A novel histidine-acetate buffer for freeze-dried monoclonal antibody formulations.

Histidine (His)-hydrochloride (HCl) is widely used in freeze-dried monoclonal antibody (mAb) formulations, but alternative buffers are required when chloride ions are undesirable. This study evaluates His-acetate (Ac) as a substitute and its impact on the stability of two model mAbs with distinct physicochemical properties- infliximab (mAb-1) and a humanized anti-ricin mAb (mAb-2). pH shifts during freeze-drying were compared among His-Ac, His-HCl, and sodium Ac buffers, confirming strong buffering capacity of His-Ac within pH 5.5-6.5. Conformational and colloidal stability assessments revealed that both mAbs displayed higher melting temperatures or favorable diffusion interaction parameters in His-Ac formulations. Moreover, mAb-2 exhibited a higher collapse temperature in His-Ac compared to His-HCl, indicating improved structural integrity or drying efficiency during primary drying. No significant differences were observed in aggregation onset temperature and glass transition temperature. Aggregation and chemical stability under stress conditions were evaluated by micro-flow imaging, size exclusion chromatography, and ion exchange chromatography. No notable changes in subvisible particle counts or monomer content occurred after freeze-drying. Overall, His-Ac demonstrated stability comparable to or better than His-HCl, supporting its use in freeze-dried mAb formulations.