Oncolytic virus therapy in conjunction with bortezomib

Background: Both the proteasome inhibitor bortezomib and an oncolytic herpes simplex virus-1 (oHSV) expressing GMCSF are currently FDA-approved. While proteasome blockade can increase oHSV replication, immunological consequences and consequent immunotherapy potential are unknown. In this study, we investigated the impact of bortezomib combined with oHSV on tumor cell death and sensitivity to Natural Killier (NK) cell immunotherapy. Experimental Design: Western blot, flow cytometry, and caspase 3/7 activity assays were used to evaluate the induction of apoptosis/autophagy and/or necroptotic cell death. Cellular and mitochondrial reactive oxygen species (ROS) production was measured utilizing CellROX{trade mark, serif} and MitoSOX. Inhibitors/shRNA targeting ROS, JNK and RIP1 kinase (RIPK1) were utilized to investigate the mechanism of cell killing. The synergistic interaction between oHSV and bortezomib was calculated using a Chou-Talalay analysis. NK cells isolated from normal human blood were co-cultured with tumor cells to evaluate cellular interactions. Q-PCR, ELISA, and FACS analysis were used to evaluate NK cell activation. Intracranial tumor xenografts were utilized to evaluate anti-tumor efficacy. Results: Combination treatment with bortezomib and oHSV induced necroptotic cell death and increased the production of mitochondrial ROS and JNK phosphorylation. Inhibitors/shRNA of RIPK1 and JNK rescued synergistic cell killing. Combination treatment also significantly enhanced NK cell activation and adjuvant NK cell therapy of mice treated with bortezomib and oHSV improved anti-tumor efficacy. Conclusions: This study provides a significant rationale for triple combination therapy with bortezomib, oHSV, and NK cells to improve efficacy, in glioblastoma patients.

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