Celastrol was originally identified from traditional Chinese medicine Tripterygium wilfordii decades ago and used for the treatment of cancer and inflammatory diseases. Beside its superior antitumor capabilities, the underlying mechanism of the anti-tumor activity of celastrol was also mentioned, including through modulating proteasome activity, heat shock response, and NF-κB signaling pathways.

Some of these reports also mentioned the ability of celastrol to inhibit tumor metastasis; nevertheless, to date, no study has described its anti-metastatic activities comprehensively, or characterized the underlying mechanisms profoundly. In the current study, for the first time, we systematically evaluated the effects of celastrol represented in metastatic-related events including cell-ECM adhesion, migration, invasion, and development of pulmonary metastases in vivo, using corresponding assays and models. Addtionally, we revealed that celastrol inhibited the integrin-mediated Mice melanoma cell B16F10 and human lung cancer cell 95-D cell-ECM adhesion and spreading partially via p38 MAPK Pathway, which also contributed to its antimetastatic effect.

Celastrol inhibited 95-D and B16F10 cells adhesion to fibronectin in a dose-dependent manner. When 4 μM of celastrol was applied on 95-D cells, the ratio of cell adhesion was declined to 41% from 100%; similarly, celastrol (8 μM) down-regulated the B16F10 cell adhesion to fibronectin from 100% to 23%. On the contrary, the cell adhesion to poly-l-lysine (PLL), an event did not engage with integrin, was not affected upon celastrol treatment. The formation of focal adhesions was also disrupted by celastrol. Western blot and immunofluorescence assay declared that this inhibition was achieved through suppressing β1 integrin ligand affinity, focal adhesion formation, accompanied with the reduced phosphorylation of focal adhesion kinase (FAK). In understanding the underlying mechanisms, we found that celastrol activated p38 mitogen-activated protein kinase (MAPK) by phosphorylation prior to the decrement of phosphorylated FAK, and was independent on the presence of fibronectin. Using SB203580, a specific inhibitor of p38 MAPK, the effects of celastrol on β1 integrin function, cell-ECM adhesion, and phosphorylation of FAK were partially attenuated. Furthmore, focal adhesion-dependent cell migration and invasion were both inhibited by treatment with celastrol. Finally, the anti-metastatic activity of celastrol was examined in vivo using B16F10-GFP injected C57BL/6 mice model, as indicated by decreased pulmonary metastases in celastrol-administrated mice.

Collectivly, these data not only demonstrates that celastrol exerts potent anti-metastasis activity both in vitro and in vivo, but also provides new evidences for the critical roles of p38 MAPK in the regulation of integrin function and cell adhesion.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3598.