Δ2-Troglitazone promotes cytostatic rather than pro-apoptotic effects in breast cancer cells cultured in high serum conditions

We have previously shown that Delta 2-Troglitazone (Delta 2-TGZ) displayed anticancer effects on breast cancer cell lines grown in low serum conditions (1% fetal calf serum (FCS)). The present study was performed in order to characterize the effects of Delta 2-TGZ in high serum containing medium and to determine if starvation could influence the response of breast cancer cells to this compound, keeping in mind the potential interest for breast cancer therapy. We observed that in high serum conditions (10% FCS), a 48 h treatment with Delta 2-TGZ induced a decrease in cell numbers in MDA-MB-231 and MCF-7 breast cancer cell lines. The IC50 values were higher than in low serum conditions. Furthermore, in contrast to our previous results obtained in 1% FCS conditions, we observed that in 10% FCS-containing medium, MCF-7 cells were more sensitive to Delta 2-TGZ than MDA-MB-231 cells. Delta 2-TGZ also induced endoplasmic reticulum (ER) stress mainly in MDA-MB-231 cells. Besides, in high serum conditions, Delta 2-TGZ induced a G(0)/ G(1) cell cycle arrest, an inhibition of BrdU incorporation and a reduced level of cyclin D1. We observed a limited cleavage of PARP and a limited proportion of cells in sub-G1 phase. Thus, in high serum conditions, Delta 2-TGZ displayed cytostatic effects rather than apoptosis as previously reported in 1% FCS-containing medium. Our results are in accordance with studies suggesting that serum starvation could potentiate the action of diverse anti-cancer agents.