Abstract 1935: Transformation of epithelial cells through recruitment leads to polyclonal intestinal cancers
Authors: Leystra Alyssa A. , Deming Dustin A. , Wisinger Amanda M. , Zahm Christopher D. , Sievers Chelsie K. , Matkowskyj Kristina A. , Albrecht Dawn M. , Newton Michael A. , Halberg Richard B. 
Published: May 2015

Abstract
Background: Intestinal tumors in mice and humans can originate from multiple progenitors. The consequent heterogeneity within these polyclonal tumors probably causes them to be more resistant to chemotherapy. Understanding how these tumors arise is therefore likely to provide insight into more effective prevention and treatment strategies. Polyclonal tumors could form as a result of cooperation between two or more independently initiated cells in close proximity, or else recruitment in which a single initiated cell facilitates the transformation of nearby cells. We tested these two potential mechanisms using murine models of human colorectal cancer that carry clinically relevant gene mutations.
Methods: We generated mosaic mice in which the status of Apc and Pik3ca varied from crypt to crypt in the distal small intestine and colon. Some cells lost one copy of Apc, expressed an activated form of Pik3ca, or both and consequently had a high tumorigenic potential, whereas others were wild type and had an extremely low tumorigenic potential. These mosaics allowed us to address fundamental questions regarding the formation of polyclonal tumors.
Results: The clonal structure of 50 tumors from 11 mice was determined. Cells with low tumorigenic potential were frequently transformed in combination with cells with high tumorigenic potential: 1 out of 8 tumors (13%) from mice expressing the activated form of Pik3ca were heterotypic, containing a mixture of cells with low and high tumorigenic potential; 9 out 14 tumors (64%) from mice that carried only an Apc mutation were heterotypic; and 12 out of 28 tumors (43%) from mice that carried both mutations were heterotypic. Tumor progression does not affect the structure. Many adenomas (9/20; 45%) and adenocarcinomas (13/30; 43%) were polyclonal. Immunohistochemistry was used to visualize the localization and expression level of β-catenin and pAKT to ascertain the impact of the cells with high tumorigenic potential upon those with low tumorigenic potential.
Conclusion: These data indicate that initiated cells recruit cells that would not otherwise form tumors, and that this structure forms and persists even in settings in which one progenitor would be expected to have a large growth advantage over another progenitor. Recruitment might be mediated by Wnt signalling.
Citation Format: Alyssa A. Leystra, Dustin A. Deming, Amanda M. Wisinger, Christopher D. Zahm, Chelsie K. Sievers, Kristina A. Matkowskyj, Dawn M. Albrecht, Michael A. Newton, Richard B. Halberg. Transformation of epithelial cells through recruitment leads to polyclonal intestinal cancers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1935. doi:10.1158/1538-7445.AM2014-1935