcinoma cells. NO-ASA's spacer formed a conjugate with glutathione, depleting glutathione stores. This induced oxidative stress (increased intracellular levels of peroxides and$O_2^{. -}$) leads to apoptosis by activating the intrinsic apoptosis pathway. NO-ASA disrupted adherens junctions by inducing cleavage of$beta -and \gamma -catenin$, resulting in cell detachment. NO-ASA inhibited Wnt signaling by a dual mechanism: at low concentrations it blocked the formation of$\beta -catenin/Tcf$complexes (dominant mechanism), and at higher concentrations it also cleaved$\beta -catenin$. These findings provide a mechanism of action by a potent chemopreventive agent, underscore the significance of these pathways in regulating cell death in the context of cancer chemoprevention, and present a paradigm for developing agents with enhanced cancer cell growth inhibitory properties.