Ribozymes To The Rescue: Gene Therapy Shows Promise For Treatment Of Inherited Blindness

GAINESVILLE, Fla.---University of Florida researchers have designed a new genetic weapon that can--in laboratory animals--significantly slow progression of retinitis pigmentosa, a leading cause of inherited human blindness.

The weapon, a ribozyme manufactured in the laboratory, works by chopping up genetic messengers before they deliver the instructions of a mutant gene.

"This is the first case we know of where ribozymes have been used to correct a disease in an animal in a way that realistically could be used in humans," said Alfred S. Lewin, a professor of molecular genetics and microbiology in UF's College of Medicine. "We also believe this technique might be useful for other inherited diseases."

Lewin and William Hauswirth, a professor with dual appointments in ophthalmology, as well as molecular genetics and microbiology, are leading a team conducting further animal studies in preparation for human clinical trials, an estimated five years away.

About 1 in 3,000 Americans has retinitis pigmentosa, a degenerative disease whose symptoms generally first appear during adolescence. As the disorder progresses, night vision, peripheral vision and ultimately all sight can be lost. Currently, there is no way to halt the deterioration.

Since the UF research was published in the August issue of Nature Medicine, Lewin has heard from many other scientists who are working to apply "ribozyme rescue" to heart disease, neurological disorders and viral diseases.

"UF's work is a great example of how fundamental research, whose goal is to understand basic cellular processes, can lead to important advances that have a direct impact on human health," said John Burke, a professor of microbiology and molecular genetics at the University of Vermont.

UF's research builds on the Nobel Prize-winning discovery in other laboratories that ribonucleic acid, or RNA, can act as an enzyme, a substance that causes chemical reactions within cells. It is then known as a ribozyme.

In a cell, RNA is copied from a strand of DNA; it serves as the messenger that conveys DNA's genetic instructions to the cell's cytoplasm, where proteins are made. In retinitis pigmentosa, a mutant gene calls for the creation of a protein that damages the eye's light-sensitive rod cells.

About 40 percent of people with retinitis pigmentosa have the "autosomal-dominant" form; that is, they inherited a defective gene from one parent who has the disease, but also received a normal gene copy from the other parent. (About half the cases of retinitis pigmentosa occur with no known family history.)

The UF research targets the autosomal-dominant form of the disease in rats.

"We designed a ribozyme to cut up the messenger RNA that have the copies of the bad gene, while leaving alone the copies of the good gene," Lewin said.

The genes themselves--good and bad--are not disturbed.

The designer ribozyme was injected into lab rats, which were bred by a University of California School of Medicine team to have a disease similar to human retinitis pigmentosa. The California research team was led by Matthew LaVail and John Flannery. Hauswirth developed the viral tool for delivering the ribozyme to the eye.

"We have seen significant protection of the eye cells three months after injecting the ribozymes. That's a long time in a rodent's life," Lewin said. "We're now working to see if the protection lasts for six months." Additional studies will be conducted in pigs, which can provide an even closer match to the human eye.

Over time, ribozymes may be developed to fight other autosomal dominant diseases, including Marfan syndrome, a genetic disorder of the connective tissue, and some forms of ALS, more commonly known as Lou Gehrig's disease.

"As long as you can design a ribozyme that could block the expression of the mutant gene, this approach ought to work," Lewin said.

In addition to Lewin and Hauswirth, Kimberly Drenser, a UF student