Drug Development · eu
RNA Drug Crosses the Blood-Brain Barrier: Molecular Dysregulation and Exploratory Behavior Improve in Parallel in DM1 Mice
Intravenously administered antimiR-23b entered the brain in a model of myotonic dystrophy type 1, increased MBNL proteins, corrected some abnormal RNA splicing, and reversed a change in exploratory activity. The findings offer clues for addressing central nervous system symptoms but cannot yet be regarded as evidence of efficacy in humans.
Myotonic dystrophy type 1 (DM1) not only makes it difficult for muscles to relax but may also affect cognition, mood, and behavior. This presents an additional hurdle for drugs: even if they can reach muscle, they may not cross the blood-brain barrier that protects the brain. A peer-reviewed preclinical study released by ARTHEx Biotech showed that an RNA drug modified with a lipid can exert molecular effects in the brains of DM1 mice after intravenous administration and restore abnormal exploratory activity to near-normal levels.
Published in *Cell Reports Medicine*, the study used the DMSXL mouse model, whose DMPK gene carries a very long CTG repeat sequence. Researchers tested antimiR-23b, which is related to the clinical candidate ATX-01. Rather than directly removing the mutant gene, it inhibits microRNA-23b, lifting its suppression of MBNL protein production.
DM1 arises when DMPK RNA containing expanded repeat sequences accumulates in the cell nucleus and traps MBNL proteins involved in RNA splicing; elevated miR-23b further reduces MBNL expression. Together, these two forces cause many RNAs to select the wrong segments during processing, affecting the muscles, heart, and nervous system. The study showed that treatment increased MBNL1 and MBNL2 proteins in multiple brain regions, reduced toxic DMPK transcripts, and partially corrected several abnormal splicing events.
Beyond the molecular changes, the research team recorded that the model mice’s previously abnormal exploratory activity returned to normal after treatment. This establishes a preliminary connection between “target engagement in the brain” and “measurable behavioral change,” but exploratory activity is only a specific animal behavioral measure and cannot be directly equated with improvements in patients’ cognition, fatigue, sleepiness, or mood symptoms.
ARTHEx said no significant toxicity or neuroinflammation was observed in the study. These results remain limited by the scale of preclinical research: animal models cannot fully reproduce the diversity of disease in patients, and splicing correction occurred only partially. The current data have not yet answered the extent to which the drug enters the human brain, the risks of long-term repeated dosing, or what dose is required for central nervous system effects.
Background
ATX-01 has entered a Phase 1/2 clinical trial named ArthemiR. The trial registry lists it as a formulation of anti-miR-23b X82108 and uses parallel ATX-01 and placebo groups with a triple-blind design in adults with classic DM1. Early evaluations remain focused on safety, tolerability, pharmacokinetics, and pharmacodynamic measures, rather than demonstrating improvement in brain symptoms.
The study’s real advance, therefore, is the potential breadth of treatment: a systemically administered RNA therapy may not have to choose between muscle and brain. Whether it can translate the molecular and behavioral signals seen in mice into functional improvements that patients can perceive will require validation in human trials using appropriate central nervous system endpoints.