Anchorage-Independent Cell Growth Assay for Cancer Stem Cells: Tumorigenic Assay in Vitro

Anchorage-independent growth is a characteristic feature of transformed cells, which means the cells have the ability to grow independently of a solid surface. This potential of the cell growth in vitro is generally referred to the tumorigenicity as a property of cancer cells. The soft agar colony formation assay is a well-established method to evaluate this capability in vitro and is considered as one of the most stringent tests to distinguish cells transformed into malignant cells from normal cells. This evaluation of phenotype is assumed to be advantageous to that in vivo because in vitro assays should be easier and economical without sacrificing animals. Furthermore, sometimes malignant cells are not tumorigenic due to the difference of species between the cells and the host as in the cases of human cancer cells transplanted in mice due to the host defense by the immunological system. In the current chapter, we will assess the soft agar colony formation assay using CSC models derived from miPSCs. Since CSCs are distinguished from the ordinary cancer cells, in vitro growth independent of a solid surface could be an effective way to evaluate different therapeutic agents targeting CSC in the future.