Growth inhibition of human colon cancer cells by nitric oxide (NO)-donating aspirin is associated with cyclooxygenase-2 induction and beta-catenin/T-cell factor signaling, nuclear factor-kappaB, and NO synthase 2 inhibition: implications for chemoprevention.

Nitric oxide (NO)-releasing aspirin (ASA), consisting of a traditional ASA molecule to which a NO-donating moiety is covalently bound, is a promising colon cancer chemopreventive agent. NO-ASA inhibits colon cancer cell growth more potently than ASA by inhibiting cell proliferation and enhancing cell killing. We examined in cultured human colon cancer cells the effect of NO-ASA on the beta-catenin/T-cell factor signaling pathway, nuclear factor-kappaB, and NO synthase 2 and on cyclooxygenase (COX) expression, all presumed to participate in colon carcinogenesis. Besides inhibiting cell growth, NO-ASA inhibited the beta-catenin/T-cell factor signaling pathway (IC(50), 1.1 microM), nuclear factor-kappaB DNA binding (IC(50), 7.5 microM), and NO synthase 2 expression (IC(50), 2 microM). Interestingly, NO-ASA induced COX-2 expression, although it had no effect on COX-1. COX-2 induction was accompanied by increased prostaglandin E(2) production. These effects occurred at NO-ASA concentrations below or near its IC(50) for cell growth (IC(50), 2-50 microM). The metabolism of NO-ASA by these cells is characterized by a rapid deacetylation step and the formation of a conjugate with glutathione. NO-ASA had no effect on intracellular cyclic GMP concentrations. We propose a model incorporating the pleiotropic effects of NO-ASA on cell signaling and postulate that collectively these effects may contribute to its strong chemopreventive effect.