Silver nanoparticles (Ag-np) are commonly used in many consumer products, including cosmetics, textiles, electronics and medicine, largely due to their antimicrobial properties. More recently, Ag-np are being used to target and kill cancer cells. It has been known for years that silver nanoparticles (Ag-np) can induce cell death and DNA damage. Studies have also shown that Ag-np inhibit cell proliferation and induce apoptosis in cancer cells. However, cancer cells are able to fight back with DNA repair mechanisms such as non-homologous end joining repair (NHEJ). The NHEJ pathway requires the activation of DNA-dependent protein kinase catalytic subunit (DNA-PKcs), thus DNA-PKcs may protect against the Ag-np-induced DNA damage in cancer cells.

Could inhibition of DNA-PKcs increase the ability of Ag-np to kill cancer cells? In a 2017 study, Lim et al. wanted to test whether inhibition of DNA-PKcs can increase the cytotoxic effect of Ag-np in breast cancer and glioblastoma cell lines. To effectively determine cell viability in these cancer cell lines, the authors used the CellTiter-Glo® Luminescent Cell Viability Assay. The CellTiter-Glo® Assay determines the number of viable cells in culture based on quantitation of ATP, an indicator of metabolically active cells. A major advantage of this assay is its simplicity. This plate-based assay involves adding the single reagent (CellTiter-Glo® Reagent) directly to cells cultured in serum-supplemented medium. This generates a luminescent signal proportional to the amount of ATP present, which is detected using a luminometer. Cell washing, removal of medium and multiple pipetting steps are not required. Another advantage of the CellTiter-Glo® Assay is its high sensitivity. The system detects as few as 15 cells/well in a 384-well format in 10 minutes after adding reagent and mixing, making it ideal for automated high-throughput screening, cell proliferation and cytotoxicity assays.

The authors first confirmed that Ag-np treatment reduced proliferation and induced cell death/DNA damage in two breast cancer cell lines and two glioblastoma cell lines. The cytotoxic effect of Ag-np is specific to cancer cells, as minimal cytotoxicity was observed in non-cancerous human lung fibroblasts used as control. Next, they pre-treated the cancer cells with a DNA-PKcs inhibitor for 1 hour before adding Ag-np. Inhibition of DNA-PKcs increased Ag-np-mediated cell death in all four cancer cell lines. This suggests that DNA-PKcs may be protecting the cells from Ag-np cytotoxicity. The authors further showed that DNA-PKcs may repair Ag-np induced DNA damage by NHEJ and JNK1 pathways. In addition, DNA-PKcs may help recruit DNA repair machinery to damaged telomeres.

This study suggests that a combination of Ag-np treatment and DNA-PKcs inhibition may be a potential strategy to enhance the anticancer effect of Ag-np.

Reference: Hande M.P., et.al. (2017) DNA-dependent protein kinase modulates the anti-cancer properties of silver nanoparticles in human cancer cells. Mutat Res Gen Tox En. 824, 32

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Johanna Lee

Johanna is a Science Writer at Promega. She earned her PhD in Biomedical Sciences at Baylor College of Medicine. She was a freelance writer and full-time mom for five years before joining Promega. Johanna is from Taiwan and she believes Taiwanese food is the best in the world. She loves doing yoga, traveling and spending time with her two kids.

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