Despite significant improvement in both detection and treatment, breast cancer remains the second leading cause of cancer deaths for women in the United States. Tamoxifen is the most commonly used treatment for estrogen receptor positive (ER+) breast carcinoma, yet up to 50% of patients with metastatic disease present with de novo resistance to tamoxifen, and almost all patients will eventually become resistant to tamoxifen treatment. The mechanism(s) for this resistance appear to be largely dependent upon activation of growth factor signaling pathways. Aberrant activation of the PI3K/Akt and MAPK pathways and their cross talk with both the genomic and nongenomic activity of the ER is implicated in tamoxifen resistance. Breast cancer cell lines with constitutively activated Akt are characterized by high levels of the pro-survival transcription factor Nuclear Factor kappa B (NF-kB), estrogen-independent growth, and resistance to tamoxifen treatment. Studies have shown that curcumin, a polyphenol derived from the rhizome of the perennial herb Curcuma longa, is able to inhibit the activation of NF-kB, which is implicated as one mechanism by which breast cancer cells become resistant to tamoxifen treatment. Previous studies in our laboratory have demonstrated that inhibition of NF-kB is sufficient to sensitize MCF-7 cells that have constitutively activated Akt and elevated NF-kB levels to tamoxifen treatment. However, clinical NF-kB inhibitors such as Velcade generally involve suppression of the proteosome, leading to severe toxicities. Therefore, identification of alternative approaches for suppressing NF-kB activity in the absence of toxicity could prove beneficial for enhancing response to tamoxifen. In the present study, we assessed the efficacy of curcumin at inhibiting breast cancer cell proliferation and survival both as a single agent and in combination with tamoxifen in MCF-7 cells that expressed both “normal” levels of Akt (Control) activity as well as those that expressed the constitutively active form of Akt (myrAkt). As has been previously reported, curcumin treatment inhibited survival and proliferation in the Control MCF-7 cells, but importantly curcumin was also able to suppress survival and proliferation in the myrAKT MCF-7 cells. Curcumin and tamoxifen co-treatment was found to synergistically inhibit survival in myrAKT MCF-7 cells. These findings demonstrate that curcumin can sensitize myrAKT MCF-7 cells to tamoxifen treatment. This preliminary data suggests that the combination of natural NF-kB inhibitors such as curcumin with tamoxifen may be a viable strategy to either prevent tamoxifen resistant disease or to re-sensitize refractory disease to tamoxifen treatment.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3098.