Effects of Buffer Composition on Site-Specific Glycation of Lysine Residues in Monoclonal Antibodies

Candidate antibodies under consideration for development as pharmaceuticals must be screened for potential liabilities. Glycation of lysine side chains is one liability which can significantly alter the efficacy of a therapeutic antibody. Antibody candidates are often subjected to stress-testing after purification to assess liabilities that may arise from variability in the manufacturing process and gauge the manufacturability of the molecule. Because previous publications have shown significant site-specific effects of certain buffer components on the glycation rate of individual lysines, we sought to understand the effects of common buffering agents to find suitable buffers for glycation stress-testing (forced glycation). Therapeutic antibodies are typically only exposed to reducing sugars in cell culture media during production, so we sought to identify buffers that could be used as surrogates for media in forced glycation reactions. Our results indicate that common buffering agents can drastically alter the rate of glycation for specific lysines in an antibody. Forced glycation reactions performed in HEPES and citrate buffers both produce site-specific lysine glycation rates that correlate well with cell culture media, whereas bicarbonate buffer has a highly stimulatory effect on most lysines leading to higher total glycation levels and a poor correlation to glycation rates in media.