Effect of benzyl alcohol on recombinant human interleukin-1 receptor antagonist structure and hydrogen-deuterium exchange

Molecular Mechanism of Antimicrobial Excipient-Induced Aggregation in Parenteral Formulations of Peptide Therapeutics

Antimicrobial preservatives are used as functional excipients in multidose formulations of biological therapeutics to destroy or inhibit the growth of microbial contaminants, which may be introduced by repeatedly administering doses. Antimicrobial agents can also induce the biophysical instability of proteins and peptides, which presents a challenge in optimizing the drug product formulation. Elucidating the structural basis for aggregation aids in understanding the underlying mechanism and can offer valuable knowledge and rationale for designing drug substances and drug products; however, this remains largely unexplored due to the lack of high-resolution characterization. In this work, we utilize solution nuclear magnetic resonance (NMR) as an advanced biophysical tool to study an acylated 31-residue peptide, acyl-peptide A, and its interaction with commonly used antimicrobial agents, benzyl alcohol and m-cresol. Our results suggest that acyl-peptide A forms soluble octamers in the aqueous solution, which tumble slowly due to an increased molecular weight as measured by diffusion ordered spectroscopy and ¹H relaxation measurement. The addition of benzyl alcohol does not induce aggregation of acyl-peptide A and has no chemical shift perturbation in ¹H-¹H NOESY spectra, suggesting no detectable interaction with the peptide. In contrast, the addition of 1% (w/v) m-cresol results in insoluble aggregates composed of 25% (w/w) peptides after a 24-hour incubation at room temperature as quantified by ¹H NMR. Interestingly, ¹H-¹³C heteronuclear single-quantum coherence and ¹H-¹H total correlation experiment spectroscopy have identified m-cresol and peptide interactions at specific residues, including Met, Lys, Glu, and Gln, suggesting that there may be a combination of hydrophobic, hydrogen bonding, and electrostatic interactions with m-cresol driving this phenomenon. These site-specific interactions have promoted the formation of higher-order oligomerization such as dimers and trimers of octamers, eventually resulting in insoluble aggregates. Our study has elucidated a structural basis of m-cresol-induced self-association that can inform the optimized design of drug substances and products. Moreover, it has demonstrated solution NMR as a high-resolution tool to investigate the structure and dynamics of biological drug products and provide an understanding of excipient-induced peptide and protein aggregation.

Antimicrobial Excipient-Induced Reversible Association of Therapeutic Peptides in Parenteral Formulations

New classes of therapeutic peptides are being developed to prosecute biological targets which have been inaccessible to other modalities. Higher potency and longer half-life peptides have given rise to multiuse injectable formulations that enable convenient, low volume, and self-administered dosing; however, inclusion of antimicrobial preservatives to meet bactericidal requirements can impact other attributes of peptide formulations. Peptide-preservative interactions influencing solution-phase self-association of a non-insulin, linear, palmitoylated 31 amino acid peptide and two structurally similar peptides were assessed via turbidity, intrinsic fluorescence shifts and quenching, isothermal titration calorimetry, and ¹H NMR. Meta-cresol and phenol specifically interact with the peptide, result in increased hydrophobicity near the tryptophan residue, and induce conformational changes, while benzyl alcohol does not impact tryptophan fluorescence, demonstrate any interaction enthalpy, or induce conformational changes. These same trends did not hold true for the other palmitoylated peptides evaluated, reinforcing the impacts of unique peptide sequences. Importantly, the presence of benzyl alcohol does increase the physical stability and solubility of the linear, 31 amino acid peptide under salt stress. We report new insights into the physical interactions of peptides with antimicrobial excipients, demonstrating a reversible association phenomenon and highlighting practical implications for formulation design and excipient selection.

Antimicrobial preservatives induce aggregation of interferon alpha-2a: the order in which preservatives induce protein aggregation is independent of the protein

Antimicrobial preservatives (APs) are included in liquid multi-dose protein formulations to combat the growth of microbes and bacteria. These compounds have been shown to cause protein aggregation, which leads to serious immunogenic and toxic side-effects in patients. Our earlier work on a model protein cytochrome c (Cyt c) demonstrated that APs cause protein aggregation in a specific manner. The aim of this study is to validate the conclusions obtained from our model protein studies on a pharmaceutical protein. Interferon α-2a (IFNA2) is available as a therapeutic treatment for numerous immune-compromised disorders including leukemia and hepatitis C, and APs have been used in its multi-dose formulation. Similar to Cyt c, APs induced IFNA2 aggregation, demonstrated by the loss of soluble monomer and increase in solution turbidity. The extent of IFNA2 aggregation increased with the increase in AP concentration. IFNA2 aggregation also depended on the nature of AP, and followed the order m-cresol>phenol>benzyl alcohol>phenoxyethanol. This specific order exactly matched with that observed for the model protein Cyt c. These and previously published results on antibodies and other recombinant proteins suggest that the general mechanism by which APs induce protein aggregation may be independent of the protein.

Partial unfolding of a monoclonal antibody: role of a single domain in driving protein aggregation

We have examined the effect of incubating a monoclonal antibody (mAb) in low (0-2.0 M) concentrations of guanidine hydrochloride (GdnHCl) on the protein's conformation and aggregation during isothermal incubation. In GdnHCl solutions at concentrations from 1.2 to 1.6 M, the mAb was partially unfolded. As demonstrated by fluorescence and circular dichroism spectroscopy, the partially unfolded state of the antibody had perturbed tertiary structure but retained native secondary structure. Furthermore, partial unfolding of the antibody was documented by analytical ultracentrifugation, dynamic light scattering, and limited proteolysis. Subsequent aggregation of the antibody was characterized using size-exclusion chromatography, analytical ultracentrifugation, and dynamic light scattering. Over the entire concentration range (0-2.0 M) of GdnHCl, protein-protein interactions were attractive, as quantified by negative osmotic second virial coefficients measured with static light scattering. However, during isothermal incubation at 37 °C, the aggregation of the antibody was detected only in solutions that induced partial unfolding. Differential scanning calorimetry studies showed that the antibody's CH2 domains were unfolded in antibody molecules that had been incubated in 1.2 M and higher concentrations of GdnHCl. These results suggest that unfolding of the CH2 domains leads to aggregation.