Oxidation of human insulin-like growth factor I in formulation studies: kinetics of methionine oxidation in aqueous solution and in solid state

Application of Formulation Principles to Stability Issues Encountered During Processing, Manufacturing, and Storage of Drug Substance and Drug Product Protein Therapeutics

The field of formulation and stabilization of protein therapeutics has become rather extensive. However, most of the focus has been on stabilization of the final drug product. Yet, proteins experience stress and degradation through the manufacturing process, starting with fermentaition. This review describes how formulation principles can be applied to stabilize biopharmaceutical proteins during bioprocessing and manufacturing, considering each unit operation involved in prepration of the drug substance. In addition, the impact of the container on stabilty is discussed as well.

Residue-Specific Impact of EDTA and Methionine on Protein Oxidation in Biotherapeutics Formulations Using an Integrated Biotherapeutics Drug Product Development Workflow

The rational design and selection of formulation composition to meet molecule-specific and product-specific needs are critical for biotherapeutics development to ensure physical and chemical stability. This work, based on three antibody-based (mAb) proteins (mAbA, mAbB, and mAbC), evaluates residue-specific impact of EDTA and methionine on protein oxidation, using an integrated biotherapeutics drug product development workflow. This workflow includes statistical experimental design, high-throughput experimental automation and execution, structure-based in silico modeling, inferential statistical analysis, and enhanced interactive data visualization of large datasets. This oxidation study evaluates the impact of formulation parameters including pH, protein concentration, and the presence of polysorbate 80 on the oxidation of specific conserved and variable residues of mAbs A, B, and C in the presence of stressors (iron, peroxide) and/or protectants (EDTA, L-methionine). Residue-specific analysis by automated high-throughput peptide mapping demonstrates differential residue-specific effects of EDTA and methionine in protecting against oxidation, highlighting the need for molecule-specific and product-specific selection of these excipients during formulation development. Computational modeling based on a homology model and the two-shell water coordination method (WCN) was employed to gain mechanistic understanding of residue-specific oxidation susceptibility of methionine residues. The computational determinants of local solvent exposure of methionine residues showed good correlation of WCN with experimentally determined oxidation for corresponding residues. The rapid generation of high-resolution data, statistical data analysis and interactive visualization of the high-throughput residue-level data containing ∼200 unique formulations facilitate residue-specific, molecule-specific and product-specific oxidation (global and local) assessment for oxidation protectants during early development for mAbs and related mAb-based modalities.

Inhomogeneous Distribution of Components in Solid Protein Pharmaceuticals: Origins, Consequences, Analysis, and Resolutions

Successful development of stable solid protein formulations usually requires the addition of one or several excipients to achieve optimal stability. In these products, there is a potential risk of an inhomogeneous distribution of the various ingredients, specifically the ratio of protein and stabilizer may vary. Such inhomogeneity can be detrimental for stability but is mostly neglected in literature. In the past, it was challenging to analyze inhomogeneous component distribution, but recent advances in analytical techniques have revealed new options to investigate this phenomenon. This paper aims to review fundamental aspects of the inhomogeneous distribution of components of freeze-dried and spray-dried protein formulations. Four key topics will be presented and discussed, including the sources of component inhomogeneity, its consequences on protein stability, the analytical methods to reveal component inhomogeneity, and possible solutions to prevent or mitigate inhomogeneity.

A large scale Plasmodium vivax- Saimiri boliviensis trophozoite-schizont transition proteome

Plasmodium vivax is a complex protozoan parasite with over 6,500 genes and stage-specific differential expression. Much of the unique biology of this pathogen remains unknown, including how it modifies and restructures the host reticulocyte. Using a recently published P. vivax reference genome, we report the proteome from two biological replicates of infected Saimiri boliviensis host reticulocytes undergoing transition from the late trophozoite to early schizont stages. Using five database search engines, we identified a total of 2000 P. vivax and 3487 S. boliviensis proteins, making this the most comprehensive P. vivax proteome to date. PlasmoDB GO-term enrichment analysis of proteins identified at least twice by a search engine highlighted core metabolic processes and molecular functions such as glycolysis, translation and protein folding, cell components such as ribosomes, proteasomes and the Golgi apparatus, and a number of vesicle and trafficking related clusters. Database for Annotation, Visualization and Integrated Discovery (DAVID) v6.8 enriched functional annotation clusters of S. boliviensis proteins highlighted vesicle and trafficking-related clusters, elements of the cytoskeleton, oxidative processes and response to oxidative stress, macromolecular complexes such as the proteasome and ribosome, metabolism, translation, and cell death. Host and parasite proteins potentially involved in cell adhesion were also identified. Over 25% of the P. vivax proteins have no functional annotation; this group includes 45 VIR members of the large PIR family. A number of host and pathogen proteins contained highly oxidized or nitrated residues, extending prior trophozoite-enriched stage observations from S. boliviensis infections, and supporting the possibility of oxidative stress in relation to the disease. This proteome significantly expands the size and complexity of the known P. vivax and Saimiri host iRBC proteomes, and provides in-depth data that will be valuable for ongoing research on this parasite’s biology and pathogenesis.

Silk-based stabilization of biomacromolecules

Silk fibroin is a high molecular weight amphiphilic protein that self-assembles into robust biomaterials with remarkable properties including stabilization of biologicals and tunable release kinetics correlated to processing conditions. Cells, antibiotics,monoclonal antibodies and peptides, among other biologics, have been encapsulated in silk using various processing approaches and material formats. The mechanistic basis for the entrapment and stabilization features, along with insights into the modulation of release of the entrained compounds from silks will be reviewed with a focus on stabilization of bioactive molecules.

Chemical degradation of proteins in the solid state with a focus on photochemical reactions

Protein pharmaceuticals comprise an increasing fraction of marketed products but the limited solution stability of proteins requires considerable research effort to prepare stable formulations. An alternative is solid formulation, as proteins in the solid state are thermodynamically less susceptible to degradation. Nevertheless, within the time of storage a large panel of kinetically controlled degradation reactions can occur such as, e.g., hydrolysis reactions, the formation of diketopiperazine, condensation and aggregation reactions. These mechanisms of degradation in protein solids are relatively well covered by the literature. Considerably less is known about oxidative and photochemical reactions of solid proteins. This review will provide an overview over photolytic and non-photolytic degradation reactions, and specially emphasize mechanistic details on how solid structure may affect the interaction of protein solids with light.

Aqueous stability of leuprolide acetate: effect of temperature, dissolved oxygen, pH and complexation with β-cyclodextrin

In the present research, the aqueous stability of leuprolide acetate (LA) in phosphate buffered saline (PBS) medium was studied (pH = 2.0-7.4). For this purpose, the effect of temperature, dissolved oxygen and pH on the stability of LA during 35 days was investigated. Results showed that the aqueous stability of LA was higher at low temperatures. Degassing of the PBS medium partially increased the stability of LA at 4 °C, while did not change at 37 °C. The degradation of LA was accelerated at lower pH values. In addition, complexes of LA with different portions of β-cyclodextrin (β-CD) were prepared through freeze-drying procedure and characterized by Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) analyses. Studying their aqueous stability at various pH values (2.0-7.4) showed LA/β-CD complexes exhibited higher stability when compared with LA at all pH values. The stability of complexes was also improved by increasing the portion of LA/β-CD up to 1/10.

Stability of protein pharmaceuticals: an update

In 1989, Manning, Patel, and Borchardt wrote a review of protein stability (Manning et al., Pharm. Res. 6:903-918, 1989), which has been widely referenced ever since. At the time, recombinant protein therapy was still in its infancy. This review summarizes the advances that have been made since then regarding protein stabilization and formulation. In addition to a discussion of the current understanding of chemical and physical instability, sections are included on stabilization in aqueous solution and the dried state, the use of chemical modification and mutagenesis to improve stability, and the interrelationship between chemical and physical instability.

The stability and dissolution properties of solid glucagon/gamma-cyclodextrin powder

In the present study, the solid-state stability and the dissolution of glucagon/gamma-cyclodextrin and glucagon/lactose powders were evaluated. Freeze-dried powders were stored at an increased temperature and/or humidity for up to 39 weeks. Pre-weighed samples were withdrawn at pre-determined intervals and analyzed with HPLC-UV (HPLC=high performance liquid chromatography, UV=ultraviolet), HPLC-ESI-MS (ESI-MS=electrospray ionization mass spectrometry), SEC (size-exclusion chromatography), turbidity measurements and solid-state FTIR (Fourier Transform Infrared Spectroscopy). Dissolution of glucagon was evaluated at pH 2.5, 5.0 and 7.0. In addition, before storage, proton rotating-frame relaxation experiments of solid glucagon/gamma-cyclodextrin powder were conducted with CPMAS ((13)C cross-polarization magic-angle spinning) NMR (nuclear magnetic resonance) spectroscopy. In the solid state, glucagon was degraded via oxidation and aggregation and in the presence of lactose via the Maillard reaction. The solid-state stability of glucagon/gamma-cyclodextrin powder was better than that of glucagon/lactose powder. In addition, gamma-cyclodextrin improved the dissolution of glucagon at pH 5.0 and 7.0 and delayed the aggregation of glucagon after its dissolution at pH 2.5, 5.0 and 7.0. There was no marked difference between the proton rotating-frame relaxation times of pure glucagon and gamma-cyclodextrin, and thus, the presence of inclusion complexes in the solid state could not be ascertained by CPMAS NMR. In conclusion, when compared to glucagon/lactose powder, glucagon/gamma-cyclodextrin powder exhibited better solid-state stability and more favorable dissolution properties.

Dual effects of Tween 80 on protein stability

In this paper, we used IL-2 mutein as a model protein and evaluated the effect of Tween 80, a non-ionic surfactant. In summary, we found that the dual effects of Tween 80 on the stability of IL-2SA, such as that shaking-induced aggregation of IL-2 mutein was significantly inhibited in the presence of Tween 80. However, this surfactant adversely affected the stability of IL-2 mutein in solution during storage in terms of both oxidation and aggregation. These adverse effects are strongly temperature and formulation-dependent. Data particularly showed that IL-2 mutein in solution forms soluble aggregates to a different degree in different formulations during storage at 40 degrees C for 2 months. Aggregation was barely detectable during storage at 5 degrees C for 22 months. Addition of 0.1% Tween 80 significantly increased the rate of IL-2 mutein aggregation during storage. The IL-2 mutein aggregates are linked by both disulfide and non-disulfide bonds and their relative contribution is temperature-dependent. IL-2 mutein can be oxidized also to a different degree in different formulations during storage and the oxidation rate is strongly temperature-dependent with an activation energy between 21 and 25 kcal/mol. Addition of 0.1% Tween 80 not only increased the rate of oxidation in general but also altered the temperature-dependency of IL-2 mutein oxidation.

The effect of neighboring amino acid residues and solution environment on the oxidative stability of tyrosine in small peptides

The effects of neighboring residues and formulation variables on tyrosine oxidation were investigated in model dipeptides (glysyl tyrosine, N-acetyl tyrosine, glutamyl tyrosine, and tyrosyl arginine) and tripeptide (lysyl tyrosyl lysine). The tyrosyl peptides were oxidized by light under alkaline conditions by a zero-order reaction. The rate of the photoreaction was dependent on tyrosyl pK(a), which was perturbed by the presence of neighboring charged amino acid residues. The strength of light exposure, oxygen headspace, and the presence of cationic surfactant, cetyltrimethylammonia chloride had a significant effect on the kinetics of tyrosyl photo-oxidation. Tyrosine and model tyrosyl peptides were also oxidized by hydrogen peroxide/metal ions at neutral pH. Metal-catalyzed oxidation followed first-order kinetics. Adjacent negatively charged amino acids accelerated tyrosine oxidation owing to affinity of the negative charges to metal-ions, whereas positively charged amino acid residues disfavored the reaction. The oxidation of tyrosine in peptides was greatly affected by the presence of adjacent charged residues, and the extent of the effect depended on the solution environment.

Correlations between molecular mobility and chemical stability during storage of amorphous pharmaceuticals

Recent studies have demonstrated that molecular mobility is an important factor affecting the chemical stability of amorphous pharmaceuticals, including small-molecular-weight drugs, peptides and proteins. However, quantitative correlations between molecular mobility and chemical stability have not yet been elucidated. The purpose of this article is to review literature describing the effect of molecular mobility on chemical stability during storage of amorphous pharmaceuticals, and to seek a better understanding of the relative significance of molecular mobility and other factors for chemical reactivity. We first consider the feature of chemical stability often observed for amorphous pharmaceuticals; changes in temperature dependence of chemical stability around matrix glass transition temperature (Tg), and greater stability associated with higher Tg. Secondly, we review papers which quantitatively studied the effects of the global mobility (often referred to as structural relaxation or -relaxation) of amorphous pharmaceuticals on chemical stability, and discuss correlations between chemical stability and global mobility using various equations that have thus far been proposed. Thirdly, the significance of local mobility of drug and excipient molecules in chemical reactivity is discussed in comparison with that of global mobility. Furthermore, we review literature reports which show no relationship between chemical stability and molecular mobility. The lack of apparent relationship is discussed in terms of the effects of the contribution of excipient molecules as reactants, the specific effects of water molecules, the heterogeneity of the matrix, and so on. The following summary has been obtained; the chemical stability of amorphous pharmaceuticals is affected by global mobility and/or local mobility, depending on the length scale of molecular mobility responsible for the chemical reactivity. In some cases, when activation energy for degradation processes is high and when other factors such as the specific effects of water and/or excipients contribute the degradation rate, stability seems to be largely independent of molecular mobility.

Does the oxidation of methionine in thrombomodulin contribute to the hypercoaguable state of smokers and diabetics?

The leading cause of premature death in smokers is cardiovascular disease. Diabetics also suffer from increased cardiovascular disease. This results, in part, from the hypercoagulable state associated with these conditions. However, the molecular cause(s) of the elevated risk of cardiovascular disease and the prothrombotic state of smokers and diabetics remain unknown. It is well known that oxidative stress is increased in both conditions. In smokers, it is established that oxidation of methionine residues takes place in alpha(1)-antitrypsin in lungs and that this leads to emphysema. Thrombomodulin is a key regulator of blood clotting and is found on the endothelium. Oxidation of methionine 388 in thrombomodulin is known to slow the rate at which the thrombomodulin-thrombin complex activates protein C, a protein which, in turn, degrades the factors which activate thrombin and lead to clot formation. In analogy to the cause of emphysema, it is hypothesized that oxidation of this methionine is elevated in smokers relative to non-smokers and, perhaps, in conditions such as diabetes that impose oxidative stress on the body. Evidence for the hypothesis that such an oxidation and concomitant reduction in activated protein C levels would lead to elevated cardiovascular risk is presented.

Stability and degradation profiles of Spantide II in aqueous solutions

Spantide II is an 11 amino acid peptide that has been shown to be a potential anti-inflammatory agent. The stability and degradation profiles of Spantide II in aqueous solutions were evaluated with the long-term objective of developing topical formulations of this compound for various skin disorders. The stability profile of Spantide II at various temperature and pH conditions was monitored by high performance liquid chromatography (HPLC) and the resulting degradation products were identified by liquid chromatography-mass spectroscopy (LC-MS). Forced degradation of Spantide II was performed at extreme acidic (pH <2.0) and alkaline (pH >10.0) conditions and by addition of hydrogen peroxide (oxidizing agent). The degradation pattern of Spantide II followed pseudo first-order kinetics. The shelf life (T90%) of Spantide II in aqueous ethanol (50%) was determined to be 230 days at 25 degrees C. Spantide II was susceptible to degradation at pH <2 and pH >5 and showed maximum stability at pH 3-5. The stability under various pH conditions indicates that Spantide II was most stable at pH 3.0 with a half-life of 95 days at 60 degrees C. Spantide II degradation was attributed to hydrolysis of peptide bonds [Pro2-(pyridyl)Ala3, (nicotinoyl)Lys1-Pro2, Pro4-PheCl2(5), Trp7-Phe8, Phe8-Trp9, Nle11-NH2), racemization of the peptide fragments that resulted from hydrolysis, cleavage and formation of (nicotinoyl)Lys1-Pro2 diketopiperazine. In the presence of an oxidizing agent, Pro(2,4) residues degraded by ring opening to form glutamyl-semialdehyde and by bond cleavage at Pro4 to form 2-pyrrolidone, while Phe(5,8) degraded to form 2-hydroxyphenylalanine. Spantide II was found to be stable in aqueous medium with T90% of 230 days. The major degradation pathways of Spantide II were identified as hydrolysis, racemization, cleavage and formation of diketopiperazine.

Effects of conformation on the chemical stability of pharmaceutically relevant polypeptides

Control of chemical instability in protein pharmaceuticals continues to be a critical issue in developing stable formulations. While the effects of pH, buffer composition, ionic strength and temperature remain the most effective methods for controlling hydrolysis and oxidation reactions, it appears that conformational control may also be important. Addition of excipients to maintain native structure and reduce the propensity of the protein to denature and/or aggregate is already a central theme in stabilizing proteins (Arakawa et al., 1993). The same additives have now been found to slow both deamidation and oxidation, whether in solution or in the solid state. What is emerging is an additional approach for producing protein pharmaceuticals that maintain native structure and activity during long-term storage.

Peroxide formation in polysorbate 80 and protein stability

Nonionic surfactants are widely used in the development of protein pharmaceuticals. However, the low level of residual peroxides in surfactants can potentially affect the stability of oxidation-sensitive proteins. In this report, we examined the peroxide formation in polysorbate 80 under a variety of storage conditions and tested the potential of peroxides in polysorbate 80 to oxidize a model protein, IL-2 mutein. For the first time, we demonstrated that peroxides can be easily generated in neat polysorbate 80 in the presence of air during incubation at elevated temperatures. Polysorbate 80 in aqueous solution exhibited a faster rate of peroxide formation and a greater amount of peroxides during incubation, which is further promoted/catalyzed by light. Peroxide formation can be greatly inhibited by preventing any contact with air/oxygen during storage. IL-2 mutein can be easily oxidized both in liquid and solid states. A lower level of peroxides in polysorbate 80 did not change the rate of IL-2 mutein oxidation in liquid state but significantly accelerated its oxidation in solid state under air. A higher level of peroxides in polysorbate 80 caused a significant increase in IL-2 mutein oxidation both in liquid and solid states, and glutathione can significantly inhibit the peroxide-induced oxidation of IL-2 mutein in a lyophilized formulation. In addition, a higher level of peroxides in polysorbate 80 caused immediate IL-2 mutein oxidation during annealing in lyophilization, suggesting that implementation of an annealing step needs to be carefully evaluated in the development of a lyophilization process for oxidation-sensitive proteins in the presence of polysorbate.

Comparing the effect on protein stability of methionine oxidation versus mutagenesis: steps toward engineering oxidative resistance in proteins

The biological activity of some proteins is known to be sensitive to oxidative damage caused by a variety of oxidants. The model protein staphylococcal nuclease was used to explore the effect on protein structural stability of oxidizing methionine to the sulfoxide form. These effects were compared with the effects of substituting methionines with isoleucine and leucine, a potential strategy for stabilizing proteins against oxidative damage. Wild-type nuclease and various mutants were oxidized with hydrogen peroxide. Stabilities of both oxidized and unoxidized proteins were determined by guanidine hydrochloride denaturation. Oxidation destabilized the wild-type protein by over 4 kcal/mol. This large loss of stability supports the idea that in some cases loss of biological activity is linked to disruption of the protein native state. Comparison of mutant protein's stability losses upon oxidation showed that methionines 65 and 98 had a much greater destabilizing effect when oxidized than methionines 26 or 32. While substitution of methionine 98 carried as great an energetic penalty as oxidation, substitution at position 65 was less disruptive than oxidation. Thus a simple substitution mutagenesis strategy to protect a protein against oxidative destabilization is practical for some methionine residues.

Lyophilization and development of solid protein pharmaceuticals

Developing recombinant protein pharmaceuticals has proved to be very challenging because of both the complexity of protein production and purification, and the limited physical and chemical stability of proteins. To overcome the instability barrier, proteins often have to be made into solid forms to achieve an acceptable shelf life as pharmaceutical products. The most commonly used method for preparing solid protein pharmaceuticals is lyophilization (freeze-drying). Unfortunately, the lyophilization process generates both freezing and drying stresses, which can denature proteins to various degrees. Even after successful lyophilization with a protein stabilizer(s), proteins in solid state may still have limited long-term storage stability. In the past two decades, numerous studies have been conducted in the area of protein lyophilization technology, and instability/stabilization during lyophilization and long-term storage. Many critical issues have been identified. To have an up-to-date perspective of the lyophilization process and more importantly, its application in formulating solid protein pharmaceuticals, this article reviews the recent investigations and achievements in these exciting areas, especially in the past 10 years. Four interrelated topics are discussed: lyophilization and its denaturation stresses, cryo- and lyo-protection of proteins by excipients, design of a robust lyophilization cycle, and with emphasis, instability, stabilization, and formulation of solid protein pharmaceuticals.

The solid state oxidation of methionine containing peptide: a preliminary study using time of flight secondary ion mass spectrometry

PURPOSE

A surface sensitive mass spectrometric technique: Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was introduced to study the solid state instability of a methionine containing peptide caused by the oxidation of the methionine residue.

METHODS

The oxidation of a neuropeptide Methinonine-Enkephalin (ME) in air and under UV acceleration was studied by ToF-SIMS.

RESULTS

The apparent oxidation rate is defined by the peak ratio of oxidized molecular ion over unoxidized molecular ion. ME is oxidized at a faster rate to its sulfoxide derivative in the UV accelerated oxidation environment than in lab air. The calibration curve for evaluating the ionization probability ratio of the oxidized deprotonated molecular ion divided by the unoxidized deprotonated molecular ion was obtained. This could be used to extract the real oxidation rate of ME in the solid state.

CONCLUSIONS

The preliminary results showed that ToF-SIMS with simple sample handling, fast data acquisition, together with excellent surface sensitivity and detection limit could be an applicable and convenient tool to study peptide reactions in the solid state such as oxidation and deamidation process.

Effect of peptide concentration and temperature on leuprolide stability in dimethyl sulfoxide

The effects of temperature and concentration on leuprolide degradation in dimethyl sulfoxide (DMSO) were explored. Leuprolide degradation products were analyzed by reverse phase high-performance liquid chromatography (RP-HPLC), size exclusion chromatography (SEC) and structurally characterized by mass spectrometry. Leuprolide solution stability in DMSO was characterized at 50, 100, 200, 400 mg/ml at 37-80 degrees C for 2 months to 3 years. Leuprolide degradation products were identified by mass spectrometry and could generally be attributed to isomerization, hydrolysis, oxidation, or aggregation. The hydrolytic degradation products consisted primarily of backbone cleavage C-terminal to Trp(3), Ser(4), Tyr(5), Leu(6) and Leu(7), and oxidation of Trp(3) and beta-elimination of Ser(4) were identified. Leuprolide degradation at 50 degrees C, 65 degrees C and 80 degrees C proceeded in an exponential fashion (E(a)=22. 6+/-1.2 kcal/mol); however, leuprolide degradation plateau'd after approximately 6 months at 37 degrees C. Upon closer examination, degradation product peak areas were seen to vary with temperature. For example, aggregation products did not increase with time at 37 degrees C, but aggregation peak intensities increased sharply with time at 80 degrees C. Increasing the temperature also increased the proportion of leuprolide degrading via isomerization/hydrolytic pathways, and decreased the proportion degrading via oxidation. These variations suggested that solvent dielectric, free H(+) in an aprotic solvent, oxygen solubility, impurities and residual moisture may play a role. Leuprolide solubilized in DMSO yields adequate stabililty for a 1 year implantable osmotic delivery system, where use of a dry aprotic solvent results in conditions similar to solid state stability.

Instability, stabilization, and formulation of liquid protein pharmaceuticals

One of the most challenging tasks in the development of protein pharmaceuticals is to deal with physical and chemical instabilities of proteins. Protein instability is one of the major reasons why protein pharmaceuticals are administered traditionally through injection rather than taken orally like most small chemical drugs. Protein pharmaceuticals usually have to be stored under cold conditions or freeze-dried to achieve an acceptable shelf life. To understand and maximize the stability of protein pharmaceuticals or any other usable proteins such as catalytic enzymes, many studies have been conducted, especially in the past two decades. These studies have covered many areas such as protein folding and unfolding/denaturation, mechanisms of chemical and physical instabilities of proteins, and various means of stabilizing proteins in aqueous or solid state and under various processing conditions such as freeze-thawing and drying. This article reviews these investigations and achievements in recent years and discusses the basic behavior of proteins, their instabilities, and stabilization in aqueous state in relation to the development of liquid protein pharmaceuticals.

Solid-state chemical stability of proteins and peptides

Peptide and protein drugs are often formulated in the solid-state to provide stabilization during storage. However, reactions can occur in the solid-state, leading to degradation and inactivation of these agents. This review summarizes the major chemical reactions affecting proteins and peptides in the solid-state: deamidation, peptide bond cleavage, oxidation, the Maillard reaction, beta-elimination, and dimerization/aggregation. Physical and chemical factors influencing these reactions are also discussed. These include temperature, moisture content, excipients, and the physical state of the formulation (amorphous vs crystalline). The review is intended to serve as an aid for those involved in formulation, and to stimulate further research on the determinants of peptide and protein reactivity in the solid-state.

Characterization and comparison of leuprolide degradation profiles in water and dimethyl sulfoxide

The effect of solvent on the rate of leuprolide degradation and on the structure of the degradation products was explored. Leuprolide solutions (370 mg/mL) were prepared in water and dimethyl sulfoxide (DMSO) for delivery in DUROS osmotic implants. Both solvent systems demonstrated better than 90% stability after 1 year at 37 degrees C, where the DMSO formulation afforded better stability than the aqueous formulation and was used in subsequent clinical trials. The rate of leuprolide degradation in DMSO was also observed to accelerate with increasing moisture content, indicating that the aprotic solvent minimized chemical degradation. Interestingly, leuprolide degradation products varied with formulation vehicle. The proportions of leuprolide degradation products observed to form in water and DMSO at 37 degrees C were hydrolysis > aggregation > isomerization > oxidation and aggregation > oxidation > hydrolysis > isomerization, respectively. Specifically, more N-terminal hydrolysis and acetylation were observed under aqueous conditions, and increased Trp oxidation and Ser beta-elimination were seen under non-aqueous conditions. Furthermore, the major chemical degradation pathway changed with temperature in the DMSO formulation (decreasing oxidation with increasing temperature), but not in the aqueous formulation.

Multivesicular liposome (DepoFoam) technology for the sustained delivery of insulin-like growth factor-I (IGF-I)

Insulin-like Growth Factor I (IGF-I), a 7.65 kD protein which has a variety of metabolic functions, is being evaluated for its therapeutic benefit in several disease states. To sustain therapeutic blood levels in a number of these instances, IGF-I needs to be administered repeatedly. The objective of these studies was the development of a sustained-release depot delivery system for this protein which would replace repeated administration. Using a multivesicular liposome drug delivery system (DepoFoam), sustained delivery kinetics have been observed for IGF-I. IGF-I was successfully encapsulated in this system with good efficiency. The integrity of the encapsulated protein was maintained, as characterized by physiochemical (HPLC, SDS-PAGE), and by biological methods (mitogenic activity). The DepoIGF-I particles were also characterized by their morphology (particles were smooth, multivesicular, and there was no debris), particle size (ranged from 18 to 20 microm), and in vitro and in vivo release kinetics of IGF-I. The DepoIGF-I particles released the protein drug in a sustained manner both in vitro and in vivo without a rapid initial release, and the released protein maintained its structural integrity and biological activity. The in vitro studies in human plasma at 37 degreesC showed that the DepoIGF-I particles released IGF-I slowly over several days; 70-80% of the protein was released in 6-7 days. In a pharmacokinetic in vivo study, after subcutaneous injections in rats, IGF-I levels were sustained for 5-7 days with DepoIGF-I formulation, whereas IGF-I in the free form was cleared in 1 day. DepoFoam technology provides a pharmaceutically useful system of sustained delivery for proteins, which can be extended to other therapeutic macromolecules.

Oxidation of human insulin-like growth factor I in formulation studies. 3. Factorial experiments of the effects of ferric ions, EDTA, and visible light on methionine oxidation and covalent aggregation in aqueous solution

The influence of ferric ions, EDTA, and visible light on the oxidation of methionine and the covalent reducible and nonreducible dimerization in human Insulin-like Growth Factor I (hIGF-I) in aqueous (1 mM) phosphate buffer solution were studied. A reduced factorial experiment with two levels of each factor was used. Regression models for the three responses were constructed with partial least square (PLS) analysis. The hIGF-I variants were quantified by reversed-phase high-performance liquid chromatography (RP-HPLC), gel filtration, and reduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The formation of the hIGF-I variants in aqueous solution at pH 6.1 exhibited different dependencies on the variables studied. The oxidation of methionine was affected mainly by visible light and the combination of 10 ppm ferric ions and 20 ppm EDTA, whereas ferric ions alone had no significant effect. The covalent dimerization of hIGF-I was correlated to visible light and ferric ions. The interaction effects of ferric ions with either visible light or EDTA were also significant on the dimerization rates. Both reducible and nonreducible soluble covalent dimers were formed, with the reducible dimer being the most prominent. The oxidation of methionine 59 in hIGF-I is catalyzed by light and by ferric ions in combination with EDTA. The covalent dimerization of hIGF-I is mainly affected by light and by ferric ions. Both reducible and nonreducible dimerization increased by oxidative conditions. Human IGF-I appears to dimerize covalently by both disulfide scrambling and by a radical-promoted nondisulfide pathway. EDTA is necessary for ferric ions to be active in the oxidation of methionine in hIGF-I but not for the covalent dimerization.

Solvent effects on the solubility and physical stability of human insulin-like growth factor I

PURPOSE

The solubility and physical stability of human Insulin-like Growth Factor I (hIGF-I) were studied in aqueous solutions with different excipients.

METHODS

The solubility of hIGF-I was determined by UV-absorption and quantification of light blocking particles. The physical stability of hIGF-I was studied with differential scanning calorimetry (DSC) and circular dichroism (CD) spectroscopy.

RESULTS

Human IGF-I precipitated at low temperature in the presence of 140 mM benzyl alcohol and 145 mM sodium chloride. CD data showed that the tertiary structure of hIGF-I during these conditions was perturbed compared to that in 5 mM phosphate buffer. In the presence of benzyl alcohol 290 mM mannitol stabilized hIGF-I. Sodium chloride or mannitol by themselves had no effect on either the solubility or the tertiary structure. Benzyl alcohol was attracted to hIGF-I, whereas sodium chloride was preferentially excluded. The attraction of benzyl alcohol was reinforced by sodium chloride leading to salting-out of hIGF-I. The CD-data indicated interactions of benzyl alcohol with phenylalanine in hIGF-I. Thermal denaturation of hIGF-I occurred in all solutions with sodium chloride, whereas mannitol or benzyl alcohol had no effect on the thermal stability. The thermal stability of hIGF-I was thus decreased in 145 mM sodium chloride although it was excluded from hIGF-I.

CONCLUSIONS

The self-association and thermal aggregation of hIGF-I is driven by hydrophobic interactions. Benzyl alcohol is attracted to hIGF-I and induces changes in the tertiary structure causing hydrophobic attraction of the protein at low temperatures.