Abstract 2171: A new small molecule compound restoring p53 pathway induces cell death via active p73 and degradation of mutant p53 in colorectal cancer cells.
Authors: Zhang Shengliang , Zhou Lanlan , Hong Bo , Warfel Noel , Van den heuvel Antonius , Dicker David , Kopelovich Levy , El-Deiry Wafik 
Published: August 2014

Abstract
Tumor suppressor p53 is critical for protection against cancer. Over 50% of human cancers harbor mutant p53 which is hyper-stabilized and blocks p53 family member p73/p63 activity. Mutations not only abrogate the p53 tumor suppressor function, but also endow mutant p53 with gain-of-function (GOF) as pro-oncogene which contributes to tumor progression and chemotherapy resistance. Targeting mutant p53 to restore the p53 pathway is a promising strategy for cancer therapy. Small molecule restoring p53 pathway is mostly based on conformational change in mutant p53 or upregulation of wild-type p53. It is barely reported about small molecule compound with ability to both restore p53 pathway and deplete mutant p53 GOF. In this study, we describe a new small molecular compound, NCI-8 that specifically depletes mutant p53 protein and activates p73 to induce p53 responsive transcriptional activity and cell death in mutant p53 colorectal cancer cells. NCI-8 treatment increased p53 responsive bioluminescence and p53 target gene expression such as P21, Puma and DR5 specifically in mutant p53 colorectal cancer cells. Accompanied with p53 pathway restoration, NCI-8 down-regulated mutant p53 in cancer cells with no evident wild-type conformational change in mutant p53. NCI-8- mediated down-regulation of mutant p53 was rescued by MG132, a proteasome inhibitor and nutlin-3, an MDM2 inhibitor. NCI-8 induced ubiquitination of mutant p53. Taken together these results indicate that NCI-8 induces mutant p53 protein degradation via an MDM2-mediated ubiquitin-proteasome pathway. Further, we examined the role of p73 in NCI-8 action to p53 pathway restoration. NCI-8 enhanced p53-responsive bioluminescence with10-fold increase in cells overexpressing p73, but only 2-fold increase in p53-overexpressing cells. NCI-8- induced p53-responsive bioluminescence was significantly reduced by knock-down of p73, but not by knock-down of mutant p53. Knock-down of p73 significantly reduced NCI-8 induction of p53 target genes in mutant p53 cancer cells. These results indicate that p73 is required for NCI-8 to restore the p53 pathway in mutant p53-expressing cancer cells. Importantly, NCI-8 induced cell death in cancer cells, but not in normal cells. No genotoxicity of NCI-8 was detected in cancer and normal cells. Knock-down of p73 reduced cell apoptosis in mutant p53-expressing cancer cells treated with NCI-8, while, overexpression of p73 sensitized these cancer cells to NCI-8 induced cell death. Combination treatments demonstrate that NCI-8 synergizes with CPT11chemotherapy to induce cell death in mutant p53 colorectal cancer cells. These results suggest that p53 pathway restoration and cell death induced by NCI-8 occur via activation of p73 and depletion of mutant p53 GOF. NCI-8 is a promising lead compound specifically targeting mutant p53 for the development of new anti-cancer drugs.
Citation Format: Shengliang Zhang, Lanlan Zhou, Bo Hong, Noel Warfel, Antonius Van den heuvel, David Dicker, Levy Kopelovich, Wafik El-Deiry. A new small molecule compound restoring p53 pathway induces cell death via active p73 and degradation of mutant p53 in colorectal cancer cells. [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 2171. doi:10.1158/1538-7445.AM2013-2171