Abstract 3838: Functional crosstalk between histone deacetylase 5 (HDAC5) and lysine-specific demethylase 1 (LSD1) as a novel therapeutic target in triple-negative breast cancer cells

Our previous work has shown that HDAC5 knockdown led to significant increase of H3K4me2 in the TNBC cell line, MDA-MB-231, suggesting a potential role of HDAC5 in regulating LSD1 activity in breast cancer. In this study, we demonstrated that HDAC5 physically interacts with LSD1 in MDA-MB-231 cells. Overexpression of HDAC5 increased LSD1 protein level through a reduction of LSD1 polyubiquitination. siRNA-mediated knockdown of HDAC5 mRNA, but not other class II HDACs or LSD1-containing complex members (HDAC1, HDAC2 and CoREST), significantly decreased LSD1 protein expression and half-life. HDAC5 overexpression reduced levels of H3K4me1/2, suggesting that HDAC5 acts as a positive regulator of LSD1-mediated H3K4 demethylation activity. Enhanced proliferation mediated by HDAC5 overexpression in MDA-MB-231 cells was diminished by LSD1-KD, suggesting a critical role of LSD1 in regulating oncogenic activity of HDAC5. We also observed that high-grade tumorigenic MCF10A-CA1a cells (triple negative) expressed higher levels of LSD1 and HDAC5 compared with parental counterpart MCF10A cells. By gain- and loss-of-function studies using this TNBC progression model, we observed that HDAC5 possesses a critical oncogenic function in driving TNBC development by blocking LSD1 protein degradation and re-shaping epigenetic landscape. Several HDAC inhibitors were tested for their ability to inhibit LSD1 and HDAC5 interaction. Treatment with sulforaphane, a natural HDAC inhibitor found in cruciferous vegetables, blocked the association of HDAC5 and LSD1 through down-regulation of HDAC5 mRNA and protein expression that led to LSD1 protein destabilization. Sulforaphane treatment also re-expressed a unique subset of tumor suppressor genes (RGS16, BIK, PCDH1, CDKN1a, ING1, etc), which are abnormally silenced in TNBC cells, but are expressed in other breast cancer subtypes and normal breast cells. Addition of a novel LSD1 inhibitor, HCI-2509, significantly promoted antineoplastic efficacy of sulforaphane in breast cancer cells, and TNBC cells were more susceptible than other subtypes to the combination therapy. In an in vivo study, while treatment with either sulforaphane or HCI-2509 alone each displayed significant anti-tumor effects against MDA-MB-231 xenografts, combined treatment with both compounds exhibited synergistic inhibitory effect on tumor growth in the MDA-MB-231 xenografts. Taken together, these results suggest that HDAC5 promotes LSD1 protein stabilization, leading to a dysregulated chromatin landscape which functions as an antibraking system in TNBC development. Crosstalk between LSD1 and HDAC5 may represent a novel and effective therapeutic target for this devastating disease. (Supported by DOD W81XWH-14-1-0237/W81XWH-14-1-0238, Breast Cancer Research Foundation, and UPCI Core Grant NIH P30CA047904) Citation Format: Chunyu Cao, Shauna Vasilatos, Steffi Oesterreich, Nancy E. Davidson, Yi Huang. Functional crosstalk between histone deacetylase 5 (HDAC5) and lysine-specific demethylase 1 (LSD1) as a novel therapeutic target in triple-negative breast cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3838. doi:10.1158/1538-7445.AM2015-3838