Radiosensitizing effects of arsenic trioxide on MCF-7 human breast cancer cells exposed to 89 strontium chloride.

The aim of this study was to investigate the radiosensitizing effects of arsenic trioxide (As2O3) on MCF-7 human breast cancer cells irradiated with 89 strontium chloride (89SrCl2). The 50% inhibitory concentration (IC50) was calculated from results of an MTT assay. The concentration of As2O3 less than 20% IC50 was selected for subsequent experiments. Cells were treated with As2O3 and 89SrCl2. Morphological changes of cells were observed under an inverted microscope. The radiosensitivity enhancing ratio (SER) was computed based on a clone formation assay. Cell cycle distribution and apoptosis were measured by flow cytometry (FCM). Expression of Bcl-2 and Bax at both the mRNA and protein levels was assessed by RT-PCR and western blotting. The IC50 of As2O3 at 24 h was 11.7 µM. Doses of As2O3 (1 and 2 µM) were used in combination treatments and SER values were 1.25 and 1.79, respectively. As2O3 significantly suppressed cell growth, caused G2/M arrest, enhanced cell death and apoptosis induced by 89SrCl2 and decreased expression of the Bcl-2 gene. Since expression of Bax was unchanged following treatment, As2O3 effectively reduced the Bcl-2/Bax ratio. As2O3 (1-2 µM) enhances the cytotoxic effects of 89SrCl2 on the MCF-7 human breast cancer cell line by inducing G2 phase delay and promoting apoptosis through the reduction of the Bcl-2/Bax ratio.