Formulation design of acidic fibroblast growth factor

Designing Formulation Strategies for Enhanced Stability of Therapeutic Peptides in Aqueous Solutions: A Review

Over the past few decades, there has been a tremendous increase in the utilization of therapeutic peptides. Therapeutic peptides are usually administered via the parenteral route, requiring an aqueous formulation. Unfortunately, peptides are often unstable in aqueous solutions, affecting stability and bioactivity. Although a stable and dry formulation for reconstitution might be designed, from a pharmaco-economic and practical convenience point of view, a peptide formulation in an aqueous liquid form is preferred. Designing formulation strategies that optimize peptide stability may improve bioavailability and increase therapeutic efficacy. This literature review provides an overview of various degradation pathways and formulation strategies to stabilize therapeutic peptides in aqueous solutions. First, we introduce the major peptide stability issues in liquid formulations and the degradation mechanisms. Then, we present a variety of known strategies to inhibit or slow down peptide degradation. Overall, the most practical approaches to peptide stabilization are pH optimization and selecting the appropriate type of buffer. Other practical strategies to reduce peptide degradation rates in solution are the application of co-solvency, air exclusion, viscosity enhancement, PEGylation, and using polyol excipients.

Pathogen-derived peptides in drug targeting and its therapeutic approach

Peptides, short stretches of amino acids or small proteins that occupy a strategic position between proteins and amino acids, are readily accessible by chemical and biological methods. With ideal properties for forming high-affinity and specific interactions with host target proteins, they have established an important niche in the drug development spectrum complementing small molecule and biological therapeutics. Among the most successful biomedicines in use today, peptide-based drugs show great promise. This, coupled with recent advances in synthetic and nanochemical biology, has led to the creation of tailor-made peptide therapeutics for improved biocompatibility. This review presents an overview of the latest research on pathogen-derived, host-cell-interacting peptides. It also highlights strategies for using peptide-based therapeutics that address cellular transport challenges through the introduction of nanoparticles that serve as platforms to facilitate the delivery of peptide biologics and therapeutics for treating various inflammatory diseases. Finally, this paper describes future perspectives, specific pathogen-based peptides that can enhance specificity, efficiency, and capacity in functional peptide-based therapeutics, which are in the spotlight as new treatment alternatives for various diseases, and also presents verified sequences and targets that can increase chemical and pharmacological value.

Factors affecting the physical stability (aggregation) of peptide therapeutics

The number of biological therapeutic agents in the clinic and development pipeline has increased dramatically over the last decade and the number will undoubtedly continue to increase in the coming years. Despite this fact, there are considerable challenges in the development, production and formulation of such biologics particularly with respect to their physical stabilities. There are many cases where self-association to form either amorphous aggregates or highly structured fibrillar species limits their use. Here, we review the numerous factors that influence the physical stability of peptides including both intrinsic and external factors, wherever possible illustrating these with examples that are of therapeutic interest. The effects of sequence, concentration, pH, net charge, excipients, chemical degradation and modification, surfaces and interfaces, and impurities are all discussed. In addition, the effects of physical parameters such as pressure, temperature, agitation and lyophilization are described. We provide an overview of the structures of aggregates formed, as well as our current knowledge of the mechanisms for their formation.

An S116R Phosphorylation Site Mutation in Human Fibroblast Growth Factor-1 Differentially Affects Mitogenic and Glucose-Lowering Activities

Fibroblast growth factor-1 (FGF-1), a potent human mitogen and insulin sensitizer, signals through both tyrosine kinase receptor-mediated autocrine/paracrine pathways as well as a nuclear intracrine pathway. Phosphorylation of FGF-1 at serine 116 (S116) has been proposed to regulate intracrine signaling. Position S116 is located within a ∼17 amino acid C-terminal loop that contains a rich set of functional determinants including heparin∖heparan sulfate affinity, thiol reactivity, nuclear localization, pharmacokinetics, functional half-life, nuclear ligand affinity, stability, and structural dynamics. Mutational targeting of specific functionality in this region without perturbing other functional determinants is a design challenge. S116R is a non-phosphorylatable variant present in bovine FGF-1 and other members of the human FGF family. We show that the S116R mutation in human FGF-1 is accommodated with no perturbation of biophysical or structural properties, and is therefore an attractive mutation with which to elucidate the functional role of phosphorylation. Characterization of S116R shows reduction in NIH 3T3 fibroblast mitogenic stimulation, increase in fibroblast growth factor receptor-1c activation, and prolonged duration of glucose lowering in ob/ob hyperglycemic mice. A novel FGF-1/fibroblast growth factor receptor-1c dimerization interaction combined with non-phosphorylatable intracrine signaling is hypothesized to be responsible for these observed functional effects.

Accelerated healing in NONcNZO10/LtJ type 2 diabetic mice by FGF-1

The development of novel therapies to treat chronic diabetic ulcers depends upon appropriate animal models for early stage investigation. The NONcNZO10/LtJ mouse is a new polygenic strain developed to more realistically model human metabolic syndrome and obesity-induced type 2 diabetes; however, detailed wound healing properties have not been reported. Herein, we describe a quantitative wound healing study in the NONcNZO10/LtJ mouse using a splinted excisional wound. The rate of wound healing is compared to various controls, and is also quantified in response to topical administration of normal and mutant fibroblast growth factor-1 (FGF-1). Quantitation of reepithelialization shows that the diabetic condition in the NONcNZO10/LtJ mouse is concomitant with a decreased rate of dermal healing. Furthermore, topical administration of a FGF-1/heparin formulation effectively accelerates reepithelialization. A similar acceleration can also be achieved by a stabilized mutant form of FGF-1 formulated in the absence of heparin. Such accelerated rates of healing are not associated with any abnormal histology in the healed wounds. The results identify the NONcNZO10/LtJ mouse as a useful model of impaired wound healing in type 2 diabetes, and further, identify engineered forms of FGF-1 as a potential “second-generation” therapeutic to promote diabetic dermal wound healing.

Protein comparability assessments and potential applicability of high throughput biophysical methods and data visualization tools to compare physical stability profiles

In this review, some of the challenges and opportunities encountered during protein comparability assessments are summarized with an emphasis on developing new analytical approaches to better monitor higher-order protein structures. Several case studies are presented using high throughput biophysical methods to collect protein physical stability data as function of temperature, agitation, ionic strength and/or solution pH. These large data sets were then used to construct empirical phase diagrams (EPDs), radar charts, and comparative signature diagrams (CSDs) for data visualization and structural comparisons between the different proteins. Protein samples with different sizes, post-translational modifications, and inherent stability are presented: acidic fibroblast growth factor (FGF-1) mutants, different glycoforms of an IgG1 mAb prepared by deglycosylation, as well as comparisons of different formulations of an IgG1 mAb and granulocyte colony stimulating factor (GCSF). Using this approach, differences in structural integrity and conformational stability profiles were detected under stress conditions that could not be resolved by using the same techniques under ambient conditions (i.e., no stress). Thus, an evaluation of conformational stability differences may serve as an effective surrogate to monitor differences in higher-order structure between protein samples. These case studies are discussed in the context of potential utility in protein comparability studies.

Biophysical and formulation studies of the Schistosoma mansoni TSP-2 extracellular domain recombinant protein, a lead vaccine candidate antigen for intestinal schistosomiasis

A candidate vaccine to prevent human schistosomiasis is under development. The vaccine is comprised of a recombinant 9 kDa antigen protein corresponding to the large extracellular domain of a tetraspanin surface antigen protein of Schistosoma mansoni, Sm-TSP-2. Here, we describe the biophysical profile of the purified, recombinant Sm-TSP-2 produced in the yeast PichiaPink, which in preclinical studies in mice was shown to be an effective vaccine against intestinal schistosomiasis. Biophysical techniques including circular dichroism, intrinsic and extrinsic fluorescence and light scattering were employed to generate an empirical phase diagram, a color based map of the physical stability of the vaccine antigen over a wide range of temperatures and pH. From these studies a pH range of 6.0-8.0 was determined to be optimal for maintaining the stability and conformation of the protein at temperatures up to 25 °C. Sorbitol, sucrose and trehalose were selected as excipients that prevented physical degradation during storage. The studies described here provide guidance for maximizing the stability of soluble recombinant Sm-TSP-2 in preparation of its further development as a vaccine.

Pharmacokinetic properties of 2nd-generation fibroblast growth factor-1 mutants for therapeutic application

Fibroblast growth factor-1 (FGF-1) is an angiogenic factor with therapeutic potential for the treatment of ischemic disease. FGF-1 has low intrinsic thermostability and is characteristically formulated with heparin as a stabilizing agent. Heparin, however, adds a number of undesirable properties that negatively impact safety and cost. Mutations that increase the thermostability of FGF-1 may obviate the need for heparin in formulation and may prove to be useful “2nd-generation” forms for therapeutic use. We report a pharmacokinetic (PK) study in rabbits of human FGF-1 in the presence and absence of heparin, as well as three mutant forms having differential effects upon thermostability, buried reactive thiols, and heparin affinity. The results support the hypothesis that heparan sulfate proteoglycan (HSPG) in the vasculature of liver, kidney and spleen serves as the principle peripheral compartment in the distribution kinetics. The addition of heparin to FGF-1 is shown to increase endocrine-like properties of distribution. Mutant forms of FGF-1 that enhance thermostability or eliminate buried reactive thiols demonstrate a shorter distribution half-life, a longer elimination half-life, and a longer mean residence time (MRT) in comparison to wild-type FGF-1. The results show how such mutations can produce useful 2nd-generation forms with tailored PK profiles for specific therapeutic application.

Selective domain stabilization as a strategy to reduce human serum albumin-human granulocyte colony stimulating factor aggregation rate

Therapeutic proteins must be generally formulated to reduce unwanted aggregation. Fusion proteins, which comprise domains assembled from separate proteins, may require unique formulation strategies in order to maximize their stability. A fusion protein of human serum albumin (HSA) and human granulocyte colony stimulating factor (GCSF; HSA-GCSF) was used as a model to test the hypothesis that formulations that increase the thermodynamic conformational stability of the least stable domain of a fusion protein will stabilize the entire fusion protein against aggregation. Conformational stability of HSA-GCSF was modulated by addition of octanoic acid, which was previously shown to increase the conformational stability of HSA, the least stable domain. Contrary to our hypothesis, increased conformational stability of the HSA domain did not result in increased resistance to aggregation of HSA-GCSF. These results for HSA-GCSF were also compared with similar studies conducted previously on a therapeutic protein formed by the fusion of HSA and human growth hormone (hGH; HSA-hGH).

An empirical phase diagram approach to investigate conformational stability of "second-generation" functional mutants of acidic fibroblast growth factor-1

Acidic fibroblast growth factor-1 (FGF-1) is an angiogenic protein which requires binding to a polyanion such as heparin for its mitogenic activity and physicochemical stability. To evaluate the extent to which this heparin dependence on solution stability could be reduced or eliminated, the structural integrity and conformational stability of 10 selected FGF-1 mutants were examined as a function of solution pH and temperature by a series of spectroscopic methods including circular dichroism, intrinsic and extrinsic fluorescence spectroscopy and static light scattering. The biophysical data were summarized in the form of colored empirical phase diagrams (EPDs). FGF-1 mutants were identified with stability profiles in the absence of heparin comparable to that of wild-type FGF-1 in the presence of heparin while still retaining their biological activity. In addition, a revised version of the EPD methodology was found to provide an information rich, high throughput approach to compare the effects of mutations on the overall conformational stability of proteins in terms of their response to environmental stresses such as pH and temperature.

Protein-excipient interactions: mechanisms and biophysical characterization applied to protein formulation development

The purpose of this review is to demonstrate the critical importance of understanding protein-excipient interactions as a key step in the rational design of formulations to stabilize and deliver protein-based therapeutic drugs and vaccines. Biophysical methods used to examine various molecular interactions between solutes and protein molecules are discussed with an emphasis on applications to pharmaceutical excipients in terms of their effects on protein stability. Key mechanisms of protein-excipient interactions such as electrostatic and cation-pi interactions, preferential hydration, dispersive forces, and hydrogen bonding are presented in the context of different physical states of the formulation such as frozen liquids, solutions, gels, freeze-dried solids and interfacial phenomenon. An overview of the different classes of pharmaceutical excipients used to formulate and stabilize protein therapeutic drugs is also presented along with the rationale for use in different dosage forms including practical pharmaceutical considerations. The utility of high throughput analytical methodologies to examine protein-excipient interactions is presented in terms of expanding formulation design space and accelerating experimental timelines.

Interactions of formulation excipients with proteins in solution and in the dried state

A variety of excipients are used to stabilize proteins, suppress protein aggregation, reduce surface adsorption, or to simply provide physiological osmolality. The stabilizers encompass a wide variety of molecules including sugars, salts, polymers, surfactants, and amino acids, in particular arginine. The effects of these excipients on protein stability in solution are mainly caused by their interaction with the protein and the container surface, and most importantly with water. Some excipients stabilize proteins in solution by direct binding, while others use a number of fundamentally different mechanisms that involve indirect interactions. In the dry state, any effects that the excipients confer to proteins through their interactions with water are irrelevant, as water is no longer present. Rather, the excipients stabilize proteins through direct binding and their effects on the physical properties of the dried powder. This review will describe a number of mechanisms by which the excipients interact with proteins in solution and with various interfaces, and their effects on the physical properties of the dried protein structure, and explain how the various interaction forces are related to their observed effects on protein stability.

A polypeptide "building block" for the β-trefoil fold identified by "top-down symmetric deconstruction"

Fibroblast growth factor-1, a member of the 3-fold symmetric β-trefoil fold, was subjected to a series of symmetric constraint mutations in a process termed "top-down symmetric deconstruction." The mutations enforced a cumulative exact 3-fold symmetry upon symmetrically equivalent positions within the protein and were combined with a stability screen. This process culminated in a β-trefoil protein with exact 3-fold primary-structure symmetry that exhibited excellent folding and stability properties. Subsequent fragmentation of the repeating primary-structure motif yielded a 42-residue polypeptide capable of spontaneous assembly as a homotrimer, producing a thermostable β-trefoil architecture. The results show that despite pronounced reduction in sequence complexity, pure symmetry in the design of a foldable, thermostable β-trefoil fold is possible. The top-down symmetric deconstruction approach provides a novel alternative means to successfully identify a useful polypeptide "building block" for subsequent "bottom-up" de novo design of target protein architecture.

Calcium sulfate spinal cord scaffold: a study on degradation and fibroblast growth factor 1 loading and release

Currently, there is no regenerative strategy for the spinal cord that is part of clinical standard of core. Current paths usually include combinations of scaffold materials and active molecules. In a recent study, a permanent dental resin scaffold for treatment of spinal cord injury was designed. The results from studies on rats were promising. However, for potential clinical use, a biodegradable scaffold material that facilitates drug delivery and the regeneration of the spinal cord needs to be developed. Also a biodegradable material is expected to allow a better evaluation of the efficacy of the surgical method. In this article, the suitability of hardened calcium sulfate cement (CSC) for use as degradable spinal cord scaffolds is investigated in bench studies and in vitro studies. Compressive strength, degradation and microstructure, and the loading capability of heparin-activated fibroblast growth factor 1 (FGF1) via soaking were evaluated. The CSC could easily be injected into the scaffold mold and the obtained scaffolds had sufficient strength to endure the loads applied during surgery. When hardened, the CSC formed a porous microstructure suitable for loading of active substances. It was shown that 10 min of FGF1 soaking was enough to obtain a sustained active FGF1 release for 20-35 days. The results showed that CSC is a promising material for spinal cord scaffold fabrication, since it is biodegradable, has sufficient strength, and allows loading and controlled release of active FGF1.

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.

Therapeutic application of peptides and proteins: parenteral forever?

Varied therapeutic peptides and proteins represent a rapidly growing part of marketed drugs and have an undisputed place alongside other established therapies. Nevertheless, such biodrugs have several drawbacks that hinder their therapeutic application. These are undesirable physicochemical properties, such as variable solubility, low bioavailability and limited stability. These issues can be overcome by addition of stabilizing agents and directed injectable administration, which can however result in low patient compliance. Hence, there is a drive in the biotechnology industry to produce needle-free and more user-friendly drugs, and this has led to the growth of nano-enabled drug delivery systems in the last decade. As discussed here, nanobiotechnology is becoming a commercially feasible and promising opportunity for oral, pulmonary and transdermal administration routes.

Molecular crowding and solvation: direct and indirect impact on protein reactions

The typical environment for biomolecules in vivo is highly crowded. Under such conditions chemical activities, rather than simply concentrations, govern the behavior of the molecules. In this chapter we discuss the underlying solvation principles that give rise to the chemical activities. We focus on simple experimentally accessible examples, macromolecular crowding, protein folding, and ligand binding under crowded conditions. We discuss effects of high concentrations of both macromolecules and small molecules in terms of the Kirkwood-Buff theory, which couples solution structure to thermodynamics.

Past, present, and future technologies for oral delivery of therapeutic proteins

Biological drugs are usually complex proteins and cannot be orally delivered due to problems related to degradation in the acidic and protease-rich environment of the gastrointestinal (GI) tract. The high molecular weight of these drugs often results in poor absorption into the periphery when administered orally. The most common route of administration for these therapeutic proteins is injection. Most of these proteins have short serum half-lives and need to be administered frequently or in high doses to be effective. So, difficulties in the administration of protein-based drugs provides the motivation for developing drug delivery systems (DDSs) capable of maintaining therapeutic drug levels without side effects as well as traversing the deleterious mucosal environment. Employing a polymer as an entrapment matrix is a common feature among the different types of systems currently being pursued for protein delivery. Protein release from these matrices can occur through various mechanisms, such as diffusion through or erosion of the polymer matrix, and sometimes a combination of both. Encapsulation of proteins in liposomes has also been a widely investigated technology for protein delivery. All of these systems have merit and our worthy of pursuit.

Phosphatidylserine containing liposomes reduce immunogenicity of recombinant human factor VIII (rFVIII) in a murine model of hemophilia A

Factor VIII (FVIII) is a multidomain protein that is deficient in hemophilia A, a clinically important bleeding disorder. Replacement therapy using recombinant human FVIII (rFVIII) is the main therapy. However, approximately 15-30% of patients develop inhibitory antibodies that neutralize rFVIII activity. Antibodies to epitopes in C2 domain, which is involved in FVIII binding to phospholipids, are highly prevalent. Here, we investigated the effect of phosphatidylserine (PS)-containing liposomes, which bind to C2 domain with high affinity and specificity, upon the immunogenicity of rFVIII. Circular dichroism studies showed that PS-containing liposomes interfered with aggregation of rFVIII. Immunogenicity of free- versus liposomal-rFVIII was evaluated in a murine model of hemophilia A. Animals treated with s.c. injections of liposomal-rFVIII had lower total- and inhibitory titers, compared to animals treated with rFVIII alone. Antigen processing by proteolytic enzymes was reduced in the presence of liposomes. Animals treated with s.c. injections of liposomal-rFVIII showed a significant increase in rFVIII plasma concentration compared to animals that received rFVIII alone. Based on these studies, we hypothesize that specific molecular interactions between PS-containing bilayers and rFVIII may provide a basis for designing lipidic complexes that improve the stability, reduce the immunogenicity of rFVIII formulations, and permit administration by s.c. route.

Effects of Solutes on Empirical Phase Diagrams of Human Fibroblast Growth Factor 1

A variety of solutes are commonly used to increase the stability of protein in therapeutic formulations. An empirical phase diagram approach is used to evaluate the effects of different types of additives on the solution behavior of a protein of pharmaceutical interest, human fibroblast growth factor 1 (FGF-1). A specific stabilizer, heparin, and a nonspecific stabilizer, sucrose, were used in this work. The protein was characterized as a function of pH (3-8) and temperature (10-85 degrees C) using Far-UV circular dichroism (Far-UV CD), intrinsic and extrinsic fluorescence as well as second derivative UV absorption spectroscopy. Empirical phase diagrams were constructed to summarize the biophysical characterization data obtained with FGF-1 alone, in the presence of a threefold weight excess of heparin (3x heparin) or 10% sucrose (w/v). Three phases are observed in the low temperature regions at pH 3, 4, and 5-8. Phase boundaries corresponding to major heat-induced transitions are detected in the physiological temperature range. The highest thermal stabilities are observed near neutral pH (pH 6 and 7). Both heparin and sucrose appear to enhance the thermal stability of FGF-1, although their effects on the phase diagram are quite distinct. The greatest stabilization is observed at pH 8. Only heparin appears to protect FGF-1 from acid-induced unfolding to any extent.

Effect of Polyanions on the Structure and Stability of Repifermin™ (Keratinocyte Growth Factor-2)

The interaction of several of the fibroblast growth factors (FGFs) with polyanions is thought to be of physiological significance and has been exploited to create more stable pharmaceutical formulations of FGF-1 and -2. The extent of such phenomena throughout the 23-member FGF family is, however, unknown. In these studies, we examine the effect of several polyanions on the structure and stability of keratinocyte growth factor 2 (KGF-2, FGF-10), a candidate for use as a wound-healing agent. Employing a variety of methods sensitive to the protein's structure including circular dichroism (CD), intrinsic fluorescence, derivative near-UV absorption spectroscopy, bis-ANS (4,4'-dianilino-1,1'-binaphthyl-5,5-disulfonic acid) fluorescence, differential scanning calorimetry (DSC), and dynamic light scattering (DLS), we find that a variety of polyanions (e.g., heparin, sucrose octasulfate (SOS), and inositol hexaphosphate (IHP)) stabilize KGF-2 by increasing the thermal-unfolding temperature by approximately 9-15 degrees C. Negatively charged liposomes produce a similar effect, arguing for relatively nonspecific interactions of polyanions with KGF-2. Unlike some other FGFs, no evidence for the presence of a molten globule state is found during thermal perturbation of this growth factor. The generality of this polyanion/protein interaction is discussed as well as its potential role in various cellular events such as protein folding and transport.

A network-based analysis of polyanion-binding proteins utilizing human protein arrays

The existence of interactions between many cellular proteins and various polyanionic surfaces within a cell is now well established. The functional role of such interactions, however, remains to be clearly defined. The existence of protein arrays, with a large selection of different kinds of proteins, provides a way to better address a number of aspects of this question. We have therefore investigated the interaction between five cellular polyanions (actin, tubulin, heparin, heparan sulfate, and DNA) and approximately 5,000 human proteins using protein microarrays in an attempt to better understand the functional nature of such interaction(s). We demonstrate that a large number of polyanion-binding proteins exist that contain multiple positively charged regions, are often disordered, are involved in phosphorylation processes, and appear to play a role in protein-protein interaction networks. Considering the crowded nature of cellular interiors, we propose that polyanion-binding proteins interact with a wide variety of polyanionic surfaces in cells in a functionally significant manner.

A Network-based Analysis of Polyanion-binding Proteins Utilizing Yeast Protein Arrays

The high affinity of certain cellular polyanions for many proteins (polyanion-binding proteins (PABPs)) has been demonstrated previously. It has been hypothesized that such polyanions may be involved in protein structure stabilization, stimulation of folding through chaperone-like activity, and intra- and extracellular protein transport as well as intracellular organization. The purpose of the proteomics studies reported here was to seek evidence for the idea that the nonspecific but high affinity interactions of PABPs with polyanions have a functional role in intracellular processes. Utilizing yeast protein arrays and five biotinylated cellular polyanion probes (actin, tubulin, heparin, heparan sulfate, and DNA), we identified proteins that interact with these probes and analyzed their structural and amino acid sequence requirements as well as their predicted functions in the yeast proteome. We also provide evidence for the existence of a network-like system for PABPs and their potential roles as critical hubs in intracellular behavior. This investigation takes a first step toward achieving a better understanding of the nature of polyanion-protein interactions within cells and introduces an alternative way of thinking about intracellular organization.

Interaction of dicaproyl phosphatidylserine with recombinant factor VIII and its impact on immunogenicity

Replacement therapy with exogenous recombinant factor VIII (rFVIII) to control bleeding episodes results in the development of inhibitory antibodies in 15% to 30% of hemophilia A patients. The inhibitory antibodies are mainly directed against specific and universal immunodominant epitopes located in the C2 domain. Previously we have shown that complexation of O-phospho-L-serine (phosphatidylserine head group) with the phospholipid binding region of the C2 domain can lead to an overall reduction in the immunogenicity of rFVIII. Here, we have investigated the hypothesis that dicaproyl phosphatidylserine, a short-chain water-soluble phospholipid, can reduce the immunogenicity of rFVIII. Circular dichroism and fluorescence spectroscopy studies suggest that dicaproyl phosphatidylserine interacts with rFVIII, causing subtle changes in the tertiary and secondary structure of the protein. Sandwich enzyme-linked immunosorbent assay studies indicate that dicaproyl phosphatidylserine probably interacts with the phospholipid binding region of the C2 domain. The immunogenicity of FVIII-dicaproyl phosphatidylserine complexes prepared at concentrations above and below the critical micellar concentrations of the lipid were evaluated in hemophilia A mice. Our results suggest that micellar dicaproyl phosphatidylserine may be useful to reduce the immunogenicity of rFVIII preparations.

Influence of aggregation on immunogenicity of recombinant human Factor VIII in hemophilia A mice

Recombinant human factor VIII (rFVIII), a multidomain glycoprotein is used in replacement therapy for treatment of hemophilia A. Unfortunately, 15%-30% of the treated patients develop inhibitory antibodies. The pathogenesis of antibody development is not completely understood. The presence of aggregated protein in formulations is generally believed to enhance the immune response. rFVIII has a tendency to aggregate but the effect of such aggregation on the immunogenicity of rFVIII is not known. We have, therefore, characterized aggregated rFVIII produced by thermal stress and evaluated its effect on the immunogenicity of rFVIII in hemophilia A mice. Aggregated rFVIII alone and mixtures of rFVIII with aggregated rFVIII were less immunogenic than native rFVIII. In vitro Th-cell proliferation studies and cytokine analyses conducted on splenocytes obtained from immunized animals suggest that aggregated rFVIII behaves as a unique antigen compared to native monomeric rFVIII. The antigenic properties of the aggregated and native rFVIII were compared using ELISAs (epitope availability) and cathepsin-B (an antigen processing enzyme) digestion. The data suggest significant differences in the antigenic properties of rFVIII and aggregated rFVIII. Overall it appears that aggregated rFVIII does not enhance the immunogenicity (inhibitor development) of rFVIII in hemophilia A mice but rather acts as a distinct antigen.

Enhanced stability of recombinant keratinocyte growth factor by mutagenesis

Native sequence keratinocyte growth factor (KGF) is fairly unstable, as manifested by the loss of the monomeric native protein accompanied by the accumulation of aggregated species during storage at moderate temperatures. Several different types of analogs were generated and the storage stability of the protein assessed. In the first type of analog one or more of the five cysteinyl residues in KGF were replaced; in the second class the N-terminal residues that included the first disulfide bond were deleted. Both of these types of analogs involved removal of the disulfide bond between cysteines 1 and 15. The third group involved mutating one of the basic amino acids located in a cluster of positive charges (involved in heparin binding) around Arg144 to a neutral or acidic amino acyl residue. Among the cysteine replacement analogs, the double mutation of Cys1 and 15 to Ser resulted in significantly increased stability without compromising the mitogenic activity, while Cys to Ser mutations at other positions were either destabilizing or had no effect. Deletion of the 15, 23 or 27 N-terminal amino acyl residues also increased the stability of the protein. The activity of the analogs was not affected by the deletion of 15 or 23 amino acids, but it was significantly decreased upon removal of the 27 N-terminal amino acyl residues. Much greater stability was achieved by mutation of the basic amino acids, especially Arg144, to Glu or Gln, but this increase in stability was accompanied by large decrease in activity. The analog with the 23 N-terminal amino acyl residues deleted represents one of the best compromises between increased stability and retention of activity.

Minimization of aggregation of secreted bivalent anti-human T cell immunotoxin in Pichia pastoris bioreactor culture by optimizing culture conditions for protein secretion

In a bioreactor culture of genetically engineered Pichia pastoris secreting a bivalent immunotoxin, 64% of the secreted immunotoxin was present in aggregate forms and this resulted in a loss of bioactivity. Biochemical analyses of the secreted immunotoxin and an in vitro aggregation study using purified monomeric immunotoxin suggested that aggregation was primarily an extracellular event. By employing limited methanol feeding at 0.75 mlmin(-1) per 10l initial medium, oxygen consumption was reduced, permitting a lowering of the bioreactor agitation speed from 800 to 400 rpm. By increasing the anti-foam reagent to 0.6 mll(-1), the thickness of the air/liquid interfacial foam layer was reduced by 80%. These steps reduced the immunotoxin aggregates from 64% to 5%. Consequently immunotoxin purification yield was increased from 53.0% to 73.8%. Simultaneously this methodology enhanced immunotoxin secretion to 120 mgl(-1) at 163 h of methanol induction in a toxin resistant production strain. We conclude that minimizing shearing force and reducing the air/liquid interfacial foam area are crucial factors in reducing hydrophobic protein aggregation upon secretory expression in yeast bioreactor cultures.

Lipid binding region (2303-2332) is involved in aggregation of recombinant human FVIII (rFVIII)

Factor VIII (FVIII) is a multi-domain protein that is important in the clotting cascade. Its deficiency causes Hemophilia A, a bleeding disorder. The unfolding of protein domains can lead to physical instability such as aggregation, and hinder their use in replacement therapy. It has been shown that the aggregation of rFVIIII is initiated by small fluctuations in the protein's tertiary structure (Grillo et al., 2001, Biochemistry 40:586-595). We have investigated the domain(s) involved in the initiation of aggregation using circular dichroism (CD), size exclusion chromatography (SEC), fluorescence anisotropy, domain specific antibody binding, and clotting activity studies. The studies indicated that aggregation may be initiated as a result of conformational change in the C2 domain encompassing the lipid-binding region (2303-2332). The presence of O-phospho-L-Serine (OPLS), which binds to the lipid-binding region of FVIII, prevented aggregation of the protein.

Stabilization of somatropin by heparin

Somatropin, human growth hormone (hGH), is an unstable protein, posing challenging problems for its formulation and long-term stability. Since hGH formed insoluble adducts with heparin our aim was to evaluate heparin as a stabilizing agent for the drug. These adducts were characterized by particle diameter, tertiary structure variations and release studies. Studies were also carried out to determine the stability of hGH in the presence and absence of heparin by an interfacial denaturation method and real-time stability studies by measuring hGH activity and particle diameter. Moreover, biological activity of hGH and hGH/UH (unfractionated heparin) adducts was identified by daily subcutaneous injections to hypophysectomized rats. There was a decrease in mean hydrodynamic particle diameter of hGH/UH adducts with increased pH (54.4 to 12.2 nm from pH 3 to pH 7) indicating that the adducts were either dissociating or dissolving at high pH. Furthermore, second-derivative spectroscopy indicated that complexation of hGH with heparin did not cause a major disruption in the tertiary structure of hGH but decreased the hydrophilic environment around the tyrosine residues. Release of hGH from hGH/UH adducts was pH and ionic strength dependent with the highest release at pH 8 (93%) and lowest release at pH 3 (0%) over the first hour. Interfacial denaturation methods indicated that vortex agitation over 120 s resulted in no change in the optical density of hGH/UH adducts compared with a substantial increase for hGH alone at pH 6.8. Real-time stability studies over 93 days demonstrated that hGH/UH adducts at both pH 3 and 7 with an excess of heparin produced the highest percent of active hGH remaining in the solution at 4 degrees C and 37 degrees C. The higher stability of hGH/UH adducts with excess heparin compared with the stoichiometric ratio was also confirmed by particle size measurements during storage. The biological activity of these adducts was comparable with hGH alone by weight-gain studies in hypophysectomized rats. The findings suggest the value of using hGH/heparin adducts to stabilize the protein.

Lower inhibitor development in hemophilia A mice following administration of recombinant factor VIII-O-phospho-L-serine complex

Factor VIII is a multidomain protein composed of A1, A2, B, A3, C1, and C2 domains. Deficiency or dysfunction of factor VIII causes hemophilia A, a bleeding disorder. Administration of exogenous recombinant factor VIII as a replacement leads to development of inhibitory antibodies against factor VIII in 15-30% of hemophilia A patients. Hence, less immunogenic preparations of factor VIII are highly desirable. Inhibitory antibodies against factor VIII are mainly directed against immunodominant epitopes in C2, A3, and A2 domains. Further, several universal epitopes for CD4+ T-cells have been identified within the C2 domain. The C2 domain is also known to interact specifically with phosphatidylserine-rich lipid vesicles. Here, we have investigated the hypothesis that complexation of O-phospho-l-serine, the head group of phosphatidylserine, with the C2 domain can reduce the overall immunogenicity of factor VIII. The biophysical (circular dichroism and fluorescence) and biochemical studies (ELISA and size exclusion chromatography) showed that O-phospho-l-serine binds to the phospholipid-binding region in the C2 domain, and this interaction causes subtle changes in the tertiary structure of the protein. O-Phospho-l-serine also prevented aggregation of the protein under thermal stress. The immunogenicity of the factor VIII-O-phospho-l-serine complex was evaluated in hemophilia A mice. The total and inhibitory antibody titers were lower for factor VIII-O-phospho-l-serine complex compared with factor VIII alone. Moreover, factor VIII administered as a complex with O-phospho-l-serine retained in vivo activity in hemophilia A mice. Our results suggest that factor VIII-O-phospho-l-serine complex may be beneficial to increase the physical stability and reduce immunogenicity of recombinant factor VIII preparations.

An investigation of the long-term bioactivity of endogenous growth factor in OASIS Wound Matrix

OBJECTIVE

To examine the retention and bioactivity of endogenous FGF-2 after prolonged storage within a complex matrix. FGF-2 is a growth factor found in OASIS Wound Matrix, a purified collagen wound-care product containing other endogenous components of the extracellular matrix.

METHOD

FGF-2 content was measured by ELISA. FGF-2 activity was measured using an in vitro bioassay in rat pheochromocytoma (PC12) cells.

RESULTS

FGF-2 content ranged from 15.3 ng/g to 84.3 ng/g. The bioassay showed that the FGF-2 retained in the matrix was present in a bioactive form able to cause differentiation of cells in culture.

CONCLUSION

The results demonstrate that wound-care products can be developed to retain their bioactivity over time and that inherently unstable purified growth factors are preserved if stored as bound factors within their natural extracellular matrix. The results also suggest that use of acellular matrices containing active growth factors would have advantages in terms of simplicity and cost over purified recombinant growth factor therapies.

Protein aggregation and its inhibition in biopharmaceutics

Protein aggregation is arguably the most common and troubling manifestation of protein instability, encountered in almost all stages of protein drug development. Protein aggregation, along with other physical and/or chemical instabilities of proteins, remains to be one of the major road barriers hindering rapid commercialization of potential protein drug candidates. Although a variety of methods have been used/designed to prevent/inhibit protein aggregation, the end results are often unsatisfactory for many proteins. The limited success is partly due to our lack of a clear understanding of the protein aggregation process. This article intends to discuss protein aggregation and its related mechanisms, methods characterizing protein aggregation, factors affecting protein aggregation, and possible venues in aggregation prevention/inhibition in various stages of protein drug development.

Symmetric Primary and Tertiary Structure Mutations within a Symmetric Superfold: A Solution, not a Constraint, to Achieve a Foldable Polypeptide

In previous studies designed to increase the primary structure symmetry within the hydrophobic core of human acidic fibroblast growth factor (FGF-1) a combination of five mutations were accommodated, resulting in structure, stability and folding kinetic properties similar to wild-type (despite the symmetric constraint upon the set of core residues). A sixth mutation in the core, involving a highly conserved Met residue at position 67, appeared intolerant to substitution. Structural analysis suggested that the local packing environment of position 67 involved two regions of apparent insertions that distorted the tertiary structure symmetry inherent in the beta-trefoil architecture. It was postulated that a symmetric constraint upon the primary structure within the core could only be achieved after these insertions had been deleted (concomitantly increasing the tertiary structure symmetry). The deletion of these insertions is now shown to permit mutation of position 67, thereby increasing the primary structure symmetry relationship within the core. Furthermore, despite the imposed symmetric constraint upon both the primary and tertiary structure, the resulting mutant form of FGF-1 is substantially more stable. The apparent inserted regions are shown to be associated with heparin-binding functionality; however, despite a marked reduction in heparin-binding affinity the mutant form of FGF-1 is surprisingly approximately 70 times more potent in 3T3 fibroblast mitogenic assays. The results support the hypothesis that primary structure symmetry within a symmetric protein superfold represents a possible solution, rather than a constraint, to achieving a foldable polypeptide.

Physical stability of proteins in aqueous solution: mechanism and driving forces in nonnative protein aggregation

Irreversible protein aggregation is problematic in the biotechnology industry, where aggregation is encountered throughout the lifetime of a therapeutic protein, including during refolding, purification, sterilization, shipping, and storage processes. The purpose of the current review is to provide a fundamental understanding of the mechanisms by which proteins aggregate and by which varying solution conditions, such as temperature, pH, salt type, salt concentration, cosolutes, preservatives, and surfactants, affect this process.

Benzyl Alcohol‐Induced Destabilization of Interferon‐γ: A Study by Hydrogen‐Deuterium Isotope Exchange

The destabilizing effect of a multidose preservative, benzyl alcohol, on IFN-gamma was investigated. Hydrogen-deuterium isotope exchange (HX) detected by mass spectrometry (MS) was used to detect tertiary structure changes and measure global unfolding rates. The experiments showed that tertiary structure changes previously reported using circular dichroism may involve only a limited portion of the protein with the hydrophobic core of the protein remaining intact. Protein unfolding rates measured by hydrogen exchange were very sensitive to benzyl alcohol concentration, and increased markedly when salt was also added. Dynamic light scattering and size-exclusion chromatography showed that a small fraction of the protein formed large aggregates during the first few days. Measurements at longer incubation times (up to 8 days) showed that a significant fraction of protein was trapped in a structure less protected from hydrogen exchange, but not completely unfolded. This fraction of protein may be responsible for the irreversible loss of activity observed in earlier studies.

Polyanions and the proteome

The behavior of the proteome reflects spatial and temporal organization both within and without cells. We propose that various macromolecular entities possessing polyanionic character such as proteoglycans, lipid bilayer surfaces, microtubules, microfilaments, and polynucleotides may provide a functional network that mediates a variety of cellular phenomena. The interaction of proteins with this array of polyanions is characterized by a lower degree of specificity than seen with most commonly recognized macromolecular interactions. In this commentary, potential roles for this polyanion network in diverse functions such as protein/protein interactions, protein folding and stabilization, macromolecular transport, and various disease processes are all considered, as well as the use of polyanions as therapeutic agents. The role of small polyanions in the regulation of protein/polyanion interactions is also postulated. We provide preliminary experimental analysis of the extent to which proteins interact with polyanions inside cells using a combination of two-dimensional chromatographic and electrophoretic methods and antibody arrays. We conclude that many hundreds to thousands of such interactions are present in cells and argue that future understanding of the proteome will require that the "polyanion world" be taken into account.

Long-term stabilization of recombinant human interferon alpha 2b in aqueous solution without serum albumin

The development of parenteral solution dosage forms of interferon alpha 2 (rhIFN-alpha2) without human albumin may significantly diminish the problem of forming highly immunogenic rhIFN-alpha 2b aggregates and the potential risk of blood-transmitted diseases caused by infectious viruses and often living pathogens that may be present in the plasma. With this purpose, we evaluated the compatibility of type I borosilicate glass vials and chlorobutyl stoppers with rhIFN-alpha 2b in an aqueous solution. At the same time, we carried out a targeted formulation screen at 37 degrees C of single or combined (e.g. polysorbate 80, EDTA Na(2), PEG 400) potentially stabilizing excipients. Quantified biochemical results from 12 independent batches of rhIFN-alpha 2b in a polysorbate/benzyl alcohol-based vehicle formulated at pH 7.4 were all found within the limits established by the World Health Organization for this cytokine. Real-time storage data confirmed the excellent biochemical long-term (30 months) stability of rhIFN-alpha 2b in this aqueous solution formulation. Analyses were performed at intervals throughout the time period using reverse-phase high-performance liquid chromatography, a sandwich-type enzyme-linked immunosorbent assay, and antiviral activity as stability-indicating assays. Furthermore, both the physical stability (color, odor, appearance, pH, and absence of particulate material) and the sterility of this formulation were maintained under the proposed shelf conditions.

Biodegradable microspheres for protein delivery

In a very short time, since their emergence, the field of controlled delivery of proteins has grown immensely. Because of their relatively large size, they have low transdermal bioavailabilities. Oral bioavailability is generally poor since they are poorly absorbed and easily degraded by proteolytic enzymes in the gastrointestinal tract. Ocular and nasal delivery is also unfavorable due to degradation by enzymes present in eye tissues and nasal mucosa. Thus parenteral delivery is currently most demanding and suitable for delivery of such molecules. In systemic delivery of proteins, biodegradable microspheres as parenteral depot formulation occupy an important place because of several aspects like protection of sensitive proteins from degradation, prolonged or modified release, pulsatile release patterns. The main objective in developing controlled release protein injectables is avoidance of regular invasive doses which in turn provide patient compliance, comfort as well as control over blood levels. This review presents the outstanding contributions in field of biodegradable microspheres as protein delivery systems, their methods of preparation, drug release, stability, interaction with immune system and regulatory considerations.