Abstract 4357: Tumor initiating cells promoting angiogenesis as a model of tumor re-growth following chemotherapy

Abstract

Abstract Tumor stem-like cells, also referred to as tumor initiating cells (TICs), are thought to display the only cells in the tumor with the proliferative capacity to seed tumor growth when transplanted into immune deficient mice, implying that they are critical in initiating and driving tumorigenesis. Previous studies linked TICs with angiogenesis, a process critical for tumor growth. We hypothesized that tumors enriched with TICs, in addition to their proliferative capacity, may be strong inducers of tumor angiogenesis in particular after chemotherapy. To study the pro-angiogenic capabilities of TICs, we isolated and characterized TIC populations from a series of human established cell lines; including U87 glioma, HT29 colon carcinoma, A549 non-small cell lung adenocarcinoma, MCF7 breast carcinoma, PANC1 pancreatic adenocarcinoma. We generated long-term cultures grown either as monolayers in serum-containing medium (‘TIC-low’) or as non-adherent tumor spheres in serum-free medium containing factors promoting stem cell growth (‘TIC-high’). Here we demonstrate that an increased expression of stem cell surface markers, a high activity of aldehyde dehydrogenase, a high expression of P21, a potent cyclin-dependent kinase inhibitor, and resistance to standard chemotherapy and radiotherapy were observed in TIC-high fractions of all cell lines in comparison to TIC-low fractions. TIC-high conditioned media of U87 and HT29 cells but not MCF7, A549, and PANC1, significantly induced endothelial cell migration, invasion, and aortic ring endothelial cell tube formation as opposed to TIC-low conditioned media. Matrigel plugs containing TIC-high conditioned media of U87 and HT29 were enriched with blood vessel capillaries and bone marrow derived proangiogenic cells (BMDCs) including hemangiocytes, and Gr-1+/CD11b+ myeloid derived suppressor cells, when compared to TIC-low conditioned media. No significant differences in BMDC colonization and endothelial cell number were observed in Matrigel plugs containing TIC-high conditioned media from MCF7, A549, and PANC1. Interestingly, the addition of an antiangiogenic drug to conditioned media of U87 and HT29 but not PANC1 inhibited angiogenesis using aortic ring assay. Results from experiments conducted on U87 and PANC1 tumor bearing mice to further investigate the angiogenesis properties of TICs following chemotherapy, will be presented in the meeting. Collectively, our results indicate that TICs of U87 and HT29 act as significant contributors to tumor angiogenesis and vasculogenesis by actively recruiting BMDCs and promoting endothelial cell function. Since TICs are resistant to chemotherapy they may contribute to tumor re-growth, at least in part, by inducing angiogenesis. These results indicate the necessity of new strategies for targeting TICs in combination with chemotherapy in order to improve clinical outcome. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4357. doi:10.1158/1538-7445.AM2011-4357