A Study in Participants With Duchenne Muscular Dystrophy Amenable to Exon 45 Skipping to Evaluate the Safety and Efficacy of ENTR-601-45

Inclusion Criteria: 1. Genetic diagnosis of DMD and confirmed pathologic variant in the dystrophin gene amenable to exon 45 skipping as reviewed by a central genetic counselor. 2. Assigned male at birth with clinical signs compatible with Duchenne muscular dystrophy as determined by the investigator. 3. Part A: 4-20 years of age, inclusive. 4. Ambulatory Status Part A: ambulatory with a Performance of the Upper Limb v2.0 (PUL 2.0) Entry as per protocol at Screening. 5. Adequate muscle for obtaining tissue biopsy as assessed by the investigator. 6. Other protocol-defined criteria apply. Exclusion Criteria: 1. Any significant concomitant medical condition that might interfere with the ability to comply with protocol requirements. 2. Has an acute illness within 4 weeks prior to the first dose of study drug which may interfere with study measurements or jeopardize participant's safety. 3. Use of the following medications : 1. Prior or current treatment with any exon skipping therapy within the previous 12 months 2. Prior or current treatment with any gene therapy 3. Use of anti-coagulants, anti-thrombotics, or anti-platelet agents from 30 days prior to screening and until the end of the study 4. Use of an immunosuppressant (other than systemic or oral corticosteroid for DMD condition) from 30 days prior to screening until the end of the study. 5. Treatment with a histone deacetylase (HDAC) inhibitor, including (but not limited to) givinostat from 30 days prior to screening until the end of the study 4. Laboratory abnormalities. 5. Daytime ventilator dependence or any use of invasive mechanical ventilation via tracheostomy. 6. Has an abnormal electrocardiogram (ECG) reading assessed as clinically significant by the investigator, and/or a QT interval with Fridericia correction method (QTcF) \>450 msec at Screening or prior to the first dose of study drug on Day 1. 7. Received any experimental or investigational drug, etc. within 3 months prior to first dose or within 5 half-lives (whichever is longer). 8. Other protocol-defined criteria apply.