Ultrasound targeted gene therapy in a mouse model of prostate cancer: Evaluation of immune response.

Abstract

120 Background: Gene transfer to malignant sites using human adenoviruses (hAd) has been limited because of their immunogenicity. Murine cells often lack some of the receptors needed for hAd infection; therefore, are generally non-permissive for hAd infection and replication, which limits translational studies of adenoviral gene transfer techniques. We developed a gene transfer method, which uses a combination of lipid-encapsulated perfluorocarbon microbubbles (MBs) and ultrasound (US) to shield and deliver hAds to a specific tissue bypassing the requirement of the coxsackie and adenovirus receptor (CAR). Methods: Transduction efficiency and GFP protein expression of hAd.GFP was assessed by flow cytometry and fluorescence microscopy in murine TRAMP-C2 and human DU145 prostate cancer cells. Innate and acquired immunity response was determined by ELISA and CTL assay in C57BL/6 mice bearing TRAMP-C2 syngeneic tumor grafts following injections of MBs-Ad.GFP complexes in the presence or absence of ultrasound. Results: We observed that the murine prostate cancer cells TRAMP-C2 were transduced less efficiently by hAd.GFP than the human DU145 cells. We showed in vitro that the transduction rate was increased significantly in both TRAMP-C2 and DU145 prostate cancer cells when delivering the Ad particles by a combination of MBs and US. Moreover, we observed expression of the GFP transgene in both cell lines at 48 hours and 72 hours. Lack of activation of the innate and acquired immunity was observed in vivo by quantifying IL-6 and TNF-α cytokines, and by assaying neutralizing IgG antibodies and CTLs activity, following intratumoral or intravenous injections of MBs-Ad.GFP complexes in the presence or absence of ultrasound. Conclusions: This study demonstrates the feasibility of using the TRAMP-C2 murine model of prostate adenocarcinoma to translate our ultrasound-mediated MB-Ad delivery system from the bench to the clinic. Our data provides evidence that the TRAMP-C2 prostate cancer graft model is a suitable system to study in immune competent animals the capacity of lipid-encapsulated perfluorocarbon MBs and US, to shield and deliver hAds to a site-specific tissue bypassing the requirement of specific receptors.