Gelatin-Based Vectors Deliver Genes to Solid Tumors

Gelatin-based nanoparticles offer a new delivery route for gene therapy that avoids the complications of viral-based vectors.

The gelatin-based nanovectors could serve as a safe and effective gene delivery vehicle for inhibiting the growth of solid tumors. The vectors were modified in such a manner that the therapeutic genes stayed in the body for up to 15 hours.

In a preclinical trial, researchers from Northeastern University (Boston, MA, USA) examined the potential of engineered gelatin-based nanoparticulate vectors for the systemic delivery of therapeutic genes to human solid tumor xenografts in vivo. The trial was reported in the March 2007 edition of the journal Cancer Gene The therapeutic procedure was performed by Prof. 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 gelatin in formulating the nanoparticles because of its long history of safe use in the human body.

To enhance the intracellular delivery potential of the gelatin, the researchers synthesized thiolated gelatin through covalent modification of the epsilon-amino groups of gelatin with 2-iminothiolane. Nanoparticles were then prepared with the thiolated gelatine, using a mild solvent exchange method optimized 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 tumor uptake and retention of the nanoparticles after administration, according to the researchers.

In a two-part experiment, Prof. Amiji and Mr. 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 gelatin and thiolated gelatin nanoparticles, as well as the PEG-modified versions of the same.

When these were used in vivo to treat a MDA-MB-435 estrogen-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, although, with the PEG-modified versions of nanoparticles prepared with gelatin and thiolated gelatin.

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% and 13%, respectively, of the recovered doses of the PEG-thiolated gelatin and PEG-gelatin nanoparticles were retained in the tumour for up to 12 hours post-administration. Plasmid DNA encapsulated in the PEG-thiolated gelatin nanoparticles showed the highest expression efficiency in the tumor 40 days after tumor implantation.

The expressed Flt-1 delivered through PEG-modified gelatin nanoparticles was also shown to be therapeutically active, as evidenced by suppression of tumor growth--particularly in the case of mice treated with the PEG-thiolated gelatin nanoparticles, where tumor volumes at the end of the study were comparable to those at the start of treatment--and by a significant reduction in the tumor neovasculature.

These results confirmed the potential of PEG-gel and PEG-thiolated gel nanoparticles as safe and effective systemic gene delivery systems to solid tumors, the researchers concluded


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