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MINI 21 - Novel Targets (ID 133)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
MINI21.07 - Oncogenic EZH2 Is an Actionable Target in Patients with Adenocarcinoma of the Lung (LUAD) (ID 3169)
16:45 - 18:15 | Author(s): E. Riquelme
The methyltransferase enhancer of zeste homolog 2 (EZH2) belongs to the polycomb repressive 2 complex (PRC2). EZH2 is upregulated in several malignancies including prostate, breast and lung cancer. The EZH2 protein forms one of the critical protein complexes of PRC2 by partnering with EED (embryonic ectoderm development) protein. This EED/EZH2 complex has been shown to interact with histone deacytelase (HDAC). This interaction is highly specific and HDAC does not interact with any other PRC2 protein complexes. In the present study, we investigated the link between EZH2 and HDAC in lung cancer cell lines and in human tumor tissue microarrays (TMAs). We also further investigated EZH2 as a marker for response to HDAC inhibitors.
We analyzed EZH2 and HDAC1 mRNA expression in two lung adenocarcinoma datasets (MDACC n=152, and TCGA n=308), and correlated the gene expression with tumors’ clinico-pathological characteristics and patients’ outcome. To study the association of EZH2 and HDAC1 expression with response to the HDAC1 inhibitor suberanilohydroxamic acid (SAHA), we examined mRNA and protein expression by RT-PCR and Western blot, respectively, in twelve lung adenocarcinoma (LUAD) cell lines at baseline and after overexpression or knock-down of EZH2 or HDAC1 gene expression using siRNA. Response to (SAHA) in cell lines was measured by MTT assay and correlated with protein and mRNA expression levels of EZH2 and HDAC1.
Direct and positive correlation was found between EZH2 and HDAC1 expression NSCLC cell lines (P <0.0001). This correlation was confirmed in NSCLC specimens from MDACC (Spearman’s correlation r=0.416; p < 0.0001) and TCGA datasets (r=0.221; p <0.0001).Patients with high EZH2 and high HDAC1 expression in stage I NSCLC specimens of MDACC and TCGA datasets had lowest survival compared to the patients who had either or both low expressions. Overall survival in the univariate analysis (MDACC dataset; Hazard Ratio (HR)=2.97; p=0.031 and TCGA dataset; HR=2.6 and p=0.041) and multivariate analysis (MDACC; HR=2.92 and p=0.034 and TCGA; HR=3.17 p=0.016). When EZH2 expression was knock down, there was a significant reduction in HDAC1 expression; conversely, when HDAC1 was knocked down EZH2 expression was also decreased. These concordant change in expression was seen both at the protein and mRNA level. Importantly, while all 8 cell lines with high EZH2 protein expression responded to SAHA treatment with average inhibition rate reaching 73.1%, three out of four cell lines with low EZH2 expression had a significantly lower response rate to SAHA inhibition with average inhibition rate 43.2% (P<0.0001). Additionally, altering the expression of EZH2 concordantly altered the sensitivity to SAHA i. e. forced increased expression of EZH2 increased the response to SAHA and vice versa.
Our data suggest that EZH2 and HDAC expression are correlated in LUAD cell lines in human tissue microarrays and overexpression of both is a negative prognostic indicator. Additionally we show that increased EZH2 expression predicts for response to HDAC inhibitors and thus could serve as a biomarker for selecting LUAD patients with HDAC inhibitors.
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