Gelatine-based nanoparticles may offer a new delivery route for gene therapy that skirts the complications of viral-based vectors.
In a preclinical trial, researchers from Northeastern University in Boston, US showed that the gelatine-based nanovectors could serve as a safe and effective gene delivery vehicle for inhibiting the growth of solid tumours. They also succeeded in modifying the vectors so that the therapeutic genes stayed in the body for up to 15 hours.
The study, which examined the potential of engineered gelatine-based nanoparticulate vectors in the systemic delivery of therapeutic genes to human solid tumour xenografts in vivo, was reported in the US journal Cancer Gene Therapy (2007; 14, 488-498) by Professor Mansoor Amiji and graduate student Sushma Kommareddy of Northeastern University's Department of Pharmaceutical Sciences.
As the researchers noted, non-viral vectors are increasingly in demand for gene therapy applications due to advantages such as ease of manufacture and avoidance of toxic side-effects or a ceiling on plasmid DNA size. They chose to work with gelatine in formulating the nanoparticles because of its long history of safe use in the human body.
To enhance the intracellular delivery potential of the gelatine, the researchers synthesised thiolated gelatine through covalent modification of the epsilon-amino groups of gelatine with 2-iminothiolane. Nanoparticles were then prepared with the thiolated gelatine, using a mild solvent exchange method optimised in the Northeastern University laboratories.
The surface of these nanovectors was also modified with methoxy-poly(ethylene glycol) (PEG)-succinimidyl glutarate to prolong circulation time in vivo. This enabled the gene therapy to remain in the body for up to 15 hours, compared with just three hours for unmodified nanoparticles. PEG modification also enhanced tumour uptake and retention of the nanoparticles after administration, the researchers said.
In a two-part experiment, Amiji and Kommareddy encapsulated plasmid DNA encoding for the soluble form of the extracellular domain of vascular endothelial growth factor receptor-1 (VEGF-R1 or sFlt-1) in both gelatine and thiolated gelatine nanoparticles, as well as the PEG-modified versions of the same.
When these were used in vivo to treat a MDA-MB-435 oestrogen-negative human breast adenocarcinoma cell line, significant transfection and expression of the secreted sFlt-1 was achieved by both the gel-encapsulated and the control plasmid DNA. The highest levels of sFlt-1 expression were observed, though, with the PEG-modified versions of nanoparticles prepared with gelatine and thiolated gelatine.
In the second part of the study, control plasmid DNA and PEG-modified nanoparticles containing sFlt-1-expressing plasmid were administered intravenously to female Nu/Nu mice bearing orthotopic MDA-MB-435 breast adenocarcinoma xenografts.
In this animal model, about 15 per cent and 13 per cent respectively of the recovered doses of the PEG-thiolated gelatine and PEG-gelatine nanoparticles were retained in the tumour for up to 12 hours post-administration. Plasmid DNA encapsulated in the PEG-thiolated gelatine nanoparticles showed the highest expression efficiency in the tumour 40 days after tumour implantation.
The expressed Flt-1 delivered through PEG-modified gelatine nanoparticles was also shown to be therapeutically active, as evidenced by suppression of tumour growth - particularly in the case of mice treated with the PEG-thiolated gelatine nanoparticles, where tumour volumes at the end of the study were comparable to those at the start of treatment - and by a significant reduction in the tumour neovasculature.
These results confirmed the "enormous potential" of PEG-gel and PEG-thiolated gel nanoparticles as safe and effective systemic gene delivery systems to solid tumours, the researchers concluded. They hope shortly to begin clinical trials with the drug delivery system, which they believe can be extended beyond the treatment of cancer.
"From heart disease and diabetes to glaucoma and macular degeneration, this is a versatile platform solution that could prove successful in a variety of applications," Amiji commented.