Abstract LB-014: Targeting p53 aggregation in ovarian cancer chemoresistant cells
Authors: Yang-Hartwich Yang , Cardenas Carlos , Pitruzzello Mary , Lima Eydis , Alvero Ayesha B. , Mor Gil 
Published: August 2015

Background: About half of patients diagnosed with ovarian cancer develop chemoresistance and succumb to the disease. The underlying mechanisms that lead to the development of chemoresistance are poorly understood. We previously demonstrated that p53 protein aggregation inhibited p53 pro-apoptotic activities consequently leading to platinum resistance in ovarian cancer cells with cancer stem cell properties. Since heat shock protein 90 (HSP90), a molecular chaperone, can sustain the accumulation of protein aggregates, the purpose of this study is to determine if HSP90 inhibitors can inhibit the accumulation of p53 aggregates, reactivate p53 pro-apoptotic function, and sensitize ovarian cancer stem cells (OCSCs) to carboplatin.

Method: Chemoresistant CD44+/MyD88+ OCSCs were treated with the HSP90 inhibitor, 17-AAG, carboplatin, or the combination of 17-AAG and carboplatin. Cell viability was monitored by IncuCyte ZOOM live-cell imaging system. Caspase activation was determined by Caspase-Glo assay. p53 aggregation was detected by non-denaturing gel and western blot. The interaction between p53 and HSP90 proteins was determined by co-immunoprecipitation (co-IP). Chromatin immunoprecipitation (CHIP) of p53 and RT-QPCR of p53 targets (PUMA, BAX, et al.) were performed to demonstrate p53 transcriptional activation.

Result: OCSCs were resistant to single treatment with Carboplatin. In line with results from our previous studies, carboplatin neither decreased cell viability nor induced caspase activation in these cells. Interestingly, carboplatin enhanced the levels of aggregated p53 and hence failed to upregulate the expression of p53-related pro-apoptotic genes. Co-IP results demonstrated that 17-AAG blocked the interaction between p53 and HSP90. More importantly, 17-AAG was able to sensitize OCSCs to carboplatin. The combination therapy effectively induced the transcriptional activity of p53, upregulated pro-apoptotic genes, and stimulated caspase activity and cell death in the carboplatin-resistant OCSCs.

Conclusion: The HSP90 inhibitor, 17-AAG can inhibit the formation of p53 aggregates by blocking the interaction between p53 and HSP90. By releasing p53 from the aggregates, 17-AAG reactivates the ability of p53 to bind to DNA and to upregulate the expression of target genes, which leads to the apoptosis of OCSCs. 17-AAG sensitizes chemoresistant OCSCs to carboplatin treatment. Using HSP90 inhibitors to target p53 aggregation and sensitize chemoresistant cells with protein aggregates may significantly improve the response of ovarian cancer to conventional chemotherapies.

Citation Format: Yang Yang-Hartwich, Carlos Cardenas, Mary Pitruzzello, Eydis Lima, Ayesha B. Alvero, Gil Mor. Targeting p53 aggregation in ovarian cancer chemoresistant cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-014. doi:10.1158/1538-7445.AM2015-LB-014