Ethanol promotes oxaliplatin resistance in colorectal cancer by activating the TGF-β/Smad/P21 axis

Resistance to chemotherapy, particularly oxaliplatin, remains a major challenge in treating colorectal cancer (CRC), leading to poor patient outcomes. While lifestyle factors like alcohol consumption are known CRC risk factors, their direct role in modulating chemotherapy efficacy is less understood. This study investigates how ethanol contributes to oxaliplatin resistance and elucidates the underlying molecular mechanisms, specifically focusing on the TGF-β/Smad/P21 signaling axis, a pathway critically involved in cell proliferation, differentiation, and apoptosis, and often implicated in drug resistance.

Researchers analyzed lifetime alcohol consumption data from the PLCO cohort to link drinking with CRC risk. They examined ADH1B and ADH1C gene expression in CRC vs. normal tissues using GEO datasets, correlating them with recurrence and survival in chemotherapy-treated patients. Fecal ethanol levels were measured via GC-MS in healthy non-drinkers and CRC patients. In a mouse model with subcutaneous CRC xenografts, the effects of continuous ethanol exposure (via Lieber-DeCarli liquid diet) and 4-methylpyrazole (4-MP) treatment on tumor growth were evaluated alongside oxaliplatin therapy. In SW480 and HCT116 cells, 100 and 200 mg/dL ethanol effects on oxaliplatin sensitivity, apoptosis, cell cycle, and TGF-β1, p-Smad2, P21, p-Rb protein levels were assessed, with pirfenidone used to validate findings.

High-frequency alcohol drinkers exhibited a significantly increased risk of colorectal cancer. Alcohol metabolism-related genes ADH1B and ADH1C were significantly downregulated in CRC tissues, with low expression correlating with a higher recurrence rate and poorer overall survival in chemotherapy-treated patients. Ethanol was detected in fecal samples from both healthy individuals and CRC patients. In oxaliplatin-treated tumor-bearing mice, alcohol exposure resulted in greater tumor volume compared to controls. In SW480 and HCT116 cells, ethanol significantly increased oxaliplatin IC₅₀, indicating enhanced resistance. Ethanol also reduced cell apoptosis, induced G0/G1 arrest, and decreased S-phase fraction. Mechanistically, ethanol upregulated TGF-β1, p-Smad2, and P21 protein expression while downregulating p-Rb expression, consistent with activation of the TGF-β/Smad/P21 axis. > Pirfenidone, a TGF-β inhibitor, partially reversed these cellular changes and attenuated drug resistance, confirming the pathway's involvement.