Synergistic apoptosis-inducing effect of aspirin and isosorbide mononitrate on human colon cancer cells

Aspirin and isosorbide mononitrate (ISMN) are two commonly used drugs, which are clinically applied for the treatment of inflammatory and cardiovascular diseases, respectively. Recently, aspirin has attracted interest due to its potential application for the treatment of cancer, particularly colon cancer. NO-aspirin, an aspirin derivative containing a covalently bound NO-donating moiety, has been proven to be an effective anti-tumor agent with apoptosis-inducing ability. In the present study, ISMN was used as an NO donor and its synergic effect with aspirin was assessed in human colon cancer cells. In vitro, an MTT assay demonstrated that ISMN had a synergistic effect on the growth inhibitory effects of aspirin on HCT116 and SW620 colon cancer cells, while the growth of EA.hy926 normal endothelial cells was unaffected. This synergistic anti-tumor effect was further validated in vivo using nude mouse HCT116 cell xenograft model. Observation of nuclear morphology, Annexin V-fluorescein isothiocyanate/propidium iodide double staining and a caspase-3 activity assay suggested that the combination of the two drugs induced apoptosis in HCT116 cells. Furthermore, the molecular mechanisms of the apoptotic effect of the drugs was assessed using an NO release assay, reverse transcription quantitative polymerase chain reaction analysis, western blot analysis and a luciferase reporter assay. It was certified that the increase in the amount of NO release, the decrease in the luciferase promoter activity and the expression of cyclin D1 and c-myc in HCT116 cells were affected by aspirin and ISMN in a synergistic manner. In conclusion, the present study was the first, to the best of our knowledge, to report on the synergistic apoptosis-inducing effects of aspirin and ISMN in human colon cancer cells, which were mediated via Wnt and NO signaling pathways. The results of the present study will facilitate the development of future therapeutic strategies.