During the process of tumor progression, melanoma cells must exit the epidermis to form a dermal tumor, recruit lymphatic vessels, and then migrate to lymph nodes before metastasizing to distant organs. Melanoma prognosis directly correlates with tumor depth and lymph node metastasis. Therefore, ideal therapeutic agents for early stage melanoma would not only block melanoma invasion but also prevent tumor cells from accessing lymphatic vessels. Published work from our group determined that RhoJ, a gene that allows melanoma cells to resist BRAF oncogene-induced stress, is highly expressed in melanoma tumors that metastasize to the lymph node. RhoJ deletion stalled the growth of BRAF mutant melanoma tumors and inhibited the formation of BRAF mutant nevi in vivo. In addition to its selective role in controlling the growth of BRAF mutant melanocytes, RhoJ plays a specific role in tumor angiogenesis. RhoJ signaling in peritumoral endothelial cells induces them to generate vessels that serve as conduits for both nutrients to enter tumors and metastasizing cells to exit tumors. Recent yet unpublished work suggested that RhoJ deletion inhibited the ability of lymphatic endothelial cells to form vessels around tumors. Moreover, small molecules that inhibit RhoJ signaling seemed to not only block the growth of melanoma tumors in vivo, but also blocked the ability of endothelial cells to generate vessels to feed tumor cells in vitro. Here we propose that RhoJ has a dual role in tumor biology- it acts within the melanocyte to promote the formation of tumors and within the endothelial cells to promote the formation of lymphatic vessels around tumors in the skin, and blood vessels around tumors in distant organs. We use a combination of state of the art single cell genomics, in vivo imaging, novel pharmacologic agents, and transgenic mouse models to: 1) determine how RhoJ acts in the melanocyte to promote the growth of early stage tumors; 2) establish whether RhoJ acts in lymphatic endothelial cells to control tumor lymphangiogenesis; 3) assess the relative contributions of RhoJ to tumor growth and lymphanigogenesis/angiogenesis in vivo and in 3D models of human tumors. Completion of these studies will define a new therapeutic strategy that halts cancer progression by simultaneously targeting both tumor cells and the vessels that feed them.
While immunotherapies and kinase inhibitors can successfully treat metastatic melanoma, they are not routinely used to treat melanomas that have not yet disseminated systemically secondary to their side effects. Our recent work suggests that RhoJ plays a dual role in tumor biology- it promotes tumor formation while also controlling the ability of endothelial cells to form vessels in and around tumors. Here we propose that RhoJ plays a selective role in tumor formation, tumor angiogenesis, and lymphangiogenesis. We test this hypothesis using genetically engineered mice, advanced imaging and genomics, and newly developed RhoJ inhibitors. Completion of these studies will identify a new therapeutic strategy that can be used to treat early stage melanoma and other cancers.
