SOD1 Inhibition by Pyrimethamine in Familial Amyotrophic Lateral Sclerosis (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. We will also assess the feasibility of
proceeding to phase II/III studies using pyrimethamine. Using futility methodology in which
patients treated with pyrimethamine will be compared to historical controls, 40 patients
with mild to moderate FALS and SOD1 mutations will receive up to 75 mg of pyrimethamine for
36 weeks. A change of 15% in the slope of decline will be deemed significant with a power of
80.7 percent. Change in ALS-FRS 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.

Inclusion Criteria:

- Subjects with definite, probable, or laboratory supported probable ALS will be
eligible.

1. ALS diagnosed as probable, laboratory supported probable or definite according
to the World Federation of Neurology El Escorial criteria [Brooks et al. 2000]

2. Age 18 or older

3. Capable of providing informed consent and complying with trial procedures

4. SOD1 mutation confirmation by study team

5. Not taking Riluzole (Rilutek) or on a stable dose for 30 days

6. Not taking Coenzyme QR10R or on a stable dose and brand for 30 days

7. Absence of exclusion criteria

Exclusion Criteria:

1. History or evidence of malabsorption syndromes

2. Exposure to any experimental agent within 30 days of onset of this protocol

3. Women who are pregnant or planning to become pregnant

4. Women of childbearing potential not practicing contraception

5. Women who are breastfeeding

6. Enrollment in another research study within 30 days of or during this trial

7. Alcoholism

8. Patients taking phenytoin (Dilantin) or other therapy affecting folate levels

9. Dementia (MMSE <22)

10. Seizure disorder

11. Folate deficiency

12. Megaloblastic anemia

13. Cardiovascular disorder/arrhythmia

14. Impaired kidney function, defined as creatinine levels of 2.5 x ULN

15. Impaired liver function, defined as AST or ALT of 3 X ULN

16. Advanced ALS patients, defined as those with any of the following: forced vital
capacity <60% (use of BIPAP is allowed); tracheostomy; or mechanical ventilation

17. Use of any of the following medications: cytosine, arabinoside, methotrexate,
daunorubicin, sulfonamides, zidovudine, lorazepam, coumadin, sulfamethoxazole, and
trimethoprim

18. Patients taking Lithium within 30 days of or during this trial

19. Incapable of providing informed consent and complying with trial procedures