Identification of Gene‐Therapy Responsive Blood Biomarkers in mdx Mouse Model

Abstract

IntroductionIdentifying serum biomarkers that reflect the restoration of dystrophin in skeletal muscle is important for evaluating the effect of dystrophin‐restoring therapies in preclinical and clinical trials. Many potential blood biomarkers have been identified in Duchenne muscular dystrophy (DMD) patients, which change with disease progression or respond to pharmacological treatment. In this study, it was suggested that a panel of such blood biomarker candidates could be used to monitor dystrophin rescue in mdx mice treated with microdystrophin based therapies.MethodsPlasma samples from mdx mice treated with the microdystrophin therapy SGT‐001 were analysed with an antibody suspension bead array consisting of 87 antibodies. The array targets 83 unique proteins previously identified as biomarker candidates for DMD. Each sample was assayed at two different plasma dilutions to cover a broader concentration range. Protein concentrations estimated as Median fluorescent intensities (MFI) were correlated to dystrophin expression in muscle tissue, as measured by immunohistochemistry and Western blot. Thirteen of the targets were selected and analysed in a DMD and Becker muscular dystrophy (BMD) longitudinal natural history cohort using a suspension bead array.ResultsTen proteins were found to be significantly elevated in untreated mdx mice compared with C57 wild‐type mice and to correlate with dystrophin expression (Spearman's correlation, FDR < 0.05) upon gene transfer in mdx mice. Translatability of these biomarkers from animal models to patients was evaluated by exploring abundance trajectories over time in both DMD and BMD patients and association with dystrophin expression in BMD patients. Consistent with the observations in mouse, six of these biomarker candidates were more abundant in DMD patients compared with controls, and six were also differentially abundant between BMD and DMD patients. Among them, serum titin was shown to be associated with dystrophin expression in BMD patients, having a steeper decline over time in patients with low dystrophin expression in tibialis anterior compared with patients with high expression. Myosine light chain 3 had a steeper decline with time in DMD patients compared with BMD patients.ConclusionsThe 10 biomarker candidates identified in mouse plasma are related to muscle contraction, glycolysis, microtubule formation and protein degradation. Human titin and myosine light chain 3 were the most interesting candidates as explorative biomarkers to monitor microdystrophin expression in gene therapies. If confirmed, these biomarkers could be used to detect restoration of dystrophin expression per se, monitor changes in dystrophin expression over time and potentially confirm disease phenotype changes from severe to mild disease forms.