Abstract C185: Head and neck squamous carcinoma cells are susceptible to the attenuated vesicular stomatitis virus expressing suicide genes

Abstract

Abstract Background: The predominant loco-regional progression of Head and Neck Squamous Cell Carcinoma (HNSCC) makes it suitable for testing oncolytic viruses. Recent work from several laboratories including ours has focused on developing vesicular stomatitis virus (VSV) as a replication-competent anticancer viral vector. Attenuated strains, such as M protein mutant VSV (M51R) are more likely to be promoted in clinical research. The major shortcoming of viral therapy is related to the large proportion of tumor cells remaining uninfected. We are addressing this limitation in two ways: the expression of the cytosine deaminase-uracil phosphoribosyltransferase (C:U) suicide gene by the rVSV vector, expected to produce a strong bystander effect and the exploitation of the radiosensitizing potential of the 5-fluorouracil (5-FU) chemo-drug produced intratumorally, as well as of the VSV virus itself. Methods: We determined the susceptibility to oncolytic VSV in a collection of HNSCC cell lines and in patient HN primary tumor cells by measuring: 1) the level of GFP expression after infection with rVSV-GFP and M51R-GFP; 2) the viral production by plaque assay and 3) cell death by Trypan blue exclusion. The extent of defectiveness in interferon pathways was tested by employing pre-treatment with IFN and INF-blocking antibodies before the infection with the oncolytic VSV. We have generated the rVSV-C:U and M51R-C:U viruses and we tested our collection of HNSCC cell models to infection with these viruses in the presence and absence of 5-fluorocytosine. SQ20B cell line is a model of radiation resistant HNSCC. Regular SQ20B and SQ20B infected with low-dose M51R-VSV were evaluated by clonogenic assay. Results: 1) All HNSCC cell models tested are susceptible to the infection with the rVSV but many present a degree of resistance to the attenuated M51R-VSV. 2) Human Primary HNSCC cells are more resistant than the HNSCC cell lines to the M51R-VSV; 3) The activation of IFN pathways is contributing to the resistance to M51R-VSV. 4) Addition of the suicide gene C:U to the attenuated VSV model significantly increased the oncolytic effect in vitro; 5) HNSCC cells infected with M51R-VSV become more radiation sensitive. Conclusions: The decreased oncolytic effect of the attenuated M51R-VSV can be overcome by the expression of suicide genes such as the yeast C:U fusion model. The demonstrated radiosensiting potential of the M51R-VSV virus as well as the known radiosensitizing effect of the generated chemotherapeutic 5-FU can be further exploited against the loco-regional HNSCC tumors. Finally, we have important new information, both from cell lines and patient tissues, for proof-of-principle that cancers can down-regulate antiviral responses. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C185.