Abstract LB-473: The HDAC inhibitor entinostat targets erbB2/erbB3 receptors via functional cooperation of miR-125a, miR-125b, and miR-205 in breast cancer cells

Abstract

Abstract Breast cancer is highly heterogeneous and has been classified into five distinct subtypes, among which erbB2-overexpressing (erbB2+) and basal breast cancers have the least favorable prognosis and express erbB receptors that are excellent targets for anti-cancer therapies. We previously reported that the class I HDAC inhibitor, entinostat (also known as MS-275, SNDX-275, Syndax Pharmaceuticals, Inc., Waltham, MA) selectively inhibited proliferation and induced apoptosis in erbB2+ breast cancer cells. Entinostat preferably targeted erbB2 and erbB3 receptors rather than the epidermal growth factor receptor (EGFR). Here, we study the molecular mechanism through which entinostat downregulates erbB2/erbB3 and promotes the breast cancer cells undergoing apoptosis. We showed that entinostat dramatically reduced the protein levels of erbB2/erbB3, whereas it had no significant effect on their mRNA expression in MDA-MB-453 and BT474 breast cancer cells. In addition, entinostat specifically decreased the endogenous, but not the exogenous erbB2/erbB3, suggesting that it did not promote erbB2/erbB3 protein degradation. Therefore, we hypothesizes that entinostat reduces erbB2/erbB3 receptors through transcription-independent mechanism; it may inhibit erbB2/erbB3 protein translation via induction of specific miRNA. Quantitative real-time (qRT) PCR revealed that entinostat significantly upregulated the expression of three erbB2/erbB3-targeting miRNAs, miR-125a, miR-125b, and miR-205 in erbB2+ breast cancer cells. Specific miRNA inhibitors were used to determine whether these miRNAs played a causal role in entinostat-induced downregulation of erbB2/erbB3 and apoptosis. While inhibition of any one of the three miRNAs failed to block entinostat action, simultaneous inhibition of any two of them significantly abrogated entinostat-induced erbB2/erbB3 reduction and apoptosis. Collectively, these data demonstrate that entinostat targets erbB2/erbB3 receptors via functional cooperation of miR-125a, miR-125b, and miR-205. Our findings suggest that miRNA-mediated epigenetic regulation may represent a novel strategy targeting erbB2/erbB3 to treat the aggressive erbB2+ breast cancer. The combinations of entinostat and erbB2-targeted therapy may be more efficacious for breast cancer patients whose tumors overexpress erbB2. This hypothesis will be directly tested by a recently initiated clinical study determining the activity of entinostat in combination with lapatinib in breast cancer patients that are erbB2+ and progressed on trastuzumab. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-473. doi:1538-7445.AM2012-LB-473