Predicting the Stability of Formulations Containing Lyophilized Human Serum Albumin and Sucrose/Trehalose Using Solid-State NMR Spectroscopy

Molecular mechanisms for stabilizing biologics in the solid state

Protein drugs exhibit challenges of biophysical and biochemical instability due to their structural complexity and rich dynamics. Solid-state biologics aim to enhance stability by increasing molecular rigidity within the formulation matrix, representing a primary category of drug products alongside sterile liquid formulations. Understanding the molecular mechanisms behind the stabilization and destabilization of protein drugs, influenced by formulation composition and drying processes, provides scientific rationale for drug product design. This review aims to elaborate on the two primary models of water-to-sugar substitution and matrix vitrification, respectively, via thermodynamic and kinetic stabilization. It offers an up-to-date review of experimental investigations into these hypotheses, specifically elucidating protein structure and protein-excipient interactions at the molecular level, molecular dynamics across a broad range of motion regimes, and microscopic attributes such as protein-sugar and protein-salt miscibility and microenvironmental acidity, in relevant liquid, frozen, and solid states, using advanced biophysical techniques for solid-state analysis. Moreover, we discuss how these mechanistic understandings facilitate the investigation and prediction of critical stability behaviors and enables the design of solid biological drug products.

The Role of Phase Separation and Local Mobility in the Stabilization of a Lyophilized IgG2 Formulation

The utility of employing solid-state NMR (SSNMR) to assess parameters governing the stability of a lyophilized IgG2 protein was the focus of the present work. Specifically, the interaction between the sugar stabilizer (sucrose) and protein component was measured using SSNMR and compared to physical and chemical stability data obtained from thermally stressed samples. 1H T1 and 1H T1⍴ relaxation times were measured by SSMNR for 5 different formulation conditions, and the resultant values were used to examine local mobility and phase separation, respectively. From the SSNMR measurements, it was found local mobility decreased as the sucrose to protein weight ratio increased. The decrease in local mobility corresponded to an increase in storage stability (both chemical and physical) of the lyophilized solids up to a critical weight ratio of sucrose to protein. Additionally, 1H T1⍴ measurements obtained on formulations having higher protein to sucrose weight ratios indicated phase separation of the protein and sucrose phases was occurring, at least on a small scale. Along with an increase in local mobility, phase separation in these specific formulations is thought to have played a role in their decreased storage stability in the solid state.