Anti-Fibrotic ADCs Show Promise in Muscle Preservation for DMD

Progressive fibrosis is a defining feature of Duchenne muscular dystrophy (DMD), making it a key target for research that aims to improve cardiac and skeletal muscle function in patients. One such study was published in iScience by Odeh et al. and introduces a targeted approach to addressing fibrosis in DMD using an antibody-drug conjugate (ADC).

Here’s a quick look at the research and what its findings may mean for DMD patients.

Study Design and Molecular Targeting Strategy

For context, Lysyl oxidase (LOX) enzymes are responsible for maintaining the extracellular matrix (ECM), and upregulation or dysregulation of these enzymes are implicated in fibrotic disease pathologies. The ADC was designed to deliver a LOX inhibitor specifically to M2 macrophage concentrated fibrotic muscle regions. This preclinical investigation in mdx mice, a well-established DMD model, evaluated the construct’s biochemical specificity, biodistribution, and effects on muscle function and histology over time.

The ADC was engineered by conjugating a LOX inhibitor (CCT365623) to an anti-CD206 monoclonal antibody to selectively inhibit LOX activity in fibrotic ECM while sparing intracellular LOX functions involved in myogenesis. CD206 is primarily expressed by M2 macrophages, which are abundant in fibrotic tissue but minimally present in healthy muscle or myogenic cells.

In vitro experiments demonstrated that the ADC maintained specificity for M2 macrophages and preserved the bioactivity of the conjugated inhibitor. Internalization of the ADC by macrophages did not impair their viability or proliferation.

Biodistribution and Target Engagement in vivo

In 6-month-old mdx mice, intraperitoneal injection of the ADC led to its accumulation in fibrotic areas of skeletal and cardiac muscle (for example, gastrocnemius, diaphragm, and heart), but not in non-fibrotic tissues such as the liver, kidneys, or lungs. Immunofluorescence confirmed ADC colocalization macrophages, with no significant overlap observed with fibroblasts or endothelial cells, supporting the targeting specificity.

Functional and Histological Outcomes

Over the course of the study, mice were treated weekly from three to six months of age with ADC, unconjugated anti-CD206, free CCT365623, or control IgG. Functional assessments included treadmill endurance tests and echocardiography. The results demonstrated the following:

• Skeletal muscle function: ADC-treated mice showed significantly improved treadmill performance following three weeks of treatment, which was sustained over 12 weeks (p<0.005).
• Cardiac function: Significant improvements in fractional shortening and ejection fraction were observed in ADC-treated mice compared to controls (p<0.005).
• Fibrosis: Collagen type I staining revealed reduced fibrotic burden in the diaphragm and heart (p<0.01–0.005), while mRNA expression of fibrotic markers such as TGF-β1 and Col1a1 were upregulated, suggesting effects primarily at the protein level.

Muscle Preservation Beyond Fibrosis

Interestingly, ADC administration in younger mdx mice, which were three months old, for only three weeks appeared to reduce myofiber necrosis. This was evidenced by a lower number of necrotic fibers and reduced embryonic myosin expression (p < 0.001). No significant changes were observed in muscle fiber cross-sectional area.

Effects in Later Disease Stages

When the treatment window was shifted to six to 10 months of age, the functional benefits were more limited:

• No improvement was seen in treadmill performance.
• Cardiac function (EF and FS) remained better in ADC-treated mice than IgG controls (p<0.01).
• Diaphragm fibrosis showed a trend toward reduction (p=0.02, adjusted p=0.07), and fibrosis in the gastrocnemius muscle was significantly decreased (p<0.001).

These findings indicate that the ADC may be more effective during earlier disease intervention.

Interpretation and Considerations

Breaking down the results, this study presents a targeted method for modulating fibrosis in DMD by leveraging ADC technology to deliver a LOX inhibitor selectively to fibrotic regions. The findings suggest potential benefits in muscle preservation and function, particularly when treatment is initiated before fibrosis becomes extensive. However, the ADC’s effects appear to diminish in more advanced disease, possibly due to changes in macrophage infiltration or ECM architecture.

While promising, these findings are based on a murine model that does not fully capture the complexity of human DMD. Additionally, CD206 is not exclusively expressed on M2 macrophages, raising the need for further safety evaluation in more representative preclinical systems.

This study contributes to a growing body of work exploring fibrosis-targeted strategies in muscular dystrophies and underscores the importance of timing and tissue targeting in therapeutic design. Further investigation will be necessary to evaluate clinical applicability and long-term outcomes.

Reference:

1. Odeh A, Sela M, Zaffryar-Eilot S, et al. Anti-fibrotic, muscle-promoting antibody-drug conjugates for the improvement and treatment of DMD. iScience. 2025;28(5):112335. doi:10.1016/j.isci.2025.112335