This is the first study to demonstrate a protective effect against CRC associated with the lowest dose of aspirin (75 mg per day) after only 5 years use in the general population. NSAID use prior to CRC diagnosis does not influence survival from the disease.

The aim of this study was to determine whether aspirin mediates an anti-tumor effect by modulation of NF-B signaling. PRINCIPAL FINDINGS Aspirin induces cell death by an active apoptotic processA dose-dependent reduction in cell viability was observed in SW480 colorectal cancer cells treated with aspirin in the dose range 0 -10 mM for 24 h or 0 -2 mM aspirin for 48 h. These doses are comparable to salicylate levels we measured in serum (0.05-1.13 mM) from human subjects given a short analgesic dose (600 mg qid) of aspirin. The reduction in cell viability was accompanied by an increase in cell death due to apoptosis, as determined by quantitation of cells showing phosphatidylserine externalization and cell morphology. Treatment in the presence of cycloheximide showed that aspirin-induced (10 mM) cell by death required de novo protein synthesis, confirming that death occurred through an active process, not passive necrosis. Aspirin induces apoptosis in association with degradation of IB␣ and nuclear translocation of NF-BNext, we examined the involvement of the NF-B signaling pathway in the apoptotic response of SW480 cells to aspirin. Experiments were performed in the absence of tumor necrosis factor (TNF) or other stimulating cytokines, as it is under these experimental conditions that aspirin induced apoptosis. We found that prolonged treatment with aspirin (0.5-2 mM for 48 h or 3-20 mM for 24 h) induced a dose-dependent reduction in cytoplasmic IB␣ levels that correlated with the reduction in the number of viable cells. Levels of control protein (Cu/ZnSOD) were unaffected by aspirin. Mutation of IB␣ at the critical S32/36 phosphorylation sites (IB S32/36 -tag) and preincubation of cells with the MG132 proteasome inhibitor blocked aspirin-induced reduction in IB␣ levels. These results indicate that aspirin mediates phosphorylation and subsequent proteosome-mediated degradation of IB␣ and suggest that this degradation is associated with aspirin-induced cell death.Electrophoretic mobility shift assays (EMSAs) revealed that aspirin-induced IB␣ degradation was accompanied by a dose-dependent specific increase in nuclear NF-B (p50/p65) DNA binding complexes (Fig. 1A, B). The findings from EMSAs were further corroborated by immunocytochemistry. Before aspirin treatment, p65 was localized mainly in the cytoplasm, but after 24 h treatment with 10 mM aspirin, there was extensive nuclear staining for the protein (Fig. 1D). These results establish that 24 h exposure to aspirin activates the NF-B pathway colorectal cancer cells. Aspirin-induced IB␣ degradation and NF-B nuclear translocation precede cell deathTo investigate the possibility that NF-B nuclear translocation was a consequence of cell death, we studied the kinetics of the aspirin effects on NF-B signaling and apoptosis. Aspirin (10 mM) treatment induced complete degradation of IB␣ after 2-5 h. Similarly, an increase in nuclear NF-B DNA binding was observed 2 h after treatment and persisted for Ͼ 16 h. In comparison, aspirin-induced apoptosis, determined by externa...