Stabilization of basic fibroblast growth factor with dextran sulfate

Computer-aided engineering of stabilized fibroblast growth factor 21

FGF21 is an endocrine signaling protein belonging to the family of fibroblast growth factors (FGFs). It has emerged as a molecule of interest for treating various metabolic diseases due to its role in regulating glucogenesis and ketogenesis in the liver. However, FGF21 is prone to heat, proteolytic, and acid-mediated degradation, and its low molecular weight makes it susceptible to kidney clearance, significantly reducing its therapeutic potential. Protein engineering studies addressing these challenges have generally shown that increasing the thermostability of FGF21 led to improved pharmacokinetics. Here, we describe the computer-aided design and experimental characterization of FGF21 variants with enhanced melting temperature up to 15 °C, uncompromised efficacy at activation of MAPK/ERK signaling in Hep G2 cell culture, and ability to stimulate proliferation of Hep G2 and NIH 3T3 fibroblasts cells comparable with FGF21-WT. We propose that stabilizing the FGF21 molecule by rational design should be combined with other reported stabilization strategies to maximize the pharmaceutical potential of FGF21.

Acceleration of Bone Healing by In Situ-Forming Dextran-Tyramine Conjugates Containing Basic Fibroblast Growth Factor in Mice

An enzymatic crosslinking strategy using hydrogen peroxide (H₂O₂) and horseradish peroxidase (HRP) has been receiving increasing attention for use with in situ-formed hydrogels (IFHs). Several studies have reported the application of IFHs in cell delivery and tissue engineering. IFHs may also be ideal carrier materials for bone repair, although their potential as a carrier for basic fibroblast growth factor (bFGF) has yet to be evaluated. Here, we examined the effect of an IFH made of dextran (Dex)-tyramine (TA) conjugates (IFH-Dex-TA) containing bFGF in promoting bone formation in a fracture model in mice. Immediately following a fracture procedure, animals either received no treatment (control) or an injection of IFH-Dex-TA/phosphate-buffered saline (IFH-Dex-TA/PBS) or IFH-Dex-TA containing 1 μg bFGF (IFH-Dex-TA/bFGF) into the fracture site (n=10, each treatment). Fracture sites injected with IFH-Dex-TA/bFGF showed significantly greater bone volume, mineral content, and bone union than sites receiving no treatment or treated with IFH-Dex-TA/PBS alone (each n=10). This Dex-TA gel may be an effective drug delivery system for optimizing bFGF therapy.

Local pharmacological induction of angiogenesis: Drugs for cells and cells as drugs

The past decades have seen significant advances in pro-angiogenic strategies based on delivery of molecules and cells for conditions such as coronary artery disease, critical limb ischemia and stroke. Currently, three major strategies are evolving. Firstly, various pharmacological agents (growth factors, interleukins, small molecules, DNA/RNA) are locally applied at the ischemic region. Secondly, preparations of living cells with considerable bandwidth of tissue origin, differentiation state and preconditioning are delivered locally, rarely systemically. Thirdly, based on the notion, that cellular effects can be attributed mostly to factors secreted in situ, the cellular secretome (conditioned media, exosomes) has come into the spotlight. We review these three strategies to achieve (neo)angiogenesis in ischemic tissue with focus on the angiogenic mechanisms they tackle, such as transcription cascades, specific signalling steps and cellular gases. We also include cancer-therapy relevant lymphangiogenesis, and shall seek to explain why there are often conflicting data between in vitro and in vivo. The lion's share of data encompassing all three approaches comes from experimental animal work and we shall highlight common technical obstacles in the delivery of therapeutic molecules, cells, and secretome. This plethora of preclinical data contrasts with a dearth of clinical studies. A lack of adequate delivery vehicles and standardised assessment of clinical outcomes might play a role here, as well as regulatory, IP, and manufacturing constraints of candidate compounds; in addition, completed clinical trials have yet to reveal a successful and efficacious strategy. As the biology of angiogenesis is understood well enough for clinical purposes, it will be a matter of time to achieve success for well-stratified patients, and most probably with a combination of compounds.

Effect of a dextran derivative associated with TGF-β1 or FGF-2 on dermal fibroblast behaviour in dermal equivalents

Dextran derivatives that mimic the action of heparin have been shown to protect heparin-binding growth factors, such as Transforming Growth Factor-beta1 (TGF-beta1) and Fibroblast Growth Factor-2 (FGF-2). The aim of this study was to investigate the effect of LS21 DMCBSu, a dextran derivative which contains methylcarboxylate, benzylamide and sulfate groups, both by itself and when combined with TGF-beta1 and FGF-2, on the behaviour of fibroblasts. Two systems were assessed: a monolayer culture and three-dimensional collagenous matrices (dermal equivalent). Polymeric biomaterial LS21 DMCBSu and LS21 DMCBSu associated with either TGF-beta1 or FGF-2, were added to the monolayer culture on day 3. After 7 days of culture the number of cells was determined. Two treatments were carried out on the dermal equivalents: 9 days of treatment from day 0 to day 9 of culture and 9 days of treatment from day 21 to day 30 of culture for the premature and the mature dermal equivalents respectively. In the monolayer culture, the bioactive polymer produced a slight increase in fibroblast growth (10% with 10 microg/ml of LS21 DMCBSu) and promoted the stimulating effect of the growth factors on cell growth. In the premature dermal equivalents growth was stimulated by 20% when 10 microg/ml LS21 DMCBSu was added. The dextran derivative mixed with TGF-beta1 slightly inhibited the growth effect of the growth factor in the dermal equivalents. The functionalized dextran with FGF-2 enhanced the stimulating effect of the growth factor in the premature dermal equivalent. A significant increase in cell growth was observed with the fibroblasts treated with the FGF-2 LS21 DMCBSu mixture and FGF-2 (51% and 40%, respectively). However, none of the described treatments affected the cell growth in the mature dermal equivalent. Furthermore, the dextran derivative had no effect on dermal contraction under these experimental conditions (3D culture).

Controlled release of vascular endothelial growth factor from alginate hydrogels nano-coated with polyelectrolyte multilayer films

Alginate (ALG) hydrogels incorporating vascular endothelial growth factor (VEGF) were nano-coated with polyelectrolyte multilayer (PEM) films composed of chitosan (CT) and dextran sulfate (DEX) in order to control the VEGF release from the hydrogels. When non- and nano-coated ALG hydrogels containing VEGF were incubated in phosphate-buffered saline (PBS) at 37 degrees C for the prescribed times, the nano-coated hydrogels were stable, even after incubation for a week, whereas the non-coated hydrogels collapsed after 6 h. The release profile of VEGF from the non- and nano-coated ALG hydrogels was evaluated by an enzyme-linked immunosorbent assay (ELISA). Although all of the VEGF incorporated into the non-coated ALG hydrogels was released within 6 h by the collapse, only a few percent of the VEGF incorporated in the nano-coated hydrogels was released. Furthermore, the incorporated VEGF in the nano-coated hydrogels was released continuously, even after a month, without any initial burst release. The release percentage of VEGF was easily controlled by the PEM film thickness on the surface of the ALG hydrogels. The VEGF released from the nano-coated hydrogels retained its activity without denaturation. Consequently, the nano-coating of hydrogel surfaces with PEM films may be useful for controlled and sustained drug-delivery systems.

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.

Applying macromolecular crowding to enhance extracellular matrix deposition and its remodeling in vitro for tissue engineering and cell-based therapies

With the advent of multicellular organisms, the exterior of the cells evolved dramatically from highly aqueous surroundings into an extracellular matrix and space crowded with macromolecules. Cell-based therapies require removal of cells from their crowded physiological context and propagating them in dilute culture medium to attain therapeutically relevant numbers whilst preserving their phenotype. However, bereft of their microenvironment, cells under perform and lose functionality. Major efforts currently aim to modify cell culture surfaces and build three dimensional scaffolds to improve this situation. We discuss here alternative strategies that enable cells to re-create their own microenvironment in vitro, using carbohydrate-based macromolecules as culture media additives that create an excluded volume effect at defined fraction volume occupancies. This biophysical approach dramatically enhances extracellular matrix deposition by differentiated cells and stem cells, and boosts progenitor cell differentiation and proliferation. We begin to understand how well cells really can perform ex vivo if given the chance.

Thiol-modified chitosan sulfate nanoparticles for protection and release of basic fibroblast growth factor

A series of chitosan (CS) derivatives, the 6-O-carboxymethylchitosan (6-O-CC), 2-N sulfated 6-O-carboxymethylchitosan (N-SOCC) and the 2-N and 3,6-O sulfated 6-O-carboxymethyl chitosan (N,O-SOCC) were synthesized in this study. The chemical structures and the degrees of substituted carboxymethyl and sulfate groups of the synthesized compounds were respectively determined by FT-IR spectra and elemental analysis. N,O-SOCC displayed the highest protective efficiency for basic fibroblast growth factor (bFGF) as examined by the L929 fibroblast culture test and docking simulation. N,O-SOCC-4-thio-butylamidine (TBA) conjugates prepared by modification of N,O-SOCC with 2-iminothiolane were in situ cross-linkable. The degrees of thiol substitution of the 2-iminothiolane modified N,O-SOCC polymers were determined to be in the ranges of 45.9 +/- 3.7 and 415.6 +/- 12.5 micromol SH/g SOCC by quantifying the amount of thiol groups on the thiolated polymers with Ellman's reagent. The 2-iminothiolane modified N,O-SOCC and CS complex could be used for preparing nanoparticles by a polyelectrolyte self-assembly method, and the release of bFGF from the nanoparticles was successfully controlled. L929 fibroblast culture tests showed that the thiol modified N,O-SOCC/CS nanoparticles could effectively protect bFGF from inactivation over a 120 h period. The results of this study suggest that the thiol modified N,O-SOCC/CS nanoparticles may be useful as novel materials for specific delivery of bFGF with mitogenic activity.

Release of model proteins and basic fibroblast growth factor from in situ forming degradable dextran hydrogels

Our previous studies showed that degradable dextran hydrogels are rapidly formed in situ upon mixing aqueous solutions of dextran vinyl sulfone (dex-VS) conjugates and tetrafunctional mercapto poly(ethylene glycol) (PEG-4-SH) by Michael addition. The hydrogel degradation time and storage modulus could be controlled by the degree of vinyl sulfone substitution (DS) and dextran molecular weight. The degradation time could further be adjusted by the spacer between the thioether and the ester bond of the dex-VS conjugates (ethyl vs. propyl, denoted as dex-Et-VS and dex-Pr-VS, respectively). In this paper, the release of three model proteins, i.e. immunoglobulin G (d(h)=10.7 nm, IgG), bovine serum albumin (BSA, d(h)=7.2 nm) and lysozyme (d(h)=4.1 nm), as well as basic fibroblast growth factor (bFGF) from these in situ forming dextran hydrogels is studied. Proteins could be easily loaded into the hydrogels by mixing protein containing solutions of dex-VS and PEG-4-SH. The release of IgG from dex-Et-VS hydrogels followed biphasic release kinetics, with a slow, close to first order release for the first 9 days followed by an accelerated release and over 80% of IgG was released in 12 to 25 days. Interestingly, the release of IgG from dex-Pr-VS hydrogels followed close to zero order kinetics, wherein approximately 95% was released in 21 days. The release of BSA from dex-Pr-VS hydrogels followed biphasic kinetics, with almost first order release followed by close to zero order release. Approximately 75% of the entrapped BSA could be released from dex-Pr-VS hydrogels in 16 days. Dex-Pr-VS hydrogels released 40% of lysozyme in 14 days, with full preservation of the enzymatic activity of the released lysozyme, as determined by bacteria lysis experiments. The release of basic fibroblast growth factor (bFGF) from dex-Pr-VS hydrogels showed first order kinetics, with quantitative release in 28 days. These results show that the in situ forming degradable dextran hydrogels can be used for the controlled release of proteins.

Effects of Cyclodextrins on Chemically and Thermally Induced Unfolding and Aggregation of Lysozyme and Basic Fibroblast Growth Factor

Effects of cyclodextrin (CyDs) on unfolding and aggregation of lysozyme and basic fibroblast growth factor (bFGF) were investigated. CyDs inhibited the chemically induced aggregation and its inhibition was generally in the order of gamma-CyDs < alpha-CyDs < beta-CyDs. Among these CyDs, branched beta-CyDs and dimethyl-beta-CyD (DM-beta-CyD) significantly reduced the aggregation of lysozyme. Hydrophilic CyDs reduced the thermally induced unfolding of lysozyme as shown by a decrease in the thermal unfolding temperature (T(m)) value of lysozyme, suggesting that CyDs destabilize native lysozyme or stabilize the unfolded state of lysozyme. In the case of bFGF, branched beta-CyDs showed greater effects on inhibition of the chemically and thermally induced denaturation. Interestingly, sulfobutyl ether beta-CyD (SBE-beta-CyD), which was not effective in case of lysozyme, provided the inhibitory effect for bFGF on the chemically, thermally and acid-induced denaturation, suggesting that both the inclusion and electrostatic interaction may be operative in the inhibition of aggregation of the positively charged protein. The results indicated that the use of CyDs for protein stabilization is dependent not only on the structure and property of CyDs but also on the nature of the denaturing stimuli, and the most appropriate CyD should be used for the stabilization of each protein.

Neprilysin Inhibits Angiogenesis via Proteolysis of Fibroblast Growth Factor-2

Neprilysin is a cell surface peptidase that catalytically inactivates neuropeptide substrates and functions as a tumor suppressor via its enzymatic function and multiple protein-protein interactions. We investigated whether neutral endopeptidase could inhibit angiogenesis in vivo utilizing a murine corneal pocket angiogenesis model and found that it reduced fibroblast growth factor-2-induced angiogenesis by 85% (p < 0.01) but had no effect on that of vascular endothelial growth factor. Treatment with recombinant neprilysin, but not enzymatically inactive neprilysin, resulted in a slight increase in basic fibroblast growth factor electrophoretic mobility from proteolytic cleavage between amino acids Leu-135 and Gly-136, which was inhibited by the neutral endopeptidase inhibitor CGS24592 and heparin. Cleavage kinetics were rapid, comparable with that of other known neprilysin substrates. Functional studies involving neprilysin-expressing vascular endothelial cells demonstrated that neutral endopeptidase inhibition significantly enhanced fibroblast growth factor-mediated endothelial cell growth, capillary array formation, and signaling, whereas exogenous recombinant neprilysin inhibited signaling. Recombinant constructs confirmed that cleavage products neither promoted capillary array formation nor induced signaling. Moreover, mutation of the cleavage site resulted in concomitant loss of cleavage and increased the potency of fibroblast growth factor-2 to induce capillary array formation. These data indicate that neprilysin proteolytically inactivates fibroblast growth factor-2, resulting in negative regulation of angiogenesis.

Anion Binding and Controlled Aggregation of Human Interleukin-1 Receptor Antagonist

Highly concentrated human recombinant interleukin-1 receptor antagonist (IL-1ra) aggregates at elevated temperature without perturbation in its secondary structure. The protein aggregation can be suppressed depending on the buffer ionic strength and the type of anion present in the sample solution. Phosphate is an approximately 4-fold weaker suppressant than either citrate or pyrophosphate on the basis of the measured protein aggregation rates. This is in agreement with the strength of protein-anion interactions at the IL-1ra single anion-binding site as judged by the estimated dissociation constant values of 2.9 mM, 3.8 mM, and 13.7 mM for pyrophosphate, citrate, and phosphate, respectively. The strength of binding also correlates with the anion size and with the number of ionized groups available per molecule at a given pH. Affinity probing of IL-1ra with methyl acetyl phosphate (MAP) in combination with proteolytic digestion and mass spectral analysis show that an anion-binding site location on the IL-1ra surface is contributed by lysine-93 and lysine-96 of the loop 84-98 as well as by lysine-6 of the unstructured N-terminal region 1-7. The replacement of lysine-93 with alanine by site-directed mutagenesis results in dramatically suppressed IL-1ra aggregation. Furthermore, when the unstructured N-terminal region of IL-1ra is removed by limited proteolysis, a 2-fold increase in the time course of the aggregation lag phase is observed for the truncated protein. An anion-controlled mechanism of IL-1ra aggregation is proposed by which the anion competition for the protein cationic site prevents formation of intermolecular cation-pi interactions and, thus, interferes with the protein asymmetric self-association pathway.

Novel Functional Biodegradable Polymer II: Fibroblast Growth Factor-2 Activities of Poly(γ-glutamic acid)-sulfonate

Basic fibroblast growth factor (FGF-2) mitogenic activities of sulfonated poly(gamma-glutamic acid) (gamma-PGA-S) were investigated with chlorate-treated L929 fibroblast culture tests. When 72% of the carboxyl groups in gamma-PGA were sulfonated (gamma-PGA-S72), cell numbers reached a maximum. The activity of gamma-PGA-S72 was higher than that of gamma-PGA and synthetic heparinoids and was almost comparable to that of heparin. Cytotoxicity of gamma-PGA-S72 was not observed, regardless of the degree of sulfonation. FGF-2-protective effects of gamma-PGA-S72 against acid and thermal inactivation were also evaluated, and gamma-PGA-S72 showed higher FGF-2-protective effects in comparison to nonsulfonated gamma-PGA. The steric structures of various sulfonated gamma-PGA-Ss were analyzed by molecular modeling (molecular orbital method (MOPAC)) and indicated that gamma-PGA-Ss are helical in vacuo. Results from MOPAC and the molecular mechanics method (MM2) demonstrated that electrostatic interactions can take place between sulfonic and carboxyl groups of gamma-PGA-S and basic amino acid residues in FGF-2. gamma-PGA-S72 can interact with FGF-2 strongly.

Nucleosomes Bind Fibroblast Growth Factor-2 for Increased Angiogenesis In vitro and In vivo

Solid tumors often display sites of necrosis near regions of angiogenesis in vivo. As tumor cell necrosis would result in the release of nucleosomes into the extracellular environment, we explored the potential role of nucleosomes in the promotion of angiogenesis. Data indicate that nucleosomes acted similar to heparin and bound to several heparin-binding, proangiogenic factors [i.e., fibroblast growth factor (FGF)-1, FGF-2, vascular endothelial growth factor, and transforming growth factor-β1]. Nucleosomes modestly enhanced FGF-2 growth of human umbilical vein endothelial cells when grown in restricted media as well as increased human umbilical vein endothelial cell migration and primitive blood vessel tube formation in vitro. On s.c. injection in mice, nucleosomes aided FGF-2 in promoting angiogenesis. These results suggest that nucleosomes released from dying tumor cells aid in the formation of blood vessels and may provide a novel means by which tumor cells increase angiogenesis.

Synthesis of sulfated colominic acids and their interaction with fibroblast growth factors

Colominic acid, an alpha (2-->8)-linked poly(sialic acid), was sulfated and characterized by NMR spectroscopy. During sulfation, the secondary hydroxyl group at C-4 had almost the same reactivity as the primary hydroxyl group at C-9, while the secondary hydroxyl group at C-7 was hardly substituted. Analysis by molecular modeling suggested that the lack of substitution at C-7 was due to a steric hindrance. A mobility shift assay indicated that FGF-2 bound to the sulfated colominic acid. Synthetic sulfated colominic acid potentiated the mitogenic activity of FGFs for fibroblasts in the same manner as heparin. Sulfated colominic acid with a low degree of sulfation was able to potentiate FGF activity. Regardless of the degree of sulfation, sulfated colominic acid-induced cytotoxicity was not observed. It was suggested that the carboxyl groups in sulfated colominic acid cooperate with the sulfate groups to reinforce the interaction with FGFs and to reduce the cytotoxicity of sulfated colominic acids.

Formation of an active dimer during storage of interleukin-1 receptor antagonist in aqueous solution

The degradation products of recombinant human interleukin-1 receptor antagonist (rhIL-1ra) formed during storage at 30 degrees C in aqueous solution were characterized. Cationic exchange chromatography of the stored sample showed two major, new peaks eluting before (P1) and after (L2) the native protein, which were interconvertible. Size-exclusion chromatography and electrophoresis documented that both the P1 and L2 fractions were irreversible dimers, formed by noncovalent interactions. A competition assay with interleukin-1 indicated that on a per monomer basis the P1 and L2 dimers retained about two-thirds of the activity of the native monomer. Infrared and far-UV circular dichroism spectroscopies showed that only minor alterations in secondary structure arose upon the formation of the P1 dimer. However, alteration in the near-UV circular dichroism spectrum suggested the presence of disulfide bonds in the P1 dimer, which are absent in the native protein. Mass spectroscopy and tryptic mapping, before and after carboxymethylation, demonstrated that the P1 dimer contained an intramolecular disulfide bond between Cys-66 and Cys-69. Although conversion of native protein to the P1 dimer was irreversible in buffer alone, the native monomer could be regained by denaturing the P1 dimer with guanidine hydrochloride and renaturing it by dialysis, suggesting that the intramolecular disulfide bond does not interfere with refolding. Analysis of the time course of P1 formation during storage at 30 degrees C indicated that the process followed first-order, and not second-order, kinetics, suggesting that the rate-limiting step was not dimerization. It is proposed that a conformational change in the monomer is the rate-limiting step in the formation of the P1 dimer degradation product. Sucrose stabilized the native monomer against this process. This result can be explained by the general stabilization mechanism for this additive, which is due to its preferential exclusion from the protein surface.

Lyophilized keratinocyte cell lysates contain multiple mitogenic activities and stimulate closure of meshed skin autograft-covered burn wounds with efficiency similar to that of fresh allogeneic keratinocyte cultures

For several years, grafting with allogeneic keratinocyte cultures has been used successfully as a wound-healing therapy both by us and by many other groups. Since their postgrafting survival time is limited, the effect of these cultures is generally explained by the production of wound repair-stimulating factors that promote proliferation and migration of resident cells. In this study we show that lysates of cultured keratinocytes contain mitogenic activity for keratinocytes, endothelial cells, and fibroblasts. In addition, the lysates inhibit the contraction of collagen gels by human skin fibroblasts. On the basis of these observations and of in vivo data obtained by ourselves and others, we have evaluated the effect of total keratinocyte lysates on the healing of meshed skin autograft-covered burn wounds. Twenty burn wounds were tangentially excised and autografted with one to three meshed conventional skin transplants. An area treated with a gel containing lysated keratinocyte cultures was compared with an area treated with placebo-gel in terms of epithelialization on day 5. In six patients an additional fresh keratinocyte alloculture was applied as a positive control. Results indicate that the newly formed epithelium (difference between percentage of epithelialization on day 5 and on day 0) was 31.1 percent in the treated area compared with 16.5 percent in the placebo area. This result is comparable with the value obtained by treatment with fresh keratinocyte allocultures, namely, 33.8 percent. These figures show a twofold stimulation of epithelialization.

The importance of Arg40 and 45 in the mitogenic activity and structural stability of basic fibroblast growth factor: effects of acidic amino acid substitutions

High-affinity binding of basic fibroblast growth factor (bFGF) to the tyrosine kinase receptor requires cell-surface heparan sulfate proteoglycan or exogenous addition of heparin. The crystal structure of bFGF shows Arg40 and 45 on the surface opposite to the heparin-binding region, suggesting that these charged residues may be involved in the receptor binding. Therefore, these amino acids were mutated to aspartic acid separately or simultaneously, and also a simultaneous mutation to glutamic acid was introduced. These mutants displayed a mitogenic activity decreased greater than tenfold compared to the wild-type protein. Addition of heparin had no effect on the activity, while these mutants showed heparin-binding characteristics resembling those of the native sequence protein. The mutants exhibited decreased stability compared to the native sequence protein. Gradual changes in conformation were observed by circular dichroic and infrared spectroscopy. Heparin chromatography also showed the presence of denatured form for these mutants. However, in the presence of multivalent anions such as citrate, sucrose octasulfate, and heparin, the conformation of the mutants resembled that of the wild-type protein, as revealed by X-ray crystallography and circular dichroism spectra of the mutant with a Arg40-->Asp substitution.

Phosphorothioate oligodeoxynucleotides bind to basic fibroblast growth factor, inhibit its binding to cell surface receptors, and remove it from low affinity binding sites on extracellular matrix

We studied the interactions of phosphorothioate oligodeoxynucleotides and heparin-binding growth factors. By means of a gel mobility shift assay, we demonstrated that phosphodiester and phosphorothioate homopolymers bound to basic fibroblast growth factor (bFGF). Binding of a probe phosphodiester oligodeoxynucleotide could also be shown for other proteins of the FGF family, including acidic fibroblast growth factor (aFGF), Kaposi's growth factor (FGF-4) as well as for the bFGF-related vascular endothelial growth factor, VEGF. No binding to epidermal growth factor (EGF) was observed. In addition, using a radioreceptor assay, we have shown that phosphorothioate homopolymers of cytidine and thymidine blocked binding of not only 125I-bFGF, but also of 125I-PDGF to NIH 3T3 cells, whereas phosphodiester oligodeoxynucleotides were ineffective. The extent of blockade of binding was dependent on the chain length of the phosphorothioate oligodeoxynucleotide. Furthermore, we have examined the effects of 18-mer phosphorothioate oligodeoxynucleotides of different sequences on 125I-bFGF binding to low and high affinity sites on both NIH 3T3 fibroblasts and DU-145 prostate cancer cells. Despite the fact that we have observed inhibition of bFGF binding by the 18-mer phosphorothioate oligodeoxynucleotides for both the high and low affinity classes of bFGF receptor, the inhibition was sequence-selective only for the high affinity receptors. We have also demonstrated that phosphorothioate homopolymers of cytidine and thymidine release bFGF bound to low affinity receptors in extracellular matrix (ECM). Finally, the most potent phosphorothioate oligodeoxynucleotides used in these experiments (e.g. SdC28) were inhibitors of bFGF-induced DNA synthesis in NIH 3T3 cells.

Strategies to suppress aggregation of recombinant keratinocyte growth factor during liquid formulation development

Recombinant human keratinocyte growth factor (rhKGF) is a fairly unstable protein, posing a challenging problem for long-term storage. During storage, the protein unfolds at relatively low temperatures and the unfolded proteins aggregate rapidly, leading to the formation of large visible precipitates. Thermal unfolding of rhKGF displays a similar pattern, i.e., unfolding is followed immediately by aggregation as the temperature is increased. As the unfolding and aggregation (precipitation) of rhKGF limit the storage life of the protein, a search for stabilizers to suppress rhKGF unfolding and aggregation has been done by examining the effects of excipients on thermal melting temperature and on the rate of protein aggregation during storage. Sulfated polysaccharides and citrate are found to be effective in increasing the melting temperature of rhKGF or preventing its aggregation. In particular, 0.5% (w/v) heparin and high molecular weight dextran sulfate, and 0.5 M citrate are highly effective, decreasing the rates of rhKGF aggregation by about 50-fold. Other negatively charged small ions, such as phosphate, also have moderate stabilizing effects on rhKGF. A mechanistic study of the aggregation pathway of rhKGF has led to a better understanding of the stabilizing effects of these molecules. Molecules which enhance rhKGF conformational stability are capable of effectively suppressing rhKGF aggregation.

Aggregation pathway of recombinant human keratinocyte growth factor and its stabilization

Recombinant human keratinocyte growth factor (rhKGF) is prone to aggregation at elevated temperatures. Its aggregation pathway is proposed to proceed initially with a conformational change which perhaps results from repulsion between positively charged residues in clusters forming heparin binding sites. Unfolding of the protein leads to formation of large soluble aggregates. These soluble aggregates then form disulfide cross-linked precipitates. Finally these precipitates are converted to scrambled disulfides and/or non-disulfide cross-linked precipitates. Stabilizers such as heparin, sulfated polysaccharides, anionic polymers and citrate can greatly decrease the rate of aggregation of rhKGF at elevated temperatures. These molecules may all act by reducing charge repulsion on the protein thus stabilizing the native conformation. EDTA, on the other hand, is found to inhibit disulfide formation in aggregates and has only a moderate stabilizing effect on rhKGF.

Aluminium beta-cyclodextrin sulphate as a stabilizer and sustained-release carrier for basic fibroblast growth factor

The water-insoluble aluminium salt of beta-cyclodextrin sulphate (Al.beta-CyD-Sul) was used as a stabilizer and sustained-release carrier for recombinant human basic fibroblast growth factor (bFGF). An adsorbate of bFGF with Al.beta-CyD-Sul was prepared by incubating the protein with a suspension of Al.beta-CyD-Sul in water. The mitogenic activity of bFGF released from the adsorbate, as indicated by the proliferation of kidney cells of baby hamster (BHK-21), was almost comparable with that of the intact bFGF. Al.beta-CyD-Sul significantly protected bFGF from proteolytic degradation by pepsin and alpha-chymotrypsin, compared with the water-soluble sodium salt. The in-vitro release of bFGF from the adsorbate was sustained in proportion to a rise in the ratio of Al.beta-CyD-Sul to the protein in the adsorbate. Of the bFGF preparations evaluated, the adsorbate of bFGF with Al.beta-CyD-Sul, when given subcutaneously to the rat, showed the most prominent increase in the formation of granulation tissues, due to the stabilization and slow-release of the mitogen. The limited data presented here suggest that the adsorbate of bFGF with Al.beta-CyD-Sul has a potent therapeutic efficacy for wound healing, and may be applicable to oral protein formulations for the treatment of intestinal mucosal erosions.

Densimetric determination of equilibrium binding of sucrose octasulfate with basic fibroblast growth factor

Fibroblast growth factors (FGFs) strongly bind to heparin and are thereby stabilized against deactivation and proteolytic cleavage. Sucrose octasulfate (SOS), which has a chemical structure resembling the repeating unit of heparin, has also been shown to enhance stability of basic FGF against thermal denaturation and to induce a small conformational change. We have examined SOS binding to bFGF using equilibrium dialysis. The difference in SOS concentration across the dialysis membrane was measured using a precision density meter, since the density of SOS differs greatly from that of water. With care, this densimetric technique can measure binding with a precision of +/- 0.1 mol/mol using about 2 mg/ml of protein. These results show that the binding saturates at 2 mol of SOS per mole of bFGF as the SOS concentration increases to 3.6 mM or higher. The effect of SOS on the thermal stability of bFGF was examined using denaturation at a constant heating rate, by both turbidity and differential scanning calorimetry. Since the thermal denaturation is irreversible, the temperature where aggregation abruptly increases was taken to indicate the onset of denaturation. This temperature increased by approximately 12 degrees C as the SOS concentration increased from 0.018 to 3.6 mM and remained constant above 3.6 mM, consistent with our binding data if the binding is specific to the native state.