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The Role of the PI3K-AKT Pathway in Melanoma Brain Metastasis

Michael Davies

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National Institutes of Health (NIH)
There is a critical need to develop new strategies to prevent and treat melanoma brain metastases. Melanoma has a higher risk of CNS involvement than any other tumor type, and brain metastasis is the leading cause of death from this disease. There are no molecular markers that identify melanoma patients with an increased risk for brain metastasis, and no systemic therapies effectively prevent or treat these tumors. In a pilot study, we identified increased activation of the PI3K-AKT signaling pathway in melanoma brain metastases as compared to other distant metastases. In addition, patients with increased activation of the PI3K-AKT pathway in regional metastases had a higher risk of CNS involvement. The PI3K-AKT pathway has previously been implicated in melanoma in a number of malignant processes, but not in brain metastasis. Based on our data, we hypothesize that activation of the PI3K-AKT pathway is critical to the development and dismal outcomes of melanoma brain metastases. This hypothesis will be tested using unique clinical resources to define relevant preclinical models, and may lead to clinical strategies that may be tested in patients. First, we will analyze 100 frozen melanoma brain metastases from patients at The M. D. Anderson Cancer Center (MDACC) for genetic aberrations and activation of the PI3K-AKT pathway. The tumors will be analyzed by MIP arrays to identify copy number changes in genes that are in or that regulate this pathway, and mutational analysis of known and candidate regulators will be performed by mass-spectroscopy (MS) genotyping and Sanger sequencing. The expression and activation of proteins in the PI3K-AKT pathway will be measured directly using reverse phase protein arrays (RPPA). The genetic analyses will be compared to the RPPA results to determine the events that activate the pathway in patients, and the effectors/targets that are activated by each. In addition, for patients with available tissue (n=23), parallel profiling will be performed on matched non-CNS metastases to determine if those tumors show the same genetic changes and protein activation as the brain metastases. In order to test if activation of the PI3K-AKT pathway contributes to the development of brain metastases, we will analyze 200 regional melanoma metastases for genetic aberrations and activation of the pathway, and compare these results to the risk of CNS involvement. Using the results of these experiments to prioritize targets, we will then test if activating genetic events in the PI3K-AKT pathway increases the CNS-metastatic potential of human melanoma cells in an established mouse xenograft model. Finally, we will determine if inhibitors against targets in the PI3K-AKT pathway inhibit tumor growth and increase survival in mice with established brain metastases of human melanoma cells. These studies will improve our understanding of the prevalence, regulation, and function of PI3K-AKT activation in melanoma brain metastases. These studies may lead to clinical trials to prevent and/or treat these tumors. The studies will also establish unique resources for future investigations in this important field.

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