PROJECT SUMMARY Malignant melanoma is a tumor of the pigment-producing melanocytes, and is responsible for the majority of skin cancer related deaths. Cutaneous melanoma can be successfully treated through surgical excision; however, once the disease has metastasized, the survival rate is significantly reduced. Some recent studies have suggested that in certain contexts, cues from the tumor microenvironment can epigenetically reprogram melanoma cells into a malignant melanoma initiating cell (MIC) that is drug resistant and primed for invasion and metastasis. In the Kilian laboratory we have discovered a relationship between tumor topology and activation of a tumorigenic MIC that may prove an early transformation step preceding metastasis. In the Copland laboratory, we have developed novel combination therapies to treat melanoma, and several patient derived tumor xenograft (PDTX) models that accurately mimic patient response to standard of care. We will employ our suite of engineered extracellular matrices to decipher the interplay between topology, mechanics and matrix composition, in guiding activation of the MIC state in patient derived cells that display varying degrees of drug sensitivity. We will translate these matrix parameters into a novel 3D geometrically structured tissue engineered microtumor model. To evaluate the potential as a tool for drug development we will fabricate a 96-well plate- based format and evaluate microtumor response to standard of care and prospective new therapies. We will use orthotopic xenografts in athymic nude mice to study growth, invasion and dissemination of our cells, and use this information to inform the design of our model 3D tumor-mimics. Towards leveraging our microtumor array for therapeutic development, we will perform a small pilot study of combination therapies using our tumor-mimics? in vitro and as a novel in vivo microtumor xenograft?to discern how closely our biomimetic system recapitulates oncogenesis and drug sensitivity compared to cell lines and xenografts. This project aims to establish a complementary or even alternative approach to patient derived xenograft (PDX) models, where a patient?s cells derived from biopsy or excision may be integrated into a tumor-mimic for individualized medicine.