Neuropsychiatric symptoms are an emerging unmet need in DMD, and most boys with this disease experience psychiatric symptoms, including anxiety, attention-deficit disorder, and learning disabilities. These manifestations are driven by central nervous system (CNS) defects consistent with loss of dystrophin in the brain. Therapies for DMD that leverage phosphorodiamidate morpholino oligomers (PMO) induce exon skipping in the DMD pre-mRNA and enable translation of a shortened but functional dystrophin. Regretfully, PMO displays modest efficacy because of poor muscle delivery; furthermore, PMO do not reach the CNS.
We developed the FORCETM platform to enhance uptake of diverse therapeutic payloads in muscle via a fragment antigen binding (Fab) antibody highly specific for transferrin receptor (TfR)1. We also demonstrated that our platform delivers charged oligonucleotides and protein payloads to the CNS. Preclinical data in mdx mice and initial results from the DYNE-251 clinical program in DMD showed that the FORCE platform enhances PMO delivery to muscle where it restores dystrophin expression; however, its ability to enable PMO distribution to CNS remains to be determined.
Mdx mice exhibit anxiety freezing behavior in response to restraint. To evaluate whether the FORCE platform can correct this phenotype, we generated mdx mice expressing human TFR1 (hTfR1;mdx). In this model, we tested efficacy of a TfR1-targeting Fab and PMO conjugate designed to skip exon 23 of murine Dmd pre-mRNA (FORCE-M23D). A single intravenous dose of FORCE-M23D, but not unconjugated M23D or non-TfR1 targeting negative control conjugate, led to widespread PMO distribution to CNS in hTfR1;mdx mice. PMO delivery to CNS induced Dmd pre-mRNA exon skipping and restoration of dystrophin protein expression, leading to complete and durable resolution of anxiety-induced freezing behavior.
In conclusion, the FORCE platform resolves anxiety in mdx mice by enabling PMO delivery to the CNS, revealing the potential to address neurological manifestations of DMD.