Abstract 2046: EZH2 inhibition targets a stem cell population in a canine urothelial carcinoma model

Recent studies have revealed that aberrant epigenetic events contribute to the development and maintenance of a malignant phenotype in urothelial carcinoma (UC) of the bladder, and many other tumor types. Thus, drugs capable of reversing epigenetic alterations have been brought to focus, and in the clinic epigenetic therapies demonstrate efficacy in the treatment of particular hematopoietic tumors. However, despite encouraging results from mouse xenograft studies, the clinical application of these agents to the treatment of solid tumors has been less successful. It is clear that new models are needed for the development of therapeutic strategies that target the solid tumor epigenome. Canine UC that develops commonly and spontaneously in dogs may provide a relevant model to directly inform new clinical protocols, to permit discovery and testing of clinical biomarkers, and, ultimately, to predict the response of human tumors in the clinic. Although human and canine UC share histopathologic characteristics, molecular features, and response to medical therapy, little is known about the canine UC epigenetic status. In human UC, EZH2 is overexpressed and, as a consequence of its enzymatic activity that involves the tri-methylation of histone H3 (H3K27me3), is responsible for silencing a large number of genes, including known tumor suppressors. We have determined that EZH2 is also overexpressed in canine UC. Therefore, we hypothesize that EZH2 provides a therapeutic target for UC. Pharmacological inhibition of EZH2 (DZNep) as well as targeted knockdown inhibits cell growth and induces apoptosis in canine UC cells in vitro in anchorage-dependent (2D) and anchorage-independent (3D) cultures. By conducting these experiments in parallel with human UC cell lines, we showed that sensitivity to inhibitor is comparable between human and canine UC cell lines. Upon DZNep treatment, EZH2 is reduced and its activity is inhibited, as evidenced by both decreased global H3K27me3 and upregulation of a set of genes that are commonly silenced by EZH2. In parallel, we showed that inhibition of EZH2 reduced the sphere forming capacity of canine UC cells, suggesting an inhibitory effect in the growth of the stem cell subpopulation. Taking into account that this population is responsible for dissemination, metastasis and emergence of drug resistance, these results support the idea that EZH2 targeting in UC could be a beneficial addition to the existing therapeutic modalities. According to our data, the molecular underpinnings of spontaneous UC are also shared between dogs and humans. Therefore canine UC provides a means to understand epigenetic dysregulation in the urothelium as well as to investigate its clinical targeting. This provides the opportunity to easily evaluate tumor response in vivo and obtain serial tissue samples during treatment. Thus canine studies can provide data that are not easily obtained in human trials and may inform clinical development. Citation Format: Parthena Foltopoulou, Monica Betancur-Boissel, Laurent Boissel, Manar A. AbdelMageed, Philip N. Tsichlis, Elizabeth A. McNiel. EZH2 inhibition targets a stem cell population in a canine urothelial carcinoma model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2046. doi:10.1158/1538-7445.AM2014-2046