Date of Award
Doctor of Philosophy (PhD)
Cancer progression is characterized by the formation of tumors in primary organs and the subsequent re-formation of tumors in distant metastatic sites. The tumorigenic, or tumor-forming, capacity of cancer cells drives cancer along a continuum that includes primary tumor formation, metastatic re-initiation, and macroscopic relapse. As such, a greater understanding of the biological features and molecular determinants that govern tumor-forming capacity in the primary and metastatic site is of great importance to the scientific and biomedical communities. This thesis presents an unbiased approach to systematically select and characterize breast cancer cells with enhanced tumorigenic capacity in order to elucidate genes and cell biological features that are important to tumor-forming potential in primary and metastatic sites. The first part of this thesis describes a method to select for populations of cells with enhanced tumor-forming capacity from heterogeneous breast cancer populations. Two human Estrogen Receptor-negative (ER-negative) breast cancer cell lines, MDA-231 and CN34, were subjected to in vivo selection to yield ‘tumorigenic-enriched’ (TE) derivatives, which demonstrated enhanced tumor re-initiation capacity in multiple organ sites in a xenograft model. In the second part of this study, a systematic approach was employed to identify genes that promote tumor re-initiation. Transcriptomic profiling revealed a set of genes–LAMA4, FOXQ1, and NAP1L3–that were expressed at greater levels in tumorigenic-enriched derivatives relative to their parental populations. These genes were also expressed at greater levels in independently derived metastatic populations. All three of these genes were found to promote metastatic efficiency, and one of these genes, LAMA4, was subjected to further characterization. Functional studies revealed LAMA4 to promote clonal expansion during substratum-detachment in vitro, tumor re-initiation in multiple organ microenvironments, the proliferation of disseminated metastatic cells, and the formation of incipient micro-metastatic colonies in vivo. The final phase of this study revealed the association of LAMA4 expression with human breast cancer progression and clinical outcome in multiple patient datasets. In support of the role of LAMA4 in promoting early tumor formation, malignant breast cancer cells isolated from incipient breast cancer lesions were found to express higher levels of LAMA4 relative to pre-malignant cells from matched patient lesions. In addition, consistent with functional studies demonstrating the role of LAMA4 in driving primary and metastatic tumor re-initiation, higher levels of LAMA4 expression in ER-negative primary tumors correlated with worse relapse-free survival in multiple patient clinical cohorts.
Ross, Jason Barzel, "Molecular Determinants of Tumor Re-Initiation in Breast Cancer" (2015). Student Theses and Dissertations. 289.