Free Thiols using FabRICATOR® and FabALACTICA®

In biopharmaceutical product development and manufacturing, free thiol content is one of the product quality attributes of interest as its presence could impact structure, stability and function of the product.

At Biogen, Yi Pu et al have optimized a label-free LC (UV) / MS method for free thiol quantification at a subunit level of IgG1 and IgG4. The new method, which is based on a method developed by Faid et al*, was compared to two conventional approaches, Ellman’s assay and peptide mapping.

It is very challenging to identify free thiol forms by mass spectrometry at the intact antibody level. By combining the highly specific proteolytic enzymes FabALACTICA (IgdE) and FabRICATOR (IdeS) the authors generated the subunits Fab, hinge and Fc/2, suited for confident mass determination. The subunits were subsequently separated on a polyphenyl reversed phase column in order to separate free thiol forms from their corresponding disulphide bond-linked form. A baseline or near baseline separation was obtained making it possible to calculate the free thiol content on each subunit.

The result of the quantification of free thiols from all three methods were comparable and showed similar trends even though the peptide mapping approach generally gave a higher free thiol content.

The authors conclude that compared to Ellman’s assay, the subunit approach is more sensitive, requires less sample and provides domain-specific information of the free thiol content. Compared to peptide mapping, the subunit method is faster, less labour intensive and lacks dependence on labelling efficiency. Finally, it demonstrated promise in the quantification of free thiols in a high throughput manner with domain specific information available.

The developed method has successfully been applied to several in-house IgG1 mAbs with different hydrophobicity and isoelectric points.

 

*V. Faid Y. Leblanc N. Bihoreau G. Chevreux Middle-up analysis of monoclonal antibodies after combined IgdE and IdeS hinge proteolysis: Investigation of free sulfhydryls, J. Pharm. Biomed. Anal. 149 (2018) 541-546, https://doi.org/10.1016/j.jpba.2017.11.046

 

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