Effects of bioactive constituents of Astragalus membranaceus on the proliferation of colon cancer and endothelial cells

Abstract

Uncontrolled cell growth may lead to pathological conditions such as cancer. During the progression of cancer, cancer cells stimulate endothelial cells for angiogenesis to support their growth and migration. Previous studies suggest that Astragalus membranaceus, of which the dried root [Astragali Radix] is used as a traditional Chinese medicine, and its bioactive components, astragalus saponins (AST), astragaloside IV (AS IV) and isoflavonoid calycosin, inhibit cancer growth. The present study aimed to examine whether or not these components inhibit the growth and/or metastasis of colon cancer cells and/or angiogenesis of endothelial cells, and to determine the possible mechanisms involved.

The growth of HCT 116 colon cancer cells and human umbilical vein endothelial cells (HUVEC) after 72 hours incubation with AST (1 to 25 μg/ml), AS IV (0.5 to 100 μM) or calycosin (10 to 200 μM) were detected with thiazolyl blue tetrazolium bromide assay. Wound healing migration and tube formation assays were used to examine the metastatic and angiogenic potential of HCT 116 cells and HUVEC. Moreover, the expressions of apoptotic [B-cell lymphoma 2 and procaspase-3] and metastasis/angiogenesis-related proteins [matrix metalloproteinase (MMP)-2, MMP-9 and vascular endothelial growth factor (VEGF)] were measured with Western immunoblotting. To investigate the potential mechanism(s) through which astragalus components affect the proliferation and/or migration of HCT 116 cells and HUVEC, the activities of mitogen-activated protein (MAP) kinases [extracellular signal-regulated kinase 1 and 2 (ERK1/2), p38 MAP kinase (p38) and c-Jun amino-terminal kinases] were studied by measuring the expressions of their phosphorylated and total proteins with Western immunoblotting.

Calycosin (200 μM) inhibited the growth of HCT 116 cells without affecting that of HUVEC. While it inhibited the migration of both cell types, it stimulated tube formation only in HUVEC. In HCT 116 cells, calycosin downregulated the expressions of procaspase-3, VEGF, MMP-2 and MMP-9 proteins, inhibited ERK1/2 but activated p38. These effects of calycosin were not observed in HUVEC. Neither AST nor AS IV had any significant effects on the parameters studied in HCT 116 cells. AST also showed no effect in HUVEC; AS IV, at 100 μM, appeared to increase the number of tube formation by HUVEC.

In conclusion, the present findings suggest that AST has no significant effect on both cancer and endothelial cells while AS IV may promote angiogenesis without any direct action in colon cancer cells. In colon cancer cells, calycosin induces apoptosis, possibly through activation of caspase-3 and p38, and inhibits metastasis, possibly by downregulating MMP-2 and MMP-9, and inhibiting ERK1/2. However, in endothelial cells, the effect of calycosin is not conclusive as it promotes tube formation but inhibits migration. These findings provide the pharmacological basis for the use of Astragali Radix in the treatment of colon cancer, and the scientific evidence for a therapeutic potential of calycosin in the management of this disorder. Further studies are needed to verify the effect of calycosin on endothelial cells. In order to better mimic the clinical situation, the interaction between cancer and endothelial cells [for example, tumor-induced angiogenesis] needs to be taken into consideration.