Project 1: Tumor Cell Intrinsic Determinants of Early Dissemination in Melanoma

PROJECT 1 SUMMARY Increasing data suggest that phenotypic and transcriptional plasticity are important features that contribute to metastatic progression, tropism, and response to therapy of cancer cells. We and others have provided compelling evidence that intratumoral heterogeneity exists in primary melanomas, suggesting it is an early feature important for tumorigenesis. Further, recent reports demonstrate that melanoma cells can switch between phenotypic states, some of which are associated with more aggressive biology, implicating transcriptional plasticity in this phenotypic variation. However, the evolution of tumor cell intrinsic features associated with melanoma progression remains largely uncharacterized. The studies that have evaluated transcriptomic and epigenetic features involved in melanoma metastasis have typically focused on individual molecular features restricted to a specific cell population, and have fallen short of integrating the metastatic process as a whole. We hypothesize that emergence of transcriptional heterogeneity that gives rise to distinct cell states in primary cutaneous melanoma is a critical step driving early metastatic dissemination, and that cells with a specific transcriptional program harbor the bulk of metastatic potential. The goal of Project 1 is to investigate the timing and function of molecular drivers of metastasis, the emergence and evolution of transcriptional heterogeneity and metastatic trajectories of cell states. We will do this in novel genetically engineered mouse models that reflect human disease as well as in clinically annotated patient samples. Using an innovative approach that integrates genetic bar coding, single cell RNA sequencing, spatial transcriptomics, and highly-multiplexed immunohistochemistry, we will assess the presence of specific transcriptional cell states within murine and human primary melanomas, and assess their influence on metastatic potential using animal models and statistical correlates to known patient outcomes (Aim 1). We will then study the mechanisms driving these transcriptional cell states by testing the contribution of individual candidate genes to their emergence and maintenance and their impact on metastatic potential (Aim 2). This research project will leverage the pathological, technological, and analytical resources of Cores B and C. Integration with Projects 2 and 3 will dissect the evolving, bidirectional crosstalk between melanoma cells and their microenvironment that culminates in a metastasizing tumor. Understanding the contribution of specific cell states and the molecular programs underlying early dissemination can improve our ability to subclassify patients diagnosed with primary melanoma by their risk of metastasis and identify those patients who could benefit most from increased surveillance or adjuvant therapies. Our studies might also provide a rationale for novel therapeutic approaches to prevent or target metastasis. Finally, findings from this research may apply to other tumor types wherein early dissemination results on increased metastatic potential and worse outcomes.