Reduced camptothecin sensitivity of estrogen receptor-positive human breast cancer cells following exposure to di(2-ethylhexyl)phthalate (DEHP) is associated with DNA methylation changes.

Di(2-ethylhexyl)phthalate (DEHP) has been considered as an estrogen receptor alpha (ER alpha) agonist due to its ability to interact with ER alpha and promote the cell proliferation of ER alpha-positive breast cancer cells. The impact of DEHP on the chemical therapy in breast cancer is little known. Two breast cancer cell lines, MCF-7 (ER alpha-dependent) and MDA-MB-231 (ER alpha-independent) were examined. We found that DEHP impaired the effectiveness of camptothecin (CPT) and alleviated the CPT-induced formation of reactive oxygen species in ER alpha-positive MCF-7 cells, but not in ER alpha-negative MDA-MB-231 cells. DEHP also significantly protected MCF-7 cells against the genotoxicity of CPT. Genome-wide DNA methylation profiling revealed that after 48 hours of exposure to 100 mu M DEHP, MCF-7 cells exhibited a significant change in their DNA methylation pattern, including hypermethylation of 700 genes and hypomethylation of 221 genes. The impaired therapeutic response to CPT in DEHP-exposed MCF-7 cells is probably mediated by epigenetic changes, especially through Wnt/beta-catenin signaling. A zebrafish xenograft model confirmed the disruptive effect of DEHP on CPT-induced anti-growth of MCF-7 cells. In summary, DEHP exposure induces acquired CPT-resistance in breast cancer cells and epigenetic changes associated with Wnt/beta-catenin signaling activation are probably depending on an ER-positive status.