IDENTIFICATION AND CHARACTERIZATION OF SIRT1 AS A NOVEL TARGET OF NSAIDS CHEMOPREVENTION

Several epidemiological, clinical and experimental studies proposed non-steroidal antiinflammatory drugs (NSAIDs) as promising chemopreventive agents for many types of cancer. However, their use in chronic treatment is hampered by gastrointestinal, renal and cardiovascular side effects mainly due to the inhibition of cyclooxygenase (COX) isoenzymes. The development of NSAIDs as chemopreventive agents is prevented by the limited knowledge of the mechanism underlying the anti-cancer properties of these drugs. Inhibition of COX has been proposed as the mechanism underlying their anti-neoplastic activity; however, several lines of evidence challenged this simple view, among them the antitumor activity of non-COX inhibitory metabolites, enantiomers and derivatives are perhaps the most convincing. The aim of the present project was to investigate a novel direct target of NSAIDs, which may provide a biochemical explanation of the multiplicity of the COX-independent effects. For that reason, molecular biology, cellular and in vivo tools, including innovative in vivo imaging and classical biochemical assays were applied. Here we identify, for the first time sirtuin 1 (SIRT1) as a direct target of NSAIDs, showing that inhibition of this histone deacetylase may be responsible of their COX-independent antineoplastic activity. In particular, we demonstrated that many NSAIDs through SIRT1 inhibition: increased acetylation and activation of tumour suppressor p53 and increase the expression of antiproliferative gene p21 through SIRT1 inhibition. We showed that the mechanism occurs selectively in tumour tissue in cells, animal models and also in clinical setting. Activation of the p53 signaling produces an anti-proliferative effect, which prevents the early transformation steps of the mammary gland in an animal model of early breast cancer transformation. Increased local proliferation is not the only hallmark of cancer modulated by NSAIDs, interestingly our results indicate that the local immunosuppression promoted in the mammary gland by the exposure to a genotoxic agent can be efficiently counteracted by NSAIDs. In conclusion, this thesis presents the discovery and characterization of the new target SIRT1 as effector of NSAIDs mediated chemopreventive activity. Our data disjoin the NSAIDs COXdependent anti-inflammatory activity from the SIRT1-dependent anti-tumor activity, therefore suggesting a novel strategy to design molecules displaying anti-neoplastic chemoprevetinve activity without the COX-dependent side effects.