Deciphering biological characteristics of tumorigenic subpopulations in human colorectal cancer reveals cellular plasticity

Background: It is supposed that human colorectal cancer consists of a phenotypically distinct population of tumorigenic cancer cells known as cancer stem cells (CSCs) which play a pivotal role in cancer progression, maintenance, metastasis, and the relapse. The aim of this effort was to investigate and compare biological characterizations of CD133+ with CD133- cell subsets isolated from both primary and metastatic human colorectal tumors. Materials and Methods: Using our optimized protocols, unfixed colorectal tumors were enzymatically and mechanically dissociated into single cells followed by evaluation of postdigestion viability. The obtained single cell suspensions were then subjected to cell sorting using magnetic beads according to CD133 marker. The resultant CD133+ and CD133- cell subsets were cultured in specific cell culture medium followed by aldehyde dehydrogenases (ALDH) activity assessment and flow cytometric analyses. Results: The results demonstrate that CD133+ cells have smaller size and lower complexity of intracellular structure, sphere formation ability, and ALDH enzyme activity while CD133- cells isolated from primary colon cancer samples were not able to form a sphere and did not show ALDH enzyme activity. Intriguingly, CD133- cells isolated from metastatic colorectal cancer specimen were able to form a sphere and shown ALDH enzyme activity. The present study indicates that our results are in agreement with SC theory and possibility of the existence of cellular plasticity among cancer subpopulations should be portrayed. Conclusion: We also conclude that this cellular plasticity is greatly affected by tumor microenvironment cues and the role of CSCs niche in cancer therapeutic strategies should be precisely considered.