Alan C. Herman

Characterization, Formulation, and Stability of Neupogen® (Filgrastim), a Recombinant Human Granulocyte-Colony Stimulating Factor

G-CSF is an extremely well-known and well-characterized molecule. Both the natural glycosylated form and the E. coli-produced nonglycosylated form are biologically active. A thorough understanding of the primary, secondary, and tertiary structures has enabled a rational approach to purification, folding, and formulation. Although the product can be considered mature, and testing and development of the second-generation formulation are complete, chemical and physical analysis of the product continue. It is this continued effort to understand the chemistry and stability of the product that ensure a safe and efficacious molecule.

Structure, stability, and mobility of a lyophilized IgG1 monoclonal antibody as determined using second-derivative infrared spectroscopy.

There are many aspects of stabilization of lyophilized proteins. Of these various factors, retention of native structure, having sufficient amount of stabilizer to embed the protein within an amorphous matrix, and dampening β-relaxations have been shown to be critical in optimizing protein stability during storage. In this study, an IgG1 was lyophilized with varying amounts of sucrose. In some formulations, a small amount of sorbitol was added as a plasticizer. The structure of the protein in dried state was monitored using infrared (IR) spectroscopy. The IR spectra indicated increasing retention of the native structure, which correlated with stability as indicated by size-exclusion chromatography as well as micro-flow imaging. Maximal stability was achieved with a 2:1 mass ratio of sucrose to protein, which is more than that would be expected based on earlier studies. Analysis of both high and low frequency bands associated with intramolecular β-sheet structure provides additional information on the structure of antibodies in the solid state. Finally, there is a correlation between the bandwidth of the β-sheet bands and the enthalpy of relaxation, suggesting that amide I bands can provide some indication of the degree of coupling to the sugar matrix, as well as structural heterogeneity of the protein.

Ethanol-sodium chloride-phosphate mobile phase for size-exclusion chromatography of poly(ethylene glycol) modified proteins

The use of an aqueous sodium chloride-phosphate mobile phase for size-exclusion chromatography of poly(ethylene glycol) modified (PEGylated) proteins resulted in premature degradation of silica-based gel filtration columns. This column degradation was manifested as peak tailing and loss of resolution. An aqueous ethanol-sodium chloride-phosphate mobile phase was identified which extended column lifetimes without loss of resolution or change in peak shape. We describe the effects of sodium chloride, phosphate, and ethanol concentrations on column performance. Peak shape and column lifetimes were better when an aqueous ethanol-sodium chloride-phosphate mobile phase was used than with an aqueous salt mobile phase. Also, circular dichroism was utilized to investigate possible solvent effects on the conformation of each protein.

Stability of lyophilized sucrose formulations of an IgG1: subvisible particle formation.

Eight lyophilized formulations of a IgG1 monoclonal antibody (MAb) were prepared containing increasing levels of sucrose. In addition, three of the formulations had sorbitol added at a level of 5% w/w relative to sucrose. The samples were stored for up to 4 weeks at 40°C, which is well below the Tg. Upon reconstitution, the levels of subvisible particles were measured using microflow imaging (MFI). The formulation containing no sucrose contained exceedingly high levels of subvisible particles, accounting for as much as 25% of the weight of the protein. Addition of sucrose markedly decreased the number of subvisible particles, with the maximal sucrose:protein weight ratio being 2:1 (the highest level tested). Addition of sorbitol further decreased subvisible particle levels, even for formulations where the sucrose:protein ratio was relatively high. This suggests that even small amounts of a plasticizer like sorbitol can improve the storage stability of a lyophilized antibody formulation, probably by dampening β-relaxations within the amorphous glass.

Detection of acetylated lysine residues using sequencing by edman degradation and mass spectrometry

Publisher Summary This chapter describes the application of Edman degradation sequencing in addition to mass spectrometry for the identification of post-translational, acetylation of lysine residues in a recombinant protein expressed in Escherichia coli. Acetylation of lysine residues is a posttranslational modification in recombinant proteins expressed in E. coli. Acetylation sites are used to determine the conservation of sequence in related proteins. Acetylation of lysine residues prevents carbamylation and glycosylation of some proteins. Peptide mapping in conjunction with mass spectrometry may indicate acetylation because of incomplete hydrolysis and increases in mass of +42 amu. To use sequencing as a detection method for unlabeled acetylated lysine, a PTH-derivative standard of the modified amino acid residue can be used. The scientists prepared synthetic NT-3 peptides with and without acetylation of the C-terminal lysine and used them as PTH-standards for three different sequencers. The sequencing results supported the mass spectrometry data for posttranslational acetylations sites in NT-3. The acetylation sites are also confirmed from Lys-C digested native NT-3 that was chemically acetylated. A comparison of retention time and mass of the incompletely digested peptides containing chemically acetylated lysines to the collected, modified NT-3 forms showed similarity. Edman sequencing of these peptides confirmed ɛ-N-acetylysine residues.