Fc Engineering Service for Serum Half-Life Regulation (PH Sensitivity)

With efforts to modify the Fc region to enhance effector functions, attempts have been made to improve antibody pharmacokinetics. The neonatal Fc receptor (FcRn) is an MH1Like heterodimer, which is composed of the major histocompatibility MH1Likeα chain non-covalently bound to β-2-microglobulin (β2m), and is involved in the cell transport and plays a central role in serum half-life of IgG. Studies have shown that the long circulating half-life of antibodies is largely due to their ability to bind FcRn through Fc. It is also demonstrated that enhancing the Fc-FcRn interaction at acidic pH can prolong the serum half-life of IgG and actively regulate its homeostasis, which may benefit patients by improving the therapeutic effect, reducing the frequency of administration and reducing the cost burden.

Creative Biolabs focuses on the latest developments in therapeutic Fc engineering technology. We have established advanced alanine scanning and display/directed evolution platforms, which are commonly used to identify Fc mutants that are beneficial to enhance the Fc-FcRn pH-dependent interaction. Based on these platform technologies, we have isolated high-affinity binders for FcRn and analyzed Fc mutants, which show enhanced FcRn pH-dependent affinity and prolonged serum half-life.

Fc Mutation Strategies for Modulating Serum Half-life

FcRn is mainly expressed in endosomes, where it can bind to IgG internalized by pinocytosis. The conserved histidine residues in the CH2-CH3 domain of IgG are protonated at acidic endosomal pH (6.0-6.5), thereby driving pH-dependent binding to the α chain of FcRn. Subsequent recirculation and release of IgG into the blood at physiological pH (7.4) can save antibodies from lysosomal degradation. Therefore, IgG molecules can bind to FcRn in a pH-dependent manner to avoid degradation by endosomes, thereby prolonging the half-life of monoclonal antibodies. Therefore, enhancing its affinity with FcRn through Fc modification and extending its half-life are of great significance for improving the frequency of dosing, patient compliance and cost. While enhancing the affinity of Fc and FcRn, maintaining its PH selectivity can effectively increase the half-life of the antibody.

Mutations at various locations near the CH2-CH3 interface have been designed with the goal of extending the serum half-life that may reduce the therapeutic dose and/or frequency of administration and reduce the cost of treatment, thereby benefiting patients (Table 1). A previous study found that N434W can enhance the affinity of FcRn at both pH 6.0 and pH 7.4, but the half-life is not improved. However, N434A can selectively increase the affinity of FcRn under acidic conditions, so its half-life is extended by 2.3 times. In addition, some studies have found that M252Y/S254T/T256E, M428L/N434S or T250R/M428L can prolong the half-life of antibodies in primates.

Table 1 Fc modification for enhancing half-life.

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