Abstract 2230: Luteolin selectively inhibits EZH2 and blocks H3K27 methylation in prostate cancer cells

Abstract

Abstract The histone methyltransferase enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of the polycomb repressive complex (PRC2) and is involved in chromatin remodeling and gene silencing through its methylation of histone H3 on lysine 27 (H3K27). Specifically, trimethylation of H3K27 is associated with gene silencing and plays critical role in cancer initiation and progression. Therefore, blocking EZH2 catalytic activity may present a valid preventive and/or therapeutic strategy for the treatment of cancers with EZH2 overexpression including prostate cancer. Our multistep approach of molecular modeling and direct binding has led to the identification of plant flavone luteolin (3’, 4’, 5, 7-tetrahydroxyflavone) as a specific inhibitor of EZH2 with preferential blocking of its catalytic site. Here we report luteolin, in micro molar range, inhibits EZH2 catalytic activity, demonstrates anti-proliferative and anti-invasive activities in functional cell based assays. Treatment of human prostate cancer DU145 and 22Rv1 cells, which possess high constitutive EZH2 expression, with 5-20 μM luteolin significantly inhibits EZH2 and SUZ12 protein expression in dose and time dependent manner, although luteolin treatment did not affect protein expression of EED and RbAp46/48 protein, other members of PRC2 complex. Treatment of both cell lines with luteolin also reduced H3K27me3 and H3K27me2 protein and its enzymatic activity in dose and time dependent manner without affecting total H3 protein. In addition, luteolin was also effective in suppressing in vitro methylation performed using recombinant PCR2 complex. These events led to increase in the expression of downstream tumor suppressor genes including E-cadherin, SLIT2 and TIMP3, respectively. Interestingly, treatment of cells with proteasome inhibitor, MG132 together with luteolin did not prevent EZH2 degradation indicating that proteasomal degradation might not contribute to EZH2 inhibition. Taken together, our study suggest that luteolin acts on the catalytic binding site of EZH2 to exhibit downregulation of histone H3 methylation and could be developed as a potential promising agent for the prevention and/or treatment of various human cancers including prostate cancer with EZH2 overexpression. Citation Format: Rajnee Kanwal, Xiaoping Yang, Eswar Shankar, Sanjay Gupta. Luteolin selectively inhibits EZH2 and blocks H3K27 methylation in prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2230. doi:10.1158/1538-7445.AM2017-2230