Divided by the dotted line, the top and bottom panel of the figure highlight samples with and values that are indicative of attractive and repulsive PPI, respectively

Divided by the dotted line, the top and bottom panel of the figure highlight samples with and values that are indicative of attractive and repulsive PPI, respectively. its own equilibrium constant that can be calculated by the concentration of products and reactants at equilibrium. As mentioned earlier, excipients such as salts and sugars are often included in the formulation to improve the stability of mAb molecules by reducing the extent of self-association [11]. It is known that the monomer-dimer equilibrium can change from one solution environment to another by, for example, adding small molecule inhibitors [21], salts [22] and sugars [23]. Therefore, the presence of excipients in a solution can alter oligomer formation by altering various Rabbit Polyclonal to BTK aspects that contribute to the native equilibrium constants. Both experimental and computer-based approaches have been developed to aid the formulation development of mAb products. For computer simulations, different models have been developed to capture various molecular features of mAbs for improved predictions of PPI. Among others, coarse-grained bead models that account for the shape and surface anisotropy of mAb molecules have been used to predict the stability and viscosity of concentrated mAb formulations [24,25,26]. While advancements have been made in computer simulations, experimental data are needed to validate the force field Almorexant HCl used for the simulation and select molecular features that best describe a particular mAb molecule. In recent studies of the self-association of proteins, protein molecules have been modelled as colloidal particles [27,28]. In this formalism, the interaction between two protein molecules is governed by steric repulsion. Protein molecules can also interact due to surface anisotropy and solvent-mediated interactions [29]. These interactions can be either attractive or repulsive in nature [29,30]; therefore, they diminish or enhance the interaction between two protein molecules. When considering proteins as colloid particles, the tendency of proteins to stay in their monomeric form is typically referred to as their colloidal stability, and it is dominated by the net balance between repulsive and attractive protein-protein interactions (PPI) [31]. A wide range of characterization methods has been developed to predict the colloidal stability of mAbs in various formulations. These techniques are used to extract experimental parameters containing information on the net PPI, with the underlying assumption that mAbs are colloidally stable if the net PPIs are repulsive and unstable if the net PPIs are attractive [32,33,34]. Dynamic light scattering (DLS) and static light scattering (SLS) are two widely used techniques to study the colloidal stability of protein therapeutics in solution [35,36]. The diffusion interaction parameter and the second virial coefficient and measured from small-angle X-ray and neutron scattering (SAXS/SANS) also provides information on spatial arrangements and intermolecular interactions of mAbs in solution. In recent years, there have been a number Almorexant HCl of studies of PPI using SAXS/SANS [24,44,45,46,47,48,49]. Our previous study demonstrated the use of SAXS Almorexant HCl for studying the stability and viscosity of mAbs under various formulation conditions [11]. One of the major differences between is that the latter can be measured directly from concentrated mAb solutions up to hundreds of mg/mL. Thus, provides a direct probe of PPI present in concentrated formulations. Previously, we examined the correlations between measured from commonly used excipient formulations, Almorexant HCl where excipients were formulated at particular concentrations, for example, 300 mM sucrose and 200 mM glycine [11]. In this study, we focus on only one excipient: NaCl. The thermodynamic, hydrodynamic and structure of a human anti-streptavidin monoclonal antibody (ASA-IgG2) was characterized with various amounts of NaCl in Almorexant HCl solution, ranging from 0 mmol/L (mM) up to 1200 mM. High NaCl concentrations were.