Abstract 327: Anti-tumor effect and destabilization of R175H-mutant p53 by CB002, a p53-pathway restoring small molecule that stimulates autophagy

Abstract

Abstract Tumor suppressor p53 is a master regulator of genotoxic and cellular stress signals, controlling cell fate by transcriptionally activating genes involved in DNA repair, cell cycle arrest, and apoptosis. p53 is mutated in over half of human cancers and this is associated with tumor development and chemotherapy resistance. TP53 gene mutations can result in the abolishment of p53 contact with DNA and disruption of p53 structural conformation. These mutations not only prevent p53 to exert its normal tumor suppressive functions but can result in gain-of-function activity, acquiring oncogenic characteristics. Therefore, altering the stability of mutant p53 protein is an attractive therapeutic strategy in cancer cells. We investigated small molecules that modulate mutant p53 stability and restore the p53-signaling pathway. We identified a small molecule, CB002, as a candidate for restoration of the p53 pathway in mutant p53-bearing cancer cells. Three colorectal cancer cell lines: SW480, DLD-1, HCT116-R175H and the RXF393 renal cancer cell line, were treated with different concentrations of CB002 at various time points. Cell lines exposed to CB002 showed an increase in apoptotic and cell death markers, such as NOXA/DR5 induction, cleaved caspases and PARP, as early as 16 hrs. CB002 decreased mutant p53 stability in structural conformation-mutant bearing cells (HCT116 R175H and RXF393). Our data suggests that CB002 stimulates an increase of p53 target genes and promotes expression of pro-apoptotic proteins. R175H p53 mutant protein expression was largely rescued by the co-treatment with MG132, a proteasomal inhibitor, implicating a role for the ubiquitin proteasome system. Furthermore, we observed significant autophagy induction upon CB002 treatment, as indicated by LC3 conversion and p62 levels. Autophagy inhibition decreased levels of cell death markers and increased the stability of the R175H-mutant p53, suggesting that autophagy might be required for CB002-induced cell death and mutant p53 turnover. Therefore, we hypothesize that CB002 is capable of degrading mutant p53 and restoring the p53 pathway through p53 family members in colorectal cancer cells. Currently we are investigating p53 degradation mechanism by CB002, the role of p53 family members in the restoration of the pathway and autophagy on mutant p53 stability. Hence, our results provide an insight on effective p53 pathway activation through the use of small molecules. Citation Format: Liz J. Hernandez Borrero, Shengliang Zhang, David Dicker, Wafik El-Deiry. Anti-tumor effect and destabilization of R175H-mutant p53 by CB002, a p53-pathway restoring small molecule that stimulates autophagy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 327.