Everolimus in combination with letrozole inhibit human breast cancer MCF-7/Aro stem cells via PI3K/mTOR pathway: an experimental study

Abstract

This study evaluated the effects of an mTOR inhibitor everolimus alone or in combination with letrozole on MCF-7/Aro (MCF-7 cells stably transfected with CYP19) in vitro and in vivo. In vitro studies, full-length CYP19 (aromatase) was cloned in a plasmid transfer vector pH ß-Aro and then transfected into MCF-7 stem cells which were ESA(+)CD44(+)CD24(-/low) sorted by flow cytometry. MTT assays were used to quantify the inhibitory effect of the drugs on MCF-7/Aro stem cells (SCs) and non-stem cells (NSCs). Apoptosis and the cell cycle distributions of stem cells were examined by flow cytometry. The tumorigenicity of stem cells after treatment was investigated by soft agar colony formation assays. In vivo studies, the BALB/c mice were injected with MCF-7/Aro SCs, and the different treatments were administered. After necropsy, the expression of KI67, CD31, AKT1, phospho-AKT (Thr308), and mTOR was analyzed by immunohistochemistry. In vitro, compared with MCF-7/Aro NSCs, there were greater resistance to the standard treatment doses of letrozole and everolimus in MCF-7/Aro SCs (17- and 15-fold, respectively). Treatment with everolimus or letrozole resulted in growth inhibition of SCs in a dose-dependent manner. Compared with single-agent therapy, the combination of everolimus with letrozole was more effective in the inhibition of cell growth (P < 0.001) and tumorigenicity (P < 0.01). In addition, an increase in G1 cell cycle arrest and increases in early apoptosis were observed in the combination treatment group compared with either single-agent group. In vivo, the xenograft tumor sizes were significantly decreased in everolimus alone group compared to control group, and everolimus plus letrozole therapy was much more effective compared with either single agent alone (P < 0.01). Compared with everolimus alone, the combination of everolimus and letrozole reduced the expression of KI67, mTOR, and phospho-AKT (Thr308; P < 0.01). Everolimus has effective inhibition on aromatase-overexpressing stem cell in vitro and in vivo. The combination everolimus and letrozole could be more effective than either drug alone.

IFITM1 suppression blocks proliferation and invasion of aromatase inhibitor-resistant breast cancer in vivo by JAK/STAT-mediated induction of p21

“…In breast cancer, high Pim-1 expression is associated with PI3K/Akt mediated drug resistance [38]. The PI3K/Akt pathway has long been associated with endocrine resistance in ER+ breast cancer [3, 10, 16, 45, 79]. Significantly, in this study, overexpression of IFITM1 promoted MCF-7 cell survival in estrogen-deprived conditions.…”

The combination of NVP-BKM120 with trastuzumab or RAD001 synergistically inhibits the growth of breast cancer stem cells in vivo

“…We have previously demonstrated that the combination of RAD001 with docetaxel, latrozole or trastuzumab has enhanced growth-inhibitory effects against breast cancer SCs (33,36,37). As RAD001 has been reported to act synergistically with BKM120 in lung cancer models (16), we asked whether a similar effect would be observed in triple-negative breast cancer (TNBC).…”

Inhibitory effects of aromatase inhibitor on estrogen receptor-alpha positive ovarian cancer in mice

“…AIs have also been reported to increase in vivo apoptosis significantly in combination with an mTOR inhibitor, thereby exhibiting an anti-tumor effect [27]. Amarai et al have emphasized the importance of AIs as inducers of apoptosis, by effects on both mitochondria and caspase-8 [28].…”