Hormonoradiothérapie adjuvante concomitante des cancers du sein : état de l'art

Melatonin enhancement of the radiosensitivity of human breast cancer cells is associated with the modulation of proteins involved in estrogen biosynthesis

Enhancing the radiosensitivity of cancer cells is one of the most important tasks in clinical radiobiology. Endocrine therapy and radiotherapy are two cancer treatment modalities which are often given together in patients with locally-advanced breast cancer and positive hormone-receptor status. Oncostatic actions of melatonin are relevant on estrogen-dependent mammary tumors. In the present study, we wanted to evaluate the effects of the combination of ionizing radiation and melatonin on proteins involved in estrogen biosynthesis in breast cancer cells. We demonstrated a role of melatonin in mediating the sensitization of human breast cancer cells to the ionizing radiation by decreasing around 50% the activity and expression of proteins involved in the synthesis of estrogens in these cells. Thus, melatonin pretreatment before radiation reduces the amount of active estrogens at cancer cell level. Melatonin 1 nM induced a 2-fold change in p53 expression as compared to radiation alone. The regulatory action of melatonin on p53 could be a link between melatonin and its modulatory action on the sensitivity of breast cancer cells to ionizing radiation. These findings may have implications for designing clinical trials using melatonin and radiotherapy.

Melatonin sensitizes human breast cancer cells to ionizing radiation by downregulating proteins involved in double-strand DNA break repair

Radiation and adjuvant endocrine therapy are nowadays considered a standard treatment option after surgery in breast cancer. Melatonin exerts oncostatic actions on human breast cancer cells. In the current study, we investigated the effects of a combination of radiotherapy and melatonin on human breast cancer cells. Melatonin (1 mm, 10 μm and 1 nm) significantly inhibited the proliferation of MCF-7 cells. Radiation alone inhibited the MCF-7 cell proliferation in a dose-dependent manner. Pretreatment of breast cancer cells with melatonin 1 wk before radiation led to a significantly greater decrease of MCF-7 cell proliferation compared with radiation alone. Melatonin pretreatment before radiation also decreased G2 -M phase arrest compared with irradiation alone, with a higher percentage of cells in the G0 -G1 phase and a lower percentage of cells in S phase. Radiation alone diminished RAD51 and DNA-protein kinase (PKcs) mRNA expression, two main proteins involved in double-strand DNA break repair. Treatment with melatonin for 7 days before radiation led to a significantly greater decrease in RAD51 and DNA-PKcs mRNA expression compared with radiation alone. Our findings suggest that melatonin pretreatment before radiation sensitizes breast cancer cells to the ionizing effects of radiation by decreasing cell proliferation, inducing cell cycle arrest and downregulating proteins involved in double-strand DNA break repair. These findings may have implications for designing clinical trials using melatonin and radiotherapy.

Altered radiation responses of breast cancer cells resistant to hormonal therapy

Endocrine therapy agents (the selective estrogen receptor (ER) modulators such as tamoxifen or the selective ER down-regulators such as ICI 182,780) are key treatment regimens for hormone receptor-positive breast cancers. While these drugs are very effective in controlling ER-positive breast cancer, many tumors that initially respond well to treatment often acquire drug resistance, which is a major clinical problem. In clinical practice, hormonal therapy agents are commonly used in combination or sequence with radiation therapy. Tamoxifen treatment and radiotherapy improve both local tumor control and patient survival. However, tamoxifen treatment may render cancer cells less responsive to radiation therapy. Only a handful of data exist on the effects of radiation on cells resistant to hormonal therapy agents. These scarce data show that cells that were resistant to tamoxifen were also resistant to radiation. Yet, the existence and mechanisms of cross-resistance to endocrine therapy and radiation therapy need to be established. Here, we for the first time examined and compared radiation responses of MCF-7 breast adenocarcinoma cells (MCF-7/S0.5) and two antiestrogen resistant cell lines derived from MCF-7/S0.5: the tamoxifen resistant MCF-7/TAMR-1 and ICI 182,780 resistant MCF-7/182R-6 cell lines. Specifically, we analyzed the radiation-induced changes in the expression of genes involved in DNA damage, apoptosis, and cell cycle regulation. We found that the tamoxifen-resistant cell line in contrast to the parental and ICI 182,780-resistant cell lines displayed a significantly less radiation-induced decrease in the expression of genes involved in DNA repair. Furthermore, we show that MCF-7/TAMR-1 and MCF-7/182R-6 cells were less susceptible to radiation-induced apoptosis as compared to the parental line. These data indicate that tamoxifen-resistant breast cancer cells have a reduced sensitivity to radiation treatment. The current study may therefore serve as a roadmap to the future analysis of the mechanisms of cross-resistance between hormonal therapy and radiation.

Optimal combination of radiotherapy and endocrine drugs in breast cancer treatment

PURPOSE

Breast cancer is the most common cancer in women. Radiotherapy is considered a standard treatment option after surgery and adjuvant endocrine therapy is also universally used. Tamoxifen and letrozole are the current first-line endocrine therapy drugs. However, information has been scarce about how best to sequence these therapies to maximize their effectiveness and keep toxic effects to a minimum. In this study, we observed the effect of different sequence combination of radiotherapy and endocrine drugs, tamoxifen or letrozole, to get the best treatment sequence.

MATERIALS AND METHODS

The combination effect of radiotherapy and tamoxifen was observed on breast tumour cell line MCF-7, radiotherapy and letrozole on aromatase-expressing breast tumour cell line MCF-7CA. Irradiation was performed with 6Gy, except for doses ranging from 0 to 8Gy for clone formation assay. Tamoxifen or letrozole was added before or after irradiation, respectively. Radiosensitivity was evaluated by clonogenic assay, cell viability by 3-(4,-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay. To explore the potential mechanism, cell apoptosis was determined by DNA-binding dye 4',6-diamidino-2-phenylindole dihydrochloride (DAPI) assay, the change of Bcl-2 and Bax expression was by western blot.

RESULTS

Although no significant statistical difference was observed between different sequence, tamoxifen and letrozole both increased radiosensitivity. Furthermore, the above inhibitory effect was related with apoptosis signaling pathway, especially Bcl-2 and Bax.

CONCLUSION

Taken together, these results suggested that endocrine drugs, such as tamoxifen and letrozole, have potential application with radiotherapy.