Gambogic acid inhibits tumor metastasis through blocking matrix metalloproteinases mediated TGF-β1 activation

Context: Tumor metastasis is the major death factor in cancer patients. Transforming growth factor-β (TGF-β) is an important cytokine promoting tumor metastasis and blocking TGF-β shows crucial antitumor application prospects. In the tumor microenvironment (TME), TGF-β is always highly activated and matrix metalloproteinases (MMPs) are an important TGF-β promoting factor. It gives us a crucial inspiration that TGF-β in TME can be selectively inhibited by specifically correcting TGF-β promoters in TME. Gambogic acid (GA) is an anti-tumor natural product with the activity to inhibit tumor metastasis by preventing the expression of MMP-2, 9. In this study, we explored whether GA could inhibit tumor metastasis by blocking MMPs mediated TGF-β activation. Methods: Two extremely aggressive tumor cell lines, B16F10 melanoma and 4T1 breast carcinoma were chosen for this study. The in vitro protein expression level and mRNA level of MMPs were determined by ELISA and RT-PCR respectively. The cell mobility, invasion rate, and morphological changes with various treatments were depicted via scratches, transwell assay and immunofluorescence respectively. For further in vivo confirmation, animal models of melanoma, as well as breast cancer, were respectively established using the two cell lines, and metastasis together with related protein expression levels were estimated after treatment with GA. Results: GA could suppress the expression of MMP-2, 3, 9, which further blocked TGF-β activation. Meanwhile, GM6001 presented a consistent effect. Via inhibiting MMPs-mediated TGF-β upregulation, both GA and GM6001 could suppress the migration and invasion ability of tumor cells in vitro and inhibits tumor metastasis in vivo. Also, GA and GM6001 could downregulate TGF-β downstream signaling pathway. Therefore, the present study provide an important enlightenment for tumor control by specifically blocking TGF-β in TME without affecting normal function of TGF-β. Conclusions: GA can inhibit tumor metastasis by blocking MMPs mediated TGF-β activation. Specifically correcting complicated pro-TGF-β factors in TME may be a more appropriate strategy to suppress metastasis without affecting TGF-β normal function.