2-(4-Hydroxyphenyl)-Benzo[b]thiophen-6-ol, an Estrogen-Like Compound, Induces Apoptosis in T47D/PKCα Breast Cancer Cells.

Abstract

Abstract Background: Tamoxifen (TAM) treatment failure is a major obstacle encountered in the clinical setting. Our lab has previously shown that constitutive overexpression of PKCα imparts a TAM resistant/ hormone independent phenotype in the T47D:A18 breast cancer cell line. Furthermore 17β-estradiol (E2) inhibits tumor growth in vivo as well as inhibits colony formation when cells are grown in 3D Matrigel (Zhang, 2009). Before TAM treatment was introduced, breast cancer patients received high-dose E2 and diesthystilbesterol (DES) treatment. DES treated patients may have a survival advantage over TAM treated patients in the long term (Peethambaram,1999). Others have shown that E2 can have inhibitory effects on MCF-7 cells both in vitro and in vivo (Lewis-Wambi, 2009). Taken together, this suggests an estrogenic compound may be efficacious for TAM-resistant breast cancer. The present study was designed to evaluate the effect of an estrogenic compound, 2-(4-hydroxyphenyl)-benzo[b]thiophen-6-ol (BTC), related to the SERMs raloxifene and arzoxifene, on the T47D:A18/PKCα breast cancer cell line.Methods: To determine if BTC can activate estrogen regulated genes we preformed an ERE-luciferase reporter assay 24 hours after BTC treatment. 3D Matrigel colony formation assay was performed to determine if BTC could inhibit colony formation. Colonies were stained and counted on day 10. To determine if apoptosis was occurring, cells were grown in Matrigel and the TUNEL Assay was performed on Day 6.Results: T47D:A18/PKCα cells showed a 31-fold induction in ERE-luciferase reporter activity when treated with BTC (10-7M) compared to 7-fold induction when treated with E2. In the T47D:A18/Neo parental cell line, BTC induced a 40-fold induction whereas estradiol induced a 96-fold induction. In the Matrigel colony formation assay T47D:A18/PKCα cells formed significantly fewer colonies when treated with BTC. Conversely, in the T47D:A18/Neo parental cell line BTC enhanced colony formation similar to E2 treatment. Our results indicate that BTC was able to induce significant apoptosis on day 6 (P= 0.038) as determined by the TUNEL Assay. Therefore BTC acts similarly to estradiol by inhibiting T47D:A18/PKCα colony formation and inducing apoptosis when cells are grown in Matrigel.Conclusion: These findings suggest that BTC is a potential lead compound in the treatment of PKCα overexpressing breast cancer. Furthermore, BTC was shown to be a potent inducer of the cytoprotective enzyme NQO1 in the Hepa 1c1c7 cell system as well as a strong activator of antioxidant responsive elements (Yu, 2007) indicating it may have the added benefit of chemoprotective effects which are absent in estradiol treatment. Further understanding of the mechanism in which BTC induces apoptosis in the T47D:A18/PKCα cell line may result in a clinical advantage to estradiol treatment including fewer side effects. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5140.