Development of a hypoxia-responsive vector for tumor-specific gene therapy

We are developing new gene therapy vectors whose expression is selectively activated by hypoxia, a unique feature of human solid tumors. As vascular e ndothelial growth factor (VEGF) is upregulated by hypoxia, such regulatory mechanisms would enable us to achieve hypoxia-inducible expression of thera peutic genes. Constructs with five copies of hypoxia-responsive elements (H REs) derived from the 5'-untranslated region (UTR) of the human VEGF showed excellent transcriptional activation at low oxygen tension relevant to tum or hypoxia. In an attempt to achieve higher responsiveness, various combina tions of HREs and promoters were examined. In addition, we also investigate d whether the 3' UTR of the VEGF gene would confer increased post-transcrip tional mRNA stability under hypoxic conditions. However, despite increases in the hypoxic/aerobic ratio of luciferase activity, gene expression with 3 ' UTR was lower due to mRNA destabilization by AU-rich elements (AREs). Thu s, we found no benefit from the inclusion of the 3' UTR in our vectors. Of all the vectors tested, the combination of 5HRE and a CMV minimal promoter exhibited hypoxia responsiveness (over 500-fold) to the similar level to th e intact CMV promoter We propose that this vector would be useful for tumor selective gene therapy.