Abstract B19: Genome-wide integrated epigenomics identifies FZD-X as novel modulator for platinum sensitivity in high-grade serous ovarian cancer
Authors: Tomar Tushar , Alkema Nicolette G. , Meersma Gert Jan , Meyer Tim De , Criekinge Wim van , Klip Harry G. , Zee Ate GJ van der , Jong Steven de , Wisman G. Bea A. 
Published: May 2016

The major hindrance for successful treatment of advanced stage ovarian cancer patients stems from platinum-based chemotherapy resistance. In cancer, the epigenetic alterations like DNA methylation, play a crucial role in regulation of genes related to response towards chemotherapies. Identifying these epigenetically regulated key genes, which modulate platinum response, may improve patient selection, response to therapy, and find novel targeted strategies to overcome platinum resistance. Here we applied integrated epigenomics approach to identify novel genes associated with high grade serous ovarian cancer platinum response.

We performed next generation sequencing on methylation-enriched genomic DNA of ovarian cancer patient material from responders (≥18 months progression free survival, n=8) and non-responders (≤6 months progression free survival, n=10) to platinum chemoresponse. Expression data of same patients was also integrated to identify differentially methylated and expressed genes. These genes were validated further on external patients cohort using bisulfite-pyrosequencing and other publically available datasets. Furthermore, candidate genes were functionally tested on ovarian cancer cell lines panel using several in vitro assays.

Based on integrated epigenomics analysis, we identified Frizzled receptor (FzdX) as an epigenetically regulated gene, significantly unmethylated (p&lt;0.0005) and highly expressed (p&lt;0.003) in non-responder group of ovarian cancer patients. Further, FzdX was successfully validated by bisulfite-pyrosequencing on independent external patient cohort (responder: n=21 and non-responder: n=31). Concordant hypermethylation and corresponding gene silencing of FzdX was observed in a large panel of ovarian cancer cell lines (n=11). Additionally, demethylating agents caused reduction in methylation and high expression of FzdX in ovarian cancer cell lines, confirming FzdX as an epigenetically regulated gene. Targeted genetic inhibition of FzdX using siRNAs in ovarian cancer cell lines caused significant sensitization towards cisplatin treatment in short and long-term survival assays. FzdX silencing made ovarian cancer cells more apoptosis prone as showed by apoptotic acridine orange staining and high expression of cleaved PARP and caspase 3. Furthermore, siRNAs mediated silencing of FzdX in ovarian cancer cell lines led to reduction in their migratory and invasion potential as compared to control counter parts in various functional assays.

Conclusively, our integrative epigenomics analysis revealed FzdX as novel epigenetic modulator for platinum-sensitivity in ovarian cancer patients, which might be exploited for predictive and therapeutic approaches.

This study has been granted by the Dutch Cancer Society, KWF (RUG 2010-4833).

Citation Format: Tushar Tomar, Nicolette G. Alkema, Gert Jan Meersma, Tim De Meyer, Wim van Criekinge, Harry G. Klip, Ate GJ van der Zee, Steven de Jong, G. Bea A. Wisman. Genome-wide integrated epigenomics identifies FZD-X as novel modulator for platinum sensitivity in high-grade serous ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Sep 24-27, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2016;76(2 Suppl):Abstract nr B19.