Therapeutic proteins are exposed to various wetted surfaces that could shed sub-visible particles. In this work we measured the adsorption of a monoclonal antibody (mAb) to various microparticles, characterized the adsorbed mAb secondary structure, and determined the reversibility of adsorption. We also developed and used a front-face fluorescence quenching method to determine that the mAb tertiary structure was near-native when adsorbed to glass, cellulose and silica. Initial adsorption to each of the materials tested was rapid. During incubation studies, exposure to the air-water interface was a significant cause of aggregation but acted independently of the effects of microparticles. Incubations with glass, cellulose, stainless steel or Fe 2 O 3 microparticles gave very different results. Cellulose preferentially adsorbed aggregates from solution. Glass and Fe 2 O 3 adsorbed the mAb but did not cause aggregation. Adsorption to stainless steel microparticles was irreversible, and caused appearance of soluble aggregates upon incubation. The secondary structure of mAb adsorbed to glass and cellulose was near-native. We suggest that the protocol described in this work could be a useful preformulation stress screening tool to determine the sensitivity of a therapeutic protein to exposure to common surfaces encountered during processing and storage.

No abstract

There is concern that shear could cause protein unfolding or aggregation during commercial biopharmaceutical production. In this work we exposed two concentrated immunoglobulin-G1 (IgG1) monoclonal antibody (mAb, at >100 mg/mL) formulations to shear rates of between 20,000 and 250,000 s -1 for between 5 minutes and 30 ms using a parallel-plate and capillary rheometer respectively. The maximum shear and force exposures were far in excess of those expected during normal processing operations (20,000 s -1 and 0.06 pN respectively). We used multiple characterization techniques to determine if there was any detectable aggregation. We found that shear alone did not cause aggregation, but that prolonged exposure to shear in the stainless steel parallel-plate rheometer caused a very minor reversible aggregation (<0.3%). Additionally, shear did not alter aggregate populations in formulations containing 17% preformed heat-induced aggregates of a mAb. We calculate that that the forces applied to a protein by production shear exposures (<0.06 pN) are small when compared with the 140 pN force expected at the air-water interface or the 20 to 150 pN forces required to mechanically unfold proteins described in the atomic force microscope (AFM) literature. Therefore, we suggest that in many cases air-bubble entrainment, adsorption to solid surfaces (with possible shear synergy), contamination by particulates, or pump cavitation stresses could be much more important causes of aggregation than shear exposure during production.

Particles in protein therapeutics are undesirable because they may have the potential for causing adverse immunogenicity in patients. Agitation-induced exposure to the air-water interface during manufacturing, shipping, and administration can cause particle formation in therapeutic protein products. We systematically studied how application of surface pressure during periodic interfacial compressions caused a model monoclonal antibody to form particles. Above a critical interfacial compression ratio of 5 we observed a dramatic increase in the rate of protein particle formation. During continuous interfacial compression/dilation cycles, particle numbers increased but the particle size distribution remained unchanged. When cyclic compressions were halted, particles did not nucleate additional particles or grow further in bulk solution suggesting that they are formed only at the airwater interface. In fact, we found that particles in the bulk slowly decreased in number upon standing. The rate of particle formation was only weakly dependent on both the bulk protein concentration and the period of cyclical interfacial compressions. These observations are consistent with the interfacial aggregation of proteins during periods of high surface pressure, followed by collapse of the adsorbed layer and detachment of protein particles from the interface into the bulk.