Transgene expression in the striatum following intracerebral injections of DNA nanoparticles encoding for human glial cell line-derived neurotrophic factor.

A goal of our studies is to develop a potential therapeutic for Parkinson's disease (PD) by a human glial cell line-derived neurotrophic factor (hGDNF) expression plasmid administered to the rat striatum as a compacted DNA nanoparticle (DNP) and which will generate long-term hGDNF expression at biologically active levels. In the present study, we used a DNA plasmid encoding for hGDNF and a polyubiquitin C (UbC) promoter that was previously shown to have activity in both neurons and glia, but primarily in glia. A two-fold improvement was observed at the highest plasmid dose when using hGDNF DNA incorporating sequences found in RNA splice variant 1 compared with splice variant 2; of note, the splice variant 2 sequence is used in most preclinical studies. This optimized expression cassette design includes flanking scaffold matrix attachment elements (S/MARs) as well as a CpG-depleted prokaryotic domain and, where possible, eukaryotic elements. Stable long-term GDNF activity at levels 300-400% higher than baseline was observed following a single intracerebral injection. In a previous study, DNP plasmids encoding for reporter genes had been successful in generating long-term reporter transgene activity in the striatum (>365 days) and in this study produced sustained GDNF activity at the longest assessed time point (6 months).