Phase I/II Study of SOD1 Inhibition by Pyrimethamine in Familial ALS

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease causing relentlessly progressive weakness of the arms, legs and respiratory muscles that is uniformly fatal. There are approximately 30,000 patients living with ALS in the United States. There is no treatment. The cause is uncertain in most patients. However, 3% of patients (< 1000 in number) have a familial form of ALS (FALS), phenotypically identical to the sporadic illness, that is caused by a mutation in the gene coding for the free radical scavenging enzyme copper/zinc superoxide dismutase (SOD1). Inserting the SOD1 mutant gene into mice causes them to develop a disease closely resembling ALS.

Inhibiting expression of the SOD1 gene prevents animals from developing the disease. Increasing or decreasing the number of mutated genes proportionately speeds or slows the progression of the disease. Therefore, reducing SOD1 levels in patients with SOD1 associated FALS may be a promising therapeutic approach. Through an extensive in vitro screening program for medications having the ability to reduce SOD1 levels, several molecules that reduce SOD1 protein levels are known. One of the most potent molecules is pyrimethamine, an FDA approved medication used for the treatment of malaria and toxoplasmosis. Pyrimethamine dramatically reduces SOD1 levels in mice and our preliminary studies show similar findings in humans. Our study's primary objective is to determine if familial ALS patients taking pyrimethamine will show a decline in SOD1 levels in the CSF by 15% or more. We will also determine if SOD1 and pyrimethamine are present in the blood and if the SOD-1 levels decline over the course of the study. We will also evaluate the safety and tolerability of pyrimethamine in patients with FALS. Secondary objectives will be to determine dose optimization for maximal SOD1 level reduction and tolerability of medication. We will also assess the feasibility of proceeding to phase II/III studies using pyrimethamine. Change in ALS-FRS, Appel ALS score and quality of life will also be measured. A clinical effect realized in patients with FALS associated with an SOD1 mutation may serve as an important foundation toward finding a treatment for sporadic ALS.