Abstract 1011: Cues from the tissue microenvironment redirect cancer cell fate in vivo

Breast cancer is the second leading cause of cancer deaths in the United States. Striking parallels exist between cancer cells and stem cells, supporting the idea that tumors may arise from the malignant transformation of stem cells. Influencing signals from the tissue niche are known to affect stem cells. Therefore, it may be the case that the microenvironment is able to generate signals to redirect cancer cell fate. Here, we show that human cancer cells can be redirected from their tumorigenic phenotype towards a mammary epithelial cell fate via interaction with the regenerating mouse mammary gland in vivo. Human cancer cells (NTERA-2c1 (NT2) cells) were mixed with mouse mammary epithelial cells at ratios of 1:5 and 1:50, respectively, in phosphate-buffered saline. Ten microliters of the solution was injected into the cleared mammary fat pads of 3-week-old female athymic nude mice. Human cancer cells (1K and 10K) and mouse mammary epithelial cells (50K) were independently inoculated into epithelium-free fat pads as controls. Ten to twelve weeks later, mice were euthanized and their glands harvested for histological examination and immunostaining. Tissue fragments obtained from first generation glands were implanted into the cleared mammary fat pads of a new group of 3-week-old female athymic nude mice to yield second generation outgrowths. The transplantation of NT2 cells or chimeric gland fragments, and mouse mammary epithelial cells resulted in chimeric mammary outgrowths, whereas inoculation of NT2 cells alone lead to no growth. Human-specific CD133 was identified in approximately 20% of cells in the resulting second generation outgrowths. DNA isolated from the CD133 cell fraction contained the human male Y-specific chromosomal marker SRY suggesting that the human NT2 cells contributed to progeny in the secondary outgrowths. NT2 cells in the chimeric mammary glands also expressed human (h) keratin (K) 5, hK8, hK14, and the milk proteins halpha-lactalbumin and hlysozyme (during pregnancy) in both first and second generation chimeric mammary outgrowths. Approximately one in three cells in the chimeric gland was positive for hK5 and hK8, whereas hK14 was expressed in one in four cells. Cells staining for keratins were found to be unevenly distributed throughout the gland, however in subsequent generations human-specific keratin expression was detected in a more uniform pattern, supporting the idea that regions of the regenerating gland were biased toward either human or mouse cell repopulation. Overall, these data suggest that human cancer cells can be redirected towards a non-tumorigenic phenotype by signals produced by the regenerating mouse mammary gland. These results additionally provide evidence the developmental cues in the mouse mammary gland and those present during human breast development may be indistinguishable. Supported by the National Institutes of Health, National Cancer Institute Intramural Program. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1011.