e22021 Background: Melanoma brain metastases (MBM) are common with a median overall survival of 4-5 months. Although immunotherapies have improved clinical outcomes and have doubled overall survival in MBM, there is a high incidence rate of relapse caused by drug resistance. AXL, a receptor tyrosine kinase (RTK), is associated with drug resistance and metastasis in many cancers. The activation of AXL via trans-phosphorylation regulates multiple signaling pathways that induce tumor survival, metastasis, drug resistance, and epithelial-to-mesenchymal transition (EMT). In MBM, AXL is upregulated and associated with disease progression, promoting cell invasion and migration. This suggests that targeting AXL can be a novel strategy to overcome treatment-related resistance in MBM. TP-0903, an investigational small molecule inhibitor of AXL, has shown efficacy in reversing the mesenchymal phenotype and re-sensitizing resistant cancer cells to targeted therapies in heme malignancies, pancreatic, and breast cancer. We aim to investigate the efficacy of TP-0903 in MBM. Methods: The Cancer Genome Atlas (TCGA) data was utilized to investigate the signaling pathways downstream of AXL that are upregulated in advanced melanoma. Nine signaling molecules including AKT1, mTOR, and PAK4 were analyzed to identify any correlation between gene expression levels and overall survival. Four metastatic melanoma cell lines were used to evaluate the effect of TP-0903 on cell viability and active AXL downregulation was assessed in vitro through MTS cell viability assays and Immunoblotting. Wound closure assays were executed to understand the functional consequences of AXL downregulation. Results: In all nine genes, high expression levels confer poor survival probability. Cell viability assays of four malignant melanoma cell lines showed that TP-0903 treatment resulted in IC50 values ranging from 32 – 692 nM. Western blot analysis indicated that TP-0903 reduced the levels of phosphorylated AXL in malignant melanoma cell lines. In addition, increasing TP-0903 concentrations reduced the rate of cell migration in these malignant melanoma cell lines. Conclusions: AXL plays a role in EMT, treatment resistance, and metastasis in MBM, resulting in poor survival. Our findings suggest TP-0903 is effective in reducing cell migration, inhibit metastasis, and can be a potential therapeutic option in MBM.
Loss of stromal caveolin-1 expression in malignant melanoma metastases predicts poor survival
