Stem cells in tumor development, progression and therapy
1. Biology of Normal and Malignant Stem Cells (Mingyuan Zhou, Ph.D., Susan Zabierowski, Ph.D., Patricia Brafford, M.S., Ling Li, M.D., Katrin Sproesser, M.S., Jennifer Marmion, B.S., Ben Himes). Human embryonic stem cells and pluri-potent stem cells from the human dermis are differentiated into melanocytes to test the hypothesis that melanocyte stem cells are more prone to transformation than fully differentiated cells and that neighboring cells and matrix in the microenvironment play critical roles in differentiation and transformation. We are then characterizing melanoma stem cells (tumor-initiating cells) from melanoma spheres that represent a subpopulation in malignant lesions and that have characteristics of stem cells. We are distinguishing four populations of melanoma cells with stem cell-like characteristics: a. CD20+ cells, b. side population cells with increased drug resistance, c. label-retaining cells that turn over very slowly, and d. CD133 positive cells. Investigations of cancer stem cells will help us to understand tumor dormancy, recurrence, metastasis, and therapy resistance. Our primary model is melanocyte/melanoma but the laboratory is also investigating the role of tumor stem cells in carcinomas of esophagus, kidney, oral cavity, lung and breast.
2. Transformation (John Lee, Ph.D., Jessie Villanueva, Ph.D., Ronan McDaid, B.S., Jun Kong, M.S., Himatibindu Gaddipati, M.D., Gao Zhang, Patricia Possik, M.S.) The development of melanoma is a complex process, in which environmental cues such as ultraviolet light and activation of signaling pathways lead to uncontrolled proliferation. We are testing the hypothesis that melanocyte stem cells are the primary target for transformation to melanoma. Using a complex model of skin equivalents mimicking the human skin microenvironment the laboratory is reconstructing each step in the melanoma progression cascade. Genes associated with melanoma are overexpressed or expression is silenced with shRNAi constructs in lentiviral vectors. Our recent experiments suggest that as few as two genetic ‘hits’ can induce malignant transformation of melanocytes if the microenvironmental conditions are supporting cells to survive the initial crisis.
3. Targeted Therapies (Keiran Smalley, Ph.D., Mercedes Lioni, M.D., Bin Li, Ph.D., Kazuhiro Noma, M.D., Rooha Contractor, M.S., Brijal Desai, M.S., Min Xiao, M.S., Thiennga Nguyen, M.S.). We are defining the signal transduction pathways that are constitutively activated in melanoma cells through autocrine and paracrine growth factors and through genetic alterations. Through RNAi approaches we are selecting those genes in tumor cells and stromal fibroblasts that are potential targets for therapy. Three-dimensional culture models and orthotopic in vivo models are proving ideal for selecting small molecules as therapeutics in melanoma and esophageal and renal carcinomas. In melanoma, the MAPK pathway is the primary target for therapy but additional pathways need to be explored to not only induce cytostatic but cytotoxic effects. We expect that melanoma stem cells require strategies for elimination that are different from those targeting the main population. In esophagus carcinoma, therapy is even more difficult as these cells show astounding resistance to all conventional therapies. In both esophageal and renal cell cancer, tumor vascularization and its targeting is a major subject for our investigations.
4. Tumor Dormancy. (Mizuho Fukunaga M.D., Ph.D., Gabriela Martinez, M.S., Ademi Santiago-Walker, Ph.D., Devraj Basu, M.D., Ph.D., Alexander Roesch, M.D., Sarah Telson). Dormancy of tumor cells can occur in primary lesions or at any time after metastatic dissemination and can last for many years. Our working hypothesis is that tumor stem cells (tumor-initiating cells or tumor cells with self-renewing capacity) are central for dormancy due to their non-proliferation or very slow turnover and their non-responsiveness to growth signals. We are defining tumor dormancy in melanoma and characterize stem cell populations with a major focus on non-proliferating cells with high proliferation potential (label-retaining cells) hypothesizing that these are critical for maintaining dormancy. We are then defining the escape of tumor stem cells from dormancy for growth, invasion and metastasis and develop strategies for therapy. The hypothesis is that activation of Notch signaling is key for melanoma stem cells to break out of dormancy. Notch signaling activates both MAPK and PI3K signaling pathways and leads to a highly invasive and metastatic phenotype. Using our unique three-dimensional melanoma models we are determining how microenvironmental cues drive Notch activation that leads to a signaling cascade for proliferation and invasion.
5. Stem cells in Breast Tumor Development and Therapy. (Jung-im Huh, Ph.D., Julia Tchou, M.D., Ph.D, Adina Vultur, Ph.D. [expected Oct.07]. This evolving program seeks to define stem cells for both normal and malignant breast tissues and develop novel models for premalignant and malignant breast diseases that will provide the future basis for rational therapies.