"Attempting to intervene is very risky, but because the problem is important, it's worth doing," he said.
In the current study, the researchers created short lengths of molecules that resemble ribonucleic acid (RNA), the chemical cousin of DNA. These mimics, called PNAs and LNAs, were specifically designed to bind to CAG repeats, preventing cells from creating the abnormal proteins. The researchers also designed short lengths of RNA called small interfering RNA, or siRNA, to interfere with CAG repeats.
In cells from Huntington's patients, the PNAs, LNAs and siRNAs decreased the amount of mutant protein produced, in some cases up to 100 percent. The effect was greatest when the compounds interfered with long lengths of CAG repeats; the effectiveness varied, however, among cells taken from different patients.
Some forms of these compounds left the normal forms of huntingtin and ataxin-3 proteins undisturbed, but other compounds partly or completely blocked their formation. In some cells, some of the RNA mimics drastically cut the production of both mutant and normal proteins an undesirable effect, Dr. Corey said.
These findings indicate that further tweaking of the molecular structures of the RNA mimics will be needed to minimize the effects on normal proteins.
"It is encouraging that small chemical changes could substantially enhance selectivity," Dr. Corey said. "If we can test a handful of compounds and identify better ones, we have reason to believe that more testing will continue to produce significant improvement."
Because this study was done in cultured cells, and not in whole animals or humans, it does not indicate how much of the abnormal proteins must
|Contact: Aline McKenzie|
UT Southwestern Medical Center