Bortezomib sensitizes human osteosarcoma cells to adriamycin-induced apoptosis through ROS-dependent activation of p-eIF2α/ATF4/CHOP axis

Osteosarcoma is the most common bone cancer, and chemotherapy is currently indispensable for its treatment. Adriamycin has been claimed to be the most effective agent for osteosarcoma, however, the outcome of adriamycin chemotherapy remains unsatisfactory. Here, we reported a potent combination therapy that bortezomib, a proteasome inhibitor, enhances adriamycin-induced apoptosis to eliminate osteosarcoma cells and we revealed that the activation of p-eIF2 alpha/ATF4/CHOP axis is the underlying associated mechanisms. First, we observed that bortezomib enhances adriamycin-mediated inhibition of cell proliferation and enhances the apoptosis in osteosarcoma cell lines. Moreover, this drug combination produced more potent tumor-growth inhibitory effects in human osteosarcoma cell line KHOS/NP xenografts. Our study showed that reactive oxygen species (ROS) plays an important role in apoptosis induced by adriamycin plus bortezomib, whereas ROS scavenger NAC could almost completely block the apoptosis induced by the combination treatment. Meanwhile, p-eIF2 alpha is remarkably elevated in the combination group. As a result, ATF4 exhibits strong activation which consequently induces the activation of CHOP and leads to the cell death. Finally, 13 primary osteosarcoma cells demonstrated potent response to the combination treatment. In a human osteosarcoma patient-derived xenograft (PDX) model, our finding suggests that when combined with bortezomib, a relatively low dose of adriamycin produced more potent tumor-growth inhibitory effects without increased toxicity. Thus, our findings not only provide a promising combination strategy to overcome osteosarcoma but also shed new light on the strategy of combining increased ROS and inhibited proteasome to open up new opportunities for the clinical development of chemotherapy regimens.