Biosensor Targets Retina Cells

Layered anatomy of the DNA tethered nanoparticle.
Layered anatomy of the DNA tethered nanoparticle. Credit: Tarl Prow and Gerard A. Lutty / JHU

Researchers affiliated with the Institute for NanoBioTechnology at Johns Hopkins have created a new biosensor that treats damaged cells in the eye’s retina with targeted gene therapy. The approach also may be useful in designing treatments for diseases such as cancer and psoriasis, according to the researchers, since it targets uncontrolled growth of new blood vessels.

Led by cell biologist Gerard Lutty and Research Associate Tarl Prow of the Wilmer Eye Institute at Johns Hopkins, the project includes collaborations with chemists, pathologists, and biomedical engineers.

The biosensor is a DNA promoter sequence tethered to multi-layered magnetic nanoparticles. When activated by oxidative stress, the biosensor allows the cell to regulate its own therapeutic gene expression and quickly respond to damage caused by free radicals.

Once injected into the eye, the layered nanoparticles react like tiny peeling onions, each layer performing a distinct function. A targeting protein is being developed to help the nanoparticles find the endothelial cells lining the eye’s blood vessels, and smooth entry into the cells is facilitated by a lipid coating.

The biosensor, attached to the third layer of the nanoparticle, controls two genes: a fluorescent reporter gene and a therapeutic gene. If the fluorescent reporter gene is activated by the biosensor, it can be used to detect damage in individual cells. If oxidative stress is detected in the cell, the therapeutic gene is activated to eliminate the stress and prevent damage to the blood vessels.

“The fundamental idea of this system is that only the cells that need therapy will be treated,“ says Prow. “Another application of these nanoparticles would be to deliver genes that inhibit new blood vessel growth to endothelial cells, which could be used in proliferative forms of retinopathy or cancer.“

The biosensor has been tested in the laboratory on cells and in large animal models including mouse, rabbit, and dog. In toxicity experiments, nanoparticles composed of different materials were shown to be nontoxic on cells in test tubes but displayed varying levels of toxicity in animals.

In order to decrease toxicity and improve functionality of the nanoparticles used with the biosensor, Lutty and Prow began working with physical chemist Jennifer Sample of the Applied Physics Laboratory a year ago. Sample is experimenting with nanoparticle compositions, including biologically-friendly materials like silica.

“No one scientist can do this kind of work by themselves,“ says Lutty. “You need engineers, chemists, biologists, and clinicians working together to find the best solutions.“

Additional collaborators include the University of Texas, Harvard University, and Purdue University. The work is funded by the National Eye Institute and a Johns Hopkins hematology training grant.

Citation:

T. Prow, R. Grebe, C. Merges, J. N. Smith, D. S. McLeod, J. F. Leary, G. A. Lutty. Nanoparticle tethered antioxidant response element as a biosensor for oxygen induced toxicity in retinal endothelial cells, Molecular Vision 12:616-625 (2006).

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