The first gene therapy clinical trials began in 1990 with the anticipation of many breakthroughs in medicine. Unfortunately, no human gene therapy product, to date, has passed the FDA. A major setback for gene therapy occurred in 1999 with the death of Jesse Gelsinger and in 2003 when a child treated with retroviral vector developed a leukemia-like condition. Boht incidents caused FDA to temporary halt all gene therapy trials. Man factors contributed to the failure of gene therapy. The use of viral vectors has a large role in its advancement as well as its failures.
Our approach to advancing gene therapy is a non-viral technique where biodegradable polymers are used instead of viruses. Thus, the patients are not exposed to immunogenic agents, such as viral coats. In addition, we can mimic many viral functions into our nanoparticles. Such as cellular recognition, evading the immunes system (for retroviruses), transporting nuclear acids to the cytoplasm by endosomal escape. We have already published our nanoparticle data on these functions. Our current reach is to enhance the transport of DNA into the cell's nucleus and is funded by the National Scientific Foundation.
The L-tyrosine based (LTP) nanoparticle have been encapsulated with plasmid DNA. LTP provide a rapidly degrading and a biocompatible package. The surface has been decorated with PEG for preventing protein adsorption and evading the immune response. Complexing DNA with linear polyethylenimine induces the proton sponge effect once cell endocytosed the nanoparticles and allows endosomal escape. A portion of PEG also has been functionalized for the conjugation of targeting moieties.
Scanning electron microscopy shows that LTP nanoparticles are spherical. Dynamic light scattering data show the size distribution ranges from 200 to 700 nm. Confocal microscopy shows that LTP nanoparticles (labeled with FITC) are readily endocytosed by human dermal fibroblasts. In our studies, these nanoparticles transfect these cells as efficiently as commercial transfection reagents. However, we also have shown that our nanoparticles are much less toxic to cells. In vivo, our nanoparticles show efficient transfection of certain organs.
For drug delivery projects using LTP nanoparticles, see the Cancer and Infectious Diseases sections.
Schematic and SEM of the LTP-DNA nanoparticles. The surface has been decorated with PEG.
Confocal microscopy of LTP-FITC nanoparticles imaged at 2.5 µm form the bottom of the cells.
Confocal microscopy of an organ exposed to LTP-DNA nanoparticles. Red shows positive antibody staining of protein expression induced by LTP-DNA nanoparticles.