Arenobufagin, isolated from toad venom, inhibited epithelial-to-mesenchymal transition and suppressed migration and invasion of lung cancer cells via targeting IKKβ/NFκB signal cascade.

ETHNOPHARMACOLOGICAL RELEVANCE: Lung cancer is the leading cause of cancer incidence and mortality worldwide. Arenobufagin (Arg), a representative natural bufadienolide compound, is one of the major bioactive components isolated from toad venom ("Chan Su"named in Chinese to treat multifarious clinical neoplasms in China). However, the underlying molecular mechanisms that Arg inhibited the metastasis of lung cancer cells remain poorly understood.
MATERIALS AND METHODS: The mobility capacities of lung cancer cells treated with Arg were evaluated using wound healing assay. The anti-migratory and anti-invasive effects of Arg on lung cancer cells were investigated by transwell invasion assay and matrigel invasion assay. iTRAQ-labeled LC-MS proteomics was used to analyze the potential proteins related to metastasis in lung cancer cells treated with Arg and differentially-expressed proteins related to EMT and NFκB signaling cascade were further confirmed by Western blotting assay. The changed subcellular localization of p65 in lung cancer A549 and H1299 cells treated with Arg was detected by immunofluorescence staining. Molecular docking and molecular dynamic (MD) simulation assay were performed to verify the binding between Arg and IKKα/IKKβ. siRNA knockdown was used to check whether Arg inhibited EMT of lung cancer cells via targeting NFκB signaling cascade, which was further verified by in vivo study of lung cancer cell xenograft mice model and pulmonary metastasis mice model accompanying with immunohistochemical and hematoxylin-eosin (HE) staining.
RESULTS: Arg suppressed the wound closure of lung cancer cells using wound healing assay. Moreover, Arg significantly inhibited the migration and invasion of lung cancer cells by transwell invasion assay and matrigel invasion assay. 24 unique differentially-expressed proteins related to metastasis in lung cancer cells treated with Arg were identified using iTRAQ-labeled LC-MS proteomics and 14 differentially-expressed proteins related to EMT were further confirmed by Western blotting assay. Arg significantly decreased the phosphorylation of IKKβ, IκBα and p65 in the cytoplasm of lung cancer cells by Western blotting assay, and remarkably reduced the release of p65 from the cytoplasm to the nucleus. Arg could be bound in the ATP binding pocket of IKKα and IKKβ by molecular docking assay, and MD simulation assay further demonstrated that Arg binding to the ATP-binding pocket of IKKβ was very stable in 300 ns MD simulation, compared with the binding of Arg and IKKα. IKKβ/NFκB signaling cascade was also involved in the inhibitory effect of Arg on EMT of lung cancer cells by siRNA knockdown assay. The study of lung cancer cell xenograft mice model and pulmonary metastasis mice model in vivo indicated that Arg inhibited EMT and suppressed migration and invasion of lung cancer cells via downregulating IKKβ/NFκB signaling cascade.
CONCLUSION: In the present study, we explored the molecular mechanism of Arg prohibiting the metastasis of lung cancer cells in vitro and in vivo, which displayed Arg could target IKKβ to inactive NFκB signaling cascade and further change the expression of proteins related to EMT. These results highlight the potential of toad venom as a potential chemotherapeutic agent and warrant its development as the clinical therapy for lung cancer.