The primary purpose of this study is to evaluate the safety and tolerability of prosetin in healthy volunteers and participants with ALS.

PRO-101 is a four-part study. Parts A and B, which respectively evaluated the safety, tolerability, and PK of single and multiple ascending doses of prosetin in 48 healthy volunteers, have been completed.

Parts C and D, which are ongoing, will evaluate the effects of prosetin on safety, tolerability, PK, and biomarkers in 24 participants with ALS. Part C is a double-blind, placebo-controlled, multiple ascending dose component of the study, and Part D is an optional 52-week open-label extension available to ALS participants who complete 14 days of dosing in Part C.

PRO-101, Parts A and B, were completed in healthy volunteers.

PRO-101, Parts C and D are ongoing in participants with ALS. Key eligibility criteria are summarized below:

Key Inclusion Criteria - Part C

• Adults ≥18 years of age
• Diagnosis of ALS based on the Gold Coast diagnostic criteria
• Slow Vital Capacity (SVC) >50% predicted
• If being concomitantly treated with riluzole and/or locally approved standard of care treatments, the participant must be on a stable dose for at least 30 days prior to screening and throughout the study
• In the opinion of the Investigator, participant is able to swallow liquid in order to ingest the study medication.

Key Exclusion Criteria - Part C

• Active dementia, neurologic diseases other than ALS, or psychiatric illness that in the opinion of the investigator would affect participation in the current study.
• Significant history or clinical manifestation of comorbid disease in any organ system that currently requires active treatment or is likely to require treatment during the study.
• Any episodes of vertigo in the previous 12 months prior to screening.
• Any medical history of seizures, or any clinically significant EEG finding at Screening or at Day -1.
• A diagnosis of cancer or evidence of continued disease within five years before screening. Protocol-specified exceptions may be considered with approval from the Sponsor's Medical Monitor.
• Participation in any other investigational study drug trial in which receipt of an investigational study drug occurred within 30 days prior to the first dose of study medication.
• Prior exposure to any stem cell or gene therapies (investigational or off-label) for the treatment of ALS.

Key Inclusion Criteria- Part D

Participants who meet all of the following criteria may be included in Part D of the study:

• Participants must have completed 14 days of blinded treatment in Part C.
• Participants taking approved ALS standard-of-care medications must remain on stable doses through Day 28 of open-label treatment.
• In the judgment of the Investigator, the participant's participation in the open-label portion of the study is medically appropriate

Key Exclusion Criteria- Part D

• Treatment with any other investigational drug or device throughout the duration of the study is excluded, with the exception of any COVID-19 vaccine or treatment with an emergency use authorization.

NOTE: Other protocol-defined Inclusion/Exclusion Criteria may apply. Please contact trials@projenx.com with any questions about eligibility criteria.

Parts A, B, and C of PRO-101 are double-blind, dose escalating portions of the study. Part D is an open-label extension in which no parties are masked and all participants receive the study drug.