April 25, 2005
Researchers funded by The ALS Association (ALSA) report the additional success in animal models with a new technique to silence a specific gene. Investigators reported in the April 25 online Annals of Neurology that mutant mice modeling ALS, also referred to as Lou Gehrig’s disease, can be aided by muscle injection of a therapeutic that produces small molecules of ribonucleic acid (RNA) as it moves inside the supplying nerves.
The treatment acts to silence the gene which codes for a mutated version of the protein, copper/zinc superoxide dismutase (SOD1). This gene is changed in some people who have inherited ALS. Mice are available that express this mutant SOD1, and they show symptoms remarkably similar to all cases of ALS, inherited or not.
The RNA therapeutic, injected into muscle, preserved grip strength of that hind limb when treated, as compared to untreated, SOD1 mutant mice. The fact that three different teams, using different viral delivery systems, all achieved therapeutic success in mice sends a strong signal of hope for rapid progress towards clinical testing of the approach, said Lucie Bruijn, Ph.D., ALSA’s science director and vice president.
The therapeutic targets the gene for SOD1 by producing RNA molecules that prevent translation of the gene into protein. An engineered virus, called a vector, carried the instructions to make the RNA. The virus, although no longer infectious, still retained its ability to enter cells and produces the silencing RNA within cells.
These researchers, including Timothy Miller and Don Cleveland of the Ludwig Institute at the University of California, San Diego, collaborating with Fred Gage of the Salk Institute in La Jolla, California, Brian Kaspar of the Columbus Children Research Institute in Ohio, and other colleagues, used an adeno-associated virus to get the RNA therapeutic into cells.
“While safety will be an important initial concern for applying this therapy to ALS patients, we are enthusiastic about the previous excellent safety profile of this virus (AAV-2) in humans,” said Miller. “Since patients present to clinic after development of symptoms, we are very encouraged by the positive effects we see in animals treated close to the first signs of disease.”
Two recent reports obtained success in the same mouse model of ALS using different lentiviruses to get the RNA produced inside cells (click here for more information).
The two groups reporting prior success both found that mice with the SOD1 mutation live longer and have slower onset of symptoms when treated with RNA inhibition. One team, Swiss researchers funded by ALSA and collaborators, injected the RNA construct into the spinal cord. The other team, a group at Oxford Biomedica, a biotech company in Britain, obtained positive results with injection of their construct into muscle, as did the Miller and Cleveland team.
Transport back to the cell bodies, a normal process in nerve cells, may allow treatment of ALS by injecting muscles. Direct injection of RNA into the spinal cord would pose practical difficulties for treating the disease in people, Miller and Cleveland noted in their report.
The therapeutic contained a marker that allowed the scientists to see that the construct appeared in the spinal cord after injection into muscle. This suggests that the virus with its gene cargo is taken up from muscle by the nerve endings and moved back into the nerve cell bodies in the cord. The amount of SOD1 protein was reduced in the spinal motor neurons that contained the marker, the researchers verified.
They noted that they cannot rule out that the RNA silencing therapy is also working by affecting the injected muscle. The exact role of muscle in ALS is not yet clear. Studies are beginning to focus on this topic, to determine if muscle cells are instigating damage, or if they are only reflecting the damage to their supplying nerve cells.
Click here for thePubMed article
