In breast cancer, especially in the relatively early stage cases, there have been emerging reports that bone marrow (BM) micrometastasis is seen or cancer stem cells (CSC) metastasize into BM. They suggest that breast CSCs are related with BM adhesion and general dissemination.Purpose
We hypothesized that BM metastasis cells contain CSCs. To purify BM metastasis cells, we established the in vivo selection system by using immunodeficiency mice and analyzed the biological features of the selected cells in terms of the CSCs.Methods
GFP-expressing breast cancer cell line MDA-MB231 were orthotopically transplanted in RAG2 gamma C (KO) mice, and GFP-positive tumor cells from BM cells were purified. Tumorigenicity, cell growth and metastasis, specific features of CSCs, between parent cells and BM meta cells were compared in vitro and in vivo. Next, gene-expression profiles of the two types of cells were also compared to analyze the differences of phenotypes by cDNA microarray.Results and discussion
Tumorigenicity and tumor growth were convinced by orthotopical transplantation. BM meta was confirmed pathologically. Purified BM meta cells exhibited higher sphere formation ability and higher drug resistance in vitro. They showed higher serial transplantability, higher growth and metastasis abilities in vivo. From the result of gene-expression analyses, BM meta cells highly expressed Notch1, CD44 and CD49f. Besides that, BM cells growth was inhibited by Notch signaling inhibitor. Together, BM selects a cell population possessing characters of CSC, and control of BM meta may contribute to cancer cure and individualized therapy.