Abstract 245: Phenotypically diverse cancer cell subpopulations in a luminal-like breast cancer xenograft model are associated with different signaling pathways.

Abstract High degree of intratumor cellular diversity represent a major challenge when attempting to cure cancer. The presence of tumor cell subpopulations with enhanced in vivo tumorigenic capacity (tumor initiating cells, TICs), and high resistance to conventional cancer therapy, compared with the “bulk” tumor cell populations, has for the last decade been the focus of many breast cancer research groups. The cellular heterogeneity of an orthotopic luminal-like breast cancer xenograft model was investigated using IHC, flow cytometry, whole genome expression profiling and mass spectrometry-based proteomics combined with in vivo tumorigenicity and targeted therapy assays. Epithelial cell adhesion molecule, EpCAM, highly specific for the human tumor epithelial cells, was used to separate human tumor cells from the mouse stromal compartment. Further flow analysis of the EpCAM positive tumor cell population revealed diverse expression of several cell surface markers, including CD24 and SSEA-4 (stage specific embryonic antigen 4). SSEA-4-/CD24-, SSEA-4+/CD24- and SSEA-4-/CD24+ populations were capable of initiating tumors in NOD SCID mice while SSEA-4+/CD24+ cells were non-tumorigenic. Tumors resulting from the SSEA-4+/CD24- subpopulation did not express CD24, while tumors arising from the SSEA-4-/CD24- and SSEA-4-/CD24+ populations, contained all four subpopulations. As measured by whole genome expression analysis and mass spectrometry-based proteomics, the molecular differences were most pronounced between tumorigenic subpopulations and the non-tumorigenic subpopulation. While the mRNA expression data revealed a high degree of similarity among the four subpopulations, the proteomics data suggested that several signaling pathways might have distinct and different activity across the populations. The effects of targeted therapy against ER and WNT signaling on heterogeneity and tumorigenicity have been evaluated by in vivo experiments. Citation Format: Nirma Skrbo, Kristin Andersen, Alexandr Kristian, Linn Antberg, Geir Olav Hjortland, Olav Egenbråten, Peter James, Gunhild Mari Mælandsmo, Therese Sørlie. Phenotypically diverse cancer cell subpopulations in a luminal-like breast cancer xenograft model are associated with different signaling pathways. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 245. doi:10.1158/1538-7445.AM2013-245