Targeting EZH2 in progesterone receptor-positive breast cancer

CENCIARINI, MAURO EZEQUIEL; AMASINO, MATÍAS; GIL DEZA, ERNESTO; IZZO, FRANCO; WU, YANMING; DE MARTINO, MARA; PROIETTI, CECILIA JAZMÍN; GERCOVICH, FELIPE GUSTAVO; CHERVO, MARÍA FLORENCIA; ARES, SANDRA; SCHILLACI, ROXANA; XU, KEXIN; ELIZALDE, PATRICIA VIRGINIA

São Paulo

Conferencia; Second AACR International Conference Translational Cancer Medicine Cancer Discoveries for Clinical Application; 2018

American Association for Cancer Research

On the basis of Estrogen Receptor (ER)presence, breast cancer (BC) patients are treated with selective ER modulators(SERMs), such as tamoxifen (TAM). However, approximately 40% of women receivingTAM experience tumor relapse. Even though Progesterone Receptor (PR)involvement in BC progression has been well acknowledged by us and others, themolecular mechanisms involved remain unclear. We have recently described thatthe synthetic progestin medroxiprogesterone acetate (MPA) induced therecruitment of PR and the epigenetic regulator Enhancer of Zeste Homolog 2(EZH2) to tumor suppressor GATA3 promoter. EZH2 catalyzes the trimethylation oflysine 27 of histone H3 (H3K27me3), an epigenetic mark associated withtranscriptional repression. This results in the down-regulation of tumorsuppressor GATA3 and the increase in cell proliferation and tumor growth. EZH2is often overexpressed in different types of cancers and associated with pooroverall survival. We therefore hypothesized that EZH2 could function as a mediatorof the pro-tumorigenic effects of progestins, targeting specific tumorsuppressors and differentiating genes to allow ER/PR-positive BC growth. Theobjective of this work was to study the role of EZH2 in progestin-induced BCgrowth. In vitro studies were carried out in the T47D human BC cell line and inprimary cultures of the MPA dependent C4HD murine breast tumor. Firstly, MPA(10 nM) induced EZH2 expression after 18 and 24 h of treatment, seen byincreased levels of both mRNA (qPCR, p<0.05) and protein (SDS-PAGE/WB).RU486, a PR antagonist, prevented these effects. Inoculation of a progesteronedepot in ovariectomized BALB/c mice for 7 days induced an increase in EZH2expression, in H3K27me3 global levels, and in the proliferation marker Ki67, andthe down-regulation of GATA3 in the mammary gland. In addition, we found thatEZH2 expression is higher in the progestin-induced C4HD murine breast tumorthan in the normal mammary gland. Interestingly, when EZH2 was knocked-down bya specific siRNA or when EZH2 activity was specifically inhibited by GSK126 (5uM), MPA-induced cell proliferation and GATA3 transcriptional repression in BCcells was prevented (p<0.001). These results confirm EZH2 requirement forprogestin-induced proliferative effects. In a pre-clinical study, BALB/c micecarrying syngeneic C4HD tumors were randomly separated in two groups, andtreated i.p. once daily for 14 days with vehicle (captisol 20%) or GSK126 (50mg/kg). Blockage of EZH2 activity diminished MPA-induced tumor growth (p<0.001).Lastly, EZH2 protein expression was analyzed by IHC in a cohort of 118 ER+/PR+BC patients treated only with tamoxifen. Patients with higher EZH2 expressionshowed to have lower DFS probability (p=0.0099). These results show a key roleof EZH2 in progestin-induced BC, possibly hijacking physiological mechanisms ofthe mammary gland, and point it out as a possible novel therapeutic target forTAM-resistant BC.