Nucleic Acid Nanoparticles for Treating Human Diseases
Retinitis Pigmentosa (RP) is a genetic blinding disorder presenting either shortly after birth or during the first few decades of life. Over 100,000 patients in the US have retinitis pigmentosa and mutations in over 100 different genes can cause this syndrome, so the number of patients with a given gene mutation range from several hundred to a few thousand. Common RP symptoms include progressive visual loss, night blindness, and visual field defects, typically with a tunnel vision presentation with later loss of central vision. The disease process results in injury and death of photoreceptor cells, with a significant loss of these cells at the time of initial diagnosis. Patients presenting with RP symptoms can be genetically diagnosed by sequencing DNA from an oral swab or blood for specific mutations in those genes that cause RP. The rationale for gene therapy treatment for RP is to introduce and express a normal copy of the mutant gene that is causing RP. Gene therapy clinical trials to date have evaluated adeno-associated virus (AAV) vectors and a surgical procedure (subretinal injection) is used to inject these viruses in the eye. Although some peripheral field improvements in vision have been reported, this injection approach causes a transient retinal detachment that can further injure RP photoreceptor cells, and introduction of genes into central vision cone cells of the macula has proven to be difficult without introducing cell injury.
In conjunction with the lab of Dr. Muna Naash at the University of Oklahoma , Copernicus has published a series of papers demonstrating that DNA nanoparticles have activity in the eye, including photoreceptor cells, retinal pigment epithelial cells, and cells of the lens and other cell types. In animal models, disease correction with delay or prevention of visual loss has been achieved by injecting DNA NPs encoding a normal gene for a given type of RP. This improvement in vision has been achieved in the rds model of RP (peripherin 2 gene mutation), which is a fairly common form of RP. Visual correction in this mouse model has been evaluated based on electrical signals generated by photoreceptor cells following visual stimulation (electroretinograms), histologic assessment of photoreceptor viability, and even visual behavioral testing. Importantly, cones, the cells in humans that are responsible for central vision, were most protected in this model. In safety studies in both wildtype and rds RP mice, there was no evidence of inflammatory cytokine induction or NP-related histologic abnormalities following DNA NP subretinal injection. In other programs, very positive visual protection was noted in an animal model of juvenile onset macular degeneration (photoreceptor disease) and RPE65 deficiency (retinal pigment epithelial disease). A current NIH grant from the National Eye Institute is supporting further optimization of our DNA NPs for ocular indications.
Although the above positive animal results were generated following the relatively invasive subretinal injection method, early findings suggest that the less invasive intravitreal approach may be successful in introducing therapeutic DNA into the deepest layers of the retina. Importantly, both subretinal and intravitreal dosing of Copernicus DNA NPs in the eyes of baboons have generated positive results. Ocular dosing has produced sufficiently levels of gene expression to be detected on standard protein assays, such as Western blots.
These data are quite significant, since the eyes of
baboons and man are quite similar with respect to biology and
structure. Hence, the positive baboon data are highly predictive of
similar DNA NP activity in the eyes of man.