Antitumor activity of photo-stimulated zinc oxide nanoparticles combined with paclitaxel or cisplatin in HNSCC cell lines

Zinc oxide nanoparticles (ZnO-NPs) exhibit photocatalytic properties and are used in sunscreen cosmetics and for the degradation of environmental pollutants. Furthermore, ZnO-NPs have proven to induce tumor-selective cell death in human squamous cell carcinoma (HNSCC) in vitro. The aim of the current study was to evaluate cytotoxic effects of UVA-1-activated ZnO-NPs in combination with paclitaxel and cisplatin in HNSCC. Three HNSCC cell lines (HLaC-78, Cal-27 and PJ-41) were incubated with ZnO-NPs at concentrations of 0.02 and 0.2 μg/ml in combination with paclitaxel (0.5–5 nM) or cisplatin (0.03–3 μM) for 24 h. Afterwards, cells were irradiated with UVA-1 for 15 min. Viability was measured by MTT assay, fluorescein-diacetate (FDA) test and annexin/propidiumiodide flow cytometry. A significant decrease in viable cells could be observed in all three HNSCC cell lines treated by photocatalytic therapy with 0.2 μg/cm2 ZnO-NPs alone. A combination with paclitaxel or cisplatin at low concentrations resulted in a further increase in cytotoxicity in vitro revealing a synergistic effect. Flow cytometry revealed a combination of apoptosis and necrosis. These results indicate that photocatalytic therapy of HNSCC with ZnO-NPs could enhance the cytotoxic action of chemotherapeutic agents synergistically, indicating a promising potential for ZnO-NPs in antitumor applications.