Abstract LB-53: Prodigiosin rescues mutant p53 signaling and antitumor effects via p73 upregulation and disruption of mutant p53:p73 interaction.
Authors: Hong Bo , Van Den Heuvel Antonius , Kopelovich Levy , El-Deiry Wafik S. 
Published: August 2014

Rescue of mutant p53 function is an attractive strategy for cancer therapy development. Using high throughput drug screening, we identified prodigiosin, which can reactivate p53-dependent transcriptional activity in p53 mutant cancer cells. We find that prodigiosin has the therapeutic potential of p53 signaling restoration in a panel of cancer cells with p53 hotspot mutants. Our study has indicated that prodigiosin can up-regulate the expression of p73. However, the function of the increased p73 could be inhibited by interacting with the overexpressed mutant p53 in cancer cells. The immunoprecipitation assay indicates that prodigiosin treatment disrupts the interaction of mutant p53 and p73 in mutant p53-containing SW480 cells. Prodigiosin has been reported to be able to bind to mTOR and inhibit mTOR activity. In order to determine whether prodigiosin disrupts the interaction of mutant p53/p73 complex through mTOR inhibition, we treated SW480 cells with the mTOR inhibitor rapamycin to assess whether mTOR inhibition can disrupt the interaction. The results indicate that prodigiosin disrupts the physical interaction of mutant p53 and p73, but rapamycin does not disrupt this interaction. Western blot confirms that both prodigiosin and rapamycin inhibit the mTOR pathway as indicated by the decrease of phospho-mTOR, phospho-p70 S6 Kinase and phospho-4E-BP1 when SW480 cells are treated with either prodigiosin or rapamycin. The result suggests that prodigiosin disrupts the interaction of mutant p53/p73 complex independent of mTOR inhibition. Furthermore, we examine the role of mutant p53 in the mechanism of p53 restoration by prodigiosin. By the knock-down of mutant p53 by siRNA treatment, we find that prodigiosin-induced p53 activity is increased in mutant p53 knock-down SW480 cells and mutant p53 knock-down SW480 cells are more sensitive to prodigiosin-induced cell death. The result suggests that mutant p53 has the dominant-negative function. Our study implies that the only p73 up-regulation may not have a potent anti-tumor effect in p53 mutant cancers, as overexpressed mutant p53 would be expected to inhibit p73 function by protein-protein interaction. Our study indicates that prodigiosin not only up-regulates p73, but also prevents p73 from interacting with mutant p53. Therefore, the dual effects (up-regulation of p73 and disruption of the interaction between mutant p53 and p73) of prodigiosin make it a very promising candidate in anti-cancer drug development. This work was supported by the NCI Developmental Therapeutics Program through NCI Contract N01-CN-43302.

Citation Format: Bo Hong, Antonius Van Den Heuvel, Levy Kopelovich, Wafik S. El-Deiry. Prodigiosin rescues mutant p53 signaling and antitumor effects via p73 upregulation and disruption of mutant p53:p73 interaction. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-53. doi:10.1158/1538-7445.AM2013-LB-53