Abstract 2313: ER stress-mediated unfolded protein response inhibits angiogenesis and breast tumor growth

Abstract

Abstract Normal vasculature is quiescent in healthy adults with each endothelial cell dividing once every 10 years. But, angiogenesis is crucial for the growth and metastasis of breast cancer, and has been targeted for developing therapeutics. The current treatments are effective in only a small percentage of the total patient population. In addition, they are expensive, and accompanied by a host of side effects detrimental to patient's quality of life. Our laboratory has recently established that tunicamycin (an antibiotic and a glucosamine-containing pyrimidine nucleoside) interferes with the dynamic process of asparagine-linked protein glycosylation inhibiting angiogenesis in vitro and in vivo Matrigel™ implants. It causes cell cycle arrest in G1 and induces endoplasmic reticulum (ER) stress-mediated unfolded protein response (upr), and apoptosis by down regulated expression of Bcl-2 and cyclin D1, and upregulated expression of GRP-78/Bip and caspases3, 9 and 12. High expression of ATF6 and PERK in capillary endothelial cells indicates transcriptional and translational attenuation. Irreversibility of cellular proliferation by either IGF-1 or VEGF or inhibition of cell growth by clonogenic assay supports that tunicamycin can stand tumor microenvironment. There is down-regulation of phosphotyrosine kinase activity as well as the phosphoVEGFR1 and VEGFR2 levels. Most importantly, tunicamycin reduces the progression of a double negative (ER−/PR−/EGFR+) grade III breast adenocarcinoma and a triple negative (ER−/PR−/EGFR−) breast tumor xenograft in nude mice. Histopathology indicates reduced microvascular density and low tumor mitotic index along with reduced K-67 and VEGF expression. A significant reduction of N-glycan expression on the vessel wall correlates with the vessels size, and a high expression of GRP-78/Bip in CD144 positive vessels supports vessel death due to ER stress-mediated upr. WGA staining of tumor epithelia indicates loss of structural integrity with a high GRP-78/Bip expression, and has raised a question if induction of ER stress in tumor epithelia is an indirect effect of nutrient deprivation due to reduced blood flow in the absence of angiogenesis or does tunicamycin directly induce ER stress in the tumor cells. To test this hypothesis we have used a triple negative MDA-MB-231 human breast cancer cell line and cultured them with tunicamycin in a custom made media. Our results show that tunicamycin inhibits cell proliferation in a dose- and time-dependent manner as well as the colony formation. Expression of cyclin D1, wild type p53, phopspho p53(ser 392), Bcl-2 and caspase-3 supports cell cycle arrest followed by induction of apoptosis. High expression of GRP-78 and PERK/phosphoPERK concludes that tunicamycin can induce ER stress-mediated upr in MDA-MB-231 breast cancer cells. Supported in part by grants from Susan G. Komen for the Cure (BCTR06582) and NIH/NCRR/RCMI G12-RR03035 (KB) 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 2313. doi:1538-7445.AM2012-2313