Cucurbitacin B Causes Increased Radiation Sensitivity of Human Breast Cancer Cells via G2M Cell Cycle Arrest

Abstract EN

Purpose.

To explore the effects of cucurbitacin B on the radiation survival of human breast cancer cells and to elucidate the cellular mechanism of radiosensitization if any.

Materials and Methods.

Human breast carcinoma cell lines were treated with cucurbitacin B before irradiation with 0–10 Gy of C137s gamma rays.

The effect of cucurbitacin B on cell-survival following irradiation was evaluated by colony-forming assay.

Cell cycle distributions were investigated using flow cytometry.

Real-time PCR and western blots were performed to investigate the expression of cell cycle checkpoints.

Results.

Cucurbitacin B inhibited breast cancer cell proliferation in a dose-dependent manner.

Only MDA-MB-231 and MCF7:5C cells but not SKBR-3 cells were radiosensitized by cucurbitacin B.

Flow cytometric analysis for DNA content indicated that cucurbitacin B resulted in G2/M arrest in MDA-MB-231 and MCF7:5C but not SKBR-3 cells.

Moreover, Real-time PCR and western blot analysis demonstrated upregulated p21 expression before irradiation, a likely cause of the cell cycle arrest.

Conclusion.

Taken together, these findings suggest that cucurbitacin B causes radiosensitization of some breast cancer cells, and that cucurbitacin B induced G2/M arrest is an important mechanism.

Therefore, combinations of cucurbitacin B with radiotherapy may be appropriate for experimental breast cancer treatment.