Silver Nanotriangles and Chemotherapeutics Synergistically Induce Apoptosis in Glioma Cells via a ROS-Dependent Mitochondrial Pathway

BACKGROUND: The synergistic effect of nanomaterials and chemotherapeutics provides a novel strategy for the treatment of tumors. Silver nanotriangles (AgNTs) exhibited some unique properties in nanomedicine. Studies on the synergy of silver-based nanomaterials and anti-tumor drugs against gliomas are rare. MATERIALS AND METHODS: Chitosan-coated AgNTs were prepared, followed by characterization using transmission electron microscopy, ultraviolet-visible spectroscopy and X-ray diffraction. The anti-glioma effect of cyclophosphamide (CTX), 5-fluorouracil (5-FU), oxaliplatin (OXA), doxorubicin (DOX) or gemcitabine (GEM) combined with AgNTs in different glioma cell lines (U87, U251 and C6) was assessed by the MTT assay to screen out a drug with the most broad-spectrum and strongest synergistic anti-glioma activity. The intracellular reactive oxygen species (ROS) level, mitochondrial membrane potential (MMP) and cell apoptosis were detected by flow cytometry. The possible underlying mechanisms of the synergy were further investigated with ROS scavenger and specific inhibitors of C-jun N-terminal kinase (JNK), p38 and extracellular signal-regulated kinase 1/2 pathways. RESULTS: The synthesized AgNTs were mainly triangular and truncated triangular with an average edge length of 125 nm. A synergistic anti-glioma effect of AgNTs combined with CTX was not observed, and the synergism between AgNTs and 5-FU was cell type-specific. AgNTs combined with OXA, DOX or GEM displayed synergistic effects in various glioma cell lines, and the combination of AgNTs and GEM showed the strongest synergistic activity. A decrease in cell viability, loss of the MMP and an increase in apoptosis rate induced by this synergy could be significantly attenuated by the ROS scavenger N-acetylcysteine and JNK inhibitor SP600125. CONCLUSION: Our results suggested that the combination of AgNTs and GEM possessed broad-spectrum and potent synergistic anti-glioma activity, resulting from cell apoptosis mediated by a ROS-dependent mitochondrial pathway in which JNK might be involved.