Anti-ganglioside GD2 monoclonal antibody synergizes with cisplatin to induce endoplasmic reticulum-associated apoptosis in osteosarcoma cells

Cisplatin is an effective chemotherapeutic agent for osteosarcoma (OS) and has been shown to induce endoplasmic reticulum (ER) stress-associated apoptosis in human cancer cells. Ganglioside GD2-specific antibodies can inhibit tumor cell viability without involvement of the immune system. A recent study has shown that antiGD2 monoclonal antibody (mAb) 14G2a effectively inhibits the viability and invasiveness of human OS cells. In this study, we explored the effect of anti-GD2 mAb and cisplatin alone and in combination on ER stress-associated apoptosis in osteosarcoma cells. MG-63 and Saos-2 human OS cells were treated with cisplatin and/or an-GD2 mAb 14G2a for 48 hours. Cisplatin and 14G2a dose-dependently induced apoptosis in MG-63 and Saos-2 cells. They in combination induced 70%-77% of apoptosis in MG-63 cells and 79%-85% of apoptosis in Saos-2 cells, exhibiting a synergistic effect stronger than addition of their individual effects over the control level. Showing no significant effect on the expression of protein kinase RNA-like ER kinase (PERK), cisplatin and 14G2a exhibited a marked synergistic effect on inducing phosphorylation/activation of PERK, phosphorylation/inactivation of eukaryotic translation initiation factor 2α (eIF2α), expression of CHOP, in parallel to inducing the caspase-3 activity and apoptosis in MG-63 and Saos-2 cells. The effects were abolished by lentivirus-mediated knockdown of PERK. Particularly, PERK knockdown abolished 63% and 65% of the combined apoptotic effect of cisplatin and 14G2a on MG-63 and Saos-2 cells, respectively. In conclusion, this study provides the first evidence supporting that cisplatin and 14G2a synergize to induce ER stress-associated apoptosis in human OS cells through activating the PERK ER stress pathway by synergistically inducing phosphorylation/activation of PERK. Our findings add new insights into the pharmacologic effects of anti-GD2 mAb in anticancer treatment and suggest that cisplatin plus anti-GD2 mAb could be a new effective therapeutic strategy for OS.