Integrated Bottom-Up and Top-Down Liquid Chromatography-Mass Spectrometry for Characterization of Recombinant Human Growth Hormone Degradation Products

Evaluating protein cross-linking as a therapeutic strategy to stabilize SOD1 variants in a mouse model of familial ALS

Mutations in the gene encoding Cu-Zn superoxide dismutase 1 (SOD1) cause a subset of familial amyotrophic lateral sclerosis (fALS) cases. A shared effect of these mutations is that SOD1, which is normally a stable dimer, dissociates into toxic monomers that seed toxic aggregates. Considerable research effort has been devoted to developing compounds that stabilize the dimer of fALS SOD1 variants, but unfortunately, this has not yet resulted in a treatment. We hypothesized that cyclic thiosulfinate cross-linkers, which selectively target a rare, 2 cysteine-containing motif, can stabilize fALS-causing SOD1 variants in vivo. We created a library of chemically diverse cyclic thiosulfinates and determined structure-cross-linking-activity relationships. A pre-lead compound, "S-XL6," was selected based upon its cross-linking rate and drug-like properties. Co-crystallographic structure clearly establishes the binding of S-XL6 at Cys 111 bridging the monomers and stabilizing the SOD1 dimer. Biophysical studies reveal that the degree of stabilization afforded by S-XL6 (up to 24°C) is unprecedented for fALS, and to our knowledge, for any protein target of any kinetic stabilizer. Gene silencing and protein degrading therapeutic approaches require careful dose titration to balance the benefit of diminished fALS SOD1 expression with the toxic loss-of-enzymatic function. We show that S-XL6 does not share this liability because it rescues the activity of fALS SOD1 variants. No pharmacological agent has been proven to bind to SOD1 in vivo. Here, using a fALS mouse model, we demonstrate oral bioavailability; rapid engagement of SOD1G93A by S-XL6 that increases SOD1G93A's in vivo half-life; and that S-XL6 crosses the blood-brain barrier. S-XL6 demonstrated a degree of selectivity by avoiding off-target binding to plasma proteins. Taken together, our results indicate that cyclic thiosulfinate-mediated SOD1 stabilization should receive further attention as a potential therapeutic approach for fALS.

Recent advances in structural mass spectrometry methods in the context of biosimilarity assessment: from sequence heterogeneities to higher order structures

Biotherapeutics and their biosimilar versions have been flourishing in the biopharmaceutical market for several years. Structural and functional characterization is needed to achieve analytical biosimilarity through the assessment of critical quality attributes as required by regulatory authorities. The role of analytical strategies, particularly mass spectrometry-based methods, is pivotal to gathering valuable information for the in-depth characterization of biotherapeutics and biosimilarity assessment. Structural mass spectrometry methods (native MS, HDX-MS, top-down MS, etc.) provide information ranging from primary sequence assessment to higher order structure evaluation. This review focuses on recent developments and applications in structural mass spectrometry for biotherapeutic and biosimilar characterization.

Near-digital amplification in paper improves sensitivity and speed in biplexed reactions

The simplest point-of-care assays are usually paper and plastic devices that detect proteins or nucleic acids at low cost and minimal user steps, albeit with poor limits of detection. Digital assays improve limits of detection and analyte quantification by splitting a sample across many wells (or droplets), preventing diffusion, and performing analyte amplification and detection in multiple small wells. However, truly digital nucleic acid amplification tests (NAATs) require costly consumable cartridges that are precisely manufactured, aligned, and operated to enable low detection limits. In this study, we demonstrate how to implement near-digital NAATs in low-cost porous media while approaching the low limits of detection of digital assays. The near-digital NAAT was enabled by a paper membrane containing lyophilized amplification reagents that automatically, passively meters and distributes a sample over a wide area. Performing a NAAT in the paper membrane while allowing diffusion captures many of the benefits of digital NAATs if the pad is imaged at a high spatial resolution during amplification. We show that the near-digital NAAT is compatible with a low-cost paper and plastic disposable cartridge coupled to a 2-layer rigid printed circuit board heater (the MD NAAT platform). We also demonstrate compatibility with biplexing and imaging with mobile phones with different camera sensors. We show that the near-digital NAAT increased signal-to-noise ratios by ~ 10×, improved limits of detection from above 10³ copies of methicillin-resistant Staphylococcus aureus genomic DNA to between 100 and 316 copies in a biplexed reaction containing 10⁵ copies of co-amplifying internal amplification control DNA, and reduced time-to-result from 45 min of amplification to 15-20 min for the positive samples.

Recent progress in the analysis of protein deamidation using mass spectrometry

Deamidation is a nonenzymatic and spontaneous posttranslational modification (PTM) that introduces changes in both structure and charge of proteins, strongly associated with aging proteome instability and degenerative diseases. Deamidation is also a common PTM occurring in biopharmaceutical proteins, representing a major cause of degradation. Therefore, characterization of deamidation alongside its inter-related modifications, isomerization and racemization, is critically important to understand their roles in protein stability and diseases. Mass spectrometry (MS) has become an indispensable tool in site-specific identification of PTMs for proteomics and structural studies. In this review, we focus on the recent advances of MS analysis in protein deamidation. In particular, we provide an update on sample preparation, chromatographic separation, and MS technologies at multi-level scales, for accurate and reliable characterization of protein deamidation in both simple and complex biological samples, yielding important new insight on how deamidation together with isomerization and racemization occurs. These technological progresses will lead to a better understanding of how deamidation contributes to the pathology of aging and other degenerative diseases and the development of biopharmaceutical drugs.

The application of HPLC/MS analysis with a multi-enzyme digest strategy to characterize different interferon product variants produced from Pichia pastoris

Interferons are signaling proteins that belong to the large class of cytokines and human interferons which are classified based on the type of receptor interactions: type I, II and III. IFNα2b belongs to the type I interferon class with a major therapeutic application for the treatment of hepatitis B and C infections. A recombinant form of IFNα2b expressed in E. coli, known as IntronA, has been approved by US Food and Drug Administration (FDA). IFN γ, also known as type II interferon, plays a significant role in the inhibition of viral replication. Actimmune^® is a US Food and Drug Administration (FDA) approved version of IFN γ for the indication of reducing infections associated with chronic granulomatous disease and severe malignant osteopetrosis. In this study we have applied advanced analytical methods for the characterization of IFNα2b and IFN γ produced from Pichia pastoris. The multi-enzyme digestion approach has been developed to allow measurement of 100% sequence coverage and detailed analysis of post-translational variants and degradation products. In this manner, we identified the following variants in IFN α2b: N-terminal residual leader sequence, an amino acid substitution, oxidation of methionine residues and two sites of high mannose N-glycosylation. In the Pichia IFN γ produced material, our approach detected variants resulting from glycosylation, C-terminal proteolysis, oxidation of methionine residues and deamidation. In this manner, the analytical program was able to support rapid process development as well as identify product variants and degradation products in the resulting product.

On-demand manufacturing of clinical-quality biopharmaceuticals

Conventional manufacturing of protein biopharmaceuticals in centralized, large-scale, single-product facilities is not well-suited to the agile production of drugs for small patient populations or individuals. Previous solutions for small-scale manufacturing are limited in both process reproducibility and product quality, owing to their complicated means of protein expression and purification. We describe an automated, benchtop, multiproduct manufacturing system, called Integrated Scalable Cyto-Technology (InSCyT), for the end-to-end production of hundreds to thousands of doses of clinical-quality protein biologics in about 3 d. Unlike previous systems, InSCyT includes fully integrated modules for sustained production, efficient purification without the use of affinity tags, and formulation to a final dosage form of recombinant biopharmaceuticals. We demonstrate that InSCyT can accelerate process development from sequence to purified drug in 12 weeks. We used integrated design to produce human growth hormone, interferon α-2b and granulocyte colony-stimulating factor with highly similar processes on this system and show that their purity and potency are comparable to those of marketed reference products.