Radiosensitization of human triple-negative breast cancer MDA-MB-231 cells by antihelminthic niclosamide

Objective: To investigate the radiosensitization effect of antihelminthic niclosamide on human triple-negative breast cancer MDA-MB-231 cells and the potential mechanism related to Wnt/β-catenin signaling pathway. Methods: Four methyl thiazolyl tetrazolium(MTT) assay was used to measure the effect of niclosamide on cell viability at different concentrations and 50% inhibitory concentration(IC₅₀) value was calculated. MDA-MB-231 cells were divided into 4 groups: untreated control, niclosamide treatment alone group, radiation alone group and niclosamide plus radiation treatment group. The cells with or without 1.0 and 1.5 μmol/L niclosamide pre-treatment were irradiated with ¹³⁷Cs γ-rays at doses of 0, 2, 4 and 6 Gy. Cell survival was assayed with the colony formation method, radiation-induced γH2AX foci was analyzed with immunofluorescence, cell cycle progression was assayed with flow cytometry, and the changes of phospho-and non-phospho-β-catenin and Cyclin D1 protein expressions were measured with Western blot. Results: Niclosamde obviously inhibited the viability of MDA-MB-231 cells in a dose-dependent manner with a IC₅₀ value of 13.63 μmol/L. Pretreatment of cells with 1.0 and 1.5 μmol/L niclosamide evidently enhanced the radiosensitivity of MDA-MB-231 cells to γ-rays, and the values of SER were 1.37 and 1.62, respectively. Niclosamide pretreatment significantly increased radiation-induced γH2AX foci formation(t = 3.91, P < 0.05), diminished the radiation-induced G₂/M arrest(t = 8.05, P < 0.01), and inhibited radiation-induced expressions of phospho-β-catenin (S675),non-phospho-β-catenin and Cyclin D1 proteins in MDA-MB-231 cells. Conclusions: Niclosamide significantly can enhance the sensitivity of MDA-MB-231 cells to γ-ray irradiation through inhibiting Wnt/β-catenin signaling pathway, which results in the inhibition of DNA DSBs repair and the reduction of radiation-induced G₂/M arrest. Wnt/β-catenin signaling pathway may serve as an ideal molecular target for radiosensitization of triple-negative breast cancer. (authors)