Mechanisms of proliferation inhibition and apoptosis induced by vitamin E compounds and cyclooxygenase inhibitors in human breast cancer cells

RRR-a-tocopheryl succinate (VES) and a-TEA [2, 5, 7, 8 - tetramethyl - 2R-(4R, 8R-12-trimethyltridecyl)chroman-6-yloxyacetic acid], a nonhydrolyzable ether analog of VES, induce growth inhibition in various human breast cancer cells. Cyclooxygenase 2 (COX-2) is up-regulated in human breast tumor tissues and cell lines, and has been shown to be associated with the process of neoplastic transformation and inhibition of apoptosis. Aims of this study were to investigate the individual and combined effects of vitamin E compounds (especially, a-TEA) and COX-2 selective inhibitors (especially, celecoxib) in protection against breast cancer in vitro and in vivo, and to determine their cellular and molecular signaling mechanisms. Using an MDA-MB-435-FL-GFP human breast cancer xenograft model, a-TEA and celecoxib separately or in combination significantly reduced tumor volume in comparison to control. The combination of a-TEA + celecoxib (1,250 mg/kg diet) significantly inhibited tumor volume in comparison to single treatments. Mean numbers of microscopic lung and lymph node metastases in all treatment groups were significantly lower than control. Furthermore, the mean number of microscopic lung metastases in the a-TEA + celecoxib (1,250) group was significantly lower in comparison to separate treatments. Analyses of 5 micron tumor sections showed that all treatments, with the exception of celecoxib (500) alone, to significantly enhance apoptosis and significantly decrease cell proliferation. Similarly, in vitro studies using MDA-MB-435-FL-GFP cells showed a-TEA or celecoxib to induce apoptosis and DNA synthesis arrest. Combination of a-TEA + celecoxib synergistically enhanced apoptosis and additively enhanced DNA synthesis arrest. Celecoxib coordinately mediated aTEA’s anticancer effects by enhancing the c-Jun-N-terminal kinase (JNK) and cJun apoptotic signaling pathway, reducing cell proliferation, reducing cell cycle regulators (cyclin A and E, Proliferation Cell Nuclear Antigen), and suppressing cell migration putatively via alternating integrin-mediated cell adhesion signaling pathways. In conclusion, simultaneous targeting of breast cancer cells in vitro or in vivo with a-TEA and celecoxib separately and together inhibited cancer growth by inducing cell death by apoptosis, G0/G1 cell cycle blockage, inhibiting proliferation, and suppressing cell migration more effectively than targeting with each compound alone. These data show promise for combinations of a-TEA + celecoxib for breast cancer chemotherapy