(393h) Physicochemical Properties of Highly Concentrated Monoclonal Antibody Solutions

The physicochemical properties of highly concentrated monoclonal antibody solutions can have a significant effect on downstream processing, drug formulation, product stability, and drug delivery.  The objective of this work was to evaluate the osmotic pressure, second virial coefficient, and solution viscosity of a highly purified monoclonal antibody at concentrations up to 250 g/L over a range of pH and ionic strength.  The osmotic pressure was evaluated using classical membrane osmometry. The second virial coefficient was evaluated independently using self-interaction chromatography, and the solution viscosity was evaluated using a RFS-II rotational viscometer.  Independent measurements of the net protein charge were obtained using electrophoretic light scattering.

The osmotic pressure at pH 5 and low ionic strength was greater than 50 kPa for antibody concentrations above 200 g/L. The second virial coefficients determined from the oncotic pressure (after subtracting the Donnan contribution) were in good qualitative agreement with those determined by self-interaction chromatography. The second virial coefficient decreased with increasing ionic strength and increasing pH due to the reduction in intermolecular electrostatic repulsion. The third virial coefficient was negative under all conditions, suggesting that the multi-body interactions in this system are attractive. The solution viscosity increased significantly at antibody concentrations above 100 g/L, exceeding 20 cP under these conditions, although there was no direct correlation between the measured viscosity and the thermodynamic properties (osmotic pressure or second virial coefficient).  These results have important implications for understanding the behavior of highly concentrated antibody solutions in bioprocessing applications.