The effect of B27 supplement on promoting in vitro propagation of Her2/neu-transformed mammary tumorspheres

Abstract

A variety of human solid tumors, including breast cancer, are considered to embrace a hierarchical organization in which only rare tumor-initiating cancer stem cells are truly responsible for tumor formation. Cultivation of tumorspheres in non-adherent conditions is widely employed for enriching these putative cancer stem cells in vitro. However, the absence of a defined culture medium has handicapped further characterization and isolation of this cell population. In this study, we used mouse mammary tumor virus MMTV-HER2/neu transgenic mice that mimic the HER2/Neu-positive subtype of human breast cancer as a model system, and cultured primary tumor cells and tumorspheres from these mice under non-adherent conditions. In addition to essential growth factors, we found that B27 supplement played an important role in promoting tumorsphere formation and maintaining cultures through passaging. A tumorsphere-formation assay and measurements of average tumorsphere size provided insight into the characteristics of the putative breast cancer stem cells. Tumorspheres were enriched for cancer stem cells through serial passaging, while sphere size was determined by the innate properties of cancer stem cells and independent of the culture condition. Our study identifies B27 as an essential component of culture medium necessary for sustained propagation and enrichment of breast cancer stem cells in vitro.