Targeting of Interferon-Beta to Produce a Specific, Multi-Mechanistic Oncolytic Vaccinia Virus

Abstract

BackgroundOncolytic viruses hold much promise for clinical treatment of many cancers, but a lack of systemic delivery and insufficient tumor cell killing have limited their usefulness. We have previously demonstrated that vaccinia virus strains are capable of systemic delivery to tumors in mouse models, but infection of normal tissues remains an issue. We hypothesized that interferon-beta (IFN-β) expression from an oncolytic vaccinia strain incapable of responding to this cytokine would have dual benefits as a cancer therapeutic: increased anticancer effects and enhanced virus inactivation in normal tissues. We report the construction and preclinical testing of this virus.Methods and FindingsIn vitro screening of viral strains by cytotoxicity and replication assay was coupled to cellular characterization by phospho-flow cytometry in order to select a novel oncolytic vaccinia virus. This virus was then examined in vivo in mouse models by non-invasive imaging techniques. A vaccinia B18R deletion mutant was selected as the backbone for IFN-β expression, because the B18R gene product neutralizes secreted type-I IFNs. The oncolytic B18R deletion mutant demonstrated IFN-dependent cancer selectivity and efficacy in vitro, and tumor targeting and efficacy in mouse models in vivo. Both tumor cells and tumor-associated vascular endothelial cells were targeted. Complete tumor responses in preclinical models were accompanied by immune-mediated protection against tumor rechallenge. Cancer selectivity was also demonstrated in primary human tumor explant tissues and adjacent normal tissues. The IFN-β gene was then cloned into the thymidine kinase (TK) region of this virus to create JX-795 (TK−/B18R−/IFN-β+). JX-795 had superior tumor selectivity and systemic intravenous efficacy when compared with the TK−/B18R− control or wild-type vaccinia in preclinical models.ConclusionsBy combining IFN-dependent cancer selectivity with IFN-β expression to optimize both anticancer effects and normal tissue antiviral effects, we were able to achieve, to our knowledge for the first time, tumor-specific replication, IFN-β gene expression, and efficacy following systemic delivery in preclinical models.

Gene therapy progress and prospects cancer: oncolytic viruses

“…Pretreatment with cyclophosphamide suppressed the inflammation and resulted in reduced tumor vascular permeability. 30 Kirn et al 31 showed that systemically administered vaccinia virus resulted in infection and subsequent destruction of tumor endothelial cells, which led to loss of tumor vascular density.…”

“…42 A vaccinia virus mutant with a deletion in B18R, whose gene product neutralizes type I IFNs, showed IFN-dependent cancer selectivity and efficacy. 31 It has also been shown that adenovirusinduced ERK activation is critical to viral replication. 43 Oncolytic viruses can also be 'programmed' to replicate in cells through certain cellular signaling activities, such as b-catenin, 44 to carry therapeutic transgene that targets tumorigenic pathways, 20 or retargeted to cellular receptors that are essential for signaling (for example, epidermal growth factor receptor (EGFR)).…”

“…Two recent publications illustrate this concept. 31,55 The first article describes rational species and strain selection and genetic engineering based on updated knowledge. As described before, poxvirus was selected for this study based on human data showing that systemic delivery of poxvirus is safe and can induce significant tumor responses.…”

“…Further engineering with TK deletion and IFN-b insertion results in a multimechanistic oncolytic vaccinia virus. 31 Ex vivo studies may predict responses Genetic markers are being developed for chemotherapy and molecular-targeted therapeutics to predict responses and/or idiosyncratic reactions, and the results have been implemented into practice. Given the complexity of MOA of virotherapeutics, there is therefore a long way to go before such markers/predictors can be developed for virotherapy.…”

Integrating the biological characteristics of oncolytic viruses and immune cells can optimize therapeutic benefits of cell-based delivery

“…However, because they possess the ability to infect a broad range of cell types, only a small amount of virus delivered intravenously will infect the tumor, with the majority undergoing nonpermissive or abortive infections of non-tumor tissue. Therefore, despite the promising results of vaccina virusbased cancer therapies, [14][15][16][17][18] it appears that for effective treatment of cancers it will be necessary to both improve methods of delivery and use of vaccinia in therapeutic combinations.…”