Late-stage trial of claseprubart will aim to confirm drug’s benefits for gMG
FDA awards therapy orphan drug status with promise of marketing exclusivity
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- Dianthus Therapeutics is on track to launch a clinical trial by midyear to confirm the benefits of claseprubart, its therapy candidate for generalized myasthenia gravis.
- Earlier trial results showed positive safety and effectiveness in people with gMG
- The FDA has awarded the injection therapy orphan drug status, which would grant seven years of market exclusivity should claseprubart ultimately be approved.
Dianthus Therapeutics is on track to launch by midyear a late-stage clinical trial to confirm the safety and effectiveness of claseprubart (DNTH103), its experimental injection therapy, in people with generalized myasthenia gravis (gMG).
The Phase 3 study, called EMERGE, will be registrational, meaning it will be designed to generate sufficient data, should they be positive, to support an application for the therapy’s approval. Top-line results are expected in the second half of 2028, according to a press release from Dianthus announcing business updates and its latest financial results.
The announcement regarding the upcoming trial follows the successful completion of a meeting between Dianthus and the U.S. Food and Drug Administration (FDA). At it, the parties discussed positive top-line results from the global Phase 2 MAGIC clinical trial (NCT06282159), which strongly suggested that claseprubart can safely and effectively ease symptoms in adults with gMG.
Dianthus also now announced that the FDA has granted orphan drug status to claseprubart for treating myasthenia gravis (MG) — a designation that is expected to accelerate the therapy’s development.
Such status is awarded to treatments for rare diseases that affect fewer than 200,000 people in the U.S. It comes with several benefits for Dianthus, including tax credits for clinical trial costs, exemptions from certain FDA user fees, and the potential for seven years of market exclusivity if the drug is ultimately approved.
gMG is an autoimmune disease in which self-targeting antibodies attack proteins involved in nerve-muscle communication, leading to symptoms such as muscle weakness and fatigue. The most common target of MG-driving antibodies is the acetylcholine receptor (AChR) protein.
The binding between anti-AChR antibodies and their target AChR activates the classical pathway of the complement cascade, a part of the immune system, which further contributes to the MG-driving autoimmune responses.
Self-administered therapy designed to require less-frequent dosing
Claseprubart is an antibody-based therapy designed to suppress the classical complement pathway by selectively blocking the active form of the complement protein C1s. That, in turn, is expected to reduce complement-mediated damage and ease symptoms in gMG patients.
The treatment is formulated for self-administration via under-the-skin (subcutaneous) injection, and is engineered to remain in the body for longer periods, which would allow for less frequent dosing. The therapy is likely to be given every two or four weeks if eventually approved.
The MAGIC trial was designed to assess the safety, tolerability, pharmacological properties, and preliminary effectiveness of claseprubart in people ages 18-75 with gMG. All participants tested positive for anti-AChR antibodies.
Investigators randomly assigned study participants to receive either one of two doses (300 mg or 600 mg) or a placebo for 13 weeks, or about three months. Following an initial intravenous, or into-the-vein, loading dose, participants received subcutaneous injections every two weeks.
According to trial data reported last year, claseprubart was generally well tolerated and significantly eased disease severity by week 13, as reflected by score reductions in the standard MG Activities of Daily Living (MG-ADL) and the Quantitative MG (QMG) scales.
MG-ADL scores dropped by 1.8 points at the low dose and 2.6 points at the higher dose compared with the placebo. QMG scores were also reduced by 2.4 points at the low dose and 2.5 points at the high dose relative to the placebo. Statistically significant and clinically meaningful score reductions were seen as early as week one.
New trial data show benefits with claseprubart vs. placebo
Additional results were presented last month at the 2026 American Academy of Neurology annual meeting in Chicago. Those new data showed that more than 60% of participants treated with the low claseprubart dose achieved a minimum 5-point drop in MG-ADL and QMG scores, which are considered clinically meaningful.
Those in the 300 mg dose group were also pronouncedly more likely than those on the placebo to achieve minimal symptom expression on the MG-ADL after 13 weeks (37% vs. 14%), defined as an MG-ADL score of one or less and meaning no or minimal disease impact on daily activities.
This difference nearly reached statistical significance, though the differences between the high dose and placebo groups were far from that threshold. Those findings further support 300 mg as the optimal dose of claseprubart, according to the developer.
Gains in quality of life were also observed at both doses, but were more pronounced with the high dose, as measured by the Myasthenia Gravis Quality of Life 15-item Scale-Revised.
Those who completed MAGIC’s placebo-controlled portion could join its open-label extension (OLE) portion, in which all are receiving claseprubart for up to one year. The OLE’s early pharmacological data support a 300 mg dose given once every four weeks in the planned Phase 3 EMERGE study, per the developer.
The new trial is expected to enroll an estimated 205 adults with gMG who test positive for anti-AChR antibodies. Participants will be randomly assigned to receive either claseprubart or a placebo for 17 weeks, or about four months. After an initial loading dose, participants will be given 300 mg of claseprubart or a placebo, once every 2-4 weeks. Outcome measures in this trial match those in the Phase 2 study.
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