In Myasthenia Gravis, Antibodies Pass Open-Label Tests

PHOENIX — Open-label extension studies of two neonatal Fc receptor–blocking antibodies showed good safety and efficacy in patients with myasthenia gravis (MG). The two drugs, rozanolixizumab (Rystiggo, UCB) and efgartigimod PH20 (Vyvgart, Argenx SE), received Food and Drug Administration approval in June 2023 and December 2021, respectively, for the treatment of MG.

The neonatal Fc receptor binds to IgG within cells and recycles it back into the blood, leading to increased serum levels. The antibodies bind to the neonatal Fc receptor and promote its degradation, therefore preventing IgG recycling without interfering with its production. They do not affect the levels of other immunoglobulin isotypes.

At the 2023 annual meeting of the American Association for Neuromuscular and Electrodiagnostic Medicine (AANEM), researchers presented data from an open-label extension study following the phase 3 MycarinG trial of rozanolixizumab and the ADAPT-SC+ study of efgartigimod.

In the MycarinG study, rozanolixizumab “showed both statistically significant and clinically meaningful improvements in multiple endpoints,” said Vera Bril, MD, during a presentation of the results.

Rozanolixizumab is approved for MG patients who are anti–acetylcholine receptor (AchR) or anti–muscle-specific tyrosine kinase (MuSK) antibody positive. Efgartigimod is approved for MG patients who are AChR positive.

After completing MycarinG, patients were eligible to enroll in one of two open-label studies, one of each dose.

The new efficacy analysis focused on 110 patients who underwent two or more consecutive symptom-driven treatment cycles. A safety analysis focused on 188 patients who received at least one cycle of treatment.

“The post hoc analysis showed that the clinically meaningful improvements in the generalized myasthenia gravis symptoms were maintained over time for the cohort across rozanolixizumab cycles, while individual patients move through the consecutive treatment cycles, rozanolixizumab had an acceptable safety profile that was maintained across repeated treatments cycles. This is consistent with previous results of rozanolixizumab,” said Bril, who is a clinical investigator at University of Toronto.

A Reduction in Steroid Use?

During the Q&A session, George Small, MD, asked if the study had shown a reduction in steroid use among patients with MG.

As clinical associate director of neurology at Allegheny Medical Center, Pittsburgh, he has overseen the care of several hundred patients with generalized MG, as well as participated in clinical trials. “Many physicians use steroids for very quick responses in their patients. I love steroids and I hate steroids. I’ve helped save people’s lives with them, but I’ve also probably hastened their demise, unfortunately, because of the long-term side effects of the medications. Many neurologists in the community will over-utilize steroids because they don’t have access to these more expensive therapies. I look forward to both using these medications more as they become FDA approved and being an advocate for them, because it is my belief that they help decrease the use of steroids,” said Small in an interview.

Even if new medications do reduce steroid use, there remains a hurdle with insurance companies. “I’ve felt I’ve been forced to use treatments that I know may not be efficacious in the short term in order to get authorization for more expensive therapies that I use now. I’ve had patients admitted to the hospital as I’ve tried to jump through hoops that the insurance companies demanded,” said Small.

Clinical Improvements Seen

In the MycarinG study, patients received weekly injections of 7 mg/kg, 10 mg/kg rozanolixizumab, or placebo over a 6-week period. Both treatment groups had reductions in Myasthenia Gravis Activities of Daily Living (MG-ADL) scores compared with placebo.

MG-ADL and Quantitative Myasthenia Gravis (QMG) scores were consistent across treatment cycles. The mean MG-ADL score dropped by about 4 points at week 6. At around week 10, the mean improvement declined to 2 points, and then by week 14 it increased to 3 points, where it remained consistent out to 50 weeks. A similar pattern was seen in QMG scores, with an approximate 5-point drop at 6 weeks, then about a 1.5-point improvement at 10 weeks, then a mean decrease of around 4 points that stayed stable out to 50 weeks.

Over all cycles of treatment, 89.9% of patients experienced a treatment-emergent adverse event, including 22.3% who had a serious TEAE; the study dropout rate because of TEAEs was 15.4%.

In the ADAPT-SC study, 110 patients were randomized to 10 mg/kg intravenous efgartigimod or 1,000 mg efgartigimod PH20, which is formulated with recombinant human hyaluronidase to allow for rapid administration of larger volumes. After completion of ADAPT-SC, 105 patients from both groups and an additional 79 patients entered the open-label extension study with 1,000 mg efgartigimod PH20.

The study included 141 patients who were AChR-Ab positive and 38 who were AChR-Ab negative. In the first cycle, 34.6% experienced an injection-site reaction, which steadily dropped to 11.5% by the sixth cycle. After each cycle of treatment, the mean change in MG-ADL from study baseline at week 4 was between 4.1 and 4.7 points. The mean change in Myasthenia Gravis Quality of Life 15-Item Questionnaire revisited from study baseline at week 4 was between 5.1 and 6.5 points. The mean change in EuroQoL 5-dimension, 5-level visual analog scale was between 12.3 and 16.0 points at week 4.

MyCarinG was funded by UCB Pharma. ADAPT-SC was funded by Argenx SE. Bril has financial relationships with Behring, Argenyx, Alexion, Immunovant, Alnylam, Akcea, Takeda, Sanofi, Ionis, Roche, Novo Nordisk, Octapharma, Momenta, Pfizer, CSL Behring, Grifols, Powell Mansfield, UCB, and Viela Bio. Small is on the speaker’s bureau for Alexion.

This story originally appeared on, part of the Medscape Professional Network.

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