An experimental drug call latrepirdine has produced a small improvement in the mental abilities of some patients with Huntington's disease, a finding that sets the stage for a larger clinical trial. Although the improvement was modest, the study marks the first time that a drug has been shown to improve brain function in the disorder.
Huntington's is one of the more common inherited brain disorders. About 25,000 Americans have it and an additional 60,000 carry the defective gene that causes it and will develop the disorder as they age. It strikes between age 30 and 50 and is characterized by jerky, involuntary movements called chorea; loss of control of bodily functions; and dementia, a progressive deterioration of memory and thought processes. The only drug formally approved for treatment of Huntington's is tetrabenazine, which improves chorea but does nothing for mental faculties.
Latrepirdine was originally developed in Russia nearly three decades ago as a treatment for hay fever, but it is no longer sold anywhere. Russian researchers screening compounds for potential effects on the brain found that it appears to stabilize mitochondria, the power source of brain and other cells. Because of that activity, Medivation Inc. of San Francisco and Pfizer Inc, which purchased the rights to the drug, conducted a Phase 2 clinical trial of the drug in Alzheimer's patients and found some benefit. A larger Phase 3 trial, required for Food and Drug Administration approval, is now under way and results are expected later this year.
They also began testing it against Huntington's, which is marked by a deterioration of mitochondria in brain cells. In a Phase 2 trial, Dr. Kurt Kieburtz of the University of Rochester Medical Center and his colleagues studied the drug in 91 Huntington's patients over a 90-day period. Half received the drug in three daily doses and half received a placebo. The study was primarily a safety trial and the researchers concluded that the drug posed no untoward risks: About 70% of patients receiving the drug reported adverse side effects, but so did 80% of those receiving a placebo.
The drug produced no benefits on motor function, but it did yield an improvement in a mental test called the Mini-Mental State Examination, in which patients answer questions about what year it is and where they are, count backward, and try to recall words they haver recently heard. Patients receiving the drug showed an average improvement of 0.86 point on the 30-point scale, while those on placebo showed an 0.12-point decline. Kieburtz said he was surprised to see the improvement because the exam is a relatively crude test of mental function.
The trial was sponsored by Medivation and Pfizer, which hope to market the drug under the brand name Dimebon. The company now has a larger trial of 350 Huntington's patients in progress as a final step toward winning FDA approval.
-- Thomas H. Maugh II