Eyeworld

EW RETINA January 2011 19 Non-viral particles able to deliver DNA A non-viral nanoparticle, dubbed PEG-POD, can ef- fectively deliver DNA to a mouse retinal pigment ep- ithelium, according to Ra- jendra Kumar-Singh, Ph.D., associate professor of ophthalmology, Tufts University School of Medicine, Boston. Results e-published in the August 2010 issue of Molecular Ther- apy showed that eyes injected with the DNA-relaying nanoparticle had a 27-39% greater response than con- trols eyes that did not receive the DNA. This research drives home the fact that a non-viral approach can be successfully applied to gene ther- apy. "Traditionally gene therapy has been shown to be successful using viruses as a gene delivery method," Dr. Kumar-Singh said. "Viruses are in fact nanoparticles of the natural world." However, he points out that viruses can cause problems such as inflammation, cancer, or in some cases death. The idea of the trial was to see if it was possible to replicate what a virus can do with a non-viral approach. PEG-POD particle "What we have done in our study is developed a virus-like particle, which is in fact possibly the same size as a virus," Dr. Kumar-Singh said. "Our particles are about 120 nanometers in size and the aden- ovirus, which causes the common cold and is probably one of the most common vectors used in gene ther- apy in general, is about 100 nanometers." In the study, investigators used mice, since their retinas are similar in structure to those of humans. "We wanted to answer the question, Can we inhibit the process of apop- tosis?" Dr. Kumar-Singh said. "A blue light induces apoptosis in the mouse retina, so we delivered our gene therapy and then exposed the mice to blue light for four hours." Investigators were then able to measure the rate of apoptosis in ei- ther sham-treated mice or those that received the therapeutic DNA. "We found that the mice that were treated with the therapeutic DNA were in fact undergoing very little or almost no apoptosis, whereas the control mice had a lot of apoptosis going on in the retina that led to subsequent morphologic changes," Dr. Kumar-Singh said. Fourteen days after blue light administration, the thickness of the superior retina of the PEG-POD in- jected eyes was 23.6-39.3% greater than the retinas in the control mice. This highlighted the fact that the control retinas had lost more cells. "In fact, we know that the cell types that we'd lost were actually photore- ceptor cells that are critical for vi- sion," Dr. Kumar-Singh said. From a clinical perspective he sees this as potentially having signif- icant impact. "Currently there are no therapies that are available, other than, for example, vitamin supple- mentation for retinitis pigmentosa patients," Dr. Kumar-Singh said. Likewise, many macular degenera- tion patients can potentially benefit. "There is a drug available for the wet form of the disease so patients can be treated," Dr. Kumar-Singh said. "But for the 90% of patients with the dry from, currently there is no treatment available." Dr. Kumar-Singh hopes that these novel gene therapy technologies can be applied to diseases such as retini- tis pigmentosa and macular degener- ation that currently cannot be effectively treated. However, there are still some important questions that need to be answered before this work can move into clinical trials. One current bar- rier is the length of time that the gene is expressed. Currently, investi- gators are only able to attain short- term gene expression. "That's key for humans because in mice we can do multiple injections, but for humans that would be impractical," Dr. Kumar-Singh said. "We want to set up a situation where a patient has one injection or surgical approach that should last for at least a year or longer." Once this issue is solved, there are toxicity questions to be an- swered as well. "We need to do a toxicology study as required by the FDA for a new treatment," Dr. Kumar-Singh said. "That normally takes some time." Dr. Kumar-Singh sees this latest work as having made an important in-road. "The take-home message is that we can rescue retinal degenera- tion using a non-viral approach," he said. "This is relevant because al- though gene therapy has been vali- dated in animals and humans, it has been done using viral approaches, especially in the eye." He pointed out that viruses are known to be detrimental in many gene therapy studies. "We want to get away from the use of viruses, and our study showed that it's possible to do so, al- though there are still many ques- tions to be addressed," Dr. Kumar-Singh said. Overall, Dr. Kumar-Singh firmly believes that gene therapy will be- come a standard of care. "Although it's a cliché at this point, it is true—I think that it is a new form of medi- cine that is going to be widely prac- ticed within the next decade," he said. "I think that we will be able to treat diseases that we haven't been able to up until now." EW Editors' note: Dr. Kumar-Singh has no financial interests related to his com- ments. Contact information Kumar-Singh: 617-636-3767, Rajendra.Kumar-Singh@tufts.edu by Maxine Lipner Senior EyeWorld Senior Contributing Editor Big leap with nanoparticles: attaining success with non-viral therapy approach Left: damage to the retina (pink) in eye where DNA was not delivered; right: retina protected from damage by PEG-POD DNA carrying nanoparticles Source: Rajendra Kumar-Singh, Ph.D.

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