Antitumor effects of co-treatment of resveratrol with antitumor drugs in ER- and HER2-positive breast cancer cells are due to induction of apoptosis and modulation of estrogen receptor expression.

Background: Resveratrol, a natural compound, may be an alternative to improving conventional breast cancer therapy. Thus, we assessed the capability of resveratrol at a low dose to enhance the in vitro effect of conventional theray in estrogen receptor (ER) and human epidermal growth factor receptor type 2 (HER2)-positive breast cancer cells.

Methods: Cell viability of breast cancer cells was measured with neutral red uptake assay. Apoptosis, autophagy, cell cycle progression and cell proliferation were detected through hypotonic fluorescent solution assay, formation of acidic vesicular organelles, flow cytometry, and bromodeoxyuridine assay, respectively. Western blotting was performed to study the expression of pro-apoptotic, anti-apoptotic and autophagic proteins, and estrogen receptors.

Results: Resveratrol combined with tamoxifen metabolites or trastuzumab reduced cell viability of ER- and HER2-positive breast cancer cells, respectively. This effect was mainly associated with induction of apoptosis due to a greater formation of hypodiploid nuclei, reduced protein expression of procaspase-7, Bcl-2, Bcl-xL, and PARP; and increased expression of cleaved PARP. Resveratrol decreased the expression of ERα and increased that of ERβ, contributing to the reduced viability on breast cancer cells. Combined treatments induced autophagy, evidenced by increased levels of acidic vesicular organelles and degradation of p62/SQSTM1 protein. Nevertheless, on inhibiting autophagy with 3-methyladenine, cell viability was further reduced and apoptosis was induced, suggesting a pro-survival role of autophagy, impairing apoptosis.

Conclusions: Resveratrol increasead the in vitro cytotoxic effect of conventional therapy in breast cancer cells. However, it was necessary to block resveratrol-induced autophagy to improve the therapeutic response.