Stem Cells And Cancer In Hepatology PDF Download

This dissertation, "Identification and characterization of tumorigenic liver cancer stem/progenitor cells" by Kwai-yee, Stephanie, Ma, 馬桂宜, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Identification and Characterization of Tumorigenic Liver Cancer Stem/Progenitor Cells Submitted by Stephanie Kwai-Yee Ma For the degree of Doctor of Philosophy at The University of Hong Kong July 2007 Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide affecting one million individuals annually. Despite advances in the detection and treatment of the disease, mortality rate remains high because current therapies are limited by the emergence of chemotherapy-resistant cancer cells. Existing chemotherapies against HCC are usually developed against the bulk of the tumor mass, where although they are able to initially shrink the size of the tumor, they fail to eradicate the lesion in full, thus resulting in disease relapse. Recent research efforts in stem cell biology put forth the proposal of a hierarchical "stem cell model of carcinogenesis" which suggests that tumors are organized in a hierarchy of heterogeneous cell populations and that the capability to maintain tumor formation and growth specifically resides in a small population of cells called cancer stem cells (CSCs). The stem cell-like characteristics of these cells and their limited number within the tumor bulk are believed to account for their capability to escape therapies. In this study, we pioneered the identification of an exclusive population of CSCs from human HCC cell lines and xenograft tumors. CD133 expression in cultured cell lines was found to correlate with the ability of the cells to develop tumor in vivo. Functional studies on + - + sorted CD133 and CD133 cells found CD133 cells to be inherently more tumorigenic; showing a greater colony-forming efficiency, higher proliferative output and greater ability to form tumor in vivo. As few as 1000 CD133 cells were sufficient for consistent tumor development in SCID mice while at least 50x as many CD133 cells were necessary to generate a tumor in the same model. Moreover, these cells were found to be endowed with characteristics of stem cells including the preferential expression of "stemness" genes, the ability to self-renew and the ability to differentiate into angiomyogenic-like, non-hepatocyte- like lineages. Further, CD133 was found to be maintained in rare numbers in CD133 induced xenograft tumors and human HCC specimens. In addition, CD133 cells were found to be more resistant to anticancer drugs, doxorubicin and 5-fluorouracil; the molecular mechanism by which was mediated via the PI3K/Akt and Bcl-2 survival pathway. Treatment of CD133 cells with an inhibitor specific to AKT1 particularly reduced the expression of 473 136 survival proteins (P-Akt-Ser, P-Bad-Ser, Bcl-2) normally expressed endogenously. In addition, treatment of unsorted cells with both drugs in culture specifically enriched the CD133 subpopulation. Subsequent investigation by 2D-PAGE technique led to the elucidation of aldehyde dehydrogenase 1A1 (ALDH1A1) as an additional differentially expressed marker useful for HCC CSC identification. ALDH1A1 was exclusively expressed + + + in the CD133 subpopulation. More importantly, CD133 ALDH1A1 cells displayed significant preferential tumorigenic potential in vitro, when compared with their respective + - - - CD133 ALDH1A1 or CD133 ALDH1A1 counterparts. In summary, our findings provide a previously uncharacterized model of liver tumor biology in