Phthalate exposure promotes chemotherapeutic drug resistance in colon cancer cells

Phthalates are widely used as plasticizers. Humans can be exposed to phthalates through ingestion, inhalation, or treatments that release di(2-ethylhexyl) phthalate (DEHP) and its metabolite, mono(2-ehylhexyl) phthalate (MEHP), into the body from polyvinyl chloride-based medical devices. Phthalate exposure may induce reproductive toxicity, liver damage, and carcinogenesis in humans. This study found that colon cancer cells exposed to DEHP or MEHP exhibited increased cell viability and increased levels of P-glycoprotein, CD133, Bcl-2, Akt, ERK, GSK3β, and β-catenin when treated with oxaliplatin or irinotecan, as compared to control. The P-glycoprotein inhibitor, tariquidar, which blocks drug efflux, reduced the viability of DEHP- or MEHP-treated, anti-cancer drug-challenged cells. DEHP or MEHP treatment also induced colon cancer cell migration and epithelial-mesenchymal transformation. Elevated stemnessrelated protein levels (β-catenin, Oct4, Sox2, and Nanog) and increased cell sphere sizes indicated that DEHP- or MEHP-treated cells were capable of self-renewal. We also found that serum DEHP concentrations were positively correlated with cancer recurrence. These results suggest phthalate exposure enhances colon cancer cell metastasis and chemotherapeutic drug resistance by increasing cancer cell stemness, and that P-glycoprotein inhibitors might improve outcomes for advanced or drugresistant colon cancer patients.