Background and purpose: The success rate of any therapeutic approach depends on the therapeutic window, which can be increased by either raising the resistance of the normal tissue without protecting the tumor cells or by sensitizing the tumor cells but not the normal cells. Two promising candidate genes for normal tissue protection against radiation-induced damage may be the copper-zinc (CuZnSOD) and manganese superoxide-dismutase genes (MnSOD). The recombinant adeno-associated virus 2 (rAAV-2) offers attractive advantages over other vector systems: low immunogenicity, ability to infect dividing and non-dividing tissues and a low chance of insertional mutagenesis, due to extra-chromosomal localization. We report the production of novel rAAV-2-SOD vectors and the investigation of their modulating effects on HeLa-RC cells after irradiation.
Material and methods: rAAV-2 vectors were cloned containing the human CuZnSOD or MnSOD as transgene and vector stocks were produced. In the initial experiments human cervix carcinoma (HeLa-RC) cells were chosen for their susceptibility to rAAV-2. On day 0, cells were seeded and transduced with the rAAV-2-SOD vectors. On day 3, cells were harvested, irradiated (0.5-8 Gy) and reseeded in different assays (FACS, SOD, MTT and colony assays).
Results: Although >70% of all cells expressed SOD and significant amounts of functional SOD protein were detected, no radioprotective effect of SOD was observed after transduction of HeLa-RC cells.
Conclusions: Novel rAAV-2-SOD vectors that could be produced at high titer, were able to efficiently infect cells and express the SOD genes. The absence of a radioprotective effect in HeLa-RC cancer cells indicates an additional safety feature and suggests that rAAV-mediated MnSOD overexpression might contribute to increasing the therapeutic index when applied for normal tissue protection.