A Study to Assess the Efficacy and Safety of MNK-1411 in Duchenne Muscular Dystrophy

Inclusion Criteria: 1. Participants must have a documented diagnosis of Duchenne Muscular Dystrophy (DMD) confirmed by complete dystrophin deficiency (by immunofluorescence and/or immunoblot), or identifiable mutation in the DMD gene where reading frame can be predicated as "out of frame," or complete dystrophin gene sequencing consistent with DMD; AND in the opinion of the Investigator, a typical clinical profile consistent with DMD. 2. Participants taking approved treatments for DMD (by a Health Authority) that target dystrophin gene mutations (e.g., eteplirsen or ataluren) may be enrolled in the study if they have been on a stable dose for 30 days prior to the first dose of study drug, and plan to remain on that dose throughout the study. Exclusion Criteria: 1. Participant has had previous systemic treatment with corticosteroids within 2 months prior to the Screening Visit. Exception: In subjects who were down-titrated to a physiological dose of corticosteroids (ie, 3mg/m2 of prednisone or deflazacort) a maximum of 1 month of no greater than a physiological dose followed by 1 month completely off corticosteroids prior to the Screening Visit will be acceptable for study entry. Transient previous use of corticosteroids will be evaluated on a case-by-case basis by the sponsor or designee. The use of topical or intra-articular corticosteroids is permitted during the study 2. Participant is unable to complete the 10 meter Walk/Run test at the Screening and/or Baseline Visit. 3. Participant has Type 1 or Type 2 diabetes mellitus. 4. Participant has a history of chronic active hepatitis including acute or chronic hepatitis B, or acute or chronic hepatitis C. 5. Participant has a history of tuberculosis (TB) infection, any signs/symptoms of TB, or any close contact with an individual with an active TB infection. 6. Participant has known immune compromised status (not related to disease/condition under study), including but not limited to, individuals who have undergone organ transplantation or who are known to be positive for the human immunodeficiency virus.