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The Herlyn Lab studies the normal and malignant tissue environment to develop rational approaches to cancer therapy.

Overall Research Goals:

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. 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. Skin reconstructs can also be grafted onto immunodeficienct mice for long-term observation. Besides isolating melanocytes and keratinocytes from skin, we have begun to differentiate them from ‘induced pluripotent stem’ (iPS). This source also allows us to generate an intact human inflammatory and immune system in vivo, including from melanoma patients where we have cell lines or patient-derived xenografts (PDX).  Studies on interactions among tumor cells, fibroblasts and endothelial cells are also done in 3-D models, in which cells are embedded into collagen to mimic the tumor microenvironment. Growing cells in organ-like models induces major changes in gene expression similar to those in animals and patients, making such models 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 subpopulations 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 3-D melanoma, 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 subpopulations 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 subpopulations 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.

4. Stem cells and melanoma. Multipotent stem cells with neural crest-like properties have been identified by our lab and others in the dermis of human skin. The stem cells display self-renewal capacity and differentiate into neural crest derivatives including epidermal pigment-producing melanocytes. Neural crest-like stem cells (NCLSC) share many properties with aggressive melanoma cells, such as high migratory capabilities and expression of neural crest markers. However, little is known about which intrinsic or extrinsic signals determine proliferation or differentiation of stem cells. In our studies we have focused on major developmental pathways. Notch signaling is highly activated in stem cells, similar to cells within melanoma spheres. Inhibition of Notch signaling reduces proliferation of stem cells, induces cell death, and down-regulates non-canonical Wnt5a, suggesting that the Notch pathway contributes to maintenance and motility of the stem cells. In 3-D skin reconstructs, canonical Wnt signaling promotes differentiation of stem cells into melanocytes. This differentiation is triggered by the endogenous Notch inhibitor Numb, which is upregulated in the stem cells by Wnt7a derived from UV-irradiated keratinocytes. These studies reveal a crosstalk between the two conserved developmental pathways in human skin, and highlight the role of the skin microenvironment in driving the generation of stem cells, and possibly tumor-initiating cells. They also provide a rationale for identifying novel targets for therapy among those groups of genes that are intimately involved in melanocyte development and highly expressed in melanoma while being largely absent in normal melanocytes.