generalized myasthenia gravis Archives

On June 27, 2023, the US Food and Drug Administration approved RYSTIGGO® (rozanolixizumab-noli) for the treatment of generalized myasthenia gravis (gMG) in adult patients who are anti-acetylcholine receptor or anti-muscle-specific tyrosine kinase antibody positive. Rozanolixizumab-noli is a humanized IgG4 monoclonal antibody that binds to the neonatal Fc receptor, resulting in the reduction of circulating IgG. The drug is administered by subcutaneous infusion. UCB has indicated that rozanolixizumab-noli will be commercially available in the US during the 3rd quarter of 2023.

FDA’s approval is supported by safety and efficacy data from the pivotal Phase 3 MycarinG study (NCT03971422), published in The Lancet Neurology in May 2023. The primary efficacy endpoint was the comparison of the change from baseline between treatment groups in the MG-ADL total score at day 43. MG-ADL is a measurement tool which assesses the impact of gMG on daily functions of 8 signs or symptoms that are typically affected in gMG, such as breathing, talking, swallowing, and being able to rise from a chair. Each item is assessed on a 4-point scale where a score of 0 represents normal function and a score of 3 represents loss of ability to perform that function. A total score ranges from 0 to 24, with the higher scores indicating more impairment. A statistically significant difference favoring rozanolixizumab-noli was observed in the MG-ADL total score change from baseline [-3.4 points in rozanolixizumab-noli-treated group at either dose vs -0.8 points in the placebo-treated group (p<0.001)].

Interested in data for other antibody therapeutics that have received marketing authorizations? Go to our searchable table of approved antibody therapeutics and those in regulatory review for more information.

Summary written by Alicia Chenoweth, PhD, King’s College London

Antibody Engineering & Therapeutics, held in December 2022, offered many opportunities to hear exciting and informative presentations by experts in the field, including Dr. Hans de Haard, Chief Scientific Officer at argenx.

Dr. de Haard’s talk, Efgartigimod: A Novel FcRn Antagonist in the Treatment of Autoimmune Diseases, detailed the mechanism of action and clinical trial results of the FcRn antagonist efgartigimod. Efgartigimod is a human IgG1 Fc fragment with five “Abdeg” mutations (M252Y, S254T, T256E, H433K, N434F) to increase its affinity for FcRn at both low pH and neutral pH (1,2). It is designed to outcompete the binding of serum IgG for FcRn, leading to degradation of the unbound IgG and recycling of efgartigimod back to the surface of the cell to be released back into circulation.

Dr. de Haard discussed the findings of a recent publication in which the biochemical, structural, and in vivo properties of efgartigimod and a full-length antibody counterpart containing the same Abdeg mutations were compared (3). Crystallographic studies of FcRn in complex with the full-length antibody demonstrated that the antigen-binding fragment projects towards the membrane, leading to a potential steric clash hindering binding. This hypothesis was confirmed using a bioassay measuring receptor occupancy, showing that efgartigimod gave a better FcRn occupancy and had improved uptake compared to the full-length antibody. Furthermore, in cynomolgus monkeys, the Fc fragment gave a much faster clearance of tracer antibody and a more potent pharmacodynamic effect compared to full-length antibody. Thus, the Fc fragment was determined to be the better performing FcRn antagonist over the full-length antibody due to improved blocking of IgG recycling in vitro and the more potent PD effect in vivo.

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