Advances in Liver Cancer Stem Cell Isolation and their Characterization

Over the last decade research on cancer stem cells (CSC) significantly contributed to a better understanding of tumor biology. Given their similarity to normal stem cells, i.e. self-renewal and pluripotency the need arises to develop robust protocols for the isolation and characterization of CSCs. As with other malignancies, hepatic tumors are composed of a heterogeneous population of cells including liver cancer stem cells (LCSC). Yet, a precise understanding of why stem cells become cancerous is still lacking. There is unmet need to develop robust protocols for the successful isolation of LCSCs from human tissue resection material as to assist in the development of molecular targeted therapies. Here we review the research progress made in the isolation and characterization of LCSCs by considering a wide range of cell surface markers and sorting methods, as applied to side populations, microsphere cultures and the gradient centrifugation method. We emphasize the different fluorescence activated cell sorting methods and the possibility to enrich LCSCs by immunomagnetic beads. We review the specificity of functional assays by considering ABCG transporter and ALDH1 enzyme activities and evaluate the in vivo tumorigenicity of LCSCs in highly sensitive bioassays. Finally, we evaluate different LCSC markers in association with viral and non-viral liver disease and explore the potential of novel drug delivery systems targeting CD133, EpCAM, CD13 and CD90 for the development of molecular targeted therapies. Graphical Abstract.