BACKGROUND: Nitric oxide-releasing nonsteroidal antiinflammatory drugs (NO-NSAIDs) are reported to be safer than NSAIDs because of their lower gastric toxicity. We compared the effect of a novel NO-releasing derivate, NCX 4040, with that of aspirin and its denitrated analog, NCX 4042, in in vitro and in vivo human colon cancer models and investigated the mechanisms of action underlying its antitumor activity. METHODS: In vitro cytotoxicity was evaluated on a panel of colon cancer lines (LoVo, LoVo Dx, WiDr and LRWZ) by sulforhodamine B assay. Cell cycle perturbations and apoptosis were evaluated by flow cytometry. Protein expression was detected by Western blot. In the in vivo experiments, tumor-bearing mice were treated with NCX 4040, five times a week, for six consecutive weeks. RESULTS: In the in vitro studies, aspirin and NCX 4042 did not induce an effect on any of the cell lines, whereas NCX 4040 produced a marked cytostatic dose-related effect, indicating a pivotal role of the -NO2 group. Furthermore, in LoVo and LRWZ cell lines, we observed caspase-9 and -3-mediated apoptosis, whereas no apoptotic effect was observed after drug exposure in WiDr or LoVo Dx cell lines. In in vivo studies, both NCX 4040 and its parental compound were administered per os. NCX 4040 induced a 40% reduction in tumor weight. Conversely, aspirin did not influence tumor growth at all. CONCLUSIONS: NCX 4040, but not its parental compound, aspirin, showed an in vitro and in vivo antiproliferative activity, indicating its potential usefulness to treat colon cancer.