545. Adenovirus Mediated Gene Transfer and Oncolysis In Vitro in Head and Neck Cancer and Melanoma Cells Enhanced by Polycations

Oncolytic adenoviruses (OAVs) designed to selectively replicate and kill cancer cells are rapidly emerging as promising agents for oncolytic virotherapy. We have generated and evaluated several OAVs both in vitro and in vivo in clinical trials. In several pre-clinical and clinical studies, OAVs as monotherapy have shown limited efficacy for treatment of head and neck cancer (HNC) and melanoma. This limited efficacy may be due to low or no expression of coxsackievirus and adenovirus receptors (CAR) on the surface of cancer cells. In addition, OAV-mediated gene transfer into cancer cells may be limited by electrostatic repulsion between the net negatively charged viral capsid and negatively charged cell surface. Removal of negatively charged molecules from cell surface or neutralization of negative charge on adenovirus capsid has been demonstrated to significantly improve Ad5-mediated gene transfer. Here, the effect of polycations such as polybrene, protamine and cytopure on Ad5 mediated gene transfer into cancer cells was investigated. Pretreatment of Ad5 marker vector (Ad5-GFP) with the polycations increased transgene expression up to 65-fold in several HNC cell lines. Similarly, in several melanoma cell lines Ad5-mediated gene expression was enhanced by up to 121-fold. In addition, treatment of an OAV with polycations has improved the virus yields by more than 100-fold in both HNC and melanoma cell lines. Moreover, pretreatment of virus with polycations partially protected the virus in vitro from neutralizing antibodies. These findings may have important implications for the treatment of head and neck cancers and melanoma using oncolytic adenoviral vectors.