Discussion Of Human Breast Tissue MTOR-Notch Verification And Targeted Treatment Pathway

Breast cancer is one of the most common malignant tumors among women. Although the morbidity rate of breast cancer in China is relatively low comparing to the one in western countries, it is growing at a rate1-2%higher than the world average. Although genetic factors, hormonal influence and life style play important roles in the development of breast cancer, the underlying mechanism of the tumorigenesis is still largely unknown.The receptor tyrosine kinase (RTK)-phosphatidylinositol-3-kinase (PI3K)-AKT-mammalian target of rapamycin (mTOR) pathway regulates multiple cellular functions including proliferation, differentiation, and cell death, whereas Notch pathway plays an important role in controlling cell differentiation. Previous study in our laboratory indicates that Notch receptor is up-regulated in mTOR hyperactivated MEFs through mTOR. A large body of evidence suggests that both mTOR and Notch pathways are frequently aberrant regulated in breast cancer, however, the interaction between these two pathways exists in vivo has yet to be tested.Therefore Western Blot and immunohistochemistry (IHC) staining were used to examine the correlation between mTOR activation and Notch expression in breast cancer tissues. Our data confirm that mTOR and Notch have significant relevance in all breast cancer samples examined (30samples using Western Blot and57samples using IHC), especially in low grade differentiated group and early stage group. Furthermore, higher significance was observed in the sample groups with indicators of poor prognosis, such as higher lymph node metastasis, negative ER expression, positive HER2expression, higher Ki67index, and p53mutation. These. results are in agreement with the hypothesis that there is an mTOR-Notch cascade existing in breast cancer. We also conclude that concurrent activation of mTOR and Notch is more prevalent in tumors with higher malignancy. ERK/MAPK pathway is another classic receptor tyrosine kinase pathway which plays essential role in tumorigenisis, and has close relationship with PI3K-AKT-mTOR pathway. It was newly identified that the efficacy of mTOR inhibition could be limited by mTOR-mediated negative feed back regulation on ERK/MAPK and RTK-PI3K-AKT pathway. To develop better combined target therapy, PTEN knockout MEF cell lines were used as cellular model for malignant tumor. BEZ235, the dual inhibitor of PI3K and mTOR, and U0126, the inhibitor of MEK1/2were combined to threat the cells. The inhibitory effects to cell proliferation were monitored by MTT. Our results show that both BEZ235and U0126suppress PTEN knockout cell proliferation, and their IC50values are6.257nM and22.85μM, respectively. Surprisingly, these two drugs had antagonistic rather than synergistic effect on cell proliferation, suggesting BEZ235and U0126are not suitable for a combined target therapy regimen.This study provides further evidence of oncogenically activated mTOR up-regulating Notch signaling as the possible mechanism for the inhibition of differentiation and the subsequent tumorigenisis. The combinational usage of pathway inhibitors investigated the possible cancer treatment with improved specificity and effectiveness, and provided information for clinical therapy.