Key Inclusion Criteria:  Diagnosis of sporadic or familial ALS Less than 3 years since ALS symptom onset Stable doses of approved ALS treatments (riluzole and/or edaravone) for at least 2 months prior to screening Participants must be able to swallow the study intervention Vital capacity >50% predicted at screening Women must have been surgically sterilized or be postmenopausal Men, and sex partner if a woman of childbearing potential, must use highly effective contraception  Key Exclusion Criteria:  Any history of unstable or poorly controlled psychiatric, endocrine, pulmonary, cardiovascular, gastrointestinal, hepatic, pancreatic, renal, metabolic, hematologic, immunologic, or allergic disease, or other major disorders Positive serum pregnancy test or currently lactating or breastfeeding History of malignancy within 5 years History of clinically significant neurologic disorders other than ALS