Abstract 2579: Identifying pathways that regulate the turnover of gain-of-function p53 mutant proteins in ovarian cancer cells

Abstract

Abstract Ovarian cancer is the fifth leading cause for cancer-associated deaths among women in the US. High-grade serous ovarian carcinoma is the most common histological subtype and is characterized by frequent (>90%) mutations in the TP53 (p53) gene. Gain-of-function (GOF) p53 mutant proteins form highly stable aggregates that accumulate in ovarian cancer cells and have been shown to have oncogenic activity. Increasing evidence indicates the stabilization of GOF p53 mutants to be important for tumor progression and drug resistance. Therefore, selective degradation of the GOF p53 mutant proteins is a highly attractive therapeutic strategy to specifically target ovarian cancer cells. We identified that a small molecule named MCB-613, originally discovered as a stimulator of steroid receptor coactivator-3 (SRC-3), causes rapid degradation of the usually stable p53R175H conformational mutant aggregates leading to catastrophic cell death in human ovarian cancer cell lines. Our results indicate this effect is independent of SRC-3 mediated gene expression, but rather by post-translational modification of p53 mutant protein. Upon MCB-613 treatment, the p53R175H mutant is rapidly exported from the nucleus, ubiquitinated and degraded through a lysosomal pathway. Interestingly, in contrast to its effect on the p53R175H mutant, MCB-613 causes a slight stabilization of wild type (WT) p53 but had less of an effect on the turnover of other frequently observed p53 mutants (R248Q and R273H) in human ovarian cancer cell lines. MCB-613 also causes a rapid decrease in MDM2 protein but not mRNA. Further, the effect of MCB-613 on p53R175H is phenocopied by multiple deubiquitinase (DUB) inhibitors, confirming the role of ubiquitination in the selective turnover of p53R175H mutant aggregates. Taken together, these results show that different pathways regulate the turnover of WT p53 and the specific GOF p53 mutant proteins. We are currently investigating the precise mechanism by which MCB-613 and the different DUB inhibitors induce selective turnover of p53R175H mutant protein. We anticipate the proposed work to significantly advance our understanding of pathways important in ovarian cancer progression and pave way for the development of new targeted therapies for ovarian cancer patients with specific p53 mutations. This work is funded by NIH-CA-181808, NIH-HD-07857 and NIH-HD-076596. Citation Format: Achuth Padmanabhan, Nicholes Candelaria, Kwong-Kwok Wong, Bryan C. Nikolai, David Lonard, Bert W. O'Malley, JoAnne S. Richards. Identifying pathways that regulate the turnover of gain-of-function p53 mutant proteins in ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2579. doi:10.1158/1538-7445.AM2017-2579