Natural killer (NK) cell clearance of tumor cell emboli following surgery is thought to be vital in preventing postoperative metastases. Using a mouse model of surgical stress, we transferred surgically stressed NK cells into NK-deficient mice and observed enhanced lung metastases in tumor-bearing mice as compared with mice that received untreated NK cells. These results establish that NK cells play a crucial role in mediating tumor clearance following surgery. Surgery markedly reduced NK cell total numbers in the spleen and affected NK cell migration. Ex vivo and in vivo tumor cell killing by NK cells were significantly reduced in surgically stressed mice. Furthermore, secreted tissue signals and myeloid-derived suppressor cell populations were altered in surgically stressed mice. Significantly, perioperative administration of oncolytic parapoxvirus ovis (ORFV) and vaccinia virus can reverse NK cell suppression, which correlates with a reduction in the postoperative formation of metastases. In human studies, postoperative cancer surgery patients had reduced NK cell cytotoxicity, and we show for the first time that oncolytic vaccinia virus markedly increases NK cell activity in patients with cancer. These data provide direct in vivo evidence that surgical stress impairs global NK cell function. Perioperative therapies aimed at enhancing NK cell function will reduce metastatic recurrence and improve survival in surgical cancer patients. Cancer Res; 73(1); 97-107. Ó2012 AACR.

Autophagy and autophagy-related genes (Atg) have been attributed prominent roles in tumorigenesis, tumor growth, and metastasis. Extracellular vesicles called exosomes are also implicated in cancer metastasis. Here, we demonstrate that exosome production is strongly reduced in cells lacking Atg5 and Atg16L1, but this is independent of Atg7 and canonical autophagy. Atg5 specifically decreases acidification of late endosomes where exosomes are produced, disrupting the acidifying VV-ATPase by removing a regulatory component, ATP6V1E1, into exosomes. The effect of Atg5 on exosome production promotes the migration and in vivo metastasis of orthotopic breast cancer cells. These findings uncover mechanisms controlling exosome release and identify means by which autophagy-related genes can contribute to metastasis in autophagy-independent pathways.

Oncolytic viruses are generally designed to be cancer selective on the basis of a single genetic mutation. JX-594 is a thymidine kinase (TK) gene-inactivated oncolytic vaccinia virus expressing granulocyte-macrophage colony-stimulating factor (GM-CSF) and lac-Z transgenes that is designed to destroy cancer cells through replication-dependent cell lysis and stimulation of antitumoral immunity. JX-594 has demonstrated a favorable safety profile and reproducible tumor necrosis in a variety of solid cancer types in clinical trials. However, the mechanism(s) responsible for its cancer-selectivity have not yet been well described. We analyzed the replication of JX-594 in three model systems: primary normal and cancer cells, surgical explants, and murine tumor models. JX-594 replication, transgene expression, and cytopathic effects were highly cancer-selective, and broad spectrum activity was demonstrated. JX-594 cancer-selectivity was multi-mechanistic; replication was activated by epidermal growth factor receptor (EGFR)/Ras pathway signaling, cellular TK levels, and cancer cell resistance to type-I interferons (IFNs). These findings confirm a large therapeutic index for JX-594 that is driven by common genetic abnormalities in human solid tumors. This appears to be the first description of multiple selectivity mechanisms, both inherent and engineered, for an oncolytic virus. These findings have implications for oncolytic viruses in general, and suggest that their cancer targeting is a complex and multifactorial process.