Normal cells are dependent upon the extracellular cell matrix (ECM) for survival, and undergo apoptosis when they lose contact with the ECM - a phenomenon termed anoikis. The acquisition of anoikis resistance is a critical step for metastatic progression, and resistance to anoikis contributes prominently to the metastatic progression of cancer. In particular, molecules that induce anoikis in melanoma cells provide exciting new leads into effective therapeutic targeting of metastatic melanoma. Thus, to identify genes that confer anoikis resistance, we performed a druggable genome RNAi screen and identified Maternal Embryonic Leucine Zipper Kinase (MELK) as a gene that confers anoikis resistance, including in BRAF/NRAS wild-type metastatic melanoma. We find that MELK is overexpressed in patient-derived samples of metastatic melanoma and its overexpression predicts metastastic progression of melanoma. We hypothesize that MELK is necessary for anoikis resistance and facilitates metastatic progression of melanoma and thus represents an attractive drug target for metastatic melanoma therapy. The overall objective is to determine the role and mechanism of MELK in melanoma metastasis, including its ability to regulate anoikis resistance and evaluate MELK as a drug target for metastatic melanoma therapy. Specifically, in Aim 1, we will determine the role of MELK in facilitating melanoma metastasis and as a drug target for treating metastatic melanoma. Towards this end, we will first test whether MELK is sufficient to cause anoikis resistance in vivo using mouse models of anoikis resistance. Additionally, using complementary mouse models of melanoma metastasis, we will determine the role of MELK in facilitating metastasis to the lungs and the brain. Finally, using pharmacological inhibitors of MELK (Siomycin A and OTSSP167), we will test whether MELK inhibition prevent and/or inhibit metastatic melanoma growth in vivo in the spontaneous and genetic models of melanoma metastasis.
In Aim 2, we will determine the mechanism by which MELK confers anoikis resistance. First, we will determine the mechanism of MELK overexpression in melanoma. Towards this end, based on our results, we will determine the role of transcription factor FOXM1 in the overexpression of MELK in melanoma. Next, we will determine the mechanism by which MELK overexpression confers anoikis resistance. Towards this end, based on our complementary high-throughput approaches of RNAi screening and transcriptome-wide gene expression profiling, we will determine the role of the PUMA and possibly other candidates in mediating the downstream effects of MELK. Specifically, we will determine whether repression of PUMA is required for MELK-induced anoikis resistance and if this repression also contributes to the ability of MELK to facilitate melanoma metastasis. Collectively, the results of our experiments will identify new genes and pathways that confer anoikis resistance, facilitate melanoma metastasis and uncover novel druggable targets for treating highly aggressive metastatic melanoma, including BRAF/NRAS wild-type melanoma.
Melanoma is the leading cause of skin cancer-related deaths and due to the lack of effective therapies that can provide long-term clinical benefit over 10,000 Americans die every year due to metastatic melanoma. Using a druggable genome RNAi screen, we have identified Maternal Embryonic Leucine Zipper Kinase (MELK) as a potentially important regulator of anoikis resistance and melanoma metastasis. The research outlined in this proposal will decipher the role of MELK in anoikis resistance, metastatic melanoma and establish its effectiveness as a novel pharmacologically tractable drug target for treating metastatic melanoma, including BRAF/NRAS wild-type metastatic melanoma.
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