METTL3 antagonizes 5­FU chemotherapy and confers drug resistance in colorectal carcinoma.

Colorectal cancer (CRC) is one of top five leading causes of cancer­associated mortalities worldwide. 5­Fluorouracil (5­FU) is the first­line chemotherapeutic drug in the treatment of CRC; however, its antineoplastic efficiency is limited due to acquired drug resistance. The regulatory mechanism underlying 5­FU chemotherapeutic response and drug resistance in CRC remains largely unknown. The present study identified that silencing of methyltransferase­like 3 (METTL3) suppressed the proliferation and migration of CRC HCT­8 cells. Using cell survival assays, flow cytometric and colony formation analyses, it was revealed that inhibition of METTL3 sensitized HCT­8 cells to 5­FU by enhancing DNA damage and inducing apoptosis in HCT­8 cells under 5­FU treatment. Furthermore, the expression of METTL3 was upregulated in 5­FU­resistant CRC cells (HCT­8R), which contributed to drug resistance through regulation of RAD51 associated Protein 1 (RAD51AP1) expression. Western blotting, immunofluorescence staining and drug sensitivity assays demonstrated that knockdown of METTL3 augmented 5­FU­induced DNA damage and overcame 5­FU­resistance in HCT­8R cells, which could be mimicked by inhibition of RAD51AP1. The present study revealed that the METTL3/RAD51AP1 axis plays an important role in the acquisition of 5­FU resistance in CRC, and targeting METTL3/RAD51AP1 may be a promising adjuvant therapeutic strategy for patients with CRC, particularly for those with 5­FU­resistant CRC.

Epigallocatechin gallate inhibits dimethylhydrazine-induced colorectal cancer in rats.

BACKGROUND: Epigallocatechin gallate (EGCG) is a polyhydroxy phenolic compound extracted from tea and its antitumor effect has received widespread attention. We explored the inhibitory effect of EGCG on dimethylhydrazine (DMH)-induced colorectal cancer (CRC) using a rat model, predicted the interaction between EGCG and CRC target genes using a database, and explained the EGCG associated target pathways and mechanisms in CRC. AIM: To understand the inhibitory mechanisms of EGCG on CRC cell proliferation and identify its pharmacological targets by network pharmacology analysis. METHODS: DMH (40 mg/kg, s.c., twice weekly for eight weeks) was used to induce CRC in rats. After model establishment, the rats were administered with EGCG (50, 100, or 200 mg/kg, p.o., once daily for eight weeks) and killed 12 and 20 wk after the start of the experiment. Formation of aberrant crypt foci and tumor was studied by histological analysis. Using network pharmacology analysis, candidate and collective targets of EGCG and CRC were identified, and Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes analyses were used to predict the pathways altered by EGCG. RESULTS: At week 12, high-dose EGCG treatment significantly reduced the tumor formation rate, total number of tumors, cancerous and non-cancerous tumors, tumor volume, ascites formation, and aberrant crypt foci count. At week 20, all three doses of EGCG were effective. Seventy-eight collective targets of EGCG and CRC were identified, of which 28 genes were dysregulated in CRC. Kyoto Encyclopedia of Genes and Genomes and GO analyses showed that the dysregulated genes were enriched in hsa05210 (CRC), hsa04115 (p53 signaling pathway), and hsa04151 (PI3K-Akt signaling pathway), GO:0043124 (negative regulation of I-kappaB kinase/NF-kappaB signaling pathway), GO:0043409 (negative regulation of mitogen-activated protein kinase cascade), and GO:2001244 (positive regulation of intrinsic apoptotic signaling pathway) respectively. CONCLUSION: EGCG inhibits the formation of DMH-induced CRC by regulating key pathways involved in tumorigenesis.