Stabilizing proteins at high concentration is of broad interest in drug delivery, for treatment of cancer and many other diseases. Herein, we create highly concentrated antibody dispersions (up to 260 mg/mL) comprising dense equilibrium nanoclusters of protein (monoclonal antibody 1B7, polyclonal sheep immunoglobulin G, and bovine serum albumin) molecules which, upon dilution in vitro or administration in vivo, remain conformationally stable and biologically active. The extremely concentrated environment within the nanoclusters (∼700 mg/mL) provides conformational stability to the protein through a novel self-crowding mechanism, as shown by computer simulation, while the primarily repulsive nanocluster interactions result in colloidally stable, transparent dispersions. The nanoclusters are formed by adding trehalose as a cosolute which strengthens the short-ranged attraction between protein molecules. The protein cluster diameter was reversibly tuned from 50 to 300 nm by balancing short-ranged attraction against long-ranged electrostatic repulsion of weakly charged protein at a pH near the isoelectric point. This behavior is described semiquantitatively with a free energy model which includes the fractal dimension of the clusters. Upon dilution of the dispersion in vitro, the clusters rapidly dissociated into fully active protein monomers as shown with biophysical analysis (SEC, DLS, CD, and SDS-PAGE) and sensitive biological assays. Since the concept of forming nanoclusters by tuning colloid interactions is shown to be general, it is likely applicable to a variety of biological therapeutics, mitigating the need to engineer protein stability through amino acid modification. In vivo subcutaneous injection into mice results in indistinguishable pharmacokinetics versus a standard antibody solution. Stable protein dispersions with low viscosities may potentially enable patient self-administration by subcutaneous injection of antibody therapeutics being discovered and developed.

Although sub-100 nm nanoclusters of metal nanoparticles are of interest in many fields including biomedical imaging, sensors and catalysis, it has been challenging to control their morphologies and chemical properties. Herein, a new concept is presented to assemble equilibrium Au nanoclusters of controlled size by tuning the colloidal interactions with a polymeric stabilizer, PLA(1k)-b-PEG(10k)-b-PLA(1k). The nanoclusters form upon mixing a dispersion of ~5 nm Au nanospheres with a polymer solution followed by partial solvent evaporation. A weakly adsorbed polymer quenches the equilibrium nanocluster size and provides steric stabilization. Nanocluster size is tuned from ~20 nm to ~40 nm by experimentally varying the final Au nanoparticle concentration and the polymer/Au ratio, along with the charge on the initial Au nanoparticle surface. Upon biodegradation of the quencher, the nanoclusters reversibly and fully dissociate to individual ~5 nm primary particles. Equilibrium cluster size is predicted semi-quantitatively with a free energy model that balances short-ranged depletion and van der Waals attractions with longer-ranged electrostatic repulsion, as a function of the Au and polymer concentrations. The close spacings of the Au nanoparticles in the clusters produce strong NIR extinction over a broad range of wavelengths from 650 to 900 nm, which is of practical interest in biomedical imaging.

During production of concentrated monoclonal antibody formulations by tangential flow ultrafiltration (TFF), high viscosities and aggregation often cause extensive membrane fouling, flux decay and low product yields. To address these challenges, the co-solutes histidine or imidazole were added at high concentrations from 250 to 320 mM to reduce the viscosity by up to tenfold relative to conventional low co-solute formulations, to as low as 40 cP at 250 mg/mL. At high mAb concentrations of up to 280 mg/mL, the transmembrane flux was increased threefold by adding high concentrations of co-solutes that also lowered the viscosity. Furthermore, the co-solutes also increased the mAb gel point concentration c g by up to 100 mg/mL mAb and thus enhanced concentration polarization-driven back-diffusion of the mAb at the membrane wall, which led to increased fluxes. The low viscosity and hollow fiber filter modules with straight flow paths enabled more uniform TMP and wall shear stress τ w profiles, which mitigated the reversible flux decay that results from an axial decline in the local TMP. The concentrated mAb was stable by SEC before and after extended storage at 4°C and 37°C.

There is extensive experimental data showing that the final pH and buffer composition after protein diafiltration (DF), particularly with monoclonal antibodies, can be considerably different than that in the DF buffer due to electrostatic interactions between the charged protein and the charged ions. Previous models for this behavior have focused on the final (equilibrium) partitioning and are unable to explain the complex pH and concentration profiles during the DF process. The objective of this study is to develop a new model for antibody DF based on solution of the transient mass balance equations, with the permeate concentrations of the charged species evaluated assuming Donnan equilibrium across the semipermeable membrane in combination with electroneutrality constraints. Model predictions are in excellent agreement with experimental data obtained during DF of both acidic and basic monoclonal antibodies, with the protein charge determined from independent electrophoretic mobility measurements. The model is able to predict the entire pH/histidine concentration profiles during DF, providing a framework for the development of DF processes that yield the desired antibody formulation.

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During large-scale monoclonal antibody manufacturing, disulfide bond reduction of antibodies, which results in generation of low molecule weight species, is occasionally observed. When this happens, the drug substance does not meet specifications. Many investigations have been conducted across the biopharmaceutical industry to identify the root causes, and multiple strategies have been proposed to mitigate the problem. The reduction is correlated with the release of cellular reducing components and depletion of dissolved oxygen before, during, and after harvest. Consequently, these factors can lead to disulfide reduction over long-duration storage at room temperature prior to Protein A chromatography. Several strategies have been developed to minimize antibody reduction, including chemical inhibition of reducing components, maintaining aeration before and after harvest, and chilling clarified harvest during holding. Here, we explore the use of hydrogen peroxide in clarified harvest bulk or cell culture fluid as a strategy to prevent disulfide reduction. A lab-scale study was performed to demonstrate the effectiveness of hydrogen peroxide in preventing antibody reduction using multiple IgG molecules. Studies were done to define the optimal concentration of hydrogen peroxide needed to avoid unnecessary oxidization of the antibody products. We show that adding a controlled amount of hydrogen peroxide does not change product quality attributes of the protein. Since hydrogen peroxide is soluble in aqueous solutions and decomposes into water and oxygen, there is no additional burden involved in removing it during the downstream purification steps. Due to its ease of use and minimal product impact, we demonstrate that hydrogen peroxide treatment is a powerful, simple tool to quench reducing potential by simply mixing it with harvested cell culture fluid.

Proline demonstrated greater efficacy for improving mAb viscosity and stability in contrast to glycine and trehalose due to its amphipathic structure and partial charge on the pyrrolidine side chain. These properties likely allow proline to screen the attractive electrostatic and hydrophobic interactions that promote self-association and high viscosities. Binary proline-histidine formulations also demonstrated greater viscosity reduction effects than histidine alone at the same total co-solute concentration, while maintaining a lower total solution osmolarity.

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