Improving the potential of attenuated Salmonella typhimurium as a gene-delivering vector specifically to infarcted myocardium with hypoxia-inducible promoter system

Objectives Myocardial infarction (MI) is caused by the interruption of blood supply to a part of the heart, which results in the imbalance of oxygen supply and demand, leading to the hypoxia and necrosis in the heart. We have been developed a cardiac gene-delivery vector using attenuated Salmonella typhimurium, which could be monitored by bioluminescence imaging technique, with the necessity to design a hypoxia-inducible promoter system that is able to regulate gene expression only inside hypoxic infarcted myocardium.

Methods We isolated some candidate promoters which regulate for gene expression under hypoxic condition. Those promoters were designed to drive the expression of Rluc8 reporter gene inside attenuated S. typhimurium defective in ppGpp molecule synthesis (SLΔppGpp). Murine MI models received tolerable dose of SLΔppGpp via tail vein. Bacterial tropism for infarcted myocardium and gene expression were detected by in vivo bioluminescence imaging system (IVIS). Specific targeting of bacteria was evaluated by photon measurement as well as by bacterial viable counting from homogenized tissues.

Results Bioluminescence signal was observed in the infarcted myocardium and it was also proved by immunohistochemical staining and bacterial enumeration. No signal of Rluc8 expression was detected in the liver and spleen on day 1 after bacterial injection where high numbers of viable bacteria were present, demonstrating that gene expression could be strictly controlled under the function of hypoxia-inducible promoters.

Conclusions The engineered S. typhimurium processes a special tropism for infarcted myocardium. It could be an effective gene/protein-delivery vector, which has a potential to express angiogenic protein specifically in infarcted myocardium, by employing hypoxia-inducible promoters