Optimized Second-Generation IL-4Rα Inhibition: Structural and Molecular Dynamics Properties of Rademikibart Fab-IL-4Rα Complex

Abstract

Introduction: Global Burden of Disease studies showed atopic dermatitis (AD) and asthma are the top two immune-mediated inflammatory diseases at younger age [1]. Dupilumab was the initial first-generation interleukin-4 receptor alpha (IL-4Rα) inhibitor for treating both type I and type II IL-4Rα-dependent inflammatory disorders. Following recent clinical trials, rademikibart (previously, CBP-201) emerges as an optimized next-generation human monoclonal antibody with higher binding affinity to IL-4Rα compared to dupilumab [2]. It demonstrated better effect in inhibiting STAT6 intracellular signaling in vitro and provided similar potency inhibiting both IL-4 induced TARC release and IL-4 induced B cell activation [2].

Materials & Methods: X-ray crystallography was used to determine the atomic resolution 3D structure of rademikibart fragment antigen binding (Fab) bound to IL-4Rα. This structure was analyzed and compared computationally with the 2.82 Å resolution crystal structure of dupilumab Fab bound to IL-4Rα (Protein Data Bank Code 6WGL). Molecular dynamics studies on rademikibart and dupilumab bound to IL-4Rα examined the stability of the complexes and effects of amino acid mutations on complex formation.

Results: The x-ray crystal structure of rademikibart Fab bound to IL-4Rα was determined at 2.71Å and compared to the complex of dupilumab Fab and IL-4Rα. The rotation angle between dupilumab and rademikibart bound to IL- 4Rα is 59.17°. This rotation enables the epitope of rademikibart, but not dupilumab, on IL-4Rα to overlap more closely with the conserved binding interface utilized by IL-4 and IL-13 cytokines. Molecular dynamics simulations of rademikibart Fab and dupilumab Fab complexed with IL-4Rα showed the third interface loop (residues 148 to 152 in domain 2) of IL-4Rα interacts directly with rademikibart, which is absent in dupilumab/IL- 4Rα complex. This finding is confirmed by analysis of the hydrogen bond interactions at the interface between the antibodies and IL-4Rα, demonstrating superior binding energy for rademikibart. Through single amino acid mutation analysis on rademikibart, we identified residue Y50 on rademikibart as the key residue interacting with IL- 4Rα’s third interface loop.

Conclusion: Our data provide a molecular and structural rationale for the enhanced IL-4Rα inhibition by rademikibart over dupilumab, confirming rademikibart as an optimized second-generation IL-4Rα inhibitor.