Melanoma is a highly metastatic disease with an increasing rate of incidence worldwide.,It is treatment refractory and has poor clinical prognosis; therefore, the development of new therapeutic agents for metastatic melanoma are urgently required.,In this study, we created a lung-seeking A375LM5IF4g/Luc BRAFV600E mutant melanoma cell clone and investigated the bioefficacy of a plant sesquiterpene lactone deoxyelephantopin (DET) and its novel semi-synthetic derivative, DETD-35, in suppressing metastatic A375LM5IF4g/Luc melanoma growth in vitro and in a xenograft mouse model.,DET and DETD-35 treatment inhibited A375LM5IF4g/Luc cell proliferation, and induced G2/M cell-cycle arrest and apoptosis.,Furthermore, A375LM5IF4g/Luc exhibited clonogenic, metastatic and invasive abilities, and several A375LM5IF4g/Luc metastasis markers, N-cadherin, MMP2, vimentin and integrin α4 were significantly suppressed by treatment with either compound.,Interestingly, DET- and DETD-35-induced Reactive Oxygen Species (ROS) generation and glutathione (GSH) depletion were found to be upstream events important for the in vitro activities, because exogenous GSH supplementation blunted DET and DETD-35 effects on A375LM5IF4g/Luc cells.,DET and DETD-35 also induced mitochondrial DNA mutation, superoxide production, mitochondrial bioenergetics dysfunction, and mitochondrial protein deregulation.,Most importantly, DET and DETD-35 inhibited lung metastasis of A375LM5IF4g/Luc in NOD/SCID mice through inhibiting pulmonary vascular permeability and melanoma cell (Mel-A+) proliferation, angiogenesis (VEGF+, CD31+) and EMT (N-cadherin) in the tumor microenvironment in the lungs.,These findings indicate that DET and DETD-35 may be useful in the intervention of lung metastatic BRAFV600E mutant melanoma.
TGF-β is a cytokine thought to function as a tumor promoter in advanced malignancies.,In this setting, TGF-β increases cancer cell proliferation, survival, and migration, and orchestrates complex, pro-tumorigenic changes in the tumor microenvironment.,Here, we find that in melanoma, integrin β1-mediated TGF-β activation may also produce tumor suppression via an altered host response.,In the A375 human melanoma cell nu/nu xenograft model, we demonstrate that cell surface integrin β1-activation increases TGF-β activity, resulting in stromal activation, neo-angiogenesis and, unexpectedly for this nude mouse model, increase in the number of intra-tumoral CD8+ T lymphocytes within the tumor microenvironment.,This is associated with attenuation of tumor growth and long-term survival benefit.,Correspondingly, in human melanomas, TGF-β1 correlates with integrin β1/TGF-β1 activation and the expression of markers for vasculature and stromal activation.,Surprisingly, this integrin β1/TGF-β1 transcriptional footprint also correlates with the expression of markers for tumor-infiltrating lymphocytes, multiple immune checkpoints and regulatory pathways, and, importantly, better long-term survival of patients.,These correlations are unique to melanoma, in that we do not observe similar associations between β1 integrin/TGF-β1 activation and better long-term survival in other human tumor types.,These results suggest that activation of TGF-β1 in melanoma may be associated with the generation of an anti-tumor host response that warrants further study.