Investigation of the effects of alpha-TEA, MSA and t-RES alone and in combination on human MDA-MB-435 breast cancer cells in vitro and in vivo
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Cancer is the leading cause of death in U.S. women under 85. It is becoming increasingly clear that individual treatments will not cure cancer and that combination approaches may be more effective. Our goal was to further understand the molecular mechanisms of α-TEA's anticancer effects, and to explore its potential in combination with two other agents, MSC/MSA and t-RES. Data support the efficacy of α-TEA as a chemopreventive and chemotherapeutic agent in human breast cancer cells. We first determined that α-TEA, t-RES, and MSC/MSA inhibit cell proliferation, induce differentiation, and synergize when used in combination to induce apoptosis. Treatment enhanced cell death was seen in other cancer cell lines and no cell killing was seen in HMECs. Next, the ability of these agents to reduce tumor burden, induce apoptosis, and prevent proliferation of MDA-MB-435-F-L cells was investigated in vivo. α-TEA and low doses of t-RES reduce tumor burden in athymic nude mice but combinations of the three compounds were not as effective as α-TEA or t-RES alone. The three treatments significantly reduced visible and micrometastatic tumor foci. We showed that the efficacy of t-RES administered at low (10 mg/kg bw) and high (100 mg/kg bw) concentrations was diet-related. Our third aim was to determine if these compounds could effectively inhibit the formation of DMBA and MNU-induced lesions in the MMOC and rat mammary carcinogenesis models. Each compound inhibited cancer lesions in these models but α-TEA and t-RES were better than MSA, and a combination of α-TEA and t-RES was best. Next, we examined apoptotic and survival signaling events that could lead to synergy after α-TEA and t-RES treatment. Pre-treatment sensitized the cancer cells to cell membrane receptor-mediated apoptosis. α-TEA and cotreatment induced cell death was caspases-dependent while that for t-RES was not. Next, decreases in prosurvival survivin and c-FLIP proteins were shown to be significant to treatment induced apoptosis. Based on the results reported here, we propose a signaling model where the synergy between α-TEA and t-RES is due to a combination of apoptosis and caspase-independent cell death (CICD).