Degradation of the extracellular matrix (ECM) plays a critical role in the formation of
tumors and
metastasis and has been found to correlate with the aggressiveness of
tumor growth and invasiveness of
cancer.
Ascorbic acid, which is known to be essential for the structural integrity of the intercellular matrix, is not produced by humans and must be obtained from the diet.
Cancer patients have been shown to have very low reserves of
ascorbic acid. Our main objective was to determine the effect of ascorbate supplementation on
metastasis,
tumor growth and
tumor immunohistochemistry in mice unable to synthesize
ascorbic acid [
gulonolactone oxidase (gulo) knockout (KO)] when challenged with B16FO
melanoma or 4T1
breast cancer cells. Gulo KO female mice 36-38 weeks of age were deprived of or maintained on ascorbate in food and water for 4 weeks prior to and 2 weeks post intraperitoneal (IP) injection of 5x105 B16FO murine
melanoma cells or to injection of 5x105 4T1
breast cancer cells into the mammary pad of mice. Ascorbate-supplemented gulo KO mice injected with B16FO
melanoma cells demonstrated significant reduction (by 71%, p=0.005) in
tumor metastasis compared to gulo KO mice on the control diet. The mean
tumor weight in ascorbate supplemented mice injected with 4T1 cells was reduced by 28% compared to
tumor weight in scorbutic mice. Scorbutic
tumors demonstrated large dark cores, associated with increased necrotic areas and breaches to the
tumor surface, apoptosis and
matrix metalloproteinase-9 (MMP-9), and weak, disorganized or missing collagen I
tumor capsule. In contrast, the ascorbate-supplemented group
tumors had smaller fainter colored cores and confined areas of
necrosis/apoptosis with no breaches from the core to the outside of the
tumor and a robust collagen I
tumor capsule. In both studies, ascorbate supplementation of gulo KO mice resulted in profoundly decreased serum inflammatory
cytokine interleukin (IL)-6 (99% decrease, p=0.01 in the B16F0 study and 85% decrease, p=0.08 in the 4T1 study) compared to the levels in gulo KO mice deprived of ascorbate. In the B16FO study, ascorbate supplementation of gulo KO mice resulted in profoundly decreased serum
VEGF (98% decrease, p=0.019 than in the scorbutic gulo KO mice). As expected, mean serum ascorbate level in ascorbate-restricted mice was 2% (p<0.001) of the mean ascorbate levels in supplemented mice. In conclusion, ascorbate supplementation hinders
metastasis,
tumor growth and inflammatory
cytokine secretion as well as enhanced encapsulation of
tumors elicited by
melanoma and
breast cancer cell challenge in gulo KO mice.