BOC Sciences has developed various strategies for bioconjugation through the carbohydrate portion of antibodies. With expertise in bioconjugation, we offer tailor-made carbohydrate conjugation services to our institutional and industrial customers.
IgG is a glycoprotein and contains an N-glycan at the N297 position of the Fc fragment in each CH2 domain. This glycosylation can be used as an attachment point for payloads. Long-distance positioning between the polysaccharide and the Fab region reduces the risk of damaging antigen's binding ability in conjugation with antibodies. Furthermore, compared with the peptide chains of antibodies, polysaccharides' different chemical compositions allow site-specific modification and make them suitable coupling sites.
Fig. 1. Carbohydrate-based conjugation strategies.
Generally, carbohydrates bind to the CH2 region of a heavy chain. The FC segment includes only the constant region (CH) of a heavy chain, but the Fab segment combined with antigen consists of the variable region of the heavy chain and the variable region of the light chain (VH and VL). The heavy chain of immunoglobulin is also glycosylated, especially the Fc fragment. Thus, there may be polysaccharides near the antigen-binding sites.
Applying polysaccharide chains on the CH2 domain of an Fc fragment, polysaccharide residues can be oxidized by the periodate to form aldehyde groups. Crosslinking agents and modifying agents containing hydrazide groups can be targeted to recognize aldehyde groups and link other molecules. This method can use in antibody molecules to avoid blocking antigen-binding sites and retaining antigen-binding activity to the greatest extent after coupling. However, it should be noted that the region near the antigen-binding site will also be glycosylated, which may affect coupling processes.
Classical glycan bioconjugation involves site-specific modification on the N-glycosylation site of fructose of the IgG antibody, and fucose contains a cis-diol moiety suitable for selective oxidation. Thus, oxidative modification of fructose with periodate or metabolic engineering of thiolated analog form an aldehyde group to react with hydrazine-containing linker and links antibody with drug molecule through hydrazone bond. This strategy significantly reduces heterogeneity compared to classical cysteine conjugates and generates conjugates with more predictable pharmacokinetic and pharmacodynamic properties. According to the novel strategy for site-specific conjugation, BOC Sciences is capable of performing glycan chemical oxidation to support research and development for novel drug projects.
It has been demonstrated that glycans can be enzymatically remodeled using galactosyl and sialyltransferases. G2 glycans are obtained by the enzymatic addition of galactose, followed by the addition of terminal sialic acids. This modification enables the generation of an aldehyde group by periodate oxidation and functionalization of the antibody using a hydroxylamine-functionalized linker-payload. BOC Sciences can perform enzymatic addition of terminal sialic acids followed by periodate oxidation or incorporation of azido modified sialic acid to obtain conjugates with high target selectivity in vitro and well anti-tumor activity in vivo.
Galactose residues can also explore as modification sites. Multiple studies have reported the removal of galactose using beta-1,4 galactosidase, followed by incorporating galactose derivatives forming biorthogonal handles. By using a mutant β-1,4-galactosyltransferases, galactoses with ketone or azide functional groups were introduced, which opened the way for efficient conjugation by biorthogonal transformations. Based on this, BOC Sciences provides azide or keto-modified galactose services to escort your ADC conjugation development projects.
An IgG-specific endoglycosidase performs the enzymatic remodeling to expose the core GlcNAc of the native antibody glycan. Following the glycan cleavage, the engineered galactosyl transferase GalT combined with UDP-GalNAz incorporates an azide anchor, where biocompatible, copper-free, strain-promoted azide-alkyne chemistry reaction could be performed subsequently. BOC Sciences can apply this approach to produce GlycoConnect ADCs that demonstrate favorable in vitro potency and in vivo efficacy.