Hypoxia inducible double plasmid system for myocardial ischemia gene therapy.

Coronary artery disease frequently involves repeated bouts of myocardial ischemia. To automatically up-regulate the cardioprotective transgenes under hypoxic ischemia, a "vigilant vector" gene therapy system was developed and tested in a rat embryonic myocardial cell line (H9c2). In the vigilant vector, a hypoxia response element-incorporated promoter was used as a switch to turn on the gene expression in response to hypoxic signal. Furthermore, a novel double plasmid system was designed to elevate the potency of the vigilant vector. Instead of putting the promoter and the reporter gene in the same plasmid (single plasmid system), we separated them into two plasmids: the transactivator plasmid and reporter plasmid (double plasmid system). The hypoxia response element (HRE)-incorporated promoter increased the expression of a chimeric transcription factor consisting of the yeast GAL4 DNA binding domain and the human nuclear (transcription) factor-kappaB (NF-kappaB) p65 activation domain. The powerful chimeric regulator binds specifically to the upstream activating sequence for GAL4 in the reporter plasmid and activates the transcription of the transgene. Our experiments showed that the HRE-mediated expression could quickly increase 2.08 +/- 0.75-fold within 6 hours of hypoxia and further augmented 7.12 +/- 1.52-fold when the hypoxia condition was prolonged to 24 hours. The hypoxia-inducible double plasmid system dramatically amplified the transgene expression under both hypoxia and normoxia by 412.79 +/- 185.27-fold and 205.35 +/- 65.44-fold, respectively, relative to the single plasmid system. From these results, we concluded that this hypoxia inducible double plasmid system could be used therapeutically to switch on genes that have proven beneficial effects in myocardial ischemia.