“Fc Fusion Proteins”

Integrating ultra-high-performance liquid chromatography tandem mass spectrometry and imaged capillary isoelectric focusing for in-depth characterization of complex fusion proteins

RATIONALE

Fc-fusion proteins represent a successful class of biopharmaceutical products, which combine the tailored pharmacological properties of biological ligands with the multiple functions of the fragment crystallizable domain of immunoglobulins. There is great diversity in terms of possible biological ligands creating highly diverse structures, therefore the analytical characterization of fusion proteins is far more complex than that of monoclonal antibodies and requires the use and development of additional product-specific methods over conventional generic/platform methods.

METHODS

Employing etanercept analogues as studied fusion proteins, the Orbitrap mass analyzer with ultra-high performance liquid chromatography (UHPLC-MS) and imaged capillary isoelectric focusing (icIEF) were utilized for the in-depth fusion protein characterization.

RESULTS

The amino acid sequence coverage, peptide mapping, and post-translational modifications of etanercept analogues were analyzed by UHPLC-MS. The post-translational modification results were complemented by imaged capillary isoelectric focusing to produce quality research on etanercept analogues.

CONCLUSIONS

The developed workflow integrating UHPLC-MS and icIEF provided an innovative strategy for characterizing complex fusion proteins in the process of quality control and manufacturing.

Exendin 4-Hapten Conjugate Capable of Binding with Endogenous Antibodies for Peptide Half-life Extension and Exerting Long-Acting Hypoglycemic Activity

Hapten-specific endogenous antibodies are naturally occurring antibodies present in human blood. Herein, we investigated a new strategy in which small-molecule haptens were utilized as naturally occurring antibody binders for peptide half-life extension. The glucagon-like peptide 1 receptor agonist exendin 4 was site-specifically functionalized with the dinitrophenyl (DNP) hapten at the C-terminus via sortase A-mediated ligation. The resulting Ex4-DNP conjugates retained GLP-1 receptor activation potency in vitro and had a similar in vivo acute glucose-lowering effect comparable to that of native Ex4. Pharmacokinetic studies and hypoglycemic duration tests demonstrated that the Ex4-DNP conjugates displayed significantly elongated half-lives and improved long-acting antidiabetic activity in the presence of endogenous anti-DNP antibodies. In chronic treatment studies, once-daily administration of optimal conjugate 7 demonstrated more beneficial effects without prominent toxicity compared with Ex4. This strategy provides a new approach and represents an alternative to the well-established peptide-Fc fusion strategy to improve the peptide half-life and the therapeutic efficacy.

Therapeutic Fc-fusion proteins: Current analytical strategies

Fc-Fusion proteins represent a successful class of biopharmaceutical products, with already 13 drugs approved in the European Union and United States as well as three biosimilar versions of etanercept. Fc-Fusion products combine tailored pharmacological properties of biological ligands, together with multiple functions of the fragment crystallizable domain of immunoglobulins. There is a great diversity in terms of possible biological ligands, including the extracellular domains of natural receptors, functionally active peptides, recombinant enzymes, and genetically engineered binding constructs acting as cytokine traps. Due to their highly diverse structures, the analytical characterization of Fc-Fusion proteins is far more complex than that of monoclonal antibodies and requires the use and development of additional product-specific methods over conventional generic/platform methods. This can be explained, for example, by the presence of numerous sialic acids, leading to high diversity in terms of isoelectric points and complex glycosylation profiles including multiple N- and O-linked glycosylation sites. In this review, we highlight the wide range of analytical strategies used to fully characterize Fc-fusion proteins. We also present case studies on the structural assessment of all commercially available Fc-fusion proteins, based on the features and critical quality attributes of their ligand-binding domains.