UVM Theses and Dissertations
Format:
Print
Author:
Held, Matthew A.
Dept./Program:
Cell and Molecular Biology Program
Year:
2009
Degree:
Ph. D.
Abstract:
Malignant melanoma is the most lethal fonn of skin cancer and is increasing in incidence faster than any other form of cancer, especially in young adults. Melanoma is a heterogeneous and chemoresistant neoplasia for which there are no effective treatments once advanced stages are reached. It has been suggested that heterogeneous tumors may harbor small fractions of cancer cells that are capable of propagation and reforming cell heterogeneity. These characteristics are also coincidentally similar to those exhibited by tissue stem cells. As such, this has lead to the reemergence of an idea that suggests that tumors may derive from aberrant stem cells, and is known as the Cancer Stem Cell hypothesis. These "Cancer Stem Cells" (CSCs) are proposed to be resistant to chemotherapy and responsible for cancer relapse. Therefore, the eradication of recurrent cancers may rely on novel therapeutic targeting of CSCs.
The vast majority of literature supporting the CSC hypothesis has shown that only exceedingly rare numbers of stem cell marker-positive cancer cells are capable of fonning tumors in immunodeficient mice. In contrast, recent work has demonstrated that nearly a third of unsorted, human melanoma cells can form tumors when individually inoculated into a mouse strain with increased immunodeficiency, suggesting that human cancer stem cells may not be as rare as previously thought and that tumorigenic frequency is modeldependant. However, identification of a purified, uniformly tumorigenic subset of cancer cells has not been achieved to date. Furthermore, characterization oftumorigenic cells capable of forming tumors from single cell injections has not been performed.
The research presented in this dissertation documents reproducible tumor formation in immunodeficient mice following injection of single, purified melaInoma cells derived from three novel, conditional mouse models of melanoma. It was discovered that tumor formation occurred following every injection of individual CD34p75⁻ melanoma cells, with intermediate rates using CD34⁻p75⁻cells, and rarely with CD34⁻p75⁺ cells. The findings confirm that cells capable of propagating tumors (melanoma propagating cells/MPCs) are more common than previously thought and that multiple tumorigenic subsets may exist within a single tumor. Strikingly, single CD34⁺p75⁻MPCs underwent self-renewal after tumor formation in mice or multiple passages in culture, demonstrating that re-establishment of tumor heterogeneity is not a characteristic of all cell subsets capable of forming tumors --a trait previously thought to be concurrent with tumorigenicity, i.e. CSCs.
Purified MPCs were also found to be more resistant to high doses of chemotherapeutic agents than cells incapable of tumor formation. Finally, it was demonstrated that the expression profiles ofMPC subsets are distinct and contain upregulated messages of known importance for human melanocytic stem cell function as well as melanoma development and progression. Based on this original research, it is anticipated that these results will be profoundly influential and propel the cancer biology field forward in designing novel therapies that eradicate human chemoresistant, melanoma propagating cells in order to halt disease progression and prolong patient survival.
The vast majority of literature supporting the CSC hypothesis has shown that only exceedingly rare numbers of stem cell marker-positive cancer cells are capable of fonning tumors in immunodeficient mice. In contrast, recent work has demonstrated that nearly a third of unsorted, human melanoma cells can form tumors when individually inoculated into a mouse strain with increased immunodeficiency, suggesting that human cancer stem cells may not be as rare as previously thought and that tumorigenic frequency is modeldependant. However, identification of a purified, uniformly tumorigenic subset of cancer cells has not been achieved to date. Furthermore, characterization oftumorigenic cells capable of forming tumors from single cell injections has not been performed.
The research presented in this dissertation documents reproducible tumor formation in immunodeficient mice following injection of single, purified melaInoma cells derived from three novel, conditional mouse models of melanoma. It was discovered that tumor formation occurred following every injection of individual CD34p75⁻ melanoma cells, with intermediate rates using CD34⁻p75⁻cells, and rarely with CD34⁻p75⁺ cells. The findings confirm that cells capable of propagating tumors (melanoma propagating cells/MPCs) are more common than previously thought and that multiple tumorigenic subsets may exist within a single tumor. Strikingly, single CD34⁺p75⁻MPCs underwent self-renewal after tumor formation in mice or multiple passages in culture, demonstrating that re-establishment of tumor heterogeneity is not a characteristic of all cell subsets capable of forming tumors --a trait previously thought to be concurrent with tumorigenicity, i.e. CSCs.
Purified MPCs were also found to be more resistant to high doses of chemotherapeutic agents than cells incapable of tumor formation. Finally, it was demonstrated that the expression profiles ofMPC subsets are distinct and contain upregulated messages of known importance for human melanocytic stem cell function as well as melanoma development and progression. Based on this original research, it is anticipated that these results will be profoundly influential and propel the cancer biology field forward in designing novel therapies that eradicate human chemoresistant, melanoma propagating cells in order to halt disease progression and prolong patient survival.