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The Herlyn Lab studies the normal and malignant tissue environment to develop rational approaches to cancer therapy.
1. Modeling the normal and diseased human tissue microenvironment. We are differentiating multi-potent stem cells from the human dermis and reprogrammed stem cells 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. Reprogramming from melanocytes to stem cells is achieved by Notch activation and from skin fibroblasts of patients with high risk for melanoma to induced pluri-potent stem cells. We have developed a complex, three-dimensional model that mimics human skin, and are using it to reconstruct each step in the melanoma development and progression cascade. Genes associated with melanoma are overexpressed or silenced with shRNA constructs in lentiviral vectors and we increasingly use cDNA and sh (short hairpin) RNA libraries for our experiments. Ultraviolet light irradiation is mimicking the DNA damaging effect of sunlight. The synthetic skin model has also been expanded to organotypic cultures for the esophagus. We can introduce into each model endothelial cells to form a microcapillary network and peripheral blood mononuclear cells to mimic the innate and immune host response. Studies on interactions among tumor cells, fibroblasts and endothelial cells are also done in three-dimensional models, in which cells are embedded into collagen to mimic the tumor microenvironment. Growing cells in these organ-like models induce major changes in gene expression similar to those in animals and patients, making them superbly suited for studies of cell-cell signaling, matrix formation, and drug resistance.
2. Therapeutic targeting of signaling pathways in cancer. We are defining signal transduction pathways that are constitutively activated in melanoma and squamous cell cancer cells through autocrine and paracrine growth factors and genetic alterations. With shRNA in lentiviral vectors, we are identifying genes in tumor cells, stromal fibroblasts, and endothelial cells that are potential targets for therapy. In melanoma, the MAPK and PI3K pathways are primary targets for therapy, but other pathways are also explored for inhibition by small molecule compounds. Since therapy is increasingly guided by genetic aberrations in tumors, we are developing combinations of compounds that take into account the genetic abnormalities of tumors, with the long-term goal of individualized cancer therapy. In recent years, we have actively collaborated with pharmaceutical companies to obtain compounds in early stages of preclinical and clinical development. Increasingly, we are collaborating with academic chemists and structural biologists to select and further develop compounds for tumor inhibition.
3. Tumor dormancy and therapy resistance. Tumor cells can become dormant in primary tumors or at any time after metastatic dissemination and can persist in the dormant state for many years, allowing them to resist treatment. Our working hypothesis is that tumor-maintenance cells (tumor stem cells) are central to dormancy due to their non-proliferation or very slow turnover and their non-responsiveness to growth signals. We are delineating tumor dormancy in melanoma and characterizing sub-populations of cells with a major focus on slow-proliferating cells that have high proliferation potential hypothesizing that these cells are critical for dormancy and therapy resistance. We are then defining how tumor cells escape dormancy for growth, invasion, and metastasis, and developing strategies for therapy. Using our unique three-dimensional melanoma and squamous cell carcinoma models, we are determining how microenvironmental cues from the matrix or other cells such as B cells, macrophages, and endothelial cells drive gene activation, leading to a signaling cascade for proliferation and invasion. These studies will lead to in-depth investigations of tumor heterogeneity and the dynamic regulation of genes that define sub-populations with specialized biologic functions. Our long-term goal is to develop strategies for two therapies, one for eliminating the bulk of the tumor, the other for small sub-populations that escape all major therapeutic strategies. Such combinations should achieve elimination of all tumor cells, which is required in melanoma because single tumor cells are capable of tumor induction in immunodeficient animals.
The microscope in the image belonged to William E. Horner, M.D., a collaborator with Caspar Wistar, M.D., in the early 1800s.
Dr. Horner, a lecturer at the University of Pennsylvania, was a pioneer of the use of microscopes in anatomical and medical research. He authored Special Anatomy and Histology, a seminal text on the subject.