Abstract P1-06-06: Mammary stem cell modulation of wildtype and Trp53 null stem cells by CAPE (caffeic acid phenethyl ester), a potential therapeutic agent

CAPE is the major active component of propolis, a widely available, non-toxic, honeybee natural product with anti-inflammatory, antioxidant, and antitumor properties. We have previously shown that CAPE inhibits growth of breast cancer cells and the tumorigenic potential of breast cancer stem cells. We have identified inhibition of histone deacetylase (HDAC) as one mechanism of action, which suggests that it mediates its effects through epigenetic modifications. We postulated that CAPE may be useful in chemoprevention for women at high risk for triple-negative breast cancers since the cell-of-origin hypothesis states that these cancers likely arise from transformation of mammary stem or progenitor cells, whose self-renewal is maintained via epigenetic states. We tested the effect of CAPE on wildtype (WT) and Trp53 null mammary stem cell (MaSC) self-renewal from BALB/c mice cultured as mammospheres (MMS). Primary mammary epithelial cells were cultured as MMS for 7 days, dissociated into single cells, re-cultured in the presence of CAPE for 7 days and passaged in secondary and tertiary passages without CAPE. MMS frequency and differentiation potential was analyzed using immunofluorescence detection of luminal marker, cytokeratin 18, basal marker, cytokeratin 14, and progesterone receptor (PR). Chromatin states were identified using ATAC-seq and open chromatin areas unique to CAPE treated murine MMS were used for pathway analysis performed by Ingenuity Pathway Analysis, Gene Set Enrichment Analysis and confirmed by Integrative Genome Viewer. CAPE treatment resulted in a dose dependent decrease in both WT and p53 null mammosphere forming efficiency that persisted in secondary and tertiary passages, suggesting reduced self-renewal. CAPE treatment also shifted differentiation from predominantly basal K14 to luminal K18-positive in both WT and p53 null MMS and increased PR expression in WT MMS. ATAC-seq of CAPE treated WT MMS showed significant pathway enrichment for p53 signaling, SOX2 signaling, and enrichment of open chromatin for several genes including the SMARCA4 gene, which regulates transcription of genes involved in stem cell renewal. ATAC-seq of CAPE treated Trp53 null MMS showed that genes defining early and late response to estrogen were particularly important. Significant canonical pathways included Aryl hydrocarbon receptor signaling, whose upregulation results in inhibition of self renewal and has been targeted as a potential drug target for estrogen receptor negative breast cancer. The integrin signaling pathway was also highly enriched. These data suggest that CAPE both inhibits MaSC self-renewal and shifts the lineage commitment to a luminal, ER + lineage. ATAC-seq demonstrated genomic effects that are important in differentiation, SC renewal and adhesion. These data suggest that CAPE may have an effect on lineage commitment in support of our chemoprevention strategy to reduce triple-negative breast cancer. Citation Format: Omene C, Patel M, Kannan K, Heguy A, Barcellos-Hoff MH. Mammary stem cell modulation of wildtype and Trp53 null stem cells by CAPE (caffeic acid phenethyl ester), a potential therapeutic agent. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-06-06.