Therapeutic targeting of the pre-metastatic stage in human brain metastasis

Brain metastases (BM) result from the spread of primary tumors to the brain and are a leading cause of cancer mortality in adults. Secondary tissue colonization remains the main bottleneck in metastatic development, yet this "pre-metastatic" stage of the metastatic cascade, when primary tumor cells cross the blood-brain barrier and seed the brain before initiating a secondary tumor, remains poorly characterized. Current studies rely on specimens from fully developed macro-metastases to identify therapeutic options in cancer treatment, overlooking the potentially more treatable "pre-metastatic" phase when colonizing cancer cells could be targeted before they initiate the secondary brain tumor. Here we use our established brain metastasis initiating cell (BMIC) models and gene expression analyses to characterize pre-metastasis in human lung-to-brain metastases. Pre-metastatic BMIC engaged invasive and epithelial developmental mechanisms while simultaneously impeding proliferation and apoptosis. We identified the dopamine agonist Apomorphine to be a potential pre-metastasis-targeting drug. In vivo treatment with Apomorphine prevented BM formation, potentially by targeting pre-metastasis-associated genes KIF16B, SEPW1, and TESK2. Low expression of these genes was associated with poor survival of lung adenocarcinoma patients. These results illuminate the cellular and molecular dynamics of pre-metastasis, which is subclinical and currently impossible to identify or interrogate in human patients with BM. These data present several novel therapeutic targets and associated pathways to prevent BM initiation.

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