Protection from acute cellular injury using Sleeping Beauty mediated telomerase gene transfer

Novel therapeutic approaches for various cancer types using a modified sleeping beauty-based gene delivery system

Successful gene therapy largely depends on the selective introduction of therapeutic genes into the appropriate target cancer cells. One of the most effective and promising approaches for targeting tumor tissue during gene delivery is the use of viral vectors, which allow for high efficiency gene delivery. However, the use of viral vectors is not without risks and safety concerns, such as toxicities, a host immune response towards the viral antigens or potential viral recombination into the host's chromosome; these risks limit the clinical application of viral vectors. The Sleeping Beauty (SB) transposon-based system is an attractive, non-viral alternative to viral delivery systems. SB may be less immunogenic than the viral vector system due to its lack of viral sequences. The SB-based gene delivery system can stably integrate into the host cell genome to produce the therapeutic gene product over the lifetime of a cell. However, when compared to viral vectors, the non-viral SB-based gene delivery system still has limited therapeutic efficacy due to the lack of long-lasting gene expression potential and tumor cell specific gene transfer ability. These limitations could be overcome by modifying the SB system through the introduction of the hTERT promoter and the SV40 enhancer. In this study, a modified SB delivery system, under control of the hTERT promoter in conjunction with the SV40 enhancer, was able to successfully transfer the suicide gene (HSV-TK) into multiple types of cancer cells. The modified SB transfected cancer cells exhibited a significantly increased cancer cell specific death rate. These data suggest that our modified SB-based gene delivery system can be used as a safe and efficient tool for cancer cell specific therapeutic gene transfer and stable long-term expression.

Development of a Sleeping Beauty-based telomerase gene delivery system for hepatocytes

Telomerase is a particular reverse transcriptase that not only synthesizes and maintains the telomere but also promotes the proliferation of resting cells and prevents cellular senescence. The advantages of the Sleeping Beauty transposon system include prolonged transgene expression without eliciting an immunogenic response, no possibility of RCV and ease of construction. Tissue-specific therapeutic gene expression is extremely important in gene therapy, because non-specific expression can cause an immune response of the transduced cells that can severely limit the stability of the transgene. The SB system containing the telomerase gene controlled by two chimeric transthyretin (TTR) gene promoters/enhancers, the human alcohol dehydrogenase gene promoter (ADHp), and the SV40 viral enhancer (SV40VE) was constructed in order to activate hepatocyte cell growth. The higher expression was achieved using these elements and FACS analysis showed that this system was effective in hepatocyte targeted gene therapy. Our new SB mediated telomerase delivery system for hepatocytes can be used in human gene therapy applications.

Sleeping Beauty-mediated suicide gene therapy of hepatocellular carcinoma

The aim of this study was to use gene therapy via the Sleeping Beauty (SB) system to increase telomerase promoter activity to target hepatocellular carcinoma (HCC). In previous studies, we identified selective and increased expression of luciferase and suicide genes controlled by the hTERT (human telomerase reverse transcriptase) promoter and the SV40 enhancer in telomerase-positive cancer cell lines. Because telomerase is activated in about 80% of HCCs, it is likely that increasing the activity of the telomerase promoter with a suicide gene will effectively eradicate HCCs. We found that the telomerase promoter mediated SB system can efficiently insert transgene into HCC genomes. Also, telomerase promoter activity was increased using a SB vector expressing suicide gene HSV-TK (herpes simplex virus thymidine kinase) controlled by the hTERT promoter and a SV40 enhancer for the induction of telomerase-positive cancer-specific cell death. HCC cell lines transfected with pT.hTp.HSV-tk.Con with active helper plasmid and ganciclovir (GCV) significantly inhibited cancer cell growth. These results indicate that Sleeping Beauty transposon mediated suicide gene expression can be used in HCC-targeted cancer gene therapy.