Coadsorption of a Monoclonal Antibody and Nonionic Surfactant at the SiO2/Water Interface

Investigating the Orientation of an Interfacially Adsorbed Monoclonal Antibody and Its Fragments Using Neutron Reflection

Interfacial adsorption is a molecular process occurring during the production, purification, transport, and storage of antibodies, with a direct impact on their structural stability and subsequent implications on their bioactivities. While the average conformational orientation of an adsorbed protein can be readily determined, its associated structures are more complex to characterize. Neutron reflection has been used in this work to investigate the conformational orientations of the monoclonal antibody COE-3 and its Fab and Fc fragments at the oil/water and air/water interfaces. Rigid body rotation modeling was found to be suitable for globular and relatively rigid proteins such as the Fab and Fc fragments but less so for relatively flexible proteins such as full COE-3. Fab and Fc fragments adopted a 'flat-on' orientation at the air/water interface, minimizing the thickness of the protein layer, but they adopted a substantially tilted orientation at the oil/water interface with increased layer thickness. In contrast, COE-3 was found to adsorb in tilted orientations at both interfaces, with one fragment protruding into the solution. This work demonstrates that rigid-body modeling can provide additional insights into protein layers at various interfaces relevant to bioprocess engineering.

Interfacial Assembly Inspired by Marine Mussels and Antifouling Effects of Polypeptoids: A Neutron Reflection Study

Polypeptoid-coated surfaces and many surface-grafted hydrophilic polymer brushes have been proven efficient in antifouling-the prevention of nonspecific biomolecular adsorption and cell attachment. Protein adsorption, in particular, is known to mediate subsequent cell-surface interactions. However, the detailed antifouling mechanism of polypeptoid and other polymer brush coatings at the molecular level is not well understood. Moreover, most adsorption studies focus only on measuring a single adsorbed mass value, and few techniques are capable of characterizing the hydrated in situ layer structure of either the antifouling coating or adsorbed proteins. In this study, interfacial assembly of polypeptoid brushes with different chain lengths has been investigated in situ using neutron reflection (NR). Consistent with past simulation results, NR revealed a common two-step structure for grafted polypeptoids consisting of a dense inner region that included a mussel adhesive-inspired oligopeptide for grafting polypeptoid chains and a highly hydrated upper region with very low polymer density (molecular brush). Protein adsorption was studied with human serum albumin (HSA) and fibrinogen (FIB), two common serum proteins of different sizes but similar isoelectric points (IEPs). In contrast to controls, we observed higher resistance by grafted polypeptoid against adsorption of the larger FIB, especially for longer chain lengths. Changing the pH to close to the IEPs of the proteins, which generally promotes adsorption, also did not significantly affect the antifouling effect against FIB, which was corroborated by atomic force microscopy imaging. Moreover, NR enabled characterization of the in situ hydrated layer structures of the polypeptoids together with proteins adsorbed under selected conditions. While adsorption on bare SiO2 controls resulted in surface-induced protein denaturation, this was not observed on polypeptoids. Our current results therefore highlight the detailed in situ view that NR may provide for characterizing protein adsorption on polymer brushes as well as the excellent antifouling behavior of polypeptoids.

Recent Advances in Studying Interfacial Adsorption of Bioengineered Monoclonal Antibodies

Monoclonal antibodies (mAbs) are an important class of biotherapeutics; as of 2020, dozens are commercialized medicines, over a hundred are in clinical trials, and many more are in preclinical developmental stages. Therapeutic mAbs are sequence modified from the wild type IgG isoforms to varying extents and can have different intrinsic structural stability. For chronic treatments in particular, high concentration (≥ 100 mg/mL) aqueous formulations are often preferred for at-home administration with a syringe-based device. MAbs, like any globular protein, are amphiphilic and readily adsorb to interfaces, potentially causing structural deformation and even unfolding. Desorption of structurally perturbed mAbs is often hypothesized to promote aggregation, potentially leading to the formation of subvisible particles and visible precipitates. Since mAbs are exposed to numerous interfaces during biomanufacturing, storage and administration, many studies have examined mAb adsorption to different interfaces under various mitigation strategies. This review examines recent published literature focusing on adsorption of bioengineered mAbs under well-defined solution and surface conditions. The focus of this review is on understanding adsorption features driven by distinct antibody domains and on recent advances in establishing model interfaces suitable for high resolution surface measurements. Our summary highlights the need to further understand the relationship between mAb interfacial adsorption and desorption, solution aggregation, and product instability during fill-finish, transport, storage and administration.

Interfacial Adsorption of a Monoclonal Antibody and Its Fab and Fc Fragments at the Oil/Water Interface

The physical stability of a monoclonal antibody (mAb) solution for injection in a prefilled syringe may in part depend on its behavior at the silicone oil/water interface. Here, the adsorption of a mAb (termed COE-3) and its fragment antigen-binding (Fab) and crystallizable (Fc) at the oil/water interface was measured using neutron reflection. A 1.4 ± 0.1 μm hexadecane oil film was formed on a sapphire block by a spin-freeze-thaw process, retaining its integrity upon contact with the protein solutions. Measurements revealed that adsorbed COE-3 and its Fab and Fc fragments retained their globular structure, forming layers that did not penetrate substantially into the oil phase. COE-3 and Fc were found to adsorb flat-on to the interface, with denser 45 and 42 Å inner layers, respectively, in contact with the oil and a more diffuse 17-21 Å outer layer caused by fragments adsorbing in a tilted manner. In contrast, Fab fragments formed a uniform 60 Å monolayer. Monolayers were formed under all conditions studied (10-200 ppm, using three isotopic contrasts), although changes in packing density across the COE-3 and Fc layers were observed. COE-3 had a higher affinity to the interface than either of its constituent fragments, while Fab had a lower interfacial affinity consistent with its higher net surface charge. This study extends the application of high-resolution neutron reflection measurements to the study of protein adsorption at the oil/water interface using an experimental setup mimicking the protein drug product in a siliconized prefilled syringe.