Single chain antibody fragments with pH dependent binding to FcRn enabled prolonged circulation of therapeutic peptide in vivo

Abstract

The neonatal Fc receptor for IgG (FcRn) is considered critical for the regulation of endogenous IgG and serum albumin (SA) and their circulation half-life in vivo. Both IgG and SA can bind to FcRn tightly at acidic pH but not so much at neutral pH. Here we reported a few novel single chain antibody fragments (scFv) obtained based on screening of a phage library. FnAb-8 and FnAb-12 can bind to human FcRn with higher affinities than IgG at acidic pH but similar or lower affinities than IgG at pH7.4. Fusion proteins consisted of the therapeutic peptide, GLP-1 (Glucagon-like peptide-1) connected to the N-terminus of FnAb-8 and FnAb-12, named as G8 and G12, were shown to retain the pH-dependent binding capabilities to FcRn while also bound to the GLP-1 receptor. In vivo efficacy studies in diet induced diabetes mice confirmed the GLP-1 receptor (GLP-1R) agonist activities and sustained blood sugar lowering effect. In vivo pharmacokinetics (PK) studies were performed in nonhuman primates and FnAb-8 was found to have circulation half-life several folds longer than what have been reported for scFvs. G8 may be developed into long acting GLP-1R agonists with great potentials in clinical applications.

Prevention of diabetes-associated fibrosis: Strategies in FcRn-targeted nanosystems for oral drug delivery

“…In addition, recent research has also resulted in engineered HSA variants with improved half-life [65,68,159]. Moreover, several alternative scaffolds with FcRn-binding properties have been reported [160][161][162][163][164], but a major challenge for such engineering is fine-tuning of strict pH-dependent receptor binding in order to gain favorable recycling and transcytosis capacity. Improvements in FcRn engagement and transport may result in more favorable pharmacokinetic profiles, and consequently less frequent administration and higher patient compliance.…”

“…In another phage display approach, single chain variable fragments (scFv) were selected towards hFcRn, which yielded candidates (FnAb-8 and FnAb-12) with nanomolar affinity at acidic pH (Table 3) [164]. These scFv bound 10 to 100-fold more strongly to hFcRn than hIgG, and with no or slightly weak binding observed at neutral pH.…”

“…When FnAb-8 was studied in non-human primates, it revealed a half-life of 100-200 hours, which was about 2-fold longer than that measured for 2C10. Curiously, while the GLP-1 analog exenatide reduced blood glucose concentrations for 2 hours in WT mice, engineered scFvs fused to GLP-1 prolonged this effect for up to 8 hours, despite their inability to engage mFcRn [164].…”