314. The Epithelial Glycoprotein-2 Promoter for Highly Specific and Efficient Cancer Gene Therapy for a Broad Range of Tumors

Abstract

Top of pageAbstract Adenoviral cancer gene therapy is hampered by the lack of specific and efficient transgene expression in tumor cells. Employing tissue specific promoters to restrict transgene expression will increase specificity towards the tumor tissue. In addition, specific promoters can be used to increase the efficiency of adenoviral gene therapy by controlling adenoviral replication. However, many specific promoters are restricted to specific tumor types. The tumor specific promoter epithelial glycoprotein-2 (EGP-2) is known to be active in various epithelial-derived cancers including ovarian, colon, and breast cancer and might therefore be a good candidate to target a broad range of tumor types. In this study, the EGP-2 promoter was employed to improve the therapeutic potential of adenoviral cancer gene therapy. The EGP-2 promoter demonstrated an outstanding specificity and activity profile in vivo. In mouse liver tissue, 3 log lower activity compared to the strong constitutively active CMV promoter was shown compared with only 1 log lower activity in EGP-2 positive tumor tissue. Subsequently, the EGP-2 promoter was employed to control the expression of the suicide gene thymidine kinase (AdEGP-2 SR39TK). In vitro selective cell killing after infection with AdEGP-2 SR39TK and GCV administration was seen in EGP-2 positive cell lines, but not in EGP-2 negative cells. After iv injection of AdEGP-2 SR39TK in mice an absence of liver toxicity was demonstrated after administration of GCV, in contrast to AdCMV SR39TK which showed clear liver damage. These promising findings are currently being explored in tumor bearing mice. To successfully treat cancer, all tumor cells have to be eradicated. However, even after local administration adenoviral vectors will infect only a limited amount of tumor cells. Therefore, to increase the efficiency of the adenovirus the EGP-2 promoter was utilized to control the E1A gene, which is essential for adenoviral replication. This conditionally replicating adenovirus (CRAd) should replicate selectively in EGP-2 positive tumor cells, causing cell lysis and spread into the tumor mass. This cycle of selective replication and cell lysis is continued until no further tumor cells can be infected. The EGP-2 based CRAd was as efficient in cell killing as wild-type adenovirus in EGP-2 positive cell lines. In contrast, in EGP-2 negative cell lines replication of the EGP-2 based CRAd was attenuated up to 2 log when compared with the wild-type adenovirus. Currently, the EGP-2 based CRAd is further investigated in tumor bearing mice. Overall, it can be concluded that the EGP-2 promoter demonstrates high specificity and efficiency in adenoviral context and can therefore be a powerful tool in cancer gene therapy for the treatment of a broad range of tumor types.