Two-Dimensional SEC-SEC-UV-MALS-dRI Workflow for Streamlined Analysis and Characterization of Biopharmaceuticals.

The emergence of complex biological modalities in the biopharmaceutical industry entails a significant expansion of the current analytical toolbox to address the need to deploy meaningful and reliable assays at an unprecedented pace. Size exclusion chromatography (SEC) is an industry standard technique for protein separation and analysis. Some constraints of traditional SEC stem from its restricted ability to resolve complex mixtures and notoriously long run times while also requiring multiple offline separation conditions on different pore size columns to cover a wider molecular size distribution. Two-dimensional liquid chromatography (2D-LC) is becoming an important tool not only to increase peak capacity but also to tune selectivity in a single online method. Herein, an online 2D-LC framework in which both dimensions utilize SEC columns with different pore sizes is introduced with a goal to increase throughput for biomolecule separation and characterization. In addition to improving the separation of closely related species, this online 2D SEC-SEC approach also facilitated the rapid analysis of protein-based mixtures of a wide molecular size range in a single online experimental run bypassing time-consuming deployment of different offline SEC methods. By coupling the second dimension with multiangle light scattering (MALS) and differential refractive index (dRI) detectors, absolute molecular weights of the separated species were obtained without the use of calibration curves. As illustrated in this report for protein mixtures and vaccine processes, this workflow can be used in scenarios where rapid development and deployment of SEC assays are warranted, enabling bioprocess monitoring, purity assessment, and characterization.

Pioneering Just-in-Time (JIT) Strategy for Accelerating Raman Method Development and Implementation for Biologic Continuous Manufacturing.

Raman spectroscopy is a popular process analytical technology (PAT) tool that has been increasingly used to monitor and control the monoclonal antibody (mAb) manufacturing process. Although it allows the characterization of a variety of quality attributes by developing chemometric models, a large quantity of representative data is required, and hence, the model development process can be time-consuming. In recent years, the pharmaceutical industry has been expediting new drug development in order to achieve faster delivery of life-changing drugs to patients. The shortened development timelines have impacted the Raman application, as less time is allowed for data collection. To address this problem, an innovative Just-in-Time (JIT) strategy is proposed with the goal of reducing the time needed for Raman model development and ensuring its implementation. To demonstrate its capabilities, a proof-of-concept study was performed by applying the JIT strategy to a biologic continuous process for producing monoclonal antibody products. Raman spectroscopy and online two-dimensional liquid chromatography (2D-LC) were integrated as a PAT analyzer system. Raman models of antibody titer and aggregate percentage were calibrated by chemometric modeling in real-time. The models were also updated in real-time using new data collected during process monitoring. Initial Raman models with adequate performance were established using data collected from two lab-scale cell culture batches and subsequently updated using one scale-up batch. The JIT strategy is capable of accelerating Raman method development to monitor and guide the expedited biologics process development.

Automated Online-Sampling Multidimensional Liquid Chromatography with Feedback-Control Capability as a Framework for Real-Time Monitoring of mAb Critical Quality Attributes in Multiple Bioreactors.

Real-time monitoring of biopharmaceutical reactors is becoming increasingly important as the processes become more complex. During the continuous manufacturing of monoclonal antibodies (mAbs), the desired mAb product is continually created and collected over a 30 day process, where there can be changes in quality over that time. Liquid chromatography (LC) is the workhorse instrumentation capable of measuring mAb concentration as well as quality attributes such as aggregation, charge variants, oxidation, etc. However, traditional offline sampling is too infrequent to fully characterize bioprocesses, and the typical time from sample generation to data analysis and reporting can take weeks. To circumvent these limitations, an automated online sampling multidimensional workflow was developed to enable streamlined measurements of mAb concentration, aggregation, and charge variants. This analytical framework also facilitates automated data export for real-time analysis of up to six bioreactors, including feedback-controlling capability using readily available LC technology. This workflow increases the data points per bioreactor, improving the understanding of each experiment while also reducing the data turnaround time from weeks to hours. Examples of effective real-time analyses of mAb critical quality attributes are illustrated, showing substantial throughput improvements and accurate results while minimizing labor and manual intervention.

Biosynthetic Origin of Formylaminooxyvinylglycine and Characterization of the Formyltransferase GvgI.

4-Formylaminooxyvinylglycine (FVG) is an herbicidal and antibacterial nonproteinogenic amino acid produced by several strains of the Pseudomonas fluorescens species complex. It contains a unique vinyl alkoxyamine moiety with an O-N bond, and its biosynthetic origin remains unknown. Here, we show that the gvg cluster from P. fluorescens WH6 is responsible for the biosynthesis of FVG and two additional O-N bond-containing oxyvinylglycines, guanidinooxyvinylglycine and aminooxyvinylglycine. Feeding studies in the producing bacteria indicate that these compounds originate from homoserine. We identify a formyltransferase gvgI that is required for the production of FVG and characterize the activity of this enzyme in vitro toward amino acids with a side chain amine. Sequence similarity network analysis reveals that GvgI and homologues make up a distinct group from the main classes of formyltransferases.

Fiber-based HIC capture loop for coupling of protein A and size exclusion chromatography in a two-dimensional separation of monoclonal antibodies.

During process development and manufacturing of monoclonal antibodies (mAbs), it is critical to characterize structure-function relationships to properly control the levels of mAb aggregation and potency of the protein product. With two-dimensional high performance liquid chromatography (2D-HPLC) technology, protein A (ProA) affinity chromatography can be used in the first dimension to isolate and measure the concentration of mAb, with the effluent transferred to a second dimension of size exclusion chromatography (SEC) to measure purity (i.e. aggregation). Described here is a 2D-HPLC method for characterizing mAb concentration and aggregation level, combining ProA purification, a novel injector-loop capture step, and aggregation determination by SEC. Unique here, polyester capillary-channeled polymer (C-CP) fibers are packed into PEEK tubing and used as the inter-column injection loop, capturing and releasing the mAbs via a hydrophobic interaction chromatography (HIC) process. The applicability of the HIC capture method was investigated on three ProA columns, including a homemade C-CP fiber format, and commercial POROS® A 20 µm and TSKgel Protein A-5PW columns. The HIC fiber capture loop was compared with standard, open sample loops in terms of solute recoveries, degree of affected aggregation, and chromatographic resolution. Advantages are seen in terms of limiting in-system mAb aggregation due to reduced low-pH solvent exposure, improved 2D chromatographic resolution, better monomer/aggregate ratio fidelity, and enhanced quantitative figures of merit.

Rapid two-dimensional Protein-A size exclusion chromatography of monoclonal antibodies for titer and aggregation measurements from harvested cell culture fluid samples.

The success of monoclonal antibody (mAb) therapeutics have increased pharmaceutical investment in mAb production, which has led to a greater demand of technologies to efficiently characterize these biotherapeutics. The large size and heterogeneity of mAbs require the measurement of multiple critical quality attributes (CQAs) during production. The current workflow to measure CQAs of antibodies involves multiple one-dimensional liquid chromatography methods, including Protein-A (ProA), ion-exchange (IEX), reversed-phase, size exclusion (SEC), hydrophilic interaction, and hydrophobic interaction (HIC). Recent advances in commercial two-dimensional liquid chromatography (2D-LC) affords an opportunity to perform two separations at once to measure multiple CQAs in a single assay. Here, we describe the development of a 2D ProA-SEC method using entirely commercially available instrumentation. Each individual separation and the transfer of material between dimensions were optimized to develop a method that measures titer and aggregation of a target antibody from harvested cell culture fluid in under 5 min. We determined the effects of each parameter of the method on mAb recovery and stability, as well as speed, robustness, resolution, and accuracy of the aggregate amount detected in the second dimension (2D). While there are still sources of error caused by hardware limitations, our rapid ProA-SEC method is an effective screening tool with a significant throughput advantage over previously described methods. Additionally, this work serves as a basis for developing other 2D-LC methods with ProA as the first dimension (1D) separation coupled with different 2D separation, such as ProA-IEX and ProA-HIC.

Discovery and Characterization of FMN-Binding ß-Glucuronidases in the Human Gut Microbiome.

The human gut microbiota encodes ß-glucuronidases (GUSs) that play key roles in health and disease via the metabolism of glucuronate-containing carbohydrates and drugs. Hundreds of putative bacterial GUS enzymes have been identified by metagenomic analysis of the human gut microbiome, but less than 10% have characterized structures and functions. Here we describe a set of unique gut microbial GUS enzymes that bind flavin mononucleotide (FMN). First, we show using mass spectrometry, isothermal titration calorimetry, and x-ray crystallography that a purified GUS from the gut commensal microbe Faecalibacterium prausnitzii binds to FMN on a surface groove located 30 Šaway from the active site. Second, utilizing structural and functional data from this FMN-binding GUS, we analyzed the 279 unique GUS sequences from the Human Microbiome Project database and identified 14 putative FMN-binding GUSs. We characterized four of these hits and solved the structure of two, the GUSs from Ruminococcus gnavus and Roseburia hominis, which confirmed that these are FMN binders. Third, binding and kinetic analysis of the FMN-binding site mutants of these five GUSs show that they utilize a conserved site to bind FMN that is not essential for GUS activity, but can affect KM. Lastly, a comprehensive structural review of the PDB reveals that the FMN-binding site employed by these enzymes is unlike any structurally characterized FMN binders to date. These findings reveal the first instance of an FMN-binding glycoside hydrolase and suggest a potential link between FMN and carbohydrate metabolism in the human gut microbiota.

Gut Microbial ß-Glucuronidase Inhibition via Catalytic Cycle Interception.

Microbial ß-glucuronidases (GUSs) cause severe gut toxicities that limit the efficacy of cancer drugs and other therapeutics. Selective inhibitors of bacterial GUS have been shown to alleviate these side effects. Using structural and chemical biology, mass spectrometry, and cell-based assays, we establish that piperazine-containing GUS inhibitors intercept the glycosyl-enzyme catalytic intermediate of these retaining glycosyl hydrolases. We demonstrate that piperazine-based compounds are substrate-dependent GUS inhibitors that bind to the GUS-GlcA catalytic intermediate as a piperazine-linked glucuronide (GlcA, glucuronic acid). We confirm the GUS-dependent formation of inhibitor-glucuronide conjugates by LC-MS and show that methylated piperazine analogs display significantly reduced potencies. We further demonstrate that a range of approved piperazine- and piperidine-containing drugs from many classes, including those for the treatment of depression, infection, and cancer, function by the same mechanism, and we confirm through gene editing that these compounds selectively inhibit GUS in living bacterial cells. Together, these data reveal a unique mechanism of GUS inhibition and show that a range of therapeutics may impact GUS activities in the human gut.

In Vitro Biosynthesis of the Nonproteinogenic Amino Acid Methoxyvinylglycine.

Oxyvinylglycines are a family of nonproteinogenic amino acids featuring an essential vinyl ether conferring mechanism-based inhibition of pyridoxal phosphate enzymes. The gene clusters for a few oxyvinylglycines are known, yet the biosynthetic origin of the vinyl ether is elusive. The in vitro biosynthesis of methoxyvinylglycine or l-2-amino-4-methoxy-trans-3-butenoic acid (AMB) is reported. It is shown that AMB is made from glutamate as an alanyl-AMB dipeptide and the rationale is provided for the N-term Ala. Using a chemical capture method, the order and timing of the modifications on non-ribosomal peptide synthetase (NRPS)-bound substrates was determined, including a cryptic hydroxylation of the Glu ß-carbon. Eliminating this hydroxy group likely generates a key α,ß-dehydroamino acid intermediate that facilitates decarboxylation. This work sheds light on vinyl ether biosynthesis and uncovers new NRPS chemistry.

Enzymatic basis of "hybridity" in thiomarinol biosynthesis.

Thiomarinol is a naturally occurring double-headed antibiotic that is highly potent against methicillin-resistant Staphylococcus aureus. Its structure comprises two antimicrobial subcomponents, pseudomonic acid analogue and holothin, linked by an amide bond. TmlU was thought to be the sole enzyme responsible for this amide-bond formation. In contrast to this idea, we show that TmlU acts as a CoA ligase that activates pseudomonic acid as a thioester that is processed by the acetyltransferase HolE to catalyze the amidation. TmlU prefers complex acyl acids as substrates, whereas HolE is relatively promiscuous, accepting a range of acyl-CoA and amine substrates. Our results provide detailed biochemical information on thiomarinol biosynthesis, and evolutionary insight regarding how the pseudomonic acid and holothin pathways converge to generate this potent hybrid antibiotic. This work also demonstrates the potential of TmlU/HolE enzymes as engineering tools to generate new "hybrid" molecules.