Formulation Buffer Research Articles

Investigations into improving the standard DNA testing of trace samples at ESR

ABSTRACTSince 2007, the Institute of Environmental and Science Research (ESR) has been using the AmpF/STR Identifiler profiling kit as the standard DNA test. Whilst this approach works well for most samples with a DNA input range of 400 pg to 2 ng, samples containing less DNA often have limited to no profiling success. If required, such samples can undergo testing using a more sensitive technique, such as mini-STR analysis or Low Copy Number (LCN) DNA analysis. The introduction of a more sensitive standard DNA test into the laboratory would likely prove to be greatly beneficial. Profiling success should increase, particularly for samples containing trace DNA concentrations, and the number of samples requiring rework and further analysis using an ultra-sensitive technique would potentially reduce. A number of new generation multiplex kits with increased sensitivity are now commercially available. One such kit is the AmpF/STR Identifiler Plus profiling kit, which has enhanced buffer formulation and an optimized PCR cycling protocol. This study investigates the profiling results from trace DNA samples using Identifiler at 28 cycles and Identifiler Plus, at 28 and 29 cycles, analysed using the 3500xL Applied BioSystems Genetic Analyzer. Any further benefits from including a post-PCR clean-up step and enhanced capillary electrophoresis conditions are investigated and discussed.

Roadmap for the Development and Clinical Translation of Optical Tracers Cetuximab-800CW and Trastuzumab-800CW.

Optical molecular imaging using fluorescently labeled monoclonal antibodies is of significant added value in guiding surgical or endoscopic procedures. However, development of tracers for clinical trials is complex, and implementation in the clinic is therefore slow. We present a roadmap for development and translation of monoclonal antibody tracers into a drug product compliant with current good manufacturing processes (cGMPs). Methods: The production process for cetuximab-800CW and trastuzumab-800CW was optimized with regard to dye-to-protein ratio and formulation buffer. Promising formulations were produced under cGMP conditions and advanced to a full-scale stability study. Tracers were analyzed for stability by size-exclusion high-pressure liquid chromatography, pH measurement, osmolality, visual inspection, and sterility, as required by the European Pharmacopeia and cGMP guidelines. Results: Seven formulations were investigated for cetuximab-800CW and 10 for trastuzumab-800CW. On the basis of the formulation study results, we chose 2 formulations per antibody for investigation during the full-scale stability study. These formulations all performed well, showing good compliance with the acceptance criteria set for each product. Conclusion: We designed a roadmap to standardize the development, formulation, and cGMP translation of molecular fluorescent tracers. Using our standardized approach, we developed 2 stable antibody-based tracers for clinical use. The proposed roadmap can be used to efficiently develop a cGMP-compliant formulation and improve the translation of newly developed optical tracers to first-in-human use.

A Scalable Lentiviral Vector Production and Purification Method Using Mustang Q Chromatography and Tangential Flow Filtration.

Lentiviral vectors have rapidly become a favorite tool for research and clinical gene transfer applications which seek to permanently introduce alterations in the genome. This status can be attributed primarily to their ability to transduce dividing as well as quiescent cells. When coupled with internal promotor selection to drive expression in one cell type but not another, the ease with which the vectors can be pseudotyped to either restrict or expand tropism offers unique opportunities previously unavailable to the researcher to manipulate the genome. Although LV can be produced from stable packaging cell lines and/or in suspension culture, by and far, most LV vectors are produced using adherent 293T cells grown in plasticware and production plasmids transiently transfected with either PEI or Calcium Phosphate. The media is usually changed and un-concentrated vector supernatant collected between 24 and 48h post-transfection. The supernatant may then be purified by Mustang Q chromatography, concentrated by Tangential Flow Filtration, and finally diafiltered into the final formulation buffer of choice. Here we describe a pilot scale method for the manufacture of a Lentiviral vector that purifies and concentrates approximately 6L of un-concentrated LV supernatant to approximately 150mL. Typical titers for most vector constructs range between 1×108 and 1×109 infectious particles per mL. This method may be performed reiteratively to increase total volume or can be further scaled up to increase yield.

Hollow fiber countercurrent dialysis for continuous buffer exchange of high-value biotherapeutics.

Buffer exchange, desalting, and formulation of high-value biotherapeutics are currently performed using batch diafiltration (DF); however, this type of tangential flow filtration process may be difficult to implement as part of a fully continuous biomanufacturing process. The objective of this study was to explore the potential of using countercurrent dialysis for continuous protein formulation and buffer exchange. Experiments were performed using concentrated solutions of immunoglobuin G (IgG) with commercially available hollow fiber dialyzers having 1.5 and 1.8 m2 membrane surface area. More than 99.9% buffer exchange was obtained over a range of conditions, as determined from the removal of a model impurity (vitamin B12 ). The dialyzers were able to process more than 0.5 kg of IgG per day in an easily scalable low-cost process. In addition, buffer requirements were less than 0.02 L of buffer per gram IgG, which is several times less than that used in current batch DF processes. These results clearly demonstrate the potential of using low-cost hollow fiber dialyzers for buffer exchange and product formulation in continuous bioprocessing. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2763, 2019.

Biotherapeutic Antibody Subunit LC-MS and Peptide Mapping LC-MS Measurements to Study Possible Biotransformation and Critical Quality Attributes In Vivo

Biotransformation monitoring involves tracking drug modification occurring during in-life studies. Critical Quality Attribute monitoring from forced degraded drug material or in-life sample sets can provide an in-depth assessment of product quality for support in early- or late-stage drug development. For Critical Quality Attribute analysis, biotherapeutic monoclonal antibody (mAb) subunit analysis and peptide mapping liquid chromatography–mass spectrometry (LC-MS) approaches are used, although typically from an in vitro setting (e.g., formulation buffer) not involving biological samples or material. Here, samples from a high-dose rat study (in vivo) are subjected to analysis by ligand binding assay, mAb subunit LC-MS, and peptide mapping by LC-MS. Taken together, data from the 3 analytical approaches provide information regarding drug concentration in circulation, biotransformation, and biotherapeutic drug product quality. The concept of a multitier workflow for preclinical or clinical sample sets can be applied to other biotherapeutic mAb products such as bispecific mAbs, fusions proteins, or antibody-drug conjugates.

Thermal Shift and Stability Assays of Disease-Related Misfolded Proteins Using Differential Scanning Fluorimetry.

Systematic identification of buffer formulations and small molecule chaperones that improve the expression, stability, and storage of proteins with therapeutic interest has gained enormous importance in biochemical research as well as in biotechnology and biomedical applications. In particular, the biochemical characterization of disease-related proteins and their genetic variants that result in misfolding requires systematic determination of protein stability, screening of optimal buffer conditions for biophysical and structural studies, and in some cases, the identification of small molecule chaperones with the potential to ameliorate folding defects. Among the several techniques available, differential scanning fluorimetry (DSF) is currently an extensively employed screening and analysis method for thermal shift and protein stability assays. Here we describe a step-by-step generic protocol for fast characterization of protein thermal stability and analysis of stabilization in thermal-shift assays by additives, ligands and chemical chaperones using β-oxidation mitochondrial dehydrogenases as model. These enzymes are associated to inborn errors of metabolism caused by mutant variants with folding and stability defects for which we previously established folding correction afforded by their cognate cofactors and substrates. With this example we thus illustrate the potential applications of the method in screening small molecule folding correctors among metabolites, ligands, cofactors or candidate drugs with therapeutic potential in protein folding diseases.

A new rocuronium formulation not causing vascular pain in a flexor reflex model of anesthetized rats.

Intravenous administration of the brand formulation of rocuronium bromide, currently used as a muscle relaxant, has been associated with vascular pain accompanied by withdrawal movements of the arm and wrist. The purpose of this study was to identify the cause of vascular pain induced by the brand formulation and to develop a new rocuronium formulation, not causing vascular pain, using a vascular pain-evoked flexor reflex response model of anesthetized rats. A rat flexor reflex model, monitored by electromyography, was used to evaluate a flexor reflex response as the index of vascular pain. A catheter for drug administration was inserted into the superficial caudal epigastric artery. A needle electrode was inserted into a muscle in the femoral area to obtain an electromyogram (EMG) value. The integrated EMG values obtained after the administration of each test drug were compared to the baseline value and quantified. The acetate buffer contained in the solvent could cause flexor reflex response. Furthermore, the flexor reflex response increased in an acid concentration-dependent manner. Based on these results, we prepared a new rocuronium formulation using a low-acid-concentration buffer solution and found that it decreased the integrated EMG value in the rat model. The integrated EMG value acquired using the brand formulation was reduced by pretreatment with the TRPA1 channel inhibitor. Our findings suggest that the high acid concentration in the brand formulation buffer solution is the cause of vascular pain. The rocuronium formulation developed using a low-acid-concentration buffer solution might help eliminate vascular pain in the clinic.

Novel peptide-dendrimer/lipid/oligonucleotide ternary complexes for efficient cellular uptake and improved splice-switching activity

Despite the advances in gene therapy and in oligonucleotide (ON) chemistry, efficient cellular delivery remains an obstacle. Most current transfection reagents suffer from low efficacy or high cytotoxicity. In this report, we describe the synergism between lipid and dendrimer delivery vectors to enhance the transfection efficiency, while avoiding high toxicity. We screened a library of 20 peptide dendrimers representing three different generations and evaluated their capability to deliver a single-stranded splice-switching ON after formulating with lipids (DOTMA/DOPE). The transfection efficiency was analyzed in 5 reporter cell lines, in serum-free and serum conditions, and with 5 different formulation protocols. All formulations displayed low cytotoxicity to the majority of the tested cell lines. The complex sizes were < 200 nm; particle size distributions of effective mixtures were < 80 nm; and, the zeta potential was dependent on the formulation buffer used. The best dendrimer enhanced transfection in a HeLa reporter cell line by 30-fold compared to untreated cells under serum-free conditions. Interestingly, addition of sucrose to the formulation enabled – for the first time – peptide dendrimers/lipid complexes to efficiently deliver splice-switching ON in the presence of serum, reaching 40-fold increase in splice switching. Finally, in vivo studies highlighted the potential of these formulae to change the biodistribution pattern to be more towards the liver (90% of injected dose) compared to the kidneys (5% of injected dose) or to unformulated ON. This success encourages further development of peptide dendrimer complexes active in serum and future investigation of mechanisms behind the influence of additives on transfection efficacy.

Effect of Peroxide- Versus Alkoxyl-Induced Chemical Oxidation on the Structure, Stability, Aggregation, and Function of a Therapeutic Monoclonal Antibody

Current guidelines indicate that the effects of oxidation should be included as part of forced degradation studies on protein drugs. We probed the effect of 3 commonly used oxidants, hydrogen peroxide, tert-butyl hydroperoxide, and 2,2'-Azobis(2-amidinopropane) dihydrochloride (AAPH), on a therapeutic monoclonal IgG1 antibody (mAb8). Upon oxidation, mAb8 did not show noticeable changes in its secondary structure but showed minor changes in tertiary structure. Significant decrease in conformational stability was observed for all the 3 oxidized forms. Both hydrogen peroxide and tert-butyl hydroperoxide destabilized mainly the CH2 domain, whereas AAPH destabilized the variable domain in addition to CH2. Increased aggregation was found for AAPH-oxidized mAb8. In addition, a significant decrease in Fc receptor binding was observed for all 3 oxidized forms. Antibody dependent cell-mediated cytotoxicity, binding to target protein receptor, and cell proliferation activity were significantly reduced in the case of AAPH-oxidized mAb8. The presence of free methionine in the formulation buffer seems to alleviate the effect of oxidation. The results of this study show that the 3 oxidants differ in terms of their effects on the structure and function of mAb8 because of chemical modification of different sets of residues located in Fab versus Fc.

Buffer exchange path influences the stability and viscosity upon storage of a high concentration protein

High concentration protein solutions are generally produced by spin column concentration (SCC) during early development and by tangential flow filtration (TFF) during later stages, when greater quantities of protein become available. This is based on the assumption that the protein generated by the SCC process would be fairly similar to the TFF process material. In this study, we report the case of high concentration solutions of an Fc fusion protein produced by the two processes using the same upstream drug substance (DS) with very different storage stability.The TFF and SCC batches were characterized for aggregation, viscosity, and hydrodynamic radius before and after storage at different temperatures (5°C, 25 °C, and 40 °C). Aggregation and viscosity of the solutions processed by TFF were higher than those processed by SCC upon storage at 25 °C and 40 °C for three months. Differential scanning fluorimetry (DSF) revealed differences in initial protein conformation. Upon exposure to shear stress, protein solutions showed conformational instability and increased aggregation upon storage at 35 °C. In addition, protein solution showed higher aggregation upon shearing under mixed (downstream purification process and final formulation) buffer conditions – which are more likely to be encountered during the TFF, but not SCC, process. These results were further confirmed in an independent experiment by Fourier transform-infrared (FT-IR) spectroscopy and aggregation analysis.Taken together, these data indicate that shearing the protein in intermediate, unstable buffer conditions can lead to conformational perturbation during TFF processing, which led to higher rate of aggregation and viscosity upon storage. This study highlights the importance of testing shear stress sensitivity in the transitional buffer states of the TFF process early in development to de-risk process related product instability.

Identification of adeno-associated virus capsid proteins using ZipChip CE/MS

A simple and rapid identity test of adeno-associated virus (AAV) serotypes is important for supporting the AAV gene therapy development, as it relates to its efficacy and safety. The current mass spectrometry-based identity tests require extensive sample preparation steps, relatively large sample quantities and long analysis time. Herein, we describe a simple and novel microfluidic ZipChip CE/MS method used to characterize AAV capsid proteins. The three capsid proteins of AAV2 were separated and identified within 4 min using 5 nL of sample directly from a polysorbate-containing formulation buffer. This rapid method can be suitable to confirm AAV serotype identity.

Biophysical Properties and Heating-Induced Aggregation of Lysine-Conjugated Antibody-Drug Conjugates

The commercially available antibody-drug conjugate (ADC) product, Kadcyla® is synthesized using a 2-step reaction, wherein the linker is conjugated to native lysines on the mAb in step 1, followed by drug conjugation to the linker-modified antibody in step 2. In our study, we synthesized a lysine-conjugated ADC (Syn-ADC) on the same trastuzumab scaffold as Kadcyla® using a 1-step reaction. Mass spectrometry of both products revealed a subpopulation of Kadcyla® containing free linkers conjugated to the mAb, but not conjugated to the drug, which were absent in the 1-step reaction ADC product. Differential scanning calorimetry thermograms showed that the drug and linker conjugation significantly reduced the thermal stability and energies of activation for the denaturation of the CH2 domain of the ADCs. The heating induced aggregation events started as early as ∼57°C and ∼45°C for Kadcyla® and Syn-ADC, respectively, compared with 71°C for Herceptin®. The colloidal stability measurements clearly showed that the hydrophobic drug payload on ADCs significantly reduced the repulsive interprotein interactions when compared to the unconjugated antibody under formulation buffer conditions (pH 6.0). Attaching hydrophobic drug and linker moieties onto the antibody lowered the thermal and colloidal stabilities and increased the aggregation propensity of the ADCs.

Evaluation of the Stability of Indomethacin Oral Spray in Two Different Formulation Conditions

Indomethacin (IM) oral spray is a hospital preparation that is used to reduce pain from oral mucositis induced by radiotherapy and chemotherapy. IM oral spray consists of IM (0.25%) dissolved in KH2PO4-NaOH buffer (Formulation A) or Formulation A containing xylitol (Xyl) and glycerin (Gly) (Formulation B). To clarify the stability of IM oral spray in two different formulation conditions, we evaluated the residual rates of IM in these formulations to determine the optimal storage temperature and shelf-life. IM oral spray was stored at freezer temperature (-20°C), refrigerator temperature (4°C) and room temperature (25°C) for up to 16 weeks after preparation. The residual rate of IM was determined by using HPLC. The residual rates of IM in Formulation A and Formulation B after storage for 16 weeks at freezer temperature were ≥95%. When stored at refrigerator temperature, the residual rate of IM in Formulation A was 96.1% after 12 weeks, and the residual rates of IM in Formulation B were 95.8% after 2 weeks, 90.1% after 4 weeks and 72.7% after 12 weeks. These results suggested that Formulation A is stable for at least 12 weeks when stored at 4°C. However, degradation of IM seemed to be accelerated in the formulation containing Xyl and Gly, suggesting that the expiration date should be shortened to 2 weeks at 4°C. In addition, both formulations were stable for at least 16 weeks in a freezer, indicating that long-term preservation is possible.

Impact of Buffer, Protein Concentration and Sucrose Addition on the Aggregation and Particle Formation during Freezing and Thawing

PurposeThis study addresses the effect of freezing and thawing on a therapeutic monoclonal antibody (mAb) solution and the corresponding buffer formulation. Particle formation, crystallization behaviour, morphology changes and cryo-concentration effects were studied after varying the freezing and thawing rates, buffer formulation and protein concentration. The impact of undergoing multiple freeze/thaw (FT)-cycles at controlled and uncontrolled temperature rates on mAb solutions was investigated in terms of particle formation.MethodsPhysicochemical characteristics were analysed by Differential Scanning Calorimetry whereas morphology changes are visualized by cryomicroscopy measurements. Micro Flow Imaging, Archimedes and Dynamic Light Scattering were used to investigate particle formation.ResultsData retrieved in the present study emphasizes the damage caused by multiple FT-cyles and the need for sucrose as a cryoprotectant preventing cold-crystallization specifically at high protein concentrations. Low protein concentrations cause an increase of micron particle formation. Low freezing rates lead to a decreased particle number with increased particle diameter.ConclusionThe overall goal of this research is to gain a better understanding of the freezing and thawing behaviour of mAb solutions with the ultimate aim to optimize this process step by reducing the unwanted particle formation, which also includes protein aggregates.

In Vitro Human Placental Studies to Support Adenovirus-Mediated VEGF-DΔNΔC Maternal Gene Therapy for the Treatment of Severe Early-Onset Fetal Growth Restriction.

Severe fetal growth restriction (FGR) affects 1 in 500 pregnancies, is untreatable, and causes serious neonatal morbidity and death. Reduced uterine blood flow (UBF) is one cause. Transduction of uterine arteries in normal and FGR animal models using an adenovirus (Ad) encoding VEGF isoforms increases UBF and improves fetal growth in utero. Understanding potential adverse consequences of this therapy before first-in-woman clinical application is essential. The aims of this study were to determine whether Ad.VEGF-DΔNΔC (1) transfers across the human placental barrier and (2) affects human placental morphology, permeability and primary indicators of placental function, and trophoblast integrity. Villous explants from normal term human placentas were treated with Ad.VEGF-DΔNΔC (5 × 107-10 virus particles [vp]/mL), or virus formulation buffer (FB). Villous structural integrity (hematoxylin and eosin staining) and tissue accessibility (LacZ immunostaining) were determined. Markers of endocrine function (human chorionic gonadotropin [hCG] secretion) and cell death (lactate dehydrogenase [LDH] release) were assayed. Lobules from normal and FGR pregnancies underwent ex vivo dual perfusion with exposure to 5 × 1010 vp/mL Ad.VEGF-DΔNΔC or FB. Perfusion resistance, para-cellular permeability, hCG, alkaline phosphatase, and LDH release were measured. Ad.VEGF-DΔNΔC transfer across the placental barrier was assessed by quantitative polymerase chain reaction in DNA extracted from fetal-side venous perfusate, and by immunohistochemistry in fixed tissue. Villous explant structural integrity and hCG secretion was maintained at all Ad.VEGF-DΔNΔC doses. Ad.VEGF-DΔNΔC perfusion revealed no effect on placental permeability, fetoplacental vascular resistance, hCG secretion, or alkaline phosphatase release, but there was a minor elevation in maternal-side LDH release. Viral vector tissue access in both explant and perfused models was minimal, and the vector was rarely detected in the fetal venous perfusate and at low titer. Ad.VEGF-DΔNΔC did not markedly affect human placental integrity and function in vitro. There was limited tissue access and transfer of vector across the placental barrier. Except for a minor elevation in LDH release, these test data did not reveal any toxic effects of Ad.VEGF-DΔNΔC on the human placenta.

Optimization of a more efficient protocol for mechanical inoculation for watermelon bud necrosis orthotospovirus and its validation with different watermelon genotypes

Watermelon bud necrosis orthotospovirus (WBNV) is one of the emerging and most serious pathogens affecting watermelon cultivation in India. In the present study, the effect of different inoculation methods and buffer formulation on virus transmission was studied and validated in 17 watermelon genotypes. Among various inoculation methods used, maximum transmission efficiency 60–100% was obtained in 4–10 days post-inoculation (DPI) with pin-pricking and rubbing together, followed by rubbing (85–100%; 20–25 DPI) and pin-pricking (10–32%; 10–25 DPI) alone with the sodium buffer (PBS) having pH 7.0 supplemented with sodium sulfite (SS) and 2-mercaptoethanol (2-ME). Similarly, among the various abrasives used, maximum transmission efficiency 82–100% was obtained at 10–35 DPI with Celite and Carborundum together, followed by Celite (64–100%; 10–20 DPI) and Carborundum (72–100%; 20–40 DPI) alone. Among various additives used, maximum transmission efficiency 82–100% was obtained in 10 DPI with PBS supplemented with SS and 2-ME followed by PBS supplemented with SS alone (85–100%; 20–40 DPI) and PBS with no additive (76–85%; 20–35 DPI). The 15–20 days old watermelon plants were found suitable for the efficient mechanical transmission (100%) and to obtain maximum virus titre (Absorbance at 405 nm) i.e. 1.52–2.50 at 8–25 DPI. The 21–60% and 100% transmission was obtained at 4 and 10 DPI, respectively using the same buffer composition as mentioned above. For validation of optimized sap inoculation protocol for WBNV, 17 watermelon genotypes were inoculated under glasshouse conditions and the percent transmission ranged from 80 to 100%. Besides symptomatology, virus transmission was further confirmed by DAC-ELISA, RT-PCR and sequencing of the partial N gene. The O. D. at 405 nm ranged from 0.38 to 0.9 in naturally infected watermelon plants whereas in the glasshouse inoculated watermelon plants it was ranged from 0.30 to 0.73 at 15 DPI. This is the first effort on optimization of more efficient sap inoculation protocol for WBNV and it validated to 17 watermelon genotypes.

Characterization of the NISTmAb Reference Material using small-angle scattering and molecular simulation : Part I: Dilute protein solutions.

Both conformational and colloidal stability of therapeutic proteins must be closely monitored and thoroughly characterized to assess the long-term viability of drug products. We characterized the IgG1 NISTmAb reference material in its histidine formulation buffer and report our findings on the higher order structure and interactions of NISTmAb under a range of conditions. In this paper we present the analysis of experimental small-angle scattering data with atomistic molecular simulations to characterize the monodisperse dilute solution of NISTmAb. In part II we describe the characterization of the NISTmAb at high protein concentration (Castellanos et al. 2018). The NISTmAb was found to be a flexible protein with a radius of gyration of 49.0 ± 1.2 Å in histidine formulation buffer using a variety of neutron and X-ray scattering measurements. Scattering data were then modeled using molecular simulation. After building and validating a starting NISTmAb structure from the Fc and Fab crystallographic coordinates, molecular dynamics and torsion-angle Monte Carlo simulations were performed to explore the configuration space sampled in the NISTmAb and obtain ensembles of structures with atomistic detail that are consistent with the experimental data. Our results indicate that the small-angle scattering profiles of the NISTmAb can be modeled using ensembles of flexible structures that explore a wide configuration space. The NISTmAb is flexible in solution with no single preferred orientation of Fc and Fab domains, but with some regions of configuration space that are more consistent with measured scattering profiles. Analysis of inter-domain atomistic contacts indicated that all ensembles contained configurations where residues between domains are ≤ 4 Å, although few contacts were observed for variable and C H 3 regions. Graphical Abstract Heavy atom self contact maps of the NISTmAb indicate a highly-flexible structure.

Characterization of the NISTmAb Reference Material using small-angle scattering and molecular simulation : Part II: Concentrated protein solutions.

Protein-protein interactions in monoclonal antibody solutions are important for the stability of a therapeutic drug and directly influence viscosity in concentrated protein solutions. This study describes the use of small-angle scattering to estimate protein-protein interactions at high concentrations of the IgG1 NISTmAb reference material and validate colloidal models for interacting molecules. In particular, we studied the colloidal stability of the NISTmAb at high protein concentrations and analyzed protein-protein interactions upon adding sodium chloride and its effect on viscosity. Isotropic colloidal models for interacting molecules were combined with an ensemble of atomistic structures from molecular simulation to account for the flexibility of the NISTmAb in solution. In histidine formulation buffer, net repulsive electrostatic interactions are important for the colloidal stability of the NISTmAb at high concentrations. Addition of sodium chloride increased the viscosity of the NISTmAb and decreased the colloidal stability due to charge screening of the repulsive interactions. The interactions at high concentrations (up to ~ 250mg/mL) were consistent with those from light scattering at low concentrations (below ~ 20mg/mL). However, in the presence of sodium chloride, the screening of charges was less pronounced with increasing protein concentration and the interactions approached those of the repulsive hard-sphere models. Additionally, we studied the NISTmAb under frozen conditions using in situ neutron scattering to analyze the crowded state as proteins are excluded from the water-rich phase. In the frozen samples, where protein concentration can reach hundreds of mg/mL in the protein-rich phase, sodium chloride did not affect the molecular spacing and crowding of the NISTmAb. Graphical Abstract Net repulsive interactions in concentrated NISTmAb solutions assessed by small-angle neutronscattering.

Improved cytotoxicity of novel TRAIL variants produced as recombinant fusion proteins.

The TNF-Related Apoptosis Inducing Ligand (TRAIL) cytokine triggers apoptosis specifically in cancer cells. Susceptibility of a given cell to TRAIL depends on the activity of regulatory proteins, one of the most important of which is BID. The aim of this study was to increase the cytotoxic potential of TRAIL against cancer cells. TRAIL was fused to the BH3 domain of BID. Hence, TRAIL acted not only as an anticancer agent, but also as a specific carrier for the BID fragment. Two fusion protein variants were obtained by genetic engineering, harboring two different linker sequences. The short linker allowed both parts of the fusion protein to fold into their native structures. The long linker influenced the structure of the fused proteins but nonetheless resulted in their highest cytotoxic activity. Optimal buffer formulation was determined for all the analyzed TRAIL variants. Fusing the BH3 domain of BID to TRAIL improved the cytotoxic potential of TRAIL. Further, these findings may be useful for the optimization of other anticancer drugs based on TRAIL, since the appropriate formulation would secure their native structures during prolonged storage.

A Small-Scale Process for Predicting Donnan and Volume Exclusion Effects During Ultrafiltration/Diafiltration Process Development

Achieving the desired final protein formulation using ultrafiltration/diafiltration (UF/DF) operations is an essential component of many protein purification processes. It is well documented that differences in the excipient and buffer concentrations exist between the DF and retentate solutions when they have achieved equilibrium. Several publications have proposed ways to calculate these differences. However, the accuracy of these methods has been limited by the use of an estimated protein charge value. In this article, a small-scale system is described, which can accurately determine the protein charge by making buffer and excipient concentration measurements and applying the determined values to the Donnan and volume exclusion equations. This information can be utilized to generate a standard curve, which in turn can be applied to at-scale UF/DF operations. For 2 different antibodies, the standard curve generated by the small-scale system yielded buffer concentrations and pH values that agreed well with those generated after UF/DF operations, whereas using the theoretical protein charge caused a departure from the measured results. This model also provides good estimates as to how the final formulation pH and buffer concentration vary as a function of the pH and buffer concentration in the DF buffer. This information is of important utility for the accurate formulation of high-concentration protein solutions (>100 mg/mL) where the coconcentration of buffers and the volume exclusion of certain excipients are amplified. The low material requirements of the small-scale system are a major benefit for early phase formulation and process development when sufficient time and material may not be available, in particular to ensure successful UF/DF operations for the development of high protein concentration formulations.