Goals are to investigate the mechanisms of action of VES (vitamin E succinate; RRR-alpha-tocopheryl succinate), a potent inducer of apoptosis in human breast cancer cells but not normal mammary epithelial cells. The applicant's studies show that VES can restore both transforming growth factor-beta (TGF-beta) and Fas/CD95 impaired anti-proliferative and death signaling in human breast cancer cells that are resistant to these two important cell homeostatic signaling pathways. In this competing continuation application the applicant proposes to investigate critical signaling events involved in VES initiated apoptosis in human MDA-MB-435 breast cancer cells. Normal human mammary epithelial cells (HMECs) and immortalized, non-tumorigenic human mammary epithelial MCF-10A cells which are insensitive to VES induced apoptosis but responsive to both TGF-beta and Fas induced cell fates will be studied for comparative purposes.
Aim 1 will characterize components of the TGF-beta signal transduction pathway contributing to VES-induced apoptosis.
Aim 2 will characterize Fas signal transduction events involved in VES induced apoptosis.
Aim 3 will investigate the decision phase of apoptosis in VES treated cells with emphasis on Bax and mitochondrial mediated events that produce downstream execution phase mediators. Comparisons between VES and ligand (TGF-beta1 and anti-Fas agonistic antibody) mediated events in MDA-MB-435, HMECs and MCF-10A cells will address the molecular basis of VES's selective ability to induce apoptosis in cancer cells but not in normal or immortalized but non-tumorigenic cells. Expectations are that data generated will increase basic knowledge about TGF-beta and Fas signaling in normal and cancer cells and will provide a better understanding of how VES, a potent pro-apoptotic agent, induces cell death. Part of the significance of these mechanistic studies lies in the potential use of agents like VES for chemotherapy of human breast cancer. This possibility has been strengthened by the recent demonstration that a VES ether analog is a potent, orally active chemotherapeutic agent in a preclinical xenograft model of human breast cancer. Another aspect of the significance of these type studies lies in the belief that better understanding of signaling events will lead to the identification of critical intracellular signal transduction molecules which can be targeted for design of mechanism-based drugs to achieve improved cancer cell killing.
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