No abstract

Monoclonal antibody (mAb) drugs constitute the largest class of protein therapeutics currently on the market. Correctly folded protein higher order structure (HOS), including quinary structure, is crucial for mAb drug quality. The quinary structure is defined as the association of quaternary structures (e.g., oligomerized mAb). Here, several commonly available analytical methods, i.e., size-exclusion-chromatography (SEC) FPLC, multi-angle light scattering (MALS), circular dichroism (CD), NMR and multivariate analysis, were combined and modified to yield a complete profile of HOS and comparable metrics. Rituximab and infliximab were chosen for method evaluation because both IgG1 molecules are known to be homologous in sequence, superimposable in Fab crystal structure and identical in Fc structure. However, herein the two are identified to be significantly different in quinary structure in addition to minor secondary structure differences. All data collectively showed rituximab was mostly monomeric while infliximab was in mono-oligomer equilibrium driven by its Fab fragment. The quinary structure differences were qualitatively inferred from the less used but more reproducible dilution-injection-SEC-FPLC curve method. Quantitative principal component analysis (PCA) was performed on NMR spectra of either the intact or the in-situ enzymatic-digested mAb samples. The cleavage reactions happened directly in NMR tubes without further separation, which greatly enhanced NMR spectra quality and resulted in larger inter- and intra-lot variations based on PCA. The new in-situ enzymatic digestion method holds potential in identifying structural differences on larger therapeutic molecules using NMR.

In 2000, bovine heparin was withdrawn from the US market for fear of contamination with bovine spongiform encephalopathy (BSE) agent, the cause of variant Creutzfeldt-Jakob disease in humans. Thus, US heparin is currently sourced only from pig intestines. Availability of alternative sources of crude heparin, a life-saving drug, would benefit public health. Bovine heparin is an obvious option, but BSE clearance by the bovine heparin manufacturing process should be evaluated. To this end, using hamster 263K scrapie as a surrogate for BSE agent, we applied a four-step bench-scale heparin purification protocol resembling a typical heparin manufacturing process to investigate removal of the spiked scrapie agent. We removed aliquots from each step and analyzed them for residual abnormal prion protein (PrP) using a sensitive in vitro method, real-time quaking-induced conversion (RT-QuIC) assay, and for infectivity using animal bioassays. The purification process reduced infectivity by 3.6 log and removed PrP, measured as seeding activity, by 3.4 log. NaOH treatment was the most effective removal step tested. We also investigated NaOH at different concentrations and pH: the results showed that as much as 5.2 log of PrP seeding activity was removed at pH 12.5. Thus, changes to the concentration, treatment time, and temperature of alkaline extraction might further improve removal. Our results, using a basic heparin manufacturing process, inform efforts to reintroduce safe bovine heparin in the USA.

The structural assessment of Rituximab, an IgG1 mAb, was investigated with deep-ultraviolet resonance Raman (DUVRR) spectroscopy. DUVRR spectroscopy was used to monitor the changes to the secondary structure of Rituximab under thermal stress. DUVRR spectra showed obvious changes from 22 to 72 °C. Specifically, changes in the amide I vibrational mode were assigned to an increase in unordered structure (random coil). Structural changes in samples heated to 72 °C were related to loss in drug potency via a complement dependent cytotoxicity (CDC) bioassay. The DUVRR spectroscopic method shows promise as a tool for the quality assessment of mAb drug products and would represent an improvement over current methodology in terms of analysis time and sample preparation. To determine the scope of the method, protein pharmaceuticals of different molecular weights (ranging from 4 to 143 kDa) and secondary structure (β-sheet, α-helix and unordered structure) were analyzed. The model illustrated the method's sensitivity for the analysis of protein drug products of different secondary structure. Results show promise for DUVRR spectroscopy as a rapid screening tool of a variety of formulated protein pharmaceuticals.