Inhibition of p38 and ERK1/2 pathways by Sparstolonin B suppresses inflammation-induced melanoma metastasis

Background: Cancer related inflammation plays a fatal role in the metastatic process, which can foster tumor growth, angiogenesis and dissemination. Sparstolonin B (SsnB), derived from Chinese medicine of the tubers of Scirpus yagara, is a TLR2 and TLR4 antagonists. It has exhibited multiple activities of anti-inflammatory, anticancer, anti-obesity and anti-hepatitis. However, whether SsnB is involved in the regulation of inflammation-induced tumor metastasis is not well elucidated. Purpose: The aim of this study was to investigate the effectiveness of SsnB as a treatment of inflammation-induced tumor metastasis and identify the underlying mechanisms of its anti-tumor metastatic activity. Method: The anti-tumor metastatic activity in vitro was estimated by MTT, wound-healing assay, matrigel invasion analysis and extracellular matrix adhesion assay. Mice lung metastasis and hepatic metastasis experiments were performed to assess the activities in vivo. Lungs or livers were weighed and the number of metastatic nodules was determined after mice were sacrificed. The levels of pro-inflammatory cytokines in the serum, lungs and livers were detected by using enzyme-linked immunosorbent assay (ELISA). Micro-metastasis nodules in lungs or livers were analyzed by histological examination. Immunohistochemistry and western blot analysis were conducted to determine protein expression. Result: Herein, SsnB dose-dependently inhibited cell migration and invasion in mouse melanoma B16 cells with or without stimulation of lipopolysaccharide (LPS), Pam3csk4 or molecules from damaged tumor cells (DTC-Ms). The expression of matrix metalloproteinases (MMP)-2 was also significantly abated by SsnB in LPS-modulated B16 cells. And SsnB reduced LPS-activated B16 cells adhesion to extracellular matrix components collagen I and fibronectin in a dose-dependent manner. In vivo, SsnB obviously attenuated LPS-activated pulmonary metastasis in mice by reduction the number of metastatic nodules on the lung surfaces, lung weight and levels of tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 in serums and lungs. Moreover, in experimental hepatic metastasis model mice, SsnB remarkably repressed LPS-stimulated the number of metastatic nodules along with liver weight; and SsnB significantly suppressed LPS-activated increase levels of TNF-alpha and IL-6 in livers. Immunohistochemistry analysis indicated that SsnB inhibited the expression of TLR4 in livers. Furthermore, SsnB remarkably blocked p38 and ERK1/2 signaling pathway in LPS-induced B16 cells. P38 and ERK1/2 signaling silencing, using BIRB0796 (small molecular inhibitor of p38 MAPK) and PD184352 (inhibitor of MEK1/2 kinases that activate ERK1/2), significantly abated LPS-induced migration and invasion of B16 cells. Conclusion: The present study reports a novel use of SsnB in mitigating TLRs ligands-induced melanoma metastasis by inhibition of p38 and ERK1/2 pathway.