Exaggerated effect of fluvoxamine in heterozygote serotonin transporter knockout mice

Clearance rates for serotonin (5-HT) in heterozygote (+/-) and homozygote (-/-) serotonin transporter (5-HTT) knockout (KO) mice have not been determined in vivo. Moreover, the effect of selective serotonin reuptake inhibitors (SSRIs) on 5-HT clearance in these mice has not been examined. In this study, the rate of clearance of exogenously applied 5-HT was measured in the CA3 region of the hippocampus of anesthetized mice using high-speed chronoamperometry. Compared with wild-type mice, the maximal rate of 5-HT clearance from extracellular fluid (ECF) was decreased in heterozygotes and more markedly so in KO mice. Heterozygote mice were more sensitive to the 5-HT uptake inhibitor, fluvoxamine, resulting in longer clearance times for 5-HT than in wild-type mice; as expected, the KO mice were completely unresponsive to fluvoxamine. There were no associated changes in norepinephrine transporter density, nor was there an effect of the norepinephrine uptake inhibitor, desipramine, on 5-HT clearance in any genotype. Thus, adaptive changes in the norepinephrine transport system do not occur in the CA3 region of hippocampus as a consequence of 5-HTT KO. These data highlight the potential of the heterozygote 5-HTT mutant mice to model the dynamic in vivo consequences of the human 5-HTT polymorphism.     

Generic/matrix evaluation of SV40 clearance by anion exchange chromatography in flow-through mode

The potential of viral contamination is a regulatory concern for continuous cell line-derived pharmaceutical proteins. Complementary and redundant safety steps, including an evaluation of the viral clearance capacity of unit operations in the purification process, are performed prior to registration and marketing of biotechnology pharmaceuticals. Because process refinement is frequently beneficial, CBER/FDA has published guidance facilitating process improvement by delineating specific instances where the bracketing and generic approaches are appropriate for virus removal validation. In this study, a generic/matrix study was performed using Q-Sepharose Fast Flow (QSFF) chromatography to determine if bracketing and generic validation can be applied to anion exchange chromatography. Key operational parameters were varied to upper and lower extreme values and the impact on viral clearance was assessed using simian virus 40 (SV40) as the model virus. Operational ranges for key chromatography parameters were identified where an SV40 log(10) reduction value (LRV) of >or=4.7 log(10) is consistently achieved. On the basis of the apparent robustness of SV40 removal by Q-anion exchange chromatography, we propose that the concept of "bracketed generic" validation can be applied to this and potentially other chromatography unit operations.     

Bracketed generic inactivation of rodent retroviruses by low pH treatment for monoclonal antibodies and recombinant proteins

Viral safety is a predominant concern for monoclonal antibodies (mAbs) and other recombinant proteins (RPs) with pharmaceutical applications. Certain commercial purification modules, such as nanofiltration and low-pH inactivation, have been observed to reliably clear greater than 4 log(10) of large enveloped viruses, including endogenous retrovirus. The concept of "bracketed generic clearance" has been proposed for these steps if it could be prospectively demonstrated that viral log(10) reduction value (LRV) is not impacted by operating parameters that can vary, within a reasonable range, between commercial processes. In the case of low-pH inactivation, a common step in mAb purification processes employed after protein A affinity chromatography, these parameters would include pH, time and temperature of incubation, the content of salts, protein concentration, aggregates, impurities, model protein pI, and buffer composition. In this report, we define bracketed generic clearance conditions, using a prospectively defined bracket/matrix approach, where low-pH inactivation consistently achieves >or=4.6 log(10) clearance of xenotropic murine leukemia virus (X-MLV), a model for rodent endogenous retrovirus. The mechanism of retrovirus inactivation by low-pH treatment was also investigated.     

Molecular characterization of the rat Kupffer cell glycoprotein receptor

The Kupffer cell receptor for glycoproteins has been reported to have a role in clearance of galactose- and fucose-terminated glycoproteins from circulation. Although the gene and a cDNA encoding the receptor have been described, there has been little study of the receptor protein. To address some questions about possible ligands and functions for this receptor, fragments representing portions of the extracellular domain have been expressed and characterized. The extracellular domain consists of a trimer stabilized by an extended coiled-coil of alpha-helices. The receptor displays monosaccharide-binding characteristics similar to the hepatic asialoglycoprotein receptor, but with somewhat less selectivity. The two best monosaccharide ligands are GalNAc and galactose. alpha-Methyl fucoside is a particularly poor ligand. Analysis of Kupffer cell receptor binding to glycoproteins and oligosaccharides released from them reveals highest affinity for desialylated, complex N-linked glycans. The best glycoprotein ligands contain multiple highly branched oligosaccharides. A human ortholog of the rat receptor gene does not encode a full-length protein and is not expressed in liver. These characteristics suggest that the receptor may have functions parallel to those of the hepatocyte asialoglycoprotein receptor in some (but not all) mammalian species.     

Five thousand years of livestock in Britain

The introduction of livestock, including the rabbit and the fallow deer, to Britain is reviewed, and a summary is given of the history of husbandry arid selective breeding. The feeding or stock on foliage and its importance for survival through the winter is described. The meaning of domestication is discussed and ii is argued that there should be no separation between the old established breeds of livestock, park deer, and feral populations including Chillingham rattle, Soay sheep, and Bagot goats; all belong to the assemblage of large mammals that has created the landscape of the British Isles.     

Understanding the mechanism of virus removal by Q sepharose fast flow chromatography during the purification of CHO‐cell derived biotherapeutics

During production of therapeutic monoclonal antibodies (mAbs) in mammalian cell culture, it is important to ensure that viral impurities and potential viral contaminants will be removed during downstream purification. Anion exchange chromatography provides a high degree of virus removal from mAb feedstocks, but the mechanism by which this is achieved has not been characterized. In this work, we have investigated the binding of three viruses to Q sepharose fast flow (QSFF) resin to determine the degree to which electrostatic interactions are responsible for viral clearance by this process. We first used a chromatofocusing technique to determine the isoelectric points of the viruses and established that they are negatively charged under standard QSFF conditions. We then determined that virus removal by this chromatography resin is strongly disrupted by the presence of high salt concentrations or by the absence of the positively charged Q ligand, indicating that binding of the virus to the resin is primarily due to electrostatic forces, and that any non‐electrostatic interactions which may be present are not sufficient to provide virus removal. Finally, we determined the binding profile of a virus in a QSFF column after a viral clearance process. These data indicate that virus particles generally behave similarly to proteins, but they also illustrate the high degree of performance necessary to achieve several logs of virus reduction. Overall, this mechanistic understanding of an important viral clearance process provides the foundation for the development of science‐based process validation strategies to ensure viral safety of biotechnology products. Biotechnol. Bioeng. 2009; 104: 371–380 © 2009 Wiley Periodicals, Inc.     

PDADMAC flocculation of Chinese hamster ovary cells: Enabling a centrifuge-less harvest process for monoclonal antibodies

High titer (>10 g/L) monoclonal antibody (mAb) cell culture processes are typically achieved by maintaining high viable cell densities over longer culture durations. A corresponding increase in the solids and sub-micron cellular debris particle levels are also observed. This higher burden of solids (≥15%) and sub-micron particles typically exceeds the capabilities of a continuous centrifuge to effectively remove the solids without a substantial loss of product and/or the capacity of the harvest filtration train (depth filter followed by membrane filter) used to clarify the centrate. We discuss here the use of a novel and simple two-polymer flocculation method used to harvest mAb from high cell mass cell culture processes. The addition of the polycationic polymer, poly diallyldimethylammonium chloride (PDADMAC) to the cell culture broth flocculates negatively-charged cells and cellular debris via an ionic interaction mechanism. Incorporation of a non-ionic polymer such as polyethylene glycol (PEG) into the PDADMAC flocculation results in larger flocculated particles with faster settling rate compared to PDADMAC-only flocculation. PDADMAC also flocculates the negatively-charged sub-micron particles to produce a feed stream with a significantly higher harvest filter train throughput compared to a typical centrifuged harvest feed stream. Cell culture process variability such as lactate production, cellular debris and cellular densities were investigated to determine the effect on flocculation. Since PDADMAC is cytotoxic, purification process clearance and toxicity assessment were performed.     

Development of a modular virus clearance package for anion exchange chromatography operated in weak partitioning mode

Anion exchange chromatography (AEX) operated under weak partitioning mode has been proven to be a powerful polishing step as well as a robust viral clearance step in Pfizer's monoclonal antibody (mAb) platform purification process. A multivariate design of experiment (DoE) study was conducted to understand the impact of operating parameters and feedstream impurity levels on viral clearance by weak partitioning mode AEX. Bacteriophage was used initially as a surrogate for neutral and acidic isoelectric point mammalian viruses (e.g., retrovirus and parvovirus). Five different mAbs were used in the evaluation of process parameters such as load challenge (both product and impurities), load pH, load conductivity, and contact time (bed height and flow‐rate). The operating ranges obtained from phage clearance studies and Pfizer's historical data were used to define an appropriate operating range for a subsequent clearance study with model retrovirus and parvovirus. Both phage and virus clearance evaluations included feedstreams containing different levels of impurities such as high molecular mass species (HMMS), host cell proteins (HCPs), and host cell DNA. For all the conditions tested, over 5 log₁₀ of clearance for both retrovirus and parvovirus was achieved. The results demonstrated that weak partitioning mode AEX chromatography is a robust step for viral clearance and has the potential to be included as part of the modular viral clearance approach. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:750–757, 2015     

Prediction of viral filtration performance of monoclonal antibodies based on biophysical properties of feed

Controlling viral contamination is an important issue in the process development of monoclonal antibodies (MAbs) produced from mammalian cell lines. Virus filtration (VF) has been demonstrated to be a robust and effective clearance step which can provide ≥4 logs of reduction via size exclusion. The minimization of VF area by increasing flux and filter loading is critical to achieving cost targets as VFs are single use and often represent up to 10% of total purification costs. The research presented in this publication describes a development strategy focused on biophysical attributes of product streams that are directly applicable to VF process performance. This article summarizes a case study where biophysical tools (high‐pressure size exclusion chromatography, dynamic light scattering, and absolute size exclusion chromatography) were applied to a specific MAb program to illustrate how changes in feed composition (pH, sodium chloride concentration, and buffer salt type) can change biophysical properties which correlate with VF performance. The approach was subsequently refined and expanded over the course of development of three MAbs where performance metrics (i.e., loading and flux) were evaluated for two specific virus filters (Viresolve Pro and Planova 20N) during both unspiked control runs and virus clearance experiments. The analyses of feed attributes can be applied to a decision tree to guide the recommendation of a VF filter and operating conditions for use in future MAb program development. The understanding of the biophysical properties of the feed can be correlated to virus filter performance to significantly reduce the mass of product, time, and costs associated with virus filter step development. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:765–774, 2015