Extending Half-life by Indirect Targeting of the Neonatal Fc Receptor (FcRn) Using a Minimal Albumin Binding Domain

Abstract

The therapeutic and diagnostic efficiency of engineered small proteins, peptides, and chemical drug candidates is hampered by short in vivo serum half-life. Thus, strategies to tailor their biodistribution and serum persistence are highly needed. An attractive approach is to take advantage of the exceptionally long circulation half-life of serum albumin or IgG, which is attributed to a pH-dependent interaction with the neonatal Fc receptor (FcRn) rescuing these proteins from intracellular degradation. Here, we present molecular evidence that a minimal albumin binding domain (ABD) derived from streptococcal protein G can be used for efficient half-life extension by indirect targeting of FcRn. We show that ABD, and ABD recombinantly fused to an Affibody molecule, in complex with albumin does not interfere with the strictly pH-dependent FcRn-albumin binding kinetics. The same result was obtained in the presence of IgG. An in vivo study performed in rat confirmed that the clinically relevant human epidermal growth factor 2 (HER2)-targeting Affibody molecule fused to ABD has a similar half-life and biodistribution profile as serum albumin. The proof-of-concept described may be broadly applicable to extend the in vivo half-life of short lived biological or chemical drugs ultimately resulting in enhanced therapeutic or diagnostic efficiency, a more favorable dosing regimen, and improved patient compliance.

Dissection of the Neonatal Fc Receptor (FcRn)-Albumin Interface Using Mutagenesis and Anti-FcRn Albumin-blocking Antibodies

“…GST-h␤2-microglobulin vectors encoding GST-tagged hFcRn variants (WT, E115A/E116A, E54Q, Q56A, H161A, and H166A), mouse FcRn (mFcRn) and rat FcRn have been described previously (2,3,(33)(34)(35). In addition, cDNA sequences encoding the three extracellular domains of macaque (NCBI no.…”

Interaction with Both Domain I and III of Albumin Is Required for Optimal pH-dependent Binding to the Neonatal Fc Receptor (FcRn)

“…Examples are biopharmaceuticals such as cytokines, hormones, and antibody fragments. Also small albumin binding scaffolds, peptides, or fatty acids fused or conjugated directly to a drug of interest, which target or associate with albumin when injected into the bloodstream, are used to improve pharmacokinetics (3)(4)(5)(6).…”

Long-acting recombinant coagulation factor IX albumin fusion protein (rIX-FP) in hemophilia B: results of a phase 3 trial

“…Because albumin is protected from degradation by pH-dependent binding to the neonatal Fc receptor, 7,8 rIX-FP has an increased circulating half-life compared with recombinant FIX (rFIX).…”