Crystal structure of an HSA/FcRn complex reveals recycling by competitive mimicry of HSA ligands at a pH-dependent hydrophobic interface.

The long circulating half-life of serum albumin, the most abundant protein in mammalian plasma, derives from pH-dependent endosomal salvage from degradation, mediated by the neonatal Fc receptor (FcRn). Using yeast display, we identified human serum albumin (HSA) variants with increased affinity for human FcRn at endosomal pH, enabling us to solve the crystal structure of a variant HSA/FcRn complex. We find an extensive, primarily hydrophobic interface stabilized by hydrogen-bonding networks involving protonated histidines internal to each protein. The interface features two key FcRn tryptophan side chains inserting into deep hydrophobic pockets on HSA that overlap albumin ligand binding sites. We find that fatty acids (FAs) compete with FcRn, revealing a clash between ligand binding and recycling, and that our high-affinity HSA variants have significantly increased circulating half-lives in mice and monkeys. These observations open the way for the creation of biotherapeutics with significantly improved pharmacokinetics.

Reduction of product-related species during the fermentation and purification of a recombinant IL-1 receptor antagonist at the laboratory and pilot scale.

Through a parallel approach of tracking product quality through fermentation and purification development, a robust process was designed to reduce the levels of product-related species. Three biochemically similar product-related species were identified as byproducts of host-cell enzymatic activity. To modulate intracellular proteolytic activity, key fermentation parameters (temperature, pH, trace metals, EDTA levels, and carbon source) were evaluated through bioreactor optimization, while balancing negative effects on growth, productivity, and oxygen demand. The purification process was based on three non-affinity steps and resolved product-related species by exploiting small charge differences. Using statistical design of experiments for elution conditions, a high-resolution cation exchange capture column was optimized for resolution and recovery. Further reduction of product-related species was achieved by evaluating a matrix of conditions for a ceramic hydroxyapatite column. The optimized fermentation process was transferred from the 2-L laboratory scale to the 100-L pilot scale and the purification process was scaled accordingly to process the fermentation harvest. The laboratory- and pilot-scale processes resulted in similar process recoveries of 60 and 65%, respectively, and in a product that was of equal quality and purity to that of small-scale development preparations. The parallel approach for up- and downstream development was paramount in achieving a robust and scalable clinical process.

Design of a superior cytokine antagonist for topical ophthalmic use.

IL-1 is a key inflammatory and immune mediator in many diseases, including dry-eye disease, and its inhibition is clinically efficacious in rheumatoid arthritis and cryopyrin-associated periodic syndromes. To treat ocular surface disease with a topical biotherapeutic, the uniqueness of the site necessitates consideration of the agent's size, target location, binding kinetics, and thermal stability. Here we chimerized two IL-1 receptor ligands, IL-1ß and IL-1Ra, to create an optimized receptor antagonist, EBI-005, for topical ocular administration. EBI-005 binds its target, IL-1R1, 85-fold more tightly than IL-1Ra, and this increase translates to an ∼100-fold increase in potency in vivo. EBI-005 preserves the affinity bias of IL-1Ra for IL-1R1 over the decoy receptor (IL-1R2), and, surprisingly, is also more thermally stable than either parental molecule. This rationally designed antagonist represents a unique approach to therapeutic design that can potentially be exploited for other ß-trefoil family proteins in the IL-1 and FGF families.

A single-use purification process for the production of a monoclonal antibody produced in a PER.C6 human cell line.

Advances in single-use technologies can enable greater speed, flexibility, and a smaller footprint for multi-product production facilities, such as at a contract manufacturer. Recent efforts in the area of cell line and media optimization have resulted in bioreactor productivities that exceed 8 g/L in fed-batch processes or 25 g/L in high-density cell culture processes. In combination with the development of single-use stirred tank bioreactors with larger working volumes, these intensified upstream processes can now be fit into a single-use manufacturing setting. Contrary to these upstream advances, downstream single-use technologies have been slower to follow, mostly limited by low capacity, high cost, and poor scalability. In this study we describe a downstream process based solely on single-use technologies that meets the challenges posed by expression of a mAb (IgG(1)) in a high-density suspension culture of PER.C6 cells. The cell culture harvest was clarified by enhanced cell settling (ECS) and depth filtration. Precipitation was used for crude purification of the mAb. A high capacity chromatographic membrane was then used in bind/elute mode, followed by two membranes in flow-through (FT) mode for polishing. A proof of concept of the entire disposable process was completed for two different scales of the purification train.