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Title: Isolation and characterisation of putative colorectal cancer stem cells
Author: du Potet, Elodie
ISNI:       0000 0004 2693 862X
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2010
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The isolation and characterisation of cancer stem cells (CSCs) remain a major challenge. The ‘traditional’ (or ‘stochastic’) model of cancer suggests that cancer cells progress through clonal evolution and therefore, all cancer cells must be destroyed. The alternative model, the ‘hierarchical’ (or CSC) model proposes that a subpopulation of cancer cells, referred to as CSCs, initiates and sustains the continuous expansion of cancer growth. Studies have shown that CSCs are similar to normal stem cells as they are able to self-renew and to differentiate into a non-CSC progeny. However, their proliferation pathways are deregulated, they can form metastasis, trigger recurrences after chemotherapy and are tumourigenic. In the CSC model, the CSCs essentially need to be targeted and eradicated. Although it is recognised that CSCs do exist, there is still a large gap in defining their molecular and functional characteristics. In this study, we have explored different approaches to isolate colorectal CSCs. In the first approach, CSCs were isolated using a putative CSC marker, CD133. Cancer cell suspensions were obtained from patient tumour specimens. Several conditions were used to isolate CD133+ cells by immunoaffinity. Technical difficulties were encountered throughout the procedure that prevented the isolation of CSCs using the CD133 antibody. In the second approach, we determined whether CSCs could be isolated using chemotherapeutic drugs since it has been shown that CSCs are resistant to such treatments. Cancer cells resistant to a short-term exposure with the chemotherapy drug oxaliplatin were isolated from two colorectal cancer cell lines. Data from in vivo tumourigenicity, expression of putative CSC markers and quiescence indicated that the intrinsically resistant cells did not exhibit CSC properties when compared with the untreated population. In the third approach, CSCs were isolated based on the aldehyde dehydrogenase 1 (ALDH1) activity. A high ALDH1 activity has been shown to be a marker of stem cells/CSCs. Immunohistochemistry revealed that ALDH1hi cells expressed more putative CSC markers CD44, CD166, ABCG2 and Lgr-5 than ALDH1lo cells. However, both populations were similarly clonogenic in vitro, they were equally invasive, as resistant to chemotherapeutic regimens and their cell cycle status was similar. In conclusion, the approaches taken to isolate CSCs from cancer tissue samples or cell lines generated limited success. The data suggest that more refined techniques are required to isolate CSCs. On the other hand, they highlight the techniques that should be avoided in future studies. The results also question several concepts of the CSC theory, such as the intrinsic resistance of CSCs, and therefore emphasize on the need of gathering more evidence to validate the CSC model.
Supervisor: Levicar, Natasa Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral