Differential Senescent And Apoptotic Responses To Hdm2 Antagonism In P53 Wild-Type Human Solid Cancer Cells

The p53 protein is a primary regulator of the cellular response to DNA damage and is a critical tumor suppressor. Restoration of p53 function in soft tissue sarcomas and hepatocellular carcinomas in mice was reported to cause tumor regressions associated with cellular senescence. These findings led us to investigate the ability of HDM2 antagonism to induce cellular senescence as well as apoptosis in a broad panel of wild-type p53 cell lines derived from human solid tumors. Here we report that the small molecule HDM2 antagonist Nutlin-3a activates p53 and induces cellular senescence in 10 out of 12 human tumor cell lines tested. Only two of these tumor cell lines also demonstrated an apoptotic response to Nutlin-3a. The kinetics of senescence induction by Nutlin-3a was slower than that of the apoptotic response, suggesting that apoptosis may be the first-line response, while senescence may be triggered as a back-up program when the apoptotic response fails to execute. A distinct expression profile of p53 target genes associated with apoptosis, cell cycle and senescence was observed and corresponded with the distinct phenotypic responses in this panel of cell lines. Depletion of p53 protein expression using shRNA blocked cellular senescence induced by HDM2 antagonism demonstrating the critical role for p53 in this process. The pronounced effects of Nutlin-3a on senescence in multiple wild-type p53 tumor cell lines underscores the unique anti-tumor mechanisms of HDM2 antagonism. This approach may provide a novel therapeutic strategy for future cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3197.