Abstract #5122: \#945;-TEA sensitizes human breast cancer cells to Doxorubicin-induced apoptosis via death receptor dependent and independent mechanisms
Richa Tiwary, Weiping Yu, Bob G. Sanders, Kimberly A. Kline · Cancer Research · 2009
AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO The apoptotic-inducing properties of the combination of RRR-\#945;-tocopherol derivative \#945;-TEA (RRR-\#945;-tocopherol ether-linked acetic acid analog) and doxorubicin were investigated in human MCF-7 breast cancer cells. Sub-apoptotic levels of \#945;-TEA + doxorubicin, in comparison to single agents (i) significantly enhanced apoptosis as measured by Annexin V-FITC/PI staining, cleavage of PARP, and activation of caspases 8 and 9, (ii) activated both pJNK1/2 and pc-Jun, and (iii) enhanced Fas and Fas Ligand protein levels. siRNA knockdown of JNK and c-Jun as well as Fas and Fas Ligand reduced \#945;-TEA + doxorubicin-induced apoptosis. Doxorubicin significantly increased levels of DR5 protein expression. Combinations of \#945;-TEA + doxorubicin did not further increase protein levels of DR5 protein in comparison to doxorubicin alone. Knockdown of DR5 using siRNA blocked \#945;-TEA + doxorubicin-induced apoptosis. Treatment of the breast cancer cells with sub-apoptotic levels of doxorubicin enhanced protein levels of survival factors pAkt, pERK, pmTOR and their downstream mediators pBad (Ser 136 and Ser 112), and cFLIP; whereas, \#945;-TEA in combination with doxorubicin reduced the expression of these survival factors. Inhibitors of PI-3K/Akt, MEK/ERK and mTOR as well as siRNA to cFLIP enhanced the ability of sub-apoptotic levels of doxorubicin to induce apoptosis, suggesting that \#945;-TEA's ability to prevent doxorubicin-induced pro-survival factors (i.e. pAkt, pERK and pmTOR, cFLIP) plays a role in enhanced sensitivity to the combinations of \#945;-TEA + doxorubicin. In summary, data show enhanced apoptosis in cells treated with \#945;-TEA + doxorubicin is due to activation of JNK, Fas and DR5 apoptotic signaling pathways and down-regulation of doxorubicin-induced survival factors Akt, ERK, mTOR, and c-FLIP. T32 ES007247, Training in Molecular Toxicology/Environmental Disease, Public Health Services Grant CA59739 and The Clayton Foundation For Research. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 5122.