Abstract 1520: Down-regulation of c-MYC and hTERT gene expression in triple negative breast cancer

Breast cancer is the most common cancer affecting women, with about 1.4 million new cases diagnosed each year. Triple-negative breast cancer (TNBC) which is characterized by lack of expression of estrogen, progesterone and human epidermal growth factor receptors. Is the most aggressive group of tumors associated with a poor prognosis (15% of all mammary tumors). Previous studies have shown that specific G-rich genomic sequences in the promoters of multiple human genes can form G-quadruplex structures, resulting in decreased transcription and gene expression. These regions are generally found within gene promoters especially of oncogenes such as c-MYC, KRAS, VEGF, BCL2 or hTERT. Most of these genes are abnormally expressed in breast cancer. The c-MYC gene regulates a large array of genes essential for cell functions including proliferation, metabolism, differentiation, adhesion and apoptosis. We have recently shown that oligonucleotides encoding the G-quadruplex sequence of the c-MYC, VEGF or hTERT promoters down regulate expression of their respective genes and inhibit cell proliferation. We hypothesized that such oligonucleotides could be applied to breast cancer cell lines in order to inhibit cell proliferation and metastasis. In this study, we evaluated the effect of oligonucleotides targeted to c-MYC (Pu27 and Pu27 Palmi), KRAS (KRASq), VEGF (VEGFq), hTERT (Tert-FL) and BCL2 (BCL2q) in Breast cancer cell lines (MDA-MB-231, SKBR3, MCF7) and MCF10A (non-transformed mammary cells). The effect of each oligonucleotide on cell growth was evaluated using the MTT assay. Our results reveal that all oligos inhibit cell growth of MDA-MB-231. However, for SKBR3 and MCF7, only Tert-FL had growth inhibitory activity. The control cell line, MCF10A, did not respond suggesting that the oligonucleotides affect preferentially tumor cells. The effect of the oligonucleotides on gene expression (qRT-PCR) was performed on MDA-MB-231 exposed for 3 days. The analysis of gene expression shows the downregulation of c-MYC by Pu27 and hTERT by Tert-FL suggesting a direct effect on gene expression. In addition, Pu27 downregulated hTERT and VEGF which are both under c-MYC control. Since MDA-MB-231 is a TNBC cell line overexpressing c-MYC and is highly enriched in cancer stem cells, we evaluate the effect of Pu27 and Tert-FL on the tumorsphere formation. The results showed a very strong inhibition of tumorsphere formation in the cells treated with Pu27. Our findings suggest that oligonucleotides which target genes such as c-MYC, hTERT or KRAS very efficiently inhibit the growth of BC cell lines in particular MDA-MB-231 TN most likely by downregulating target gene expression. In addition, we demonstrate that downregulating c-MYC expression Pu27 dramatically reduces the cancer stem cell numbers. The use of G-quadruplex forming oligonucleotides targeted to c-MYC and /or hTERT may constitute a new therapeutic strategy especially for TNBC where targeted therapy is lacking. Citation Format: Elaine Stur, Shelia Thomas, Francine Rezzoug, Donald Miller. Down-regulation of c-MYC and hTERT gene expression in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1520. doi:10.1158/1538-7445.AM2017-1520