UC Berkeley

The cancer stem cell theory ascertains a subpopulation of tumorigenic cells that selectively possess the ability for tumor initiation and self-renewal capacity to differentiate into nonmalignant cancer cells, known as bulk tumor cells. Cancer stem cells were first identified in hematopoietic cancers but subsequently have been implicated in ovarian, melanoma, liver, sarcoma, head and neck, pancreatic, glioblastoma, and breast cancers since. As a result, malignant tumors can be composed of genetically and morphologically heterogeneous cell populations with varying degrees of differentiation, self-renewal ability, and metastatic capacity. Experimental pursuits have sought to isolate and analyze the cancer stem cell population in primary tumors and molecularly strategize to identify phenotypic targets. A lack of standardized cancer stem cell in vivo and in vitro models have slowed down the development of proper therapies as well as the elucidation of scientific mechanisms that dictate cancer stem cells. One method of detection has been the utilization of various stem cell markers to categorize molecular phenotypes. In breast cancer stem cells, biomarkers such as the nucleolar GTPase nucleostemin; the detoxifying enzyme, ALDH-1; and cell surface marker, CD44 aid in identification and isolation of cancer stem cells for research studies. Furthermore, exclusion of the Hoescht Dye assays for the cell’s ability to efflux current therapeutic molecules extra-cellullarly, evading apoptosis and cell cycle arrest. Furthermore, melanoma cancer stem cells, also known as malignant melanoma-initiating cells (MMICs), contain subpopulations expressing CD133, CD20, and ABCG5 have defined features of unlimited self-renewal and proliferative capacities for melanoma cancers. While cancer incidence overall has decreased, melanoma continues to rise, with patients with metastatic and malignant melanoma continue to relapse from current therapeutic strategies. This thesis details the characterization of human breast cancer and melanoma cell lines of varying tumorigenic potential and their subsequent response to the phytochemical, indole-3-carbinol, and its synthetic derivative, 1-benzyl-I3C. I3C selectively targets breast cancer stem cells through different molecular mechanisms such as protein-protein interactions of the stem cell marker nucleostemin and its binding partner, murine double mutant 2 (MDM2) in the nucleolus, thereby freeing p53 to activate apoptosis. Furthermore, I3C sensitizes cells with a wild type p53, wild type PTEN phenotype or even more tumorigenic melanoma cells that possess the rare BRAF V600D mutation and PTEN deletion. Given I3C’s and its more potent derivative, 1-benzyl-I3C’s, anti-proliferative modulation of the p53 pathway in breast cancer cells and the PTEN/ Wnt pathways in malignant melanoma cell lines, preclinical results can implicate I3C as a novel chemopreventative molecule that selectively targets cancer stem cells.