Pterostilbene supresses inflammation-induced melanoma metastasis by impeding neutrophil elastase-mediated thrombospondin-1 degradation

OBJECTIVE: Chronic inflammation plays a fatal role in tumor metastasis. Pterostilbene (PTE) is a natural dimethylated analogue of resveratrol with anticancer and anti-inflammatory activities. This study aimed to investigate the inhibitory effect of PTE on inflammation-associated metastasis and explore the underlying mechanisms. METHODS: Lipopolysaccharide (LPS)-induced lung inflammation and melanoma metastasis models were established in mice. After PTE treatment for four weeks, the organ index, histological changes, proinflammatory cytokines, and the expression and activity of neutrophil elastase (NE), a biomarker of neutrophil influx in the lungs, were analysed. Additionally, direct effects of PTE on NE-induced B16 cell migration were explored in wound healing and Transwell assays, and the expression of thrombospondin-1 (TSP-1) and epithelial-mesenchymal transition (EMT) markers were also detected. RESULTS: PTE obviously attenuated the LPS-induced metastasis of circulatory B16 cells to lungs by reducing the number of metastatic nodules on the lung surfaces and the lung weight/body weight ratio. PTE treatment also significantly reduced LPS-activated increase levels of tumor necrosis factor (TNF)-α and interleukin (IL)-6 in the lungs of tumor-bearing mice. In addition, increased expression and enzyme activity of NE and decreased expression of TSP-1 were observed, and these were blocked by PTE. In vitro, PTE at concentrations without cytotoxicity also markedly suppressed NE-triggered B16 cell migration, prevented NE-induced TSP-1 proteolysis and reversed the expression of vimentin, N-cadherin and E-cadherin. CONCLUSION: PTE could block inflammation-enhanced tumor metastasis, and the underlying mechanism might be associated with the inhibition of NE-mediated TSP-1 degradation.