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theses

ETD doctoral

Breast cancer is a heterogeneous disease; its high degrees of intra- and inter-tumoral diversity are attributable to the presence of a subset of tumor-initiating cells called breast cancer stem cells (BCSCs). BCSCs are endowed with self-renewal and differentiation potential, ultimately culminating in a hierarchically organized tumor with distinct degrees of differentiation and functions. Accumulating evidence suggests BCSCs play roles in tumor initiation, progression, metastasis, chemoresistance, and relapse. Thus, targeting BCSCs can be a promising therapeutic strategy for eradicating breast cancer.

The goal of this study is to examine the significance of cancer stem cells in breast tumorigenesis and understand the mechanism of vitamin D compounds targeting cancer stem cell signaling pathways. Specifically, we seek to investigate (1) the effects of vitamin D-mediated inhibition of BCSCs in triple negative breast cancer (TNBC), (2) transcription factor-mediated regulation of breast cancer stemness, and (3) the transcriptomic signature regulated by vitamin D compounds in early breast cancer. In the pursuit of these goals, we utilize BCSC-enriching mammosphere culture, genetic modulation, and next-generation sequencing technologies in two experimental models of breast cancer: TNBC cells (SUM159), which are reported to harbor enriched cancer stem cell populations, and pre-invasive ductal carcinoma in situ cells (MCF10DCIS). In SUM159 cells, we observed vitamin D compounds (1,25-dihydroxyvitamin D3 and the Gemini vitamin D analog BXL0124) to inhibit mammosphere forming efficiency and self-renewal by downregulating markers of pluripotency and cancer stemness pathways. To understand the mechanism by which transcription factors control cancer stemness, we further studied octamer-binding transcription factor 4 (Oct4) as a potential factor in reprogramming BCSCs. We observed Oct4 overexpression to upregulate the CD44+/CD24- BCSC subpopulation, increasing expression of CD44 and the activated form of NFB, but with no significant changes in epithelial-mesenchymal transition markers and tumor formation in vivo.

To understand whether breast cancer stem cells promote the progression of ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC), along with vitamin D-mediated inhibition of this transition, we used RNA and DNA sequencing technologies to identify transcriptomic signatures in MCF10DCIS mammospheres. Our study revealed a global view of genes differentially regulated by vitamin D compounds, along with genes potentially involved in breast cancer stemness and progression. Ingenuity Pathway Analysis identified the TP63-VDR axis as a plausible target that can be explored for inhibition of DCIS transition to IDC. Collectively, these findings suggest a role for vitamin D as a potential preventive agent in targeting cancer stemness and breast cancer progression.

ETD_11196

Ph.D.

Includes bibliographical references

doi:10.7282/t3-v8br-2413

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