Daily insulin injection is necessary for the treatment of the insulin-dependent diabetes. However

the process is painful and inconvenient. Accordingly

we have made exploratory efforts to establish an alternative method for continuous insulin supply via intramuscular injection of a designed plasmid encoding the single-strand insulin analogue (SIA)

which provides safe

effective and prolonged control of insulin-dependent diabetes. To generate a SIA

a short flexible peptide was alternatively introduced into the natural proinsulin to replace its original long and rigid C-peptide. Then

the synthetic promoter SP301 was used to drive potent and specific expression of SIA in skeletal muscle cells. By combining the Pluronic L64 and low-voltage electropulse (L/E)

the specialized gene delivery technique was applied to efficiently transfer the constructed plasmid into skeletal muscle cells via intramuscular injection. Through these efforts

a plasmid-based intramuscular gene expression system was established and improved

making it applicable for gene therapy. The plasmid-expressed SIA showed biological functions that were similar to that of natural insulin. A single L/E-pSP301-SIA administration provided sustained SIA expression

in vivo

for about 1.5 months. In addition

the diabetic mice treated with L/E-pSP301-SIA were much healthier than those with other treatments. This plasmid-based system was safe for the treatment of diabetes and did not cause immune responses or pathological damage. The results confirmed that

in a mouse model

long-term positive effects were achieved by a single intramuscular L/E-pSP301-SIA injection

which consequently provided reliable experimental basis for its clinical application for the treatment of diabetes mellitus with promising prospects.