Therapeutic targeting of stem cells needs to be strategically developed to control tumor growth and prevent metastatic burden successfully. Breast cancer presents a unique clinical problem because of the variety of cellular subtypes present, including cancer stem cells (CSCs). The development of 3D stem-like properties of human breast tumor spheroids in stem cell factor conditioned media was investigated in orthotopic xenografts for enhanced tumorgenicity in the athymic nude rat model. MCF-7, ZR-75-1, and MDA-MB-231 breast cancer cell lines were cultured in serum-free, stem cell factor-supplemented medium under non-adherent conditions and passaged to generate 3rd generation spheroids. The spheroids were co-cultured with fetal lung fibroblast (FLF) cells before orthotopic heterotransplantation into the mammary fat pads of athymic nude rats. Excised xenografts were assessed histologically by H&E staining and immunohistochemistry for breast cancer marker (ERB1), proliferation marker (Ki67), mitotic marker (pHH3), hypoxia marker (HIF-2α), CSC markers (CD47, CD44, CD24, and CD133), and vascularization markers (CD31, CD34). Breast cancer cells cultured in stem cell factor supplemented medium generated 3D spheroids exhibited increased stem-like characteristics. The 3D stem-like spheroids co-cultured with FLF as supporting stroma reproducibly and efficiently established orthotopic breast cancer xenografts in the athymic nude rat.
Keywords: cancer stem cells; multicellular 3D spheroid culture; orthotopic tumor xenograft.