Andrographolide enhances the anti-metastatic effect of radiation in Ras-transformed cells via suppression of ERK-mediated MMP-2 activity.

Background: Activation of Ras oncogene in human tumors is associated with radiation-associated metastatic potential. Although ionizing radiation is one important method of cancer treatments, it has been shown to enhance matrix metalloproteinases (MMPs) activity and facilitates a more aggressive cancer phenotype. Our previous studies showed that andrographolide with lower dose rates of radiation could inhibit RAS-transformed cancer metastasis in vivo; however, the molecular mechanisms are not yet clear. In this study, we aimed to explore the anti-metastatic effect of andrographolide combined with radiation on Ras-transformed cells.

Methods: RAS-transformed cells were treated with andrographolide in the presence or absence of irradiation (2-4 Gy) or angiotensin II to examine cell invasion. In vivo tumorigenesis assays were also performed. The MMP-2 activity was detected by using Gelatin zymography. Signal transduction of NF-κB subunit, p65 and phosphor-ERK 1/2, were examined by using Western blotting analysis.

Results: Treatment with andrographolide inhibited migration of Ras-transformed cells. Andrographolide treatment with radiation significantly inhibited cancer metastasis in vivo. We found that andrographolide exhibited anti-migration and anti-invasive ability against cancer metastasis via inhibition of MMP2 activity rather than affected MMP-9 and EMT. In addition, combined andrographolide with radiation appeared to be more effective in reducing MMP-2 expression, and this effect was accompanied by suppression of ERK activation that inhibits cancer cell migration and invasion.

Conclusions: These findings suggest that andrographolide enhances the anti-metastatic effect of radiation in Ras-transformed cells via suppression of ERK-mediated MMP-2 activity.