Comparative evaluation of disodium edetate and diethylenetriaminepentaacetic acid as iron chelators to prevent metal-catalyzed destabilization of a therapeutic monoclonal antibody.

Understanding the effect of metal chelators with respect to their ability to inhibit metal-catalyzed degradation in biologic products is a critical component for solution formulation development. Two metal chelators, disodium edetate (Na(2)EDTA) and diethylenetriaminepentaacetic acid (DTPA), were evaluated for their ability to stabilize IgG2 mAb in solution formulations spiked with various levels of iron. Real-time stability attributes such as oxidation, soluble aggregate formation, deamidation, and fragmentation demonstrated that DTPA was equivalent to Na(2)EDTA with respect to inhibiting iron-induced degradation over the range of iron concentrations studied. When sufficient chelator was present to stoichiometrically complex trace iron contamination, both Na(2)EDTA and DTPA exhibited the capacity to reduce protein degradation. However, substoichiometric ratios of both chelators were unable to inhibit the degradation induced by free iron ions, which were found to bind weakly to the mAb. This bound iron did not measurably alter the secondary or the tertiary structure of the mAb but appeared to decrease its intrinsic thermodynamic stability, probably by causing subtle perturbations in the tertiary structure. These destabilization effects were not observed when the chelators were present at stoichiometric ratios highlighting the feasibility of using DTPA as an alternate trace metal chelator to Na(2)EDTA in biologic protein formulations.