EZH2 has also been correlated with a shorter time to recurrence in muscle-invasive bladder cancer (MIBC). EZH2 is the catalytic subunit of the polycomb repressive complex 2 (PRC2) that exerts transcriptional repression via histone methylation (at H3K27). EZH2 inhibitors have been approved for the treatment of refractory follicular lymphoma. Piunti et al. examined the role of EZH2 in a mouse model of urothelial carcinoma (UC).
Piunti et al. generated a conditional mouse model in which EZH2 was specifically deleted in basal epithelial cells like urothelial cells in which UC likely originates. Knockdown mice exhibited a significant decrease in the number of high-stage tumors relative to controls. This was accompanied by a functional decrease in methylation of H3K27. Similarly, UC mice treated with an EZH2 inhibitor exhibited lower-grade tumors, increased luminal markers, and decreased expression of basal markers. In addition, bladder samples from these mice showed more immune cell infiltrates than untreated controls. Gene set enrichment analysis revealed that immunoregulatory genes were upregulated in UC mice treated with EZH2 inhibitors relative to controls, while cell cycle and DNA repair genes were downregulated. Analysis of transcriptomic data from The Cancer Genome Atlas (TCGA) revealed a similar inverse correlation between EZH2 levels and levels of immune regulation transcripts. To confirm this in vitro, Piunti et al. treated bladder cancer cell lines with an EZH2 inhibitor and detected increased levels of CXCL10 and TNF compared to untreated cells. Both immune-activating genes were found to be direct transcriptional targets of PRC2 (and, therefore, EZH2).
Major histocompatibility complex (MHC) genes are known to be targets of PRC2. The expression of MHC class II genes, which are associated with antigen-presenting cells (APCs), were significantly increased in mice treated with EZH2 inhibitor compared to controls, in addition to an increase in expression of Ciita, a master regulator of MHC class II genes. Upon treating four bladder cancer cell lines with an EZH2 inhibitor, researchers observed a significant increase in the expression of MHC class II genes and Ciita relative to untreated cells. To confirm these findings in vivo, Piunti et al. used a transgenic mouse model with ovalbumin antigen expression on urothelial cells. After induction of bladder cancer and treatment with an EZH2 inhibitor, bladder cells were isolated and co-cultured with T cells derived from mice with T-cell receptors (TCRs) against the ovalbumin antigen. Cells from mice treated with EZH2 exhibited significantly increased levels of IFN-𝝲 and IL-17 relative to cells from untreated controls. Tumor samples from treated mice showed higher levels of infiltrating immune cells relative to controls. To confirm the role of T-cells in mediating tumor suppression, bladder cancer was induced in immunocompromised mice that lack an adaptive immune system (Rag1-/-), followed by EZH inhibitor treatment. Treated mice exhibited a significant increase in high-stage tumors compared to controls, confirming that adaptive immunity is necessary for the anti-tumor activity of EZH2 inhibition.
The findings from this important study strongly support the role of EZH2 in immune suppression in bladder cancer specifically. Studies in human samples will provide additional validation of these associations. This is important as one of the limitations of the mouse model used in the study is its dependence on exposure to a carcinogen, which does not necessarily recapitulate human tumor initiation. EZH2 inhibition is a potential therapeutic strategy for increasing immune activation and enhancing response to immunotherapy. In line with this, a clinical trial was initiated to determine the efficacy of a combination of an EZH2 inhibitor and a PD1 inhibitor for treating advanced or metastatic bladder cancer.
Written by: Bishoy M. Faltas, MD, Director of Bladder Cancer Research, Englander Institute for Precision Medicine, Weill Cornell Medicine
- Piunti A, Meghani K, Yu Y, et al. Immune activation is essential for the antitumor activity of EZH2 inhibition in urothelial carcinoma. Sci Adv. 2022;8(40):eabo8043. doi:10.1126/sciadv.abo8043
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