Radiosensitization of clioquinol and zinc in human cancer cell lines

BACKGROUND: We previously reported that clioquinol acts as a zinc ionophore and inhibits the NF-κB signalling pathway. Other research has demonstrated that zinc deficiency plays a vital role in the occurrence and development of some solid tumours, and intracellular zinc supplementation may reverse this process and enhance the tumour sensitivity to anticancer treatment. Thus, we investigated the radiosensitization effects of clioquinol combined with zinc on HeLa and MCF-7 cells in vitro. METHODS: The dose effect of growth inhibition of clioquinol combined with zinc on cell viability was determined by a cell counting kit 8 (CCK-8) assay. The radiosensitization effect of clioquinol combined with zinc and/or MG132 in HeLa and MCF-7 cells was detected by the clonogenic assay. The cell cycle distribution and apoptosis of clioquinol combined with zinc on HeLa cells were analyzed by flow cytometry. A luciferase reporter construct was used to study the effect of clioquinol combined with zinc on NF-κB activity in HeLa cells. DNA double-strand breaks were detected by immunofluorescence. The mRNA and protein levels of ATM were analyzed by quantitative real-time PCR and Western blotting, respectively. RESULTS: Our research showed that clioquinol combined with zinc markedly increased the radiosensitivity of HeLa and MCF-7 cells in low toxic concentrations and resulted in a post-irradiation decrease in G2 phase arrest and an increase in apoptosis. Clioquinol combined with zinc also inhibited NF-κB activation, decreased ATM expression and increased DNA double-strand breaks (DSBs) induced by ionizing radiation. CONCLUSIONS: These findings indicated that clioquinol combined with zinc enhanced the radiosensitivity of HeLa and MCF-7 cells by the down-regulation of ATM through the NF-κB signalling pathway.