# Identification of sorbitol esterification of glutamic acid by LC-MS/MS in a monoclonal antibody stability assessment

## TL;DR

Researchers found that sorbitol can chemically modify a monoclonal antibody by attaching to glutamic acid, which could impact drug stability and formulation.

## Contribution

The study identifies a novel post-translational modification of monoclonal antibodies through sorbitol esterification of glutamic acid.

## Key findings

- Sorbitol esterifies glutamic acid residues in monoclonal antibodies under accelerated aging conditions.
- Esterification levels depend on incubation time and sorbitol concentration, with 16% of mAb modified after 4 weeks.
- No esterification was observed at aspartic acid sites despite similar chemical properties.

## Abstract

The stability of monoclonal antibodies (mAbs) is vital for their therapeutic success. Sorbitol, a common mAb stabilizer used to prevent aggregation, was evaluated for any potential adverse effects on the chemical stability of mAb X. An LC-MS/MS based analysis focusing on the post-translational modifications (PTMs) of mAb X was conducted on samples that had undergone accelerated aging at 40°C. Along with PTMs that are known to affect mAbs’ structure function and stability (such as deamidation and oxidation), a novel mAb PTM was discovered, the esterification of glutamic acid by sorbitol. Incubation of mAb X with a 1:1 ratio of unlabeled sorbitol and isotopically labeled sorbitol (13C6) further corroborated that the modification was the consequence of the esterification of glutamic acid by sorbitol. Levels of esterification varied across glutamic acid residues and correlated with incubation time and sorbitol concentration. After 4 weeks of accelerated stability with isotopically labeled sorbitol, it was found that 16% of the total mAb possesses an esterified glutamic acid. No esterification was observed at aspartic acid sites despite the free carboxylic acid side chain. This study unveils a unique modification of mAbs, emphasizing its potential significance for formulation and drug development.