High concentration antibody solutions are a stringent test for coarse grained molecular modelling because small differences in molecular surface properties can strongly affect collective behaviour, including the structure factor, osmotic compressibility, diffusion and viscosity. This is especially important for therapeutic monoclonal antibodies (mAbs), where high concentration formulations are often required, yet viscosity enhancement remains difficult to predict from sequence, net charge or simple colloidal descriptors.
In our previous allocation, we developed a coarse grained strategy representing antibodies as anisotropic bead based objects with heterogeneous charge distributions. This enabled us to link molecular electrostatic features with measurable solution properties and showed that explicit charge heterogeneity is essential to reproduce structure factors and viscosity trends. The results also indicated that electrostatics alone is insufficient: when antibodies differ in net charge, charge localization and viscosity, a predictive model must balance long range electrostatic repulsion, salt mediated screening and short range attractive interactions such as hydrophobic contributions.
The present project builds on these findings to move toward a transferable modelling framework for multiple antibodies. We will study three mAbs with available experimental data, differing in net charge and high concentration viscosity. This provides an ideal benchmark to test whether one modelling strategy can describe static and dynamic properties across distinct molecules. Instead of optimizing separate parameter sets, we will use comparisons among the three systems to identify which physical ingredients are necessary, which are antibody specific and which can remain fixed.
First we will refine coarse grained models that preserve anisotropic shape and heterogeneous charge. Building on previous models, we will vary charge mapping, the magnitude and localization of short range attractions and the strength of hydrophobic contributions. This will determine whether experimental differences arise mainly from electrostatic patterning or whether additional attractions are required. For each antibody, molecular dynamics simulations at relevant concentrations and salt conditions will yield structure factors, compressibility related quantities, diffusion observables and viscosity via stress autocorrelation. Because reproducing the structure factor does not guarantee correct viscosity, comparing static and dynamic observables will be a stringent test of physical consistency.
Salt and counterions will receive particular attention. Explicit ions were previously important for capturing screening and concentration-dependent effects. Here we will test grand canonical Monte Carlo salt exchange schemes, different ion sizes and consistent dielectric/electrostatic parameterizations. These tests address the fact that effective ionic strength inside concentrated antibody solutions differs from the reservoir value due to Donnan effects. Comparing fixed ion and grand canonical simulations will show how salt partitioning and screening influence structure and viscosity.
In parallel, we will investigate short-range non-electrostatic interactions arising from hydrophobic regions or local amino acid composition. By varying the range, strength and localization of attractive terms, we will assess whether such contributions are required to reproduce static and dynamic behaviour, especially for antibodies with unexpectedly high viscosity.
Overall, the project will deliver an experimentally constrained comparison of three antibodies with distinct charge and viscosity profiles, identifying the minimal physical ingredients needed for predictive coarse grained modelling of antibody solutions.