Expression of the fusogenic p14 FAST protein from a replication-defective adenovirus vector does not provide a therapeutic benefit in an immunocompetent mouse model of cancer.

C M Wong,T Falls,J C Bell,L A Nash,K L Poulin,R J Parks,J Del Papa

doi:10.1038/cgt.2016.41

Abstract

When injected directly into a tumor mass, adenovirus (Ad) vectors only transduce cells immediately along the injection tract. Expression of fusogenic proteins from the Ad vector can lead to syncytium formation, which efficiently spreads the therapeutic effect. Fusogenic proteins can also cause cancer cell death directly, and enhance the release of exosome-like particles containing tumor-associated antigens, which boosts the anti-tumor immune response. In this study, we have examined whether delivery of an early region 1 (E1)-deleted, replication-defective Ad vector encoding the reptilian reovirus p14 fusion-associated small transmembrane (FAST) protein can provide therapeutic efficacy in an immunocompetent mouse tumor model. A high multiplicity of infection of AdFAST is required to induce cell fusion in mouse mammary carcinoma 4T1 cells in vitro, and FAST protein expression caused a modest reduction in cell membrane integrity and metabolic activity compared with cells infected with a control vector. Cells expressing FAST protein released significantly higher quantities of exosomes. In immunocompetent Balb/C mice harboring subcutaneous 4T1 tumors, AdFAST did not induce detectable cancer cell fusion, promote tumor regression or prolong mouse survival compared with untreated mice. This study suggests that in the context of the 4T1 model, Ad-mediated FAST protein expression did not elicit a therapeutic effect.

Highlights

Finding new and effective therapeutics is an ongoing challenge in the cancer field
We examined the relative membrane permeability of these three cell lines when infected with AdEmpty or AdFAST, by determining the quantity of lactate dehydrogenase (LDH) protein released into the AdFAST for cancer therapy
We showed previously that Ad-mediated expression of fusion-associated small transmembrane (FAST) in A549 cells induced significant apoptosis at an multiplicity of infection (MOI) as low as 10.23 As 4T1 cells showed an ~ 10-fold reduction in ability to support Ad transgene expression compared with A549 cells, we examined whether higher MOI infection with AdFAST could induce apoptosis in the 4T1 cell line. 4T1 cells were infected with varying MOI (10–1000 pfu per cell) of AdFAST-HA, and crude protein samples were analysed 72 h later for expression of FAST and cleavage of caspase-3, a marker of apoptosis

Summary

Introduction

Finding new and effective therapeutics is an ongoing challenge in the cancer field. Over the years, many pre-clinical research efforts and clinical trials have utilized viruses in an attempt to combat the disease. Various viruses have been modified to express membrane fusion proteins from Gibbon ape leukemia virus (GALV), respiratory syncytial virus (RSV), measles virus (MV), Newcastle disease virus and human immunodeficiency virus type 1 (HIV-1), and in many studies these vectors were shown to be effective in tumor regression.[6,7,8,9,10,11,12,13,14] Ad vectors expressing GALV, RSV, MV or vesicular stomatitis virus (VSV) membrane fusion proteins as a sole anti-cancer agent were able to reduce tumor burden in xenograft and immunocompetent mouse models in the absence of other complementing anti-cancer therapeutic transgenes.[8,9,12,13] in many studies, the process of cancer cell fusion, and associated disruption in cellular processes, can lead to tumor regression

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