246: Effects of the potential energy restriction mimetic agent delta2-troglitazone in breast cancer cells

Abstract

Background: The development of de novo and acquired resistance to anticancer therapies and the absence of targeted therapy for some types of tumors are strong motivations for discovering new therapeutic agents. Thiazolidinediones (TZD) are studied in this context although they were initially designed for the treatment of type II diabetes due to their PPAR gamma agonist activity. They display anticancer effects that are independent of PPAR gamma, but that are not well understood. In prostate cancer cells, TZD derivatives were shown to act as energy restriction mimetic agents. Our team studies the effects of delta2 troglitazone (delta2-TGZ), a TZD devoid of PPAR gamma agonist activity, on breast cancer cell lines. The aim of this work was to better characterize delta2-TGZ-induced cell death and to understand the underlying molecular events.Material and Methods: Delta2-TGZ was obtained by chemical synthesis. We used hormone-dependent (MCF-7) and hormone-independent (MDA-MB-231) breast cancer cell lines. Gene expression was studied by RT-PCR, western blotting and immunocytochemistry. RNA interference was used for gene silencing.Results and discussion: Delta2-TGZ-induced endoplasmic reticulum (ER) stress in MCF-7 cells as shown by phosphorylation of Pancreatic endoplasmic reticulum kinase-like Endoplasmic Reticulum Kinase (PERK) detected after 1.5 hours, splicing of XBP1 (X-box binding protein 1) after 3 hours, accumulation of the chaperone BiP (Binding immunogloblulin protein) and the pro-apoptotic protein CHOP (CCAAT-enhancer-binding protein homologous protein) after 6 hours. CHOP was located in the nucleus of treated cells. Similar events were observed in MDA-MB-231 cells exposed to delta2-TGZ. In both cell lines cleavage of PARP-1 and caspase-7 revealed apoptosis. In MCF-7 cells, knock-down of CHOP or inhibition of c-Jun N-terminal kinase (JNK) did not impair apoptosis. Preliminary results also indicated that AMP-dependent kinase (AMPK) is activated early in MCF-7 cells after delta2-TGZ treatment. Conclusions: This work contributes to a better understanding of the PPARgamma-independent effects of TZD in breast cancer cells. ER stress is an early response to delta2-TGZ, occurring prior to, but not causative of apoptosis. We have now to confirm whether AMPK phosphorylation is a marker of the energy restriction mimetic action of delta2-TGZ and if this is responsible for ER stress and apoptosis.