Caffeine as a Viscosity-Reducing Agent for High-Concentration mAb Formulations: Insights from Molecular Dynamics...

Subcutaneous delivery of high-concentration monoclonal antibody (mAb) formulations is increasingly preferred for therapeutic applications but is often hindered by high formulation viscosity. While caffeine has recently been found to be an effective viscosity-reducing agent for some mAbs, such as ipilimumab and infliximab, the detailed molecular mechanism remains unclear. In this study, all-atom molecular dynamics (MD) simulations were employed to elucidate the interactions between caffeine and ipilimumab. The results reveal that hydrophobic effects, rather than electrostatic interactions, primarily drive the preferential inclusion of caffeine onto ipilimumab. Trajectory analysis identified 38 high-frequency caffeine-contact residues, some of which, such as TRP101 in the Fab heavy chain, overlap with some "hot spot" residues responsible for Fab-Fab interaction. It is hypothesized that caffeine reduces formulation viscosity by shielding these residues and thereby weakening mAb reversible self-association. The conformational analysis based on K-means clustering suggested that, in the presence of caffeine, the conformations of both the Fab and Fc fragments became more rigid without a significant change in the overall mAb compactness. These findings provide molecular-level insights into the potential use of caffeine as a new viscosity-reducing agent for high-concentration mAb formulations.