Abstract
Breast cancer recurrence after an initial favorable response to treatment is a major concern for patients who receive hormonal therapies. Additional therapies are necessary to extend the time of response, and ideally, these therapies should exhibit minimal toxicity. Our study described herein focuses on a non-toxic pro-apoptotic agent, TMS (2,4,3',5'-tetramethoxystilbene), which belongs to the Resveratrol family of stilbenes. Prior study demonstrated that TMS was more effective than Resveratrol for inducing apoptosis. Additionally, TMS was effective for invoking death of relapsing breast cancer cells. As TMS was effective for reducing tumor burden, we sought to determine the mechanism by which it achieved its effects. Microarray analysis demonstrated that TMS treatment increased tubulin genes as well as stress response and pro-apoptotic genes. Fractionation studies uncovered that TMS treatment causes cleavage of Bax from the p21 form to a truncated p18 form which is associated with the induction of potent apoptosis. Co-localization analysis of immunofluorescent studies showed that Bax moved from the cytosol to the mitochondria. In addition, the pro-apoptotic proteins Noxa and Bim (EL, L, and S) were increased upon TMS treatment. Cell lines reduced for Bax, Bim, and Noxa are compromised for TMS-mediated cell death. Electron microscopy revealed evidence of nuclear condensation, formation of apoptotic bodies and DAPI staining showed evidence of DNA fragmentation. TMS treatment was able to induce both caspase-independent and caspase-dependent death via the intrinsic death pathway.