Background and objective. Tumor heterogeneity is shown to be related to clinical outcome in cancer patients. The concept of a small subset of cancer stem cells being responsible for tumor relapse and metastasis comes out as a promising strategy for targeted cancer therapy. However, cancer stem cells are not easy to identify and isolate. The aim of this study was to determine the putative colon cancer stem cell subsets in human colon cancer cell lines HCT116 and HT29, which differ in their aggressiveness and differentiation capacity. Material and methods. Flow cytometry was used to asses HCT116 and HT29 cell lines for the expression of stemness-associated surface markers CD24, CD44, CD117, CD133, ESA, ABCB1. Both cell lines were treated with 5-fluoruracil and the phenotype of chemoresistant cells was investigated. Side population was visualized via Rhodamine 123 staining. Relative expression of ABCG2, c-Myc and Oct4 genes was quantified using qPCR analysis. Results and conclusions. It was shown that HCT116 and HT29 cell lines differ in their stemness-related properties. We imply that putative CSC subset for HCT116 cell line is CD44+/CD24-/CD133- (4,1% of all cells) and for HT29 cells – CD24+/CD44-/CD133- (4,9% of all cells).
Keywords: tumor heterogeneity, colon cancer, cancer stem cells, HCT116, HT29
The concept of tumor heterogeneity being related to the course of the disease and clinical outcome in cancer patients draws additional attention in the era of personalized medicine (1). Current cancer treatment strategies are based on the site of origin of the primary tumor. However, it was shown that tumors developed from distinct cell types differ in their prognosis and response to cytotoxic therapies (2). Diverse carcinogenic pathways orchestrating cancer development result in variations in tumor tissue architecture and genomic landscape (3). The recent spread of high-throughput analysis technologies allowed extensive investigation of genetic, molecular and functional diversity between and within tumors (4, 5).
Increasing evidence supports the idea of cancer stem cells (CSCs) being partly responsible for phenotypic and functional heterogeneity among cancer cells in tumors of same localization (6-11). CSCs are described as a small subset of highly tumorigenic cells, which are resistant to chemotherapy. Hence, ineffective elimination of CSCs during cancer treatment might account for treatment failure and tumor relapse (12). Therefore, CSCs attract significant attention as potential targets for new cancer treatment strategies. Various approaches are applied to identify and isolate CSCs, including separation by CSC-specific cell marker expression, detection of side population by dye exclusion, characterization by chemoresistane or tumorigenicity (13). However, there is no general protocol for successful isolation of putative CSC subset in solid tumors and the need for a more specific combinational approach remains.