PURPOSE: Protein higher order structure (HOS) including the oligomer distribution can be critical for efficacy, safety and stability of drug products (DP). Oligomerization is particularly relevant to chemically modified protein therapeutics that have an extended pharmacokinetics profile. Therefore, the direct assessment of protein oligomerization in drug formulation is desired for quality assurance and control.
METHODS: Here, two non-invasive methods, dynamic light scattering (DLS) and diffusion ordered spectroscopy (DOSY) NMR, were applied to measure translational diffusion coefficients (Dand D) of proteins in formulated drug products. The hydrodynamic molecular weights (MW), similar to hydrodynamic size, of protein therapeutics were derived based on a log(D) vs log(MW) correlation model established using protein standards.
RESULTS: An exponent value of -0.40 ± 0.01 was established for DLS measured log(D) vs. log(MW) using protein standards and a theoretical exponent value of -0.6 was used for unstructured polyethylene glycol (PEG) chains. The analysis of DLS derived MWof the primary species showed the fatty acid linked glucagon-like peptide 1 (GLP-1) was in different oligomer states, but the fatty acid linked insulin and PEG linked proteins were in monomer states. Nevertheless, equilibrium and exchange between oligomers in formulations were universal and clearly evidenced from DOSY-NMR for all drugs except peginterferon alfa-2a.
CONCLUSION: The correlation models of log(D) vs. log(MW) could be a quick and efficient way to predict MWof protein, which directly informs on the state of protein folding and oligomerization in formulation.