To Kaushal, who is involved in the Genzyme study as well as the LCA research, the big challenge will be broadening the use of gene therapy to dozens more diseases, and using that understanding to eventually reach beyond the eye. “If one could understand those fundamental cellular, biochemical events and identify targets, you might have the chance to treat many diseases with a single gene-therapy construct,” Kaushal said.
Earlier gene therapy programs used a type of virus called adenovirus to target genes, but both the LCA and Genzyme trials are using adeno-associated virus, which is far less inflammatory and which expresses itself over longer periods than adenovirus, therefore making the treatment last longer, Wadsworth said. Viruses are used to deliver gene therapies because they are adept at getting through cell walls.
VEGF is involved in vascular cell growth throughout the body, and its expression increases in the presence of a wound. Studies have shown that with Lucentis, virtually all the VEGF-binding protein stays within the eye, and does not significantly affect VEGF levels elsewhere in the body, Wadsworth says. Genzyme’s drug will provide even lower levels of the VEGF-binding protein, so it’s expected that the drug will not have any adverse affects throughout the body, he said.
The trick will be getting the cells to produce enough VEGF-binding protein to help patients, said Peter Campochiaro, a professor at the Wilmer Eye Institute at Johns Hopkins Medicine, who is involved in the research. In addition to establishing safety, the current phase 1 trial will explore four different doses of the study drug. “There’s no reason why this shouldn’t work, other than if the expression of the gene is not sufficient. That’s really what this trial should determine,” Campochiaro says. “It appears that the more you suppress VEGF and the more you keep it suppressed, the better the outcomes.”