Notch and breast cancer: effects of a γ-secretase inhibitor on cell cycle.

Abstract

Abstract Abstract #3016 Background:
 Notch ligands and receptors are type I membrane proteins that regulate cell fate during cell-cell contact. Notch activation is oncogenic in many instances. Within the mammary gland, aberrant activation of the Notch pathway leads to adenocarcinoma. In human, high level of Notch1 expression in breast tumor is associated with reduced patient survival while better survival was observed where tumors expressed higher level of Notch2. In a recent report, it was observed that accumulation of Notch1 NICD increase Notch signaling in a wide variety of human breast carcinomas. Breast cancer is one of the most common malignancies in women with a cumulative lifetime risk of developing the disease as high as one in every eight women. Current research focused on treatment that disrupt the molecular mechanisms leading to breast carcinogenesis, which may be a more effective in treating breast cancer. GSI (g-secretase inhibitor) which blocks the activation of Notch is presently undergoing Phase I clinical trial conducted by Merck in breast cancer patients. We have investigated the different effects of GSI treatments on ER- and ER+ breast cancer cells and the results are discussed.
 Material and Methods:
 The human breast cancer cells lines MCF-7 and T47D (ER+), MDA-MB-435S and MDA-MB-231 (ER-) were treated with GSI, a Notch inhibitor, Tamoxifen, a selective estrogen receptor modulator (SERM) and combination of both drugs. Cell proliferation was determined by BrDU ELISA assay (Roche). Apoptosis following treatment was measured with TUNEL Assay Kit (Roche). The Cellular DNA Flow Cytometric Analysis Kit was used to determine the treatment on cell cycle. Trizol Reagent was use to extracted the RNA and Real Time PCR and RT Profiler PCR Array System were perform to detected the expression of genes.
 Results and Discussion:
 GSI alone is very effective on inhibiting the proliferation and promoting apoptosis of ER- cells but not ER+ cells. When combined with Tamoxifen, however, a significant killing effect was seen in ER+ cells. Cell cycle analysis revealed S phase block. The fold repression of Hes1 and Bcl2 was confirm after treatment with GSI in both cell lines. Together, these data strengthen the rationale for applying Notch inhibitors therapeutically. It also indicates the differences of the GSI treatment on ER+ vs ER- cells. In ER+ cells, both ER and Notch signaling pathways need to be targeted to effectively inhibit tumor cell growth and induce apoptosis. In ER- cells, targeting Notch signaling pathway is sufficient in achieving the same effects. The information will be critical when translating such research into clinic on deciding treatments for the breast cancer patients. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3016.