Synergistic action of microwave-induced mild hyperthermia and paclitaxel in inducing apoptosis in the human breast cancer cell line MCF-7

Microwave mild hyperthermia and paclitaxel have been reported to be involved in variety of solid tumors. However, rare related researches have been accomplished via directly killing tumor cells using thermochemotherapy. In order to clarify the potential synergy between microwave-induced hyperthermia at temperatures <41°C and paclitaxel chemotherapy for inhibiting the growth of the human breast cancer cell line MCF-7, an MTT assay was used. The MCF-7 cells cultured in vitro were treated with paclitaxel alone, treated with microwave-induced hyperthermia for 2 h alone (at 40, 40.5 or 41°C), or treated with a combination of paclitaxel and 2 h of hyperthermia (at 40, 40.5 or 41°C). Flow cytometry was used to determine the cell apoptosis rate and it was demonstrated that paclitaxel decreased cell viability in a dose-dependent manner. Alone, hyperthermia for 2 h at 41°C induced apoptosis in MCF-7 cells, to a greater extent compared with hyperthermia for 2 h at 40.0 or 40.5°C (P<0.05). Together, paclitaxel and 2 h of hyperthermia at 40.5°C induced significantly increased apoptosis compared with either treatment alone (P<0.05). Increasing the temperature to 41°C in combination with paclitaxel increased the apoptotic ratio from 12.21±1.02% to 16.36±2.39%. The apoptotic ratio correlated positively with hyperthermia temperature and duration following hyperthermia, as did the synergistic effect obtained by combining hyperthermia and paclitaxel. Notably, the combination of 5 µg/ml paclitaxel and 2 h of hyperthermia at 40°C enhanced MCF-7 cell proliferation. Mild hyperthermia may exert anti-tumor effects by inducing apoptosis, and combining hyperthermia with paclitaxel synergistically induces apoptosis. Paclitaxel dose and hyperthermia temperature require careful optimization, as low-dose paclitaxel combined with hyperthermia at an insufficient temperature may enhance breast cancer proliferation.

[Effects of miR-449a on proliferation and migration of human breast cancer cell line MCF-7]

OBJECTIVE

To study the effects of knockdown of miR-449a on the proliferation and migration of human breast cancer cell line Michigan Cancer Foundation-7 (MCF-7).

METHODS

Using miRNA chip screening of the differential expressions of miRNA in human breast cancer cell MCF-7 and normal breast cells MCF-10A. The inhibitor of miR-449a was synthesized by chemical and detected by real-time PCR after transfection aimed to verify the expression. Cell Counting Kit-8 (CCK-8) assay was used to detect the ability of cell proliferation after transfection with miR-449a inhibitor. Scratch assay was used to detect cell migration of MCF-7, and cell invasion ability was showed by transwell assay; The MCF-7 cell proliferation and migration related proteins, β-catenin and E-cadherin, were detected by Western blot. The potential target gene of miR-449a was predicted by bioinformatics software, and Notch homolog 1 (Notch 1) was proved to be the target gene of miR-449a by luciferase assay.

RESULTS

MCF-7 and MCF-10a cells were collected separately, and miRNA chip results showed that the level of miR-449a in MCF-7 cells was significantly higher than that of MCF-10A. In this study, the cells were divided into mock group, negative control group (NC group) and treatment group, the MCF-7 cells were collected before and after treatment and CCK-8 results showed that knockdown of miR-449a decreased MCF-7 cell proliferation ability significantly. Scratch assay results showed that downregulated miR-449a was related to the decreased metastasis of MCF-7 cells. Transwell results showed that knockdown of miR-449a inhibited the invasion of MCF-7 cells. Western blot showed the expression of β-catenin was decreased and the expression of E-cadherin was increased after knockdown of miR-449a. Luciferase assay showed that miR-449a could significantly decrease the luciferase activity of Notch homolog 1-untranslated region (Notch 1-3'-UTR) plasmid (P<0.01).

CONCLUSIONS

Inhibition of miR-449a in breast cancer cell line MCF-7 can significantly inhibit the proliferation and migration of cancer cells, which may be achieved by decreasing the expression of Notch 1 protein.

S-Adenosylmethionine-mediated apoptosis is potentiated by autophagy inhibition induced by chloroquine in human breast cancer cells

The naturally occurring sulfonium compound S-adenosyl-L-methionine (AdoMet) is an ubiquitous sulfur-nucleoside that represents the main methyl donor in numerous methylation reactions. In recent years, it has been shown that AdoMet possesses antiproliferative properties in various cancer cells, but the molecular mechanisms at the basis of the effect induced by AdoMet have been only in part investigated. In the present study, we found that AdoMet strongly inhibited the proliferation of breast cancer cells MCF-7 by inducing both autophagy and apoptosis. AdoMet consistently enhanced the levels of the autophagy markers beclin-1 and LC3B-II, and caused a significant increase of pro-apoptotic Bax/Bcl-2 ratio paralleled by poly (ADP ribose) polymerase (PARP) and caspase 9, and 6 cleavage. Notably, AdoMet, already at low doses, raised the percentage of cells in G₂ /M phase of cell cycle by down-regulating the expression of cell cycle-regulatory proteins cyclin B and cyclin E with a remarkable increase of p53, p27, and p21. We also evaluated the combination of AdoMet and the autophagy inhibitor chloroquine (CLC) showing that autophagy block is synergistic in inducing both growth inhibition and apoptosis. These effects were paralleled by a strong inhibition of the activity of AKT and of the downstream effector mTOR and by an increased cleavage of caspase-6 and PARP. These data suggest, for the first time, that autophagy can act as an escape mechanism from the apoptotic activity of AdoMet, and that AdoMet could be used in combination with CLC or its analogs in the treatment of breast cancer.