Michael C. Borys

Real time monitoring of multiple parameters in mammalian cell culture bioreactors using an in‐line Raman spectroscopy probe

The FDAs process analytical technology initiative encourages drug manufacturers to apply innovative ideas to better understand their processes. There are many challenges to applying these techniques to monitor mammalian cell culture bioreactors for biologics manufacturing. These include the ability to monitor multiple components in complex medium formulations non-invasively and in-line. We report results that demonstrate, for the first time, the technical feasibility of the in-line application of Raman spectroscopy for monitoring a mammalian cell culture bioreactor. A Raman probe was used for the simultaneous prediction of culture parameters including glutamine, glutamate, glucose, lactate, ammonium, viable cell density, and total cell density.

Effects of culture conditions on N-glycolylneuraminic acid (Neu5Gc) content of a recombinant fusion protein produced in CHO cells.

CHO cells express glycoproteins containing both the N‐acetylneuraminic acid (Neu5Ac) and minor amounts of the N‐glycolylneuraminic acid (Neu5Gc) forms of sialic acid. As Neu5Gc is not expressed in humans and can be recognized as a foreign epitope, there is the potential for immunogenicity issues for glycoprotein therapeutics. During process development of a glycosylated fusion protein expressed by CHO cells, a number of culture conditions were identified that affected the Neu5Gc content of the recombinant glycoprotein. Sodium butyrate (SB), a well‐known additive reported to enhance recombinant protein productivity in specific cases, minimally affected product titers here, but did decrease Neu5Gc levels by 50–62%. A shift in culture temperature to a lower value after the exponential growth phase was used to extend the culture period. It was found that the Neu5Gc levels were 59% lower when the temperature shift occurred later near the stationary phase of the culture compared to an early‐temperature shift, near the end of the exponential growth phase. Studies on the effects of pCO2 with this product showed that the Neu5Gc levels were 46% lower at high pCO2 conditions (140 mmHg) compared to moderate pCO2 levels (20–80 mmHg). Finally, a comparison of sodium carbonate versus sodium hydroxide as the base used for pH control resulted in a reproducible 33% decrease in Neu5Gc in bioreactors using sodium hydroxide. These results are of practical importance as SB is a commonly tested additive, and the other factors affecting Neu5Gc can conveniently be used to reduce or control Neu5Gc in processes for the manufacture of glycoprotein therapeutics. Biotechnol. Bioeng. 2010;105: 1048–1057.

The use of ‘Omics technology to rationally improve industrial mammalian cell line performance

Biologics represent an increasingly important class of therapeutics, with 7 of the 10 top selling drugs from 2013 being in this class. Furthermore, health authority approval of biologics in the immuno‐oncology space is expected to transform treatment of patients with debilitating and deadly diseases. The growing importance of biologics in the healthcare field has also resulted in the recent approvals of several biosimilars. These recent developments, combined with pressure to provide treatments at lower costs to payers, are resulting in increasing need for the industry to quickly and efficiently develop high yielding, robust processes for the manufacture of biologics with the ability to control quality attributes within narrow distributions. Achieving this level of manufacturing efficiency and the ability to design processes capable of regulating growth, death and other cellular pathways through manipulation of media, feeding strategies, and other process parameters will undoubtedly be facilitated through systems biology tools generated in academic and public research communities. Here we discuss the intersection of systems biology, ‘Omics technologies, and mammalian bioprocess sciences. Specifically, we address how these methods in conjunction with traditional monitoring techniques represent a unique opportunity to better characterize and understand host cell culture state, shift from an empirical to rational approach to process development and optimization of bioreactor cultivation processes. We summarize the following six key areas: (i) research applied to parental, non‐recombinant cell lines; (ii) systems level datasets generated with recombinant cell lines; (iii) datasets linking phenotypic traits to relevant biomarkers; (iv) data depositories and bioinformatics tools; (v) in silico model development, and (vi) examples where these approaches have been used to rationally improve cellular processes. We critically assess relevant and state of the art research being conducted in academic, government and industrial laboratories. Furthermore, we apply our expertise in bioprocess to define a potential model for integration of these systems biology approaches into biologics development. Biotechnol. Bioeng. 2016;113: 26–38.

Development of robust antibody purification by optimizing protein‐A chromatography in combination with precipitation methodologies

To be administered to patients, therapeutic monoclonal antibodies must have very high purity, with process related impurities like host‐cell proteins (HCPs) and DNA reduced to <100 ppm and <10 ppb, respectively, relative to desired product. Traditionally, Protein‐A chromatography as a capture step has been the work horse for clearing a large proportion of these impurities. However, remaining levels of process and product related impurities still present significant challenges on the development of polishing steps further downstream. In this study, we have incorporated high throughput screening to evaluate three areas of separation: (i) Harvest treatment; (ii) Protein‐A Chromatography; and (iii) Low pH Viral Inactivation. Precipitation with low pH treatment of cell culture harvest resulted in selective removal of impurities while manipulating the pH of wash buffers used in Protein‐A chromatography and incorporating wash additives that disrupt various modes of protein–protein interaction resulted in further and more pronounced reduction in impurity levels. In addition, our study also demonstrate that optimizing the neutralization pH post Protein‐A elution can result in selective removal of impurities. When applied over multiple mAbs, this optimization method proved to be very robust and the strategy provides a new and improved purification process that reduces process related impurities like HCPs and DNA to drug substance specifications with just one chromatography column and open avenues for significant decrease in operating costs in monoclonal antibody purification. Biotechnol. Bioeng. 2015;112: 2292–2304.

Clarification technologies for monoclonal antibody manufacturing processes: Current state and future perspectives

Considerable progress has been made increasing productivity of cell cultures to meet the rapidly growing demand for antibody biopharmaceuticals through increased cell densities and longer culture times. This in turn has dramatically increased the burden of process and product related impurities on the purification processes. In addition, current trends in the biopharmaceutical industry point toward both increased productivity and targeting smaller patient populations for new indications. Taken together, these developments are driving the industry to explore alternative separation technologies as a future manufacturing strategy. Clarification technologies well established in other industries, such as flocculation and precipitation are increasingly considered as a viable solution to address this bottleneck in antibody processes. However, several technical issues need to be fully addressed including suitability as a platform application, robustness, process cost, toxicity, and clearance. This review will focus on recent efforts to incorporate new generation clarification technologies for mammalian cell cultures producing monoclonal antibodies as well as challenges to their implementation supported by a case study. Biotechnol. Bioeng. 2016;113: 698–716.

A mechanistic study on the effect of dexamethasone in moderating cell death in Chinese Hamster Ovary cell cultures

Dexamethasone (DEX) was previously shown (Jing et al., Biotechnol Bioeng. 2010;107:488‐496) to play a dual role in increasing sialylation of recombinant glycoproteins produced by Chinese Hamster Ovary (CHO) cells. DEX addition increased sialic acid levels of a recombinant fusion protein through increased expression of α2,3‐sialyltransferase and β1,4‐galactosyltransferase, but also decreased the sialidase‐mediated, extracellular degradation of sialic acid through slowing cell death at the end of the culture period. This study examines the underlying mechanism for this cytoprotective action by studying the transcriptional response of the CHO cell genome upon DEX treatment using DNA microarrays and gene ontology term analysis. Many of those genes showing a significant transcriptional response were associated with the regulation of programmed cell death. The gene with the highest change in expression level, as validated by Quantitative PCR assays with TaqMan® probes and confirmed by Western Blot analysis, was the antiapoptotic gene Tsc22d3, also referred to as GILZ (glucocorticoid‐induced leucine zipper). The pathway by which DEX suppressed cell death towards the end of the culture period was also confirmed by showing involvement of glucocorticoid receptors and GILZ through studies using the glucocorticoid antagonist mifepristone (RU‐486). These findings advance the understanding of the mechanism by which DEX suppresses cell death in CHO cells and provide a rationale for the application of glucocorticoids in CHO cell culture processes.

Understanding and Controlling Sialylation in a CHO Fc-Fusion Process

A Chinese hamster ovary (CHO) bioprocess, where the product is a sialylated Fc-fusion protein, was operated at pilot and manufacturing scale and significant variation of sialylation level was observed. In order to more tightly control glycosylation profiles, we sought to identify the cause of variability. Untargeted metabolomics and transcriptomics methods were applied to select samples from the large scale runs. Lower sialylation was correlated with elevated mannose levels, a shift in glucose metabolism, and increased oxidative stress response. Using a 5-L scale model operated with a reduced dissolved oxygen set point, we were able to reproduce the phenotypic profiles observed at manufacturing scale including lower sialylation, higher lactate and lower ammonia levels. Targeted transcriptomics and metabolomics confirmed that reduced oxygen levels resulted in increased mannose levels, a shift towards glycolysis, and increased oxidative stress response similar to the manufacturing scale. Finally, we propose a biological mechanism linking large scale operation and sialylation variation. Oxidative stress results from gas transfer limitations at large scale and the presence of oxygen dead-zones inducing upregulation of glycolysis and mannose biosynthesis, and downregulation of hexosamine biosynthesis and acetyl-CoA formation. The lower flux through the hexosamine pathway and reduced intracellular pools of acetyl-CoA led to reduced formation of N-acetylglucosamine and N-acetylneuraminic acid, both key building blocks of N-glycan structures. This study reports for the first time a link between oxidative stress and mammalian protein sialyation. In this study, process, analytical, metabolomic, and transcriptomic data at manufacturing, pilot, and laboratory scales were taken together to develop a systems level understanding of the process and identify oxygen limitation as the root cause of glycosylation variability.

Ultrafiltration Behavior of Monoclonal Antibodies and Fc-Fusion Proteins: Effects of Physical Properties†

Ultrafiltration (UF) is used for the final concentration and formulation of essentially all antibody‐based therapeutics including both monoclonal antibodies (mAbs) and Fc‐fusion proteins. The objective of this study was to quantitatively compare the filtrate flux behavior for two highly purified mAbs and an Fc‐fusion protein under identical flow and buffer conditions. Filtrate flux data were obtained using a Pellicon 3 tangential flow filtration cassette over a wide range of transmembrane pressures and bulk protein concentrations. Independent experimental measurements were performed to evaluate the protein osmotic pressure and solution viscosity. The maximum achievable protein concentration was directly correlated with the solution viscosity, which controls the pressure drop and extent of back‐filtration in the cassette. The filtrate flux data were analyzed using a recently developed model that accounts for the effects of intermolecular interactions and transmembrane pressure gradients on the extent of concentration polarization. These results provide important insights into the factors controlling the filtrate flux during the UF of concentrated protein solutions and an effective framework for the design/analysis of UF processes for the formulation of antibody‐based therapeutics. Biotechnol. Bioeng. 2017;114: 2057–2065.

Development of adsorptive hybrid filters to enable two-step purification of biologics

ABSTRACT Recent progress in mammalian cell culture process has resulted in significantly increased product titers, but also a substantial increase in process- and product-related impurities. Due to the diverse physicochemical properties of these impurities, there is constant need for new technologies that offer higher productivity and improved economics without sacrificing the process robustness required to meet final drug substance specifications. Here, we examined the use of new synthetic adsorptive hybrid filters (AHF) modified with the high binding capacity of quaternary amine (Emphaze™ AEX) and salt-tolerant biomimetic (Emphaze™ ST-AEX) ligands for clearance of process-related impurities like host cell protein (HCP), residual DNA, and virus. The potential to remove soluble aggregates was also examined. Our aim was to develop a mechanistic understanding of the interactions governing adsorptive removal of impurities during filtration by evaluating the effect of various filter types, feed streams, and process conditions on impurity removal. The ionic capacity of these filters was measured and correlated with their ability to remove impurities for multiple molecules. The ionic capacity of AHF significantly exceeded that of traditional adsorptive depth filters (ADF) by 40% for the Emphaze™ AEX and by 700% for the Emphaze™ ST-AEX, providing substantially higher reduction of soluble anionic impurities, including DNA, HCPs and model virus. Nevertheless, we determined that ADF with filter aid provided additional hydrophobic functionality that resulted in removal of higher molecular weight species than AHF. Implementing AHF demonstrated improved process-related impurity removal and viral clearance after Protein A chromatography and enabled a two-step purification process. The consequences of enhanced process performance are far reaching because it allows the downstream polishing train to be restructured and simplified, and chromatographic purity standards to be met with a reduced number of chromatographic steps.

Protection of therapeutic antibodies from visible light induced degradation: Use safe light in manufacturing and storage

Graphical abstract Figure. No caption available. &NA; As macromolecules, biologics are susceptible to light exposure, which induces oxidation of multiple amino acid residues including tryptophan, tyrosine, phenylalanine, cysteine and methionine. Pertaining to safety, efficacy and potency, light‐induced oxidation of biologics has been widely studied and necessary precautions need to be taken during biologics manufacturing process, drug substance and products handling and storage. Proteins will degrade to varying extents depending on the protein properties, degradation pathways, formulation compositions and type of light source. In addition to UV light, which has been widely known to degrade proteins, visible light from indoor fluorescent lighting also can mediate protein degradation. In this report, we examine and identify wavelengths in the visual spectrum (400–700 nm) that can cause monoclonal antibody and histidine buffer degradation. Installation of safe lights which exclude the identified damaging wavelengths from visible spectra in manufacturing and storage areas can provide a balance between lighting requirement for human operators and their safety and conservation of product quality.