(-)-Epigallocatechin Gallate （EGCG） enhances the sensitivity of colorectal cancer cells to 5-FU by inhibiting GRP78/NF-κB/miR-155-5p/MDR1 pathway.

Green tea accounts for approximately 20% of the world's total tea yield. (-)-Epigallocatechin gallate (EGCG) is an active catechin in green tea, which suppresses tumor growth and enhances drug sensitivity in various cancers, but the molecular mechanism is still unclear. Chemotherapy drug, such as 5-fluorouracil (5-FU), is a common strategy for clinical treatment of cancer patients, however, the lower response rate caused by prolonged use becomes the main reason of tumor recurrence. Therefore, discovering safe and effective chemo-sensitizer is an urgent task required to be solved. Here, we report that EGCG reinforces the sensitivity of colon cancer cells to 5-FU, and the IC50 values of 5-FU is decreased from 40±4.2 μM to 5±0.36 μM in one human colon carcinoma cell line-HCT-116, and from 150±6.4 μM to 11±0.96 μM in the other human colon carcinoma cell line-DLD1 when these cells are co-treated with 50 μM EGCG. Consistently, compare to 5-FU or EGCG treatment alone, the combination of both significantly promotes cancer cell apoptosis and DNA damage. Further mechanism researches reveal that treatment of colorectal cancer (CRC) with 50 μM EGCG inhibits GRP78 expression, activates NF-κB (2.55±0.05 folds for HCT-116 and 2.27±0.08 folds for DLD1) pathway and enhances miR-155-5p (2.12±0.02 folds for HCT-116 and 2.01±0.01 folds for DLD1) level. The elevated miR-155-5p strongly suppresses target gene MDR1 expression, which blocks the efflux of 5-FU. The accumulation of 5-FU resulted in caspase-3 and PARP activation, Bcl-2 reduction and Bad increase, which ultimately lead to cancer cell apoptosis. Overall, our data shows that EGCG may be act as a novel chemo-sensitizer, and GRP78/NF-κB/miR-155-5p/MDR1 pathway plays vital role in EGCG enhancing the sensitivity of colorectal cancer to 5-FU.