Now, with three human RNAi gene therapy trials under way, Kay's initial excitement is proving to be on target. However, reaching this point hasn't been without challenges. In the latest twist, Kay, professor of genetics and of pediatrics at the Stanford University School of Medicine, and postdoctoral fellow Dirk Grimm, PhD, report an unexpected side effect of another type of RNAi gene therapy not on trial - mice in that study suffered liver toxicity from the treatment and some died. Despite that initial result, to be published in the May 25 issue of Nature, Kay and Grimm went on to find a way that shows promise in resolving this side effect.
"Just like any other new drug, it is just going to mean that we need to proceed cautiously," Kay said.
In traditional gene therapy the inserted DNA produces a gene to replace one that carries a mutation. In hemophilia, for example, the inserted gene makes a protein that is missing in the blood of people with the disease. RNAi gene therapy has the opposite effect. The inserted DNA produces a molecule called an shRNA, which turns off an overactive gene.
With key genes shut off, viruses such as hepatitis B, hepatitis C or HIV are unable to multiply and cause disease. However, some reports had suggested that RNAi gene therapy might induce an immune reaction or switch off the wrong gene or genes.
As these concerns faded, things began looking up for RNAi with three RNAi therapies now in human trials - two for macular degeneration and one for a type of pneumonia. However, these studies involve simply infusing the RNAi molecules into the eye or lung. The RNAi effects in these therapies aren't permanent. Instea
Source:Stanford University Medical Center