Oral administration of xanthan gum enhances antitumor activity through Toll-like receptor 4

Xanthan gum (XG) is a complex exopolysaccharide produced by the plant-pathogenic bacterium Xanthomonas campestris pv. and is widely used as a thickener or viscosifier. We examined in this study the antitumor effects of XG.

Cytokine production by XG-stimulated murine macrophage cell lines, J772 and RAW264.7, and peritoneal adherent cells from wild type C57BL/6 mice, TLR2 or MyD88-deficient mice, C3H/HeN, and TLR4-mutant C3H/HeJ mice were examined. In order to examine in vivo antitumor effects of XG, mice were inoculated subcutaneously with tumor cells and administered orally with XG once every 5days from 1day before the tumor inoculation. Tumor growth, mouse survival, NK activity, and tumor-specific cytotoxicity were examined.

In vitro culture with XG induced interleukin-12 and tumor necrosis factor-alpha production from macrophages. XG stimulated macrophages in a MyD88-dependent manner and was mainly recognized by Toll-like receptor 4 (TLR4). Oral administration of XG significantly retarded tumor growth and prolonged survival of the mice inoculated subcutaneously with B16K(b) melanoma cells. NK activity as well as tumor-specific cytotoxicity of CD8 T cells was augmented in the XG-treated mice. The in vivo antitumor effects of XG were also dependent on TLR-4, as C3H/HeJ mice, which lack TLR4 signaling, exhibited no effect of XG on the growth of syngeneic bladder tumor, MBT-2.

These results suggest beneficial effects of oral administration of XG on immune-surveillance against neoplasms.