Nucleation and growth of microbial lipase crystals from clarified concentrated fermentation broths

Large-scale crystallization as an intermediate processing step in insulin downstream process: explored advantages and identified tool for process intensification

The rising global prevalence of diabetes and increasing demand for insulin, calls for an increase in accessibility and affordability of insulin drugs through efficient and cost-effective manufacturing processes. Often downstream operations become manufacturing bottlenecks while processing a high volume of product. Thus, process integration and intensification play an important role in reducing process steps and time, volume reduction, and lower equipment footprints, which brings additional process efficiencies and lowers the production cost. Manufacturers thrive to optimize existing unit operation to maximize its benefit replacing with simple but different efficient technologies. In this manuscript, the typical property of insulin in forming the pH-dependent zinc-insulin complex is explored. The benefit of zinc chloride precipitation/crystallization has been shown to increase the in-process product purity by reducing the product and process-related impurities. Incorporation of such unit operation in the insulin process has also a clear potential for replacing the high cost involved capture chromatography step. Same time, the reduction in volume of operation, buffer consumption, equipment footprint, and capabilities of product long time storage brings manufacturing flexibility and efficiencies. The data and capabilities of simple operation captured here would be significantly helpful for insulins and other biosimilar manufacturer to make progresses on cost-effective productions.

A workflow for the development of template-assisted membrane crystallization downstream processing for monoclonal antibody purification

Monoclonal antibodies (mAbs) are commonly used biologic drugs for the treatment of diseases such as rheumatoid arthritis, multiple sclerosis, COVID-19 and various cancers. They are produced in Chinese hamster ovary cell lines and are purified via a number of complex and expensive chromatography-based steps, operated in batch mode, that rely heavily on protein A resin. The major drawback of conventional procedures is the high cost of the adsorption media and the extensive use of chemicals for the regeneration of the chromatographic columns, with an environmental cost. We have shown that conventional protein A chromatography can be replaced with a single crystallization step and gram-scale production can be achieved in continuous flow using the template-assisted membrane crystallization process. The templates are embedded in a membrane (e.g., porous polyvinylidene fluoride with a layer of polymerized polyvinyl alcohol) and serve as nucleants for crystallization. mAbs are flexible proteins that are difficult to crystallize, so it can be challenging to determine the optimal conditions for crystallization. The objective of this protocol is to establish a systematic and flexible approach for the design of a robust, economic and sustainable mAb purification platform to replace at least the protein A affinity stage in traditional chromatography-based purification platforms. The procedure provides details on how to establish the optimal parameters for separation (crystallization conditions, choice of templates, choice of membrane) and advice on analytical and characterization methods.

Template-Assisted Crystallization Behavior in Stirred Solutions of the Monoclonal Antibody Anti-CD20: Probability Distributions of Induction Times

We present a method to determine the template crystallization behavior of proteins. This method is a statistical approach that accounts for the stochastic nature of nucleation. It makes use of batch-wise experiments under stirring conditions in volumes smaller than 0.3 mL to save material while mimicking larger-scale processes. To validate our method, it was applied to the crystallization of a monoclonal antibody of pharmaceutical interest, Anti-CD20. First, we determined the Anti-CD20 phase diagram in a PEG-400/Na₂SO₄/water system using the batch method, as, to date, no such data on Anti-CD20 solubility have been reported. Then, the probability distribution of induction times was determined experimentally, in the presence of various mesoporous silica template particles, and crystallization of Anti-CD20 in the absence of templates was compared to template-assisted crystallization. The probability distribution of induction times is shown to be a suitable method to determine the effect of template particles on protein crystallization. The induction time distribution allows for the determination of two key parameters of nucleation, the nucleation rate and the growth time. This study shows that the use of silica particles leads to faster crystallization and a higher nucleation rate. The template particle characteristics are shown to be critical parameters to efficiently promote protein crystallization.

Protein crystallisation facilitated by silica particles to compensate for the adverse impact from protein impurities

Nanonucleants for protein crystallisation in the presence of impurities.

Protein crystal occurrence domains in selective protein crystallisation for bio-separation

Bio-separation is a key bottleneck in the manufacture of biopharmaceuticals.

Continuous Manufacturing of Recombinant Therapeutic Proteins: Upstream and Downstream Technologies

Continuous biomanufacturing of recombinant therapeutic proteins offers several potential advantages over conventional batch processing, including reduced cost of goods, more flexible and responsive manufacturing facilities, and improved and consistent product quality. Although continuous approaches to various upstream and downstream unit operations have been considered and studied for decades, in recent years interest and application have accelerated. Researchers have achieved increasingly higher levels of process intensification, and have also begun to integrate different continuous unit operations into larger, holistically continuous processes. This review first discusses approaches for continuous cell culture, with a focus on perfusion-enabling cell separation technologies including gravitational, centrifugal, and acoustic settling, as well as filtration-based techniques. We follow with a review of various continuous downstream unit operations, covering categories such as clarification, chromatography, formulation, and viral inactivation and filtration. The review ends by summarizing case studies of integrated and continuous processing as reported in the literature.

From osmotic second virial coefficient (B22 ) to phase behavior of a monoclonal antibody

Antibodies are complex macromolecules and their phase behavior as well as interactions within different solvents and precipitants are still not understood. To shed some light into the processes on a molecular dimension, the occurring self-interactions between antibody molecules were analyzed by means of the osmotic second virial coefficient (B22 ). The determined B22 follows qualitatively the phenomenological Hofmeister series describing the aggregation probability of antibodies for the various solvent compositions. However, a direct correlation between crystallization probability and B22 in form of a crystallization slot does not seem to be feasible for antibodies since the phase behavior is strongly dependent on their anisotropy. Kinetic parameters have to be taken into account due to the molecular size and complexity of the molecules. This is confirmed by a comparison of experimental data with a theoretical phase diagram. On the other hand the solubility is thermodynamically driven and therefore the B22 could be used to establish a universal solubility line for the monoclonal antibody mAb04c and different solvent compositions by using thermodynamic models.

Large-scale crystallization of proteins for purification and formulation

Since about 170 years, salts were used to create supersaturated solutions and crystallize proteins. The dehydrating effect of salts as well as their kosmotropic or chaotropic character was revealed. Even the suitability of organic solvents for crystallization was already recognized. Interestingly, what was performed during the early times is still practiced today. A lot of effort was put into understanding the underlying physico-chemical interaction mechanisms leading to protein crystallization. However, it was understood that already the solvation of proteins is a highly complex process not to mention the intricate interrelation of electrostatic and hydrophobic interactions taking place. Although many basic questions are still unanswered, preparative protein crystallization was attempted as illustrated in the presented case studies. Due to the highly variable nature of crystallization, individual design of the crystallization process is needed in every single case. It was shown that preparative crystallization from impure protein solutions as a capture step is possible after applying adequate pre-treatment procedures like precipitation or extraction. Protein crystallization can replace one or more chromatography steps. It was further shown that crystallization can serve as an attractive alternative means for formulation of therapeutic proteins. Crystalline proteins can offer enhanced purity and enable highly concentrated doses of the active ingredient. Easy scalability of the proposed protein crystallization processes was shown using the maximum local energy dissipation as a suitable scale-up criterion. Molecular modeling and target-oriented protein engineering may allow protein crystallization to become part of a platform purification process in the near future.

Preparative crystallization of a single chain antibody using an aqueous two-phase system

A simultaneous crystallization and aqueous two-phase extraction of a single chain antibody was developed, demonstrating process integration. The process conditions were designed to form an aqueous two-phase system, and to favor crystallization, using sodium sulfate and PEG-2000. At sufficiently high concentrations of PEG, a second phase was generated in which the protein crystallization occurred simultaneously. The single chain antibody crystals were partitioned to the top, polyethylene glycol-rich phase. The crystal nucleation took place in the sodium sulfate-rich phase and at the phase boundary, whereas crystal growth was progressing mainly in the polyethylene glycol-rich phase. The crystals in the polyethylene glycol-rich phase grew to a size of >50 µm. Additionally, polyethylene glycol acted as an anti-solvent, thus, it influenced the crystallization yield. A phase diagram with an undersaturation zone, crystallization area, and amorphous precipitation zone was established. Only small differences in polyethylene glycol concentration caused significant shifts of the crystallization yield. An increase of the polyethylene glycol content from 2% (w/v) to 4% (w/v) increased the yield from approximately 63-87%, respectively. Our results show that crystallization in aqueous two-phase systems is an opportunity to foster process integration.

Protein crystallization in stirred systems--scale-up via the maximum local energy dissipation

Macromolecular bioproducts like therapeutic proteins have usually been crystallized with µL-scale vapor diffusion experiments for structure determination by X-ray diffraction. Little systematic know-how exists for technical-scale protein crystallization in stirred vessels. In this study, the Fab-fragment of the therapeutic antibody Canakinumab was successfully crystallized in a stirred-tank reactor on a 6 mL-scale. A four times faster onset of crystallization of the Fab-fragment was observed compared to the non-agitated 10 µL-scale. Further studies on a liter-scale with lysozyme confirmed this effect. A 10 times faster onset of crystallization was observed in this case at an optimum stirrer speed. Commonly suggested scale-up criteria (i.e., minimum stirrer speed to keep the protein crystals in suspension or constant impeller tip speed) were shown not to be successful. Therefore, the criterion of constant maximum local energy dissipation was applied for scale-up of the stirred crystallization process for the first time. The maximum local energy dissipation was estimated by measuring the drop size distribution of an oil/surfactant/water emulsion in stirred-tank reactors on a 6 mL-, 100 mL-, and 1 L-scale. A comparable crystallization behavior was achieved in all stirred-tank reactors when the maximum local energy dissipation was kept constant for scale-up. A maximum local energy dissipation of 2.2 W kg(-1) was identified to be the optimum for lysozyme crystallization at all scales under study.

Towards protein crystallization as a process step in downstream processing of therapeutic antibodies: screening and optimization at microbatch scale

Crystallization conditions of an intact monoclonal IgG4 (immunoglobulin G, subclass 4) antibody were established in vapor diffusion mode by sparse matrix screening and subsequent optimization. The procedure was transferred to microbatch conditions and a phase diagram was built showing surprisingly low solubility of the antibody at equilibrium. With up-scaling to process scale in mind, purification efficiency of the crystallization step was investigated. Added model protein contaminants were excluded from the crystals to more than 95%. No measurable loss of Fc-binding activity was observed in the crystallized and redissolved antibody. Conditions could be adapted to crystallize the antibody directly from concentrated and diafiltrated cell culture supernatant, showing purification efficiency similar to that of Protein A chromatography. We conclude that crystallization has the potential to be included in downstream processing as a low-cost purification or formulation step.

Urate oxidase purification by salting-in crystallization: towards an alternative to chromatography

BACKGROUND

Rasburicase (Fasturtec® or Elitek®, Sanofi-Aventis), the recombinant form of urate oxidase from Aspergillus flavus, is a therapeutic enzyme used to prevent or decrease the high levels of uric acid in blood that can occur as a result of chemotherapy. It is produced by Sanofi-Aventis and currently purified via several standard steps of chromatography. This work explores the feasibility of replacing one or more chromatography steps in the downstream process by a crystallization step. It compares the efficacy of two crystallization techniques that have proven successful on pure urate oxidase, testing them on impure urate oxidase solutions.

METHODOLOGY/PRINCIPAL FINDINGS

Here we investigate the possibility of purifying urate oxidase directly by crystallization from the fermentation broth. Based on attractive interaction potentials which are known to drive urate oxidase crystallization, two crystallization routes are compared: a) by increased polymer concentration, which induces a depletion attraction and b) by decreased salt concentration, which induces attractive interactions via a salting-in effect. We observe that adding polymer, a very efficient way to crystallize pure urate oxidase through the depletion effect, is not an efficient way to grow crystals from impure solution. On the other hand, we show that dialysis, which decreases salt concentration through its strong salting-in effect, makes purification of urate oxidase from the fermentation broth possible.

CONCLUSIONS

The aim of this study is to compare purification efficacy of two crystallization methods. Our findings show that crystallization of urate oxidase from the fermentation broth provides purity comparable to what can be achieved with one chromatography step. This suggests that, in the case of urate oxidase, crystallization could be implemented not only for polishing or concentration during the last steps of purification, but also as an initial capture step, with minimal changes to the current process.

Understanding structural features of microbial lipases--an overview

The structural elucidations of microbial lipases have been of prime interest since the 1980s. Knowledge of structural features plays an important role in designing and engineering lipases for specific purposes. Significant structural data have been presented for few microbial lipases, while, there is still a structure-deficit, that is, most lipase structures are yet to be resolved. A search for 'lipase structure' in the RCSB Protein Data Bank (http://www.rcsb.org/pdb/) returns only 93 hits (as of September 2007) and, the NCBI database (http://www.ncbi.nlm.nih.gov) reports 89 lipase structures as compared to 14719 core nucleotide records. It is therefore worthwhile to consider investigations on the structural analysis of microbial lipases. This review is intended to provide a collection of resources on the instrumental, chemical and bioinformatics approaches for structure analyses. X-ray crystallography is a versatile tool for the structural biochemists and is been exploited till today. The chemical methods of recent interests include molecular modeling and combinatorial designs. Bioinformatics has surged striking interests in protein structural analysis with the advent of innumerable tools. Furthermore, a literature platform of the structural elucidations so far investigated has been presented with detailed descriptions as applicable to microbial lipases. A case study of Candida rugosa lipase (CRL) has also been discussed which highlights important structural features also common to most lipases. A general profile of lipase has been vividly described with an overview of lipase research reviewed in the past.

Susceptibility of a Polycaprolactone-Based Root Canal Filling Material to Degradation. II. Gravimetric Evaluation of Enzymatic Hydrolysis

Polycaprolactone is susceptible to enzymatic biodegradation via ester bond cleavage. This study examined the susceptibility of Resilon, a polycaprolactone-based root filling material to enzymatic hydrolysis. Resilon, gutta-percha, and polycaprolactone disks, prepared by compression molding, were incubated in phosphate-buffered saline, lipase PS or cholesterol esterase at 37 degrees C for 96 h. They were retrieved at different time intervals for gravimetric analysis and scanning electron microscopy. The materials exhibited slight weight gains when incubated in phosphate-buffered saline that can be attributed to water sorption. Gutta-percha showed similar weight gains in the two enzymes. Conversely, Resilon and polycaprolactone exhibited extensive surface thinning and weight losses after incubation in lipase PS and cholesterol esterase. Glass filler particles in Resilon were exposed following surface dissolution of the polymer matrix, creating rough surface topography. Biodegradation of Resilon by bacterial and salivary enzymes warrants further investigation of their activities using cultures of endodontically relevant microbes and human saliva extracts.

High-level expression and bulk crystallization of recombinant L-methionine gamma-lyase, an anticancer agent

L-Methionine gamma-lyase is a pyridoxal 5'-phosphate-dependent enzyme which has tumor selective anticancer activity. An efficient production process for the recombinant enzyme was constructed by using the overexpression plasmid in Escherichia coli, large-scale cultivation, and practical crystallization on an industrial scale. The plasmid was optimized with a promoter and the region of the ribosome-binding site. Plasmid pMGLTrc03, which has a trc promoter and a spacing of 12 nucleotides between the Shine-Dalgarno sequence and the ATG translation initiation codon, was selected as the most suitable plasmid. The transformants produced the enzyme, which intracellularly accumulated at 2.1 mg/ml as an active form and accounted for 43% of the total proteins in the soluble fraction by simple batch fermentation using a 500-l fermentor. The crystals were directly obtained from crude enzyme with 87% yield by a crystallization in the presence of 9.0% polyethylene glycol 6000, 3.6% ammonium sulfate, and 0.18 M sodium chloride using a 100-l crystallizer. After recrystallization, the enzyme was purified by anion-exchange column chromatography to remove endotoxins and by gel filtration for polishing. We prepared 600 g of purified enzyme with a low endotoxin content of sufficient quality for therapeutical use, with a 41% overall yield in the purification process.

Protein crystals for the delivery of biopharmaceuticals

The year 2002 marked the 20th anniversary of the first successful product of modern biotechnology, the regulatory approval of recombinant insulin for biopharmaceutical applications. Insulin is also the first crystalline protein to be approved for therapeutic use. Over the past two decades, almost 150 biopharmaceuticals have gained marketing authorisation; however, insulin remains the only crystalline protein on the market. Significant research and development efforts have focused on the engineering of protein molecules, efficacy testing, model development, and protein production and characterisation. These advances have dramatically boosted the therapeutic applications of proteins, which now include treatments against acute conditions, such as cancer, cardiovascular disease and viral disease, and chronic conditions, such as diabetes, growth hormone deficiency, haemophilia, arthritis, psoriasis and Crohn's disease. Despite these successes, many challenges normally associated with biopharmaceuticals, such as poor stability and limited delivery options, remain. Protein crystals have shown significant benefits in the delivery of biopharmaceuticals to achieve high concentration, low viscosity formulation and controlled release protein delivery. This review will discuss challenges related to the broader utilisation of protein crystals in biopharmaceutical applications, as well as recent advances and valuable new directions that protein crystallisation-based technologies present.

Evaluation of a model for seeded isothermal batch protein crystallization

Bulk protein crystallization, unlike small molecule crystallization, has found very limited use in biopharmaceutical manufacture. Most work in this area targets obtaining single large crystals for molecular structure determination by crystallography. Design and optimization of bulk crystallization for protein recovery and purification is much less common, and requires a mathematical model for analysis of laboratory data suitable for scale-up purposes. Traditionally, the crystal size distribution and method of moments is used to characterize the crystallization process. A simpler method is presented in this paper that utilizes the desupersaturation curve. The method uses an approach that does not require expensive instrumentation or characterization of the seed crystal size distribution. The method is extended to allow determination of both the mass deposition rate constant and the growth rate order from a single desuperaturation curve. Experimental data for the bulk crystallization of ovalbumin are used to validate the method. The rate constants and rate order obtained using the new method compare well with literature values. Scale-up is illustrated by prediction of the impact of changes in seed mass on protein crystallization. This new method offers a straightforward and low-cost alternative to traditional methods for the analysis and scale-up of protein crystallization data.

Diamonds in the rough: protein crystals from a formulation perspective

The focus of the present review is to address the use of protein crystals in formulation design. Although this idea has been present for some time, i.e., insulin crystals were first reported back in 1920s, macromolecular crystallization has not received as much attention as the other methods for stabilizing protein drug candidates. The prospective potential of crystalline protein formulations in light of new advances in the field of macromolecular crystallization was reviewed, and the basic concepts and the tools now available for developing protein crystals into drug formulations are introduced. In addition, formulation challenges and regulatory demands, along with examples of current applications of protein crystals, are presented.

A systematic approach to the large-scale production of protein crystals

Crystallization has recently emerged as a suitable process for the manufacture of biocatalysts in the form of cross-linked enzyme crystals (CLECs) or for the recovery of proteins from fermentation broths. In both instances it is essential to define conditions which control crystal size and habit, and that yield a reliable recovery of the active protein. Experiments to define the crystallization conditions usually depend on a factorial design (either incomplete or sparse matrix) or reverse screening techniques. In this work, we describe a simple procedure that allows the effect of three factors, for example protein concentration, precipitant concentration and pH, to be varied simultaneously and smoothly over a wide range. The results are mapped onto a simple triangular diagram where a 'window of crystallization' is immediately apparent, and that conveniently describes variations either in the crystal features, such as their yield, size, and habit, or in the recovery of biological activity. The approach is illustrated with two enzymes, yeast alcohol dehydrogenase (ADH I) and Candida rugosa lipase. For ADH the formation of two crystal habits (rod and hexagonal) could be controlled as a function of pH (6.5-10) and temperature (4-25 degrees C). At pH 7, in 10 to 16% w/v polyethylene glycol (PEG) 4000, only rod-shaped crystals formed whereas at pH 8, in 10 to 14% w/v PEG, only hexagonal crystals existed. For both enzymes, catalyst recovery was greatest at high crystallization agent concentrations and low protein concentration. For ADH, the greatest activity recovery was 87% whereas for the lipase crystals, by using 45% v/v 2-methyl-2,4-pentanediol (MPD) as the crystallization agent, a crystal recovery of 250 crystals per µl was obtained. For the lipase system, the use of crystal seeding was also shown to increase the crystal recovery by up to a factor of four. From the crystallization windows, the original conditions based on literature precedent (35% v/v MPD, 1 mM CaCl(2), 1.8 mg protein/ml) were altered (47.5% v/v MPD, 2 mM CaCl(2), 3 mg protein/ml). This led to an improved recovery of the lipase under conditions that scale reliably from 0.5 ml to 500 ml with no change in size, shape or recovery of the crystals themselves. Finally, these crystals were crosslinked with 5% v/v glutaraldehyde and mass and activity balances were calculated for the entire process of CLEC production. Up to 35% of the lipase activity present in the crude solid was finally recovered in the lipase CLECs after propan-2-ol fractionation, crystallization, and crosslinking.