Dynamic evaluation of polypropylene capillary-channeled fibers as a stationary phase in high-performance liquid chromatography

Quantitative Recoveries of Exosomes and Monoclonal Antibodies from Chinese Hamster Ovary Cell Cultures by Use of a Single, Integrated Two-Dimensional Liquid Chromatography Method

Cultured cell lines are very commonly used for the mass production of therapeutic proteins, such as monoclonal antibodies (mAbs). In particular, Chinese hamster ovary (CHO) cell lines are widely employed due to their high tolerance to variations in experimental conditions and their ability to grow in suspension or serum free media. CHO cell lines are known for their ability to produce high titers of biotherapeutic products such as immunoglobulin G (IgG). An emergent alternative means of treating diseases, such as cancer, is the use of gene therapies, wherein genetic cargo is "packaged" in nanosized vesicular structures, referred to as "vectors". One particularly attractive vector option is extracellular vesicles (EVs), of which exosomes are of greatest interest. While exosomes can be harvested from virtually any human body fluid, bovine milk, or even plants, their production in cell cultures is an attractive commercial approach. In fact, the same CHO cell types employed for mAb production also produce exosomes as a natural byproduct. Here, we describe a single integrated 2D liquid chromatography (2DLC) method for the quantitative recovery of both exosomes and antibodies from a singular sample aliquot. At the heart of the method is the use of polyester capillary-channeled polymer (C-CP) fibers as the first dimension column, wherein exosomes/EVs are captured from the supernatant sample and subsequently determined by multiangle light scattering (MALS), while the mAbs are captured, eluted, and quantified using a protein A-modified C-CP fiber column in the second dimension, all in a 10 min workflow. These efforts demonstrate the versatility of the C-CP fiber phases with the capacity to harvest both forms of therapeutics from a single bioreactor, suggesting an appreciable potential impact in the field of biotherapeutics production.

Alleviation of the necessity for supernatant prefiltering in the protein a recovery of Monoclonal antibodies from Chinese hamster ovary cell cultures

Protein A (ProA) chromatography is a mainstay in the analytical and preparative scale isolation/purification of monoclonal antibodies (mAbs). One area of interest is continuous processing or continuous chromatography, where ProA chromatography is used in the large-scale purification of mAbs. However, filtration is required prior to all ProA isolations to remove large particulates in cell culture supernatant, consisting of a mixture of cell debris, host cell contaminants, media components, etc. Currently, in-line filters are used to remove particles in the supernatant, requiring replacement over time due to fouling; regardless of the scale. Here we demonstrate the ProA isolation of unfiltered Chinese hamster ovary (CHO) cell media using capillary-channel polymer (C-CP) fiber stationary phases modified with S. aureus Protein A (rSPA). The base polymer of the analytical scale C-CP columns costs ∼$5 per 30 cm column, and when modified with ProA, the base cost is ∼$25 per 30 cm column, a cost-effective option in comparison to analytical-scale commercial columns. To directly sample unfiltered media, a 5 cm gap was created at the head of the C-CP column, where the large particulates are trapped, while molecular solutes flow through the capillary channels without sacrifice in analytical performance, mAb loading capacity, or backpressure increases. The binding capacity of the gap ProA C-CP column was ∼ 2 mg mL-1 of IgG per bed volume. The same analytical column could be operated after processing a total of ∼ 56 column bed volumes of supernatant (>25 analytical cycles) without the need for caustic clean-in-place processing.

Loading characteristics of streptavidin on polypropylene capillary channeled polymer fibers and capture performance towards biotinylated proteins

The development of higher-throughput, potentially lower-cost means to isolate proteins, for a variety of end uses, is of continuing emphasis. Polypropylene (PP) capillary-channeled polymer (C-CP) fiber columns are modified with the biotin-binding protein streptavidin (SAV) to capture biotinylated proteins. The loading characteristics of SAV on fiber supports were determined using breakthrough curves and frontal analysis. Based on adsorption data, a 3-min on-column loading at a flow rate of 0.5 mL min-1 (295.2 cm h-1) with a SAV feed concentration of 0.5 mg mL-1 produces a SAV loading capacity of 1.4 mg g-1 fiber. SAV has an incredibly high affinity for the small-molecule biotin (10-14 M), such that this binding relationship can be exploited by labeling a target protein with biotin via an Avi-tag. To evaluate the capture of the biotinylated proteins on the modified PP surface, the biotinylated versions of bovine serum albumin (b-BSA) and green fluorescent protein (b-GFP) were utilized as probe species. The loading buffer composition and flow rate were optimized towards protein capture. The non-ionic detergent Tween-20 was added to the deposition solutions to minimize non-specific binding. Values of 0.25-0.50% (v/v) Tween-20 in PBS exhibited better capture efficiency, while minimizing the non-specific binding for b-BSA and b-GFP, respectively. The C-CP fiber platform has the potential to provide a fast and low-cost method to capture targeted proteins for applications including protein purification or pull-down assays.

Two-dimensional separation of water-soluble polymers using size exclusion and reversed phase chromatography employing capillary-channeled polymer fiber columns

Polymeric materials are readily available, durable materials that have piqued the interest of many diverse fields, ranging from biomedical engineering to construction. The physiochemical properties of a polymer dictate the behavior and function, where large polydispersity among polymer properties can lead to problems; however, current polymer analysis methods often only report results for one particular property. Two-dimensional liquid chromatography (2DLC) applications have become increasingly popular due to the ability to implement two chromatographic modalities in one platform, meaning the ability to simultaneously address multiple physiochemical aspects of a polymer sample, such as functional group content and molar mass. The work presented employs size exclusion chromatography (SEC) and reversed-phase (RP) chromatography, through two coupling strategies: SEC x RP and RP x RP separations of the water-soluble polymers poly(methacrylic acid) (PMA) and polystyrene sulfonic acid (PSSA). Capillary-channeled polymer (C-CP) fiber (polyester and polypropylene) stationary phases were used for the RP separations. Particularly attractive is the fact that they are easily implemented as the second dimension in 2DLC workflows due to their low backpressure (<1000 psi at ∼70 mm sec^-1) and fast separation times. In-line multi-angle light scattering (MALS) was also implemented for molecular weight determinations of the polymer samples, with the molecular weight of PMA ranging from 5 × 10⁴ to 2 × 10⁵ g mol^-1, while PSSA ranges from 10⁵ to 10⁸ g mol^-1. While the orthogonal pairing of SEC x RP addresses polymer sizing and chemistry, this approach is limited by long separation times (80 min), the need for high solute concentrations (PMA = 1.79 mg mL^-1 and PSSA = 0.175 mg mL^-1 to yield comparable absorbance responses) due to on-column dilution and subsequently limited resolution in the RP separation space. With RP x RP couplings, separation times were significantly reduced (40 min), with lower sample concentrations (0.595 mg mL^-1 of PMA and 0.05 mg mL^-1 of PSSA) required. The combined RP strategy provided better overall distinction in the chemical distribution of the polymers, yielding 7 distict species versus 3 for the SEC x RP coupling.

Determination of the Loading Capacity and Recovery of Extracellular Vesicles Derived from Human Embryonic Kidney Cells and Urine Matrices on Capillary-Channeled Polymer (C-CP) Fiber Columns

Extracellular vesicles (EVs) are 50–1000 nm membranous vesicles secreted from all cells that play important roles in many biological processes. Exosomes, a smaller-sized subset of EVs, have become of increasing interest in fundamental biochemistry and clinical fields due to their rich biological cargos and their roles in processes such as cell-signaling, maintaining homeostasis, and regulating cellular functions. To be implemented effectively in fundamental biochemistry and clinical diagnostics fields of study, and for their proposed use as vectors in gene therapies, there is a need for new methods for the isolation of large concentrations of high-purity exosomes from complex matrices in a timely manner. To address current limitations regarding recovery and purity, described here is a frontal throughput and recovery analysis of exosomes derived from human embryonic kidney (HEK) cell cultures and human urine specimens using capillary-channeled polymer (C-CP) fiber stationary phases via high performance liquid chromatography (HPLC). Using the C-CP fiber HPLC method for EV isolations, the challenge of recovering purified EVs from small sample volumes imparted by the traditional techniques was overcome while introducing significant benefits in processing, affordability (~5 $ per column), loading (~1012 particles), and recovery (1011–1012 particles) from whole specimens without further processing requirements.

Comparison of the separation of proteins of wide-ranging molecular weight via trilobal polypropylene capillary-channeled polymer fiber, commercial superficiously porous, and commercial size exclusion columns

Reversed phase and size-exclusion chromatography methods are commonly used for protein separations, though based on distinctly different principles. Reversed phase methods yield hydrophobicity-based (loosely-termed) separation of proteins on porous supports, but tend to be limited to proteins with modest molecular weights based on mass transfer limitations. Alternatively, size-exclusion provides complementary benefits in the separation of higher-mass proteins based on entropic, not enthalpic, processes, but tend to yield limited peak capacities. In this study, microbore columns packed with a novel trilobal polypropylene capillary-channeled polymer fiber were used in a reversed phase modality for the separation of polypeptides and proteins of molecular weights ranging from 1.4 to 660 kDa. Chromatographic parameters including gradient times, flow rates and trifluoroacetic acid concentrations in the mobile phase were optimized to maximize resolution and throughput. Following optimization, the performance of the trilobal fiber column was compared to two commercial-sourced columns, a superficially porous C4-derivatized silica and size exclusion, both of which are sold specifically for protein separations and operated according to the manufacturer-specified conditions. In comparison to the commercial columns, the fiber-based column yielded better separation performance across the entirety of the suite, at much lower cost and shorter separation times. This article is protected by copyright. All rights reserved.

Rapid isolation of lentivirus particles from cell culture media via a hydrophobic interaction chromatography method on a polyester, capillary-channeled polymer fiber stationary phase

Lentiviruses are increasingly used as gene delivery vehicles for vaccines and immunotherapies. However, the purification of clinical-grade lentivirus vectors for therapeutic use is still troublesome and limits preclinical and clinical experiments. Current purification methods such as ultracentrifugation and ultrafiltration are time consuming and do not remove all of the impurities such as cellular debris, membrane fragments, and denatured proteins from the lentiviruses. The same challenges exist in terms of their analytical characterization. Presented here is the novel demonstration of the chromatographic isolation of virus particles from culture media based on the hydrophobicity characteristics of the vesicles. A method was developed to isolate lentivirus from media using a hydrophobic interaction chromatography (HIC) method performed on a polyester, capillary-channeled polymer (PET C-CP) stationary phase and a standard liquid chromatography apparatus. The method is an extension of the approach developed in this laboratory for the isolation of extracellular vesicles (EVs). Quantitative polymerase chain reaction (qPCR) was used to verify and quantify lentiviruses in elution fractions. Load and elution mobile phase compositions were optimized to affect high efficiency and throughput. The process has been visualized via scanning electron microscopy (SEM) of the fiber surfaces following media injection, the elution of proteinaceous material, and the elution of lentiviruses. This effort has yielded a rapid (<10 min), low-cost (< $15 per column, providing multiple separations), and efficient method for the isolation/purification of lentivirus particles from cell culture media at the analytical scale.

Solid-phase extraction of exosomes from diverse matrices via a polyester capillary-channeled polymer (C-CP) fiber stationary phase in a spin-down tip format

Exosomes, a subset of the extracellular vesicle (EV) group of organelles, hold great potential for biomarker detection, therapeutics, disease diagnosis, and personalized medicine applications. The promise and potential of these applications are hindered by the lack of an efficient means of isolation, characterization, and quantitation. Current methods for exosome and EV isolation (including ultracentrifugation, microfiltration, and affinity-based techniques) result in impure recoveries with regard to remnant matrix species (e.g., proteins, genetic material) and are performed on clinically irrelevant time and volume scales. To address these issues, a polyethylene terephthalate (PET) capillary-channeled polymer (C-CP) fiber stationary phase is employed for the solid-phase extraction (SPE) of EVs from various matrices using a micropipette tip-based format. The hydrophobic interaction chromatography (HIC) processing and a spin-down workflow are carried out using a table-top centrifuge. Capture and subsequent elution of intact, biologically active exosomes are verified via electron microscopy and bioassays. The performance of this method was evaluated by capture and elution of exosome standards from buffer solution and three biologically relevant matrices: mock urine, reconstituted non-fat milk, and exosome-depleted fetal bovine serum (FBS). Recoveries were evaluated using UV-Vis absorbance spectrophotometry and ELISA assay. The dynamic binding capacity (50%) for the 1-cm-long (~ 5 μL bed volume) tips was determined using a commercial exosome product, yielding a value of ~ 7 × 10¹¹ particles. The novel C-CP fiber spin-down tip approach holds promise for the isolation of exosomes and other EVs from various matrices with high throughput, low cost, and high efficiency. Graphical abstract.

Isolation and quantitation of exosomes isolated from human plasma via hydrophobic interaction chromatography using a polyester, capillary-channeled polymer fiber phase

Exosomes are one class of extracellular vesicles (30-150 nm diameter) that are secreted by cells. These small vesicles hold a great deal of promise in disease diagnostics, as they display the same protein biomarkers as their originating cell. On a cellular level, exosomes are attributed to playing a key role in intercellular communication, and may eventually be exploited for targeted drug delivery. In order for exosomes to become useful in disease diagnostics, and as burgeoning drug delivery platforms, they must be isolated efficiently and effectively without compromising their structure. Plasma from peripheral blood is an excellent source of exosomes, as it is easily collected and the process does not normally cause undue discomfort to the patient. Unfortunately, blood plasma content is complex, containing abundant amounts of soluble proteins and aggregates, making exosomes extremely difficult to isolate in high purity from plasma. Most current exosome isolation methods have practical challenges including being too time-consuming and labor intensive, destructive to the exosomes, or too costly for use in clinical settings. To this end, this study examines the use of poly(ethylene terephthalate) (PET) capillary-channeled polymer (C-CP) fibers in a hydrophobic interaction chromatography (HIC) protocol to isolate exosomes from a human plasma sample. Initial results demonstrate the ability to isolate exosomes with comparable yields and size distributions and on a much faster time scale when compared to traditional isolation methods, while also alleviating concomitant proteins and other impurities. As a demonstration of the potential quantitative utility of the approach, a linear response (particles injected on-column vs peak area) using a commercial exosome standard was established using a standard UV absorbance detector. Based on the calibration function, the concentration of the original human plasma sample was determined and subsequently confirmed by NTA measurement. The potential for scalable separations covering sub-milliliter spin-down solid phase extraction tips to the preparative scale is anticipated.

Dynamic evaluation of a trilobal capillary-channeled polymer fiber shape for reversed phase protein separations and comparison to the eight-channeled form

A new, trilobal-shaped capillary-channeled polymer fiber is under development to address the issues of poor A-term performance of the previous eight-channeled form. The trilobal geometry should provide better packing homogeneity due to the fewer potential orientations of the symmetric fiber geometry. Comparisons of separation efficiency and peak shape were made between the two fiber shapes through several dynamic parameters. Column hydrodynamics were investigated with two marker compounds, uracil and bovine serum albumin, with van Deemter plots of those two compounds revealing differences in the packing qualities between the different fiber shapes. Parametric fitting to the van Deemter, Knox, and Giddings equations provides insights into the column physical structures. Separation quality for both shapes was evaluated across differences in fiber packing density, gradient rate, and mobile phase linear velocity for the reversed phase separation of a four protein mixture, containing ribonuclease A, cytochrome c, lysozyme, and myoglobin. The results of this study lay the ground work for future efforts in the use of trilobal fibers for the separation of biomacromolecules.

Microwave-assisted grafting polymerization modification of nylon 6 capillary-channeled polymer fibers for enhanced weak cation exchange protein separations

A weak cation exchange liquid chromatography stationary phase (nylon-COOH) was prepared by grafting polyacrylic acid on to native nylon 6 capillary-channeled polymer (C-CP) fibers via a microwave-assisted radical polymerization. To the best of our knowledge, this is the first study of applying microwave-assisted grafting polymerization to affect nylon material for protein separation. The C-CP fiber surfaces were characterized by attenuated total reflection (ATR) infrared spectroscopy and scanning electron microscope (SEM). The anticipated carbonyl peak at 1722.9 cm^-1 was found on the nylon-COOH fibers, but was not found on the native fiber, indicating the presence of the polyacrylic acid on nylon fibers after grafting. The nylon-COOH phase showed a ∼12× increase in lysozyme dynamic binding capacity (∼12 mg mL^-1) when compared to the native fiber phase (∼1 mg mL^-1). The loading capacity of the nylon-COOH phase is nearly independent of the lysozyme loading concentration (0.05-1 mg mL^-1) and the mobile phase linear velocity (7.3-73 mm s^-1). The reproducibility of the lysozyme recovery from the nylon-COOH (RSD = 0.3%, n = 10) and the batch-to-batch variability in the functionalization (RSD = 3%, n = 5) were also investigated, revealing very high levels of consistency. Fast baseline separations of myoglobin, α-chymotrypsinogen A, cytochrome c and lysozyme were achieved using the nylon-COOH column. It was found that a 5× increase in the mobile phase linear velocity (7.3-to-36.5 mm s^-1) had little effect on the separation resolution. The microwave-assisted grafting polymerization has great potential as a generalized surface modification methodology across the applications of C-CP fibers.

Parallel, open-channel lateral flow (immuno) assay substrate based on capillary-channeled polymer films

Presented here is a novel implementation of polypropylene capillary-channeled polymer (C-CP) films, functionalized for bioaffinity separations and implemented as a platform for lateral flow (immuno) assays.

Evidence for the Intercalation of Lipid Acyl Chains into Polypropylene Fiber Matrices

Headgroup-functionalized lipids are being developed as ligand tethers for high selectivity separations on polypropylene capillary-channeled polymer fiber stationary phases. Surface modification is affected under ambient conditions from aqueous solution. This basic methodology has promise in many areas where robust modifications are desired on hydrophobic surfaces. In order to understand the mode of adsorption of the lipid tail to the polypropylene surface, lipids labeled with the environmentally sensitive 7-nitro-2-1,3-benzoxadiazol-4-yl (NBD) fluorophore were used, with NBD covalently attached to the headgroup (NBD-PE) or the acyl chain (acyl NBD-PE) of the lipid. When modified with the acyl NBD-PE, fluorescence imaging of the fiber at excitation wavelengths increasing from 470 to 510 nm caused a 32 nm shift in emission toward the red edge of the absorption band, indicating that the NBD molecule (and thus the lipid tail) is motionally restricted. Fluorescence imaging on fibers modified with NBD-PE or the free NBD-Cl dye molecule yields no change in the emission response. The results of these imaging studies provide evidence that the acyl chain portions of the lipids intercalate into free volume of the polypropylene fiber structure, yielding a robust means of surface modification and the potential for high ligand densities.

Capillary-channeled polymer (C-CP) fibers for the rapid extraction of proteins from urine matrices prior to detection with MALDI-MS

PURPOSE

While MS is a powerful tool for biomarker determinations, the high salt content and the small molecules present in urine poses incredible challenges. Separation/extraction methods must be employed for the isolation of target species at relevant concentrations. Micropipette tips packed with capillary-channeled polymer (C-CP) fibers are employed for the SPE of proteins from a synthetic and a certified urine matrix.

EXPERIMENTAL DESIGN

Extractions are performed utilizing a very simple centrifugation method to spin-down species through the C-CP fiber tips. Proteins adsorb to the hydrophobic polypropylene fibers and are eluted in a solvent suitable for MALDI-MS analysis. Figures of merit are determined for representative compounds β2-microglobulin, retinol binding protein, and transferrin.

RESULTS

The optimum protein processing included a 100 μL aqueous rinse and an elution solvent composition was 10 μL of 55:45 ACN:water (with triflouroacetic acid). MALDI-MS responses for the target proteins are improved from nondetectable levels to eventually yield LOD ranging from 5 to 180 nM in 1 μL aliquots.

CONCLUSION AND CLINICAL RELEVANCE

C-CP fiber tips offer a plethora of advantages including low materials costs, high throughput, microvolume processing, and the determination of sub-nanogram quantities of analyte; allowing determination of biomarkers that are otherwise undetectable in urine matrices.

Evaluation of synthesized lipid tethered ligands for surface functionalization of polypropylene capillary-channeled polymer fiber stationary phases

A straight forward approach to the synthesis of ligand tethered ligands (LTLs) circumvents the purchase of less-robust, PEG-phospholipids.

Biotin-functionalized poly(ethylene terephthalate) capillary-channeled polymer fibers as HPLC stationary phase for affinity chromatography

Native poly(ethylene terephthalate) (PET) capillary-channeled polymer (C-CP) fibers have been used as the stationary phase for high-performance liquid chromatography (HPLC) of proteins via reversed-phase and ion-exchange processes. Functionalization can be used to bring about greater selectivity through surface modification. PET fibers were treated with ethylenediamine to generate primary amine groups on the fiber surface, enabling subsequent covalent attachment of ligands. The ninhydrin test for primary amines revealed surface densities of 13.9-60.0 μmol m(-2) for PET fibers exposed for periods of 3-12 min. Here, 8-amino-3,6-dioxaoctanoic acid was linked to the EDA-treated PET fiber surface as a hydrophilic spacer, and then D-biotin was attached on the end of the spacer as an affinity ligand. The streptavidin binding capacity and binding homogeneity were studied on the biotin-functionalized PET C-CP fiber microbore column. The selectivity of the biotin surface functionalization was assessed by spiking lysate with Texas Red-labeled streptavidin and enhanced green fluorescent protein. Greater than 99% selectivity was realized. This ligand-coupling strategy from standard solid-phase peptide synthesis used in stationary phase functionalization creates great potential for PET C-CP fiber-packed HPLC columns to perform a variety of chromatographic separations.