A Phase 2b/3 multicenter, randomized, double-blind, placebo-controlled, parallel group study to evaluate the efficacy, safety and tolerability of MN-166 given to ALS participants for 12 months followed by a 6-month open-label extension phase.

This is a Phase 2b/3 multicenter, randomized, double-blind, placebo-controlled, parallel group study to evaluate the efficacy, safety and tolerability of MN-166 followed by an open-label extension phase compared to matching placebo in subjects diagnosed with ALS.

The study will consist of a screening phase (up to 30 days) followed by a double-blind phase (12 months). Following the screening phase, subjects who continue to meet entry criteria will be randomly assigned to one of two treatment groups: MN-166 or matching placebo in a 1:1 ratio. Upon completion of the double-blind phase, subjects will be given the option to continue to the Open-label Extension Phase for a period of six months.

Major Inclusion Criteria:

• Male or female subjects age 18 - 80 years, inclusive;
• Diagnosis of familial or sporadic ALS as defined by the El Escorial-Revised (2000) research diagnostic criteria for ALS [clinically definite, clinically probable, probable-laboratory-supported];
• ALS onset of ≤18 months from first clinical signs of weakness prior to screening;
• If currently using riluzole, subject must be on a stable dose for at least 30 days prior to initiation of study drug;
• If currently using edaravone, subject should have completed at least 14 days of their initial treatment cycle prior to initiation of study drug;
• Last documented pulmonary function test result (i.e., slow vital capacity or forced vital capacity) must be greater than or equal to 70% predicted;
• Able to swallow study medication capsules;
• No known allergies to the study drug or its excipients;
• Received pneumococcal vaccine within 6 years prior to starting clinical trial.

Major Exclusion Criteria:

• Confirmed hepatic insufficiency or abnormal liver function (AST and/or ALT >3 times upper limit of normal);
• Currently diagnosed with a clinically significant psychiatric disorder or dementia that would preclude evaluation of symptoms;
• Currently use or treated with parenteral (intramuscular or intravenous) high dose (>25 mg/week) Vitamin B12 within 30 days prior to study drug administration;
• Poor peripheral venous access that will limit the ability to draw blood as judged by the Investigator;
• Currently participating, or has participated in a study with an investigational or marketed compound or device within 30 days or 5 half-lives, whichever is shorter, prior to signing the informed consent;
• Use of tracheostomy or >22/24-hour ventilatory support.