Abstract 1045: Activity of the LSD1 inhibitor HCI-2509 in ER-negative breast cancer cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Lysine-specific demethylase 1 (LSD1/AOF2/KDM1A) is a flavin-dependent histone demethylase that catalyzes the post-translational oxidative demethylation of mono- and di-methylated lysines on histones. Methylation of lysine residues on histones can signal transcriptional activation or repression depending on the specific residue involved. H3K4me2 is a transcription-activating chromatin mark at gene promoters and demethylation of this mark by LSD1 is thought to prevent expression of tumor suppressor genes important in human cancer. In contrast, methylation of H3K9 is a repressive mark and LSD1 activity has been shown to upregulate tumor promoting pathways. High LSD1 protein levels have been reported in tissue specimens from estrogen receptor (ER)-negative breast cancers and high expression of LSD1 in these tumors correlates with aggressive biology. Thus, LSD1 is emerging as an important target for the development of specific inhibitors as a new class of antitumor drugs. Only a few existing compounds, most of which are monoamine oxidase inhibitors, have been shown to act as inhibitors of LSD1. More potent and specific inhibitors of LSD1 lacking the monoamine oxidase activity are needed to advance LSD1 biology and test for potential efficacy in tumor models. We have previously reported using a structure-based drug discovery approach using solved 3-D crystal structures of LSD1 to computationally dock more than 10 million virtual compounds into the active site of the protein. From the docking experiments, we physically screened a selected group of compounds in an LSD1 biochemical assay. Initial hits from the screen were optimized utilizing a structure-based synthetic design strategy and a lead was identified as a potent inhibitor of LSD1 enzymatic activity, with an IC50 of 13 nM. To evaluate inhibitor specificity, our lead compounds were tested against 5 closely related flavin-dependent enzymes and showed minimal inhibition in these assays. Additionally, cell lines treated with our lead, HCI-2509, show increased levels of H3K4 methylation. To examine the cell-based activity of various cancer cell lines to our lead, a large panel of cancer cell lines was tested for sensitivity to HCI-2509 using a cell viability assay. Among the most sensitive cell lines are several derived from ER-negative breast cancers. We further demonstrated potent activity of HCI-2509 in cells taken directly from ER-negative breast cancer patients. Using gene expression analysis after treatment of highly sensitive and less sensitive breast cancer cell lines we have developed a gene expression signature associated with sensitivity to HCI-2509. Our efforts are now focused on examining HCI-2509 potential as novel therapeutic targeting LSD1 for treatment of ER-negative breast cancers using mouse models of breast cancer. 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 1045. doi:1538-7445.AM2012-1045