ARTHEx Biotech Announces Publication in The American Journal of Human Genetics Highlighting the Discovery and Preliminary Preclinical Profile of ATX-01 for Myotonic Dystrophy Type 1 (DM1)

– Data establishes miR-23b as a disease-modifying target in DM1 and demonstrates enhanced muscle delivery and functional benefit of ATX-01 –

VALENCIA, Spain, Feb. 25, 2026 /PRNewswire/ — Arthex Biotech, a clinical-stage biotechnology company advancing RNA-based therapeutics for neuromuscular disorders, today announced the publication of a peer-reviewed research article entitled “Enhanced muscle uptake of chemically optimized miR-23b antisense oligonucleotides as lead compounds for Myotonic Dystrophy type 1” in The American Journal of Human Genetics (Cell Press). The publication can be accessed online here.

The publication showcases the discovery and initial characterization of ATX-01 (formerly known as X82108), ARTHEx’s lead therapeutic candidate in clinical testing for DM1, a rare neuromuscular disorder, in the Phase I/IIa ArthemiR™ trial. ATX-01 is an anti-miR oligonucleotide designed to inhibit microRNA23b (miR-23b), which is a natural repressor of MBNL protein expression. In DM1 patients, loss of MBNL protein function is caused by (1), reduced expression of MBNL proteins due to miR-23b upregulation and (2) MBNL sequestration in toxic DMPK mRNA, which leads to a spliceopathy, and is the cause of symptomatology in DM1 patients.

“These data support miR-23b inhibition as a compelling, disease-modifying approach for myotonic dystrophy type 1 and position ATX-01 as a differentiated lead candidate,” said Beatriz Llamusi, PhD, Chief Scientific Officer and Co-Founder of Arthex. “Beyond DM1, our findings highlight the scalability of our chemistry and delivery strategy—particularly lipid conjugation—to unlock the therapeutic potential of microRNA-targeting oligonucleotides across skeletal muscle disorders. We thank Cell Press for recognizing this important preclinical work.”

DM1 is a multisystemic, RNA-mediated genetic disorder caused by expanded CTG repeats in the DMPK gene, leading to toxic RNA transcripts that disrupt post-transcriptional regulation. A central pathogenic mechanism is the depletion of Muscleblind-like (MBNL) proteins—particularly MBNL1 in skeletal muscle—resulting in widespread alternative splicing defects, persistent fetal RNA programs, muscle weakness, myotonia, and progressive atrophy. In addition to RNA sequestration, dysregulated microRNA expression contributes to disease severity. Notably, miR-23b is consistently upregulated in DM1 muscle and directly represses MBNL1 translation, further amplifying downstream molecular dysfunction.

ARTHEx establishes miR-23b as a therapeutically actionable target in DM1 and describes the development of chemically optimized anti-miR compounds designed to inhibit its activity. Using an integrated discovery and optimization strategy encompassing sequence selection, chemical modification, and lipid conjugation, ARTHEX scientists identified X82108 (now ATX-01) as the lead therapeutic candidate with markedly improved pharmacokinetic and pharmacodynamic properties compared to previous candidates.

A key innovation described in the paper is the conjugation of oleic acid to the anti-miR backbone, which substantially enhanced biodistribution to skeletal muscle—one of the primary delivery challenges in DM1 therapy. In vivo, ATX-01 reduced miR-23b levels, restored MBNL1 protein expression, and corrected disease-relevant splicing defects across two complementary DM1 mouse models, including the HSALR model. These molecular effects translated into meaningful functional improvements, including reduced myotonia and improved muscle strength.

Therapeutic activity was further validated in patient-derived human myoblasts, demonstrating consistency across distinct genetic backgrounds. Transcriptomic analyses confirmed selective derepression of endogenous miR-23b targets and partial normalization of a validated DM1 splicing biomarker panel associated with muscle function and disease severity. Importantly, the anti-miR mechanism of action was conserved across mammalian species, supporting translational relevance.

Preliminary preclinical safety evaluations showed a favorable toxicological profile, with minimal immune activation and no major renal or coagulation liabilities at therapeutically relevant doses. Compared with earlier antimiR approaches, X82107 and ATX-01 achieved sustained molecular and functional correction at significantly lower doses and with prolonged duration of action, addressing key limitations of prior oligonucleotide-based strategies in DM1.

ATX-01 is currently being evaluated in the ArthemiR™ study, which is a randomized, placebo-controlled, double-blind single (SAD) and multiple ascending dose (MAD) study evaluating ATX-01 in adults with DM1. ATX-01 has received Orphan Drug Designation for ATX-01 in DM1 from the US FDA and European authorities, as well as Rare Pediatric Disease (RPD) Designation from the FDA.

About ARTHEx Biotech

ARTHEx Biotech is a clinical-stage company developing targeted RNA medicines designed to precisely modulate gene expression. Its proprietary platform, BOOST-ON^TM, pairs selective oligonucleotides with enhanced tissue delivery to reach skeletal muscle, heart, and brain. Its lead program, ATX-01, is in clinical evaluation for myotonic dystrophy type 1 (DM1), a rare neuromuscular disorder, in the Phase I/IIa ArthemiR™ trial. Building on this foundation, ARTHEx is advancing a pipeline of therapies for additional areas of high unmet need across muscular, CNS and cardiac diseases.

The Company headquarters are in Valencia, Spain.

For more information on ArthemiR™, please visit https://www.arthemir.com or https://clintrials.gov. For more information, please visit www.arthexbiotech.com and engage with us on LinkedIn.

Company Contact.	Investor and Media Contact
Frédéric Legros	Amy Conrad
Executive Chairman and CEO	Juniper Point
[email protected]	[email protected]
+33679495790	+1 858-366-3243