Bioprocessed Black Rice Bran Potentiates the Growth Inhibitory Activity of an Immune Checkpoint Inhibitor against Murine Colon Carcinoma

Abstract

This study determined the effect of orally fed polysaccharide-rich bioprocessed (fermented) black rice bran produced by culturing with shiitake ( Lentinus edodes ) mushroom mycelium on CT-26 colon cancer cells in vivo in an intracutaneously transplanted mouse tumor alone and in combination with intraperitoneally administered anti-PD-1 immune checkpoint inhibitor. Analysis of the isolated tumor weights at the end of the study shows that the average tumor size in control mice is 3.78 grams, and the average tumor size in mice treated with anti-PD-1 antibody is 2.16 grams. The average tumor size in mice treated with BRB-F alone is 2.25 grams, and the average tumor size in mice treated with anti-PD-1 antibody BRB-F combination is 1.38 grams. Thus, BRB-F or anti-PD-1 antibody alone each reduce tumor size by 40.5% or 42.9%, whereas the combination of BRB-F and anti-PD-1 antibody reduces tumor size by 63.5%, with their cooperative effect being statistically significant. The observed anti-tumor effects were accompanied by a series of biomarkers associated with cancer formation and inhibition. These results indicate that the reported potentiation of cancer therapy using drug-based medical chemotherapies with added checkpoint inhibitors in human patients are mechanistically similar with the functional food evaluated in the present study. These beneficial effects in mice challenge clinicians to investigate if the black rice bran food product can also protect against human cancer.