Monitoring the Dynamics of Ligand−Receptor Complexes on Model Membranes

Ligand-induced cross-linking of cell surface receptors is a basic paradigm of signal activation by many transmembrane receptors. After ligand binding, the receptor complexes formed on the membrane are dynamically maintained by two-dimensional protein-protein interactions on the membrane. The biophysical principles governing the dynamics of such interactions have not been understood, mainly because the measurement of lateral interactions on membranes so far has not been experimentally addressed. Here, we describe a generic approach for measuring two-dimensional dissociation rate constants in vitro using a novel high-affinity chelator lipid for reconstituting a ternary cytokine-receptor complex on solid-supported membranes. While monitoring the interaction between the ligand and one of the receptor subunits on the membrane by fluorescence resonance energy transfer, the equilibrium on the surface was perturbed by rapidly tethering a large excess of the unlabeled receptor subunit. Displacement of labeled by unlabeled protein in the ternary complex was detected as a recovery of the donor quenching. Since the dissociation of the ligand-receptor complex in plane of the membrane was the rate-limiting step under these conditions, the two-dimensional rate constant of this process was determined. Strikingly, the two-dimensional dissociation was much slower than ligand dissociation into solution, suggesting that membrane tethering significantly affects the dissociation process. This result highlights the importance of studying ligand-receptor complexes tethered to membranes for understanding the principles governing signal activation by ligand-induced receptor assembling.

Mutational analysis of the IFNAR1 binding site on IFNalpha2 reveals the architecture of a weak ligand-receptor binding-site

Type I interferons activate cellular responses by forming a ternary complex with two receptor components, IFNAR1 and IFNAR2. While the binding of the IFNAR2 receptor to interferon is of high affinity and well characterized, the binding to IFNAR1 is weak, transient, and poorly understood. Here, we mapped the complete binding region of IFNAR1 on IFNalpha2 by creating a panel of 21 single alanine mutant proteins, and determined their binding affinities. The IFNAR1 binding site on IFNalpha2 maps to the center of the B and C helices, opposite to the binding site for IFNAR2. No hot spots for binding were found in the interface, with individual mutations having an up to fivefold effect on binding. Of the nine residues that affected binding, three adjacent conserved residues, located on the B helix, conferred an increase in the binding affinity to IFNAR1, as well as an increase in the biological activity of the interferon mutant. This suggests that binding of alpha interferons to the IFNAR1 receptor is sub-optimal. A correlation between binding affinity and biological activity was found, albeit not across the whole range of affinities. In WISH cells, but not DAUDI cells, the anti-proliferative activity was markedly affected by fluctuations in the IFNalpha2 affinity towards the IFNAR1 receptor. On the other hand, the antiviral activity of interferons on WISH cells seems to change in accordance to the binding affinity towards IFNAR1 only as long as the binding affinity is not beyond twofold of the wild-type. In accordance, the biological roles of the two interferon-receptor subunits are discussed.

Multivesicular liposome formulations for the sustained delivery of interferon alpha-2b

AIM

To develop and optimize a sustained release multivesicular liposome (MVL) formulation of interferon (IFN) alpha-2b.

METHODS

IFN alpha-2b MVL were prepared using a typical double-emulsion procedure. The sustained release effects of IFN alpha-2b MVL were investigated by monitoring the blood IFN alpha-2b concentration using an enzyme-linked immunosorbent assay test after subcutaneous administration to healthy mice.

RESULTS

IFN alpha-2b was successfully encapsulated in MVL with high efficiency, and the integrity of encapsulated protein was maintained. After subcutaneous injection, the MVL slowly released IFN alpha-2b into systemic circulation in a sustained manner. The estimated serum half-life of IFN alpha-2b was approximately 30 h. In addition, varying the size of the MVL preparations could further modify the in vivo release profile.

CONCLUSION

IFN alpha-2b MVL may be a useful sustained release formulation in the clinical treatment of viral diseases.

Structural characterization and immunogenicity in wild-type and immune tolerant mice of degraded recombinant human interferon alpha2b

PURPOSE

This study was conducted to study the influence of protein structure on the immunogenicity in wild-type and immune tolerant mice of well-characterized degradation products of recombinant human interferon alpha2b (rhIFNalpha2b).

METHODS

RhIFNalpha2b was degraded by metal-catalyzed oxidation (M), cross-linking with glutaraldehyde (G), oxidation with hydrogen peroxide (H), and incubation in a boiling water bath (B). The products were characterized with UV absorption, circular dichroism and fluorescence spectroscopy, gel permeation chromatography, reverse-phase high-pressure liquid chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis, Western blotting, and mass spectrometry. The immunogenicity of the products was evaluated in wild-type mice and in transgenic mice immune tolerant for hIFNalpha2. Serum antibodies were detected by enzyme-linked immunosorbent assay or surface plasmon resonance.

RESULTS

M-rhIFNalpha2b contained covalently aggregated rhIFNalpha2b with three methionines partly oxidized to methionine sulfoxides. G-rhIFNalpha2b contained covalent aggregates and did not show changes in secondary structure. H-rhIFNalpha2b was only chemically changed with four partly oxidized methionines. B-rhIFNalpha2b was largely unfolded and heavily aggregated. Nontreated (N) rhIFNalpha2b was immunogenic in the wild-type mice but not in the transgenic mice, showing that the latter were immune tolerant for rhIFNalpha2b. The anti-rhIFNalpha2b antibody levels in the wild-type mice depended on the degradation product: M-rhIFNalpha2b > H-rhIFNalpha2b approximately N-rhIFNalpha2b >> B-rhIFNalpha2b; G-rhIFNalpha2b did not induce anti-rhIFNalpha2b antibodies. In the transgenic mice, only M-rhIFNalpha2b could break the immune tolerance.

CONCLUSIONS

RhIFNalpha2b immunogenicity is related to its structural integrity. Moreover, the immunogenicity of aggregated rhIFNalpha2b depends on the structure and orientation of the constituent protein molecules and/or on the aggregate size.

HPLC and tandem detection to monitor conformational properties of biopharmaceuticals

High-performance liquid chromatography (HPLC) with UV, circular dichroism (CD) and intrinsic fluorescence detection was applied to monitor conformational properties of recombinant human interferon alpha2b when performing size exclusion chromatography (SEC) and reversed-phase HPLC (RP-HPLC). In this way native conditions during SEC and structural changes of the protein during RP-HPLC were demonstrated. These results were confirmed by stand-alone fluorescence and CD measurements. With respect to HPLC tandem detection, the fluorescence detector compared favourably to the UV and CD detector regarding linearity, sensitivity and selectivity. SEC combined with intrinsic fluorescence scanning detection permits conformational analysis of small amounts of aggregates in the presence of excess native monomeric protein. In conclusion, HPLC with on-line UV and intrinsic fluorescence detection provides a promising concept for analysing the amount and conformational properties of a biopharmaceutical and its impurities.

Influence of packaging material on the liquid stability of interferon-alpha2b

PURPOSE

In this article we studied the effect of the packaging material on the liquid stability of interferon alpha 2b (rhIFN-alpha2b).

METHODS

The compatibility of this cytokine with type I borosilicate glass ampoules was evaluated by ELISA and RP-HPLC, at 4 degrees C and after heat sealing. Additionally, the influence of protein concentration (3 and 10 MIU/ml), buffer species (sodium phosphate, sodium citrate and sodium citrate-phosphate) and additives (polysorbate 80 and EDTA Na(2) x 2H(2)O) were studied in samples with and without contact with chlorobutyl stoppers by RP-HPLC.

RESULTS

The compatibility of this cytokine in sodium phosphate buffer, with type I borosilicate glass ampoules showed a significant adsorption at the lowest concentration. This influence was eliminated with a polysorbate 80/benzyl alcohol-based vehicle. The effect of the heat sealing of ampoules on the stability of rhIFN-alpha2b showed two degradation peaks when a volume of 1 ml was dispensed. However, with a lower (0.5 ml) volume, the degradation was not detected. On the other hand, samples in contact with chlorobutyl stoppers increased the apparent degradation rate constant in the range of 6.74 +/- 0.38 to 46.34 +/- 3.11 x 10(3) day-(1). This effect significantly decreased in about 1.2- and 1.1-fold when sodium citrate or sodium citrate-phosphate buffers, respectively, were evaluated. Results from the evaluation of EDTA Na(2) x 2H(2)O or polysorbate 80 showed a similar behavior. These additives reduced the apparent degradation rate constant in the range of 2.01 +/- 0.14 to 25.51 +/- 3.57 x 10(3) day-(1).

CONCLUSIONS

The adsorption of the cytokine to type I borosilicate glass ampoules was eliminated with a polysorbate 80/benzyl alcohol-based vehicle, and the deleterious effect of the heat sealing decreased with a lower (0.5 ml) volume. Experimental data indicated that the contact with chlorobutyl stoppers accelerates the degradation of rhIFN-alpha2b. However, protein concentration, buffer species and pharmaceutical excipients can modulate this effect.

PEGylated interferon-alpha2b: a branched 40K polyethylene glycol derivative

PURPOSE

The conjugation of interferon-alpha2b (IFN-alpha2b) to a branched-chain (40,000) polyethylene glycol (PEG2,40K) was studied.

METHODS

We studied the conjugation of IFN-alpha2b at different pH values (6.5, 7, and 8), using the PEG2,40K reagent in either solution or solid state. MonoPEGylated interferon was isolated by ion-exchange chromatography and characterized using (1) sodium dodecyl sulfate-polyacrylamide gel electrophoresis, (2) cation exchange high-performance liquid chromatography, (3) bicinchoninic acid protein assay, (4) enzyme-linked immunosorbent assay, (5) cell-based bioassays, (6) thermal stability (at 60 degrees C), (7) tryptic digestion, and (8) pharmacokinetics in rats.

RESULTS

PEGylation reaction gave 30-55% PEG2,40K-IFN-alpha2b, 1-10% polyPEGylated interferon, and 35-70% unmodified IFN-alpha2b. Compared to the polyPEGylated IFN-alpha2b species, the pure (96%) monoPEGylated conjugate retained a significantly higher bioactivity (IU/mg): 1.7x10(4)+/-8.5x10(3) vs. 2.8x10(6)+/-1.4x10(6) for antiviral and 1.9x10(4)+/-9.5x10(3) vs. 3.1x10(6)+/-1.6x10(6) for antiproliferative activity. Immunorecognition against IFN was reduced by the PEG2,40K moiety in the conjugate. This monoPEGylated IFN-alpha2b, which migrated as a single band in gel electrophoresis, was found to be a heterogeneous, complex mixture of different positional isomers. PEGylation markedly enhanced both the resistance to tryptic degradation and the thermal stability of IFN-alpha2b. The serum half-life of 40K PEG-IFN was 330-fold longer, while plasma residence time was increased 708 times compared to native IFN.

CONCLUSION

The PEG2,40K conjugate of IFN-alpha2b has increased in vitroand in vivo stability as compared to the native cytokine.

Use of recrystallized lactose as carrier for inhalation powder of interferon a2b

The aim of the present investigation was to evaluate the effects of physical properties of the carrier on the in vitro deposition performance of dry powder inhalations (DPIs) of recombination human interferon a2b (IFN a2b). Recrystallized lactose was used as the carrier. Inverse gas chromatography (IGC) was used to assess the surface energy, and atomic force microscopy (AFM) was used to assess the roughness and topography of the carrier. In vitro performance of the powder blends was strongly correlated to the physical properties of the carrier. Plotting emitted dose (%) vs. flow rate and fine particle fraction vs. surface energy, yielded an R2 value of 0.9621 and 0.9146, respectively.

Optimization of the primary recovery of human interferon alpha2b from Escherichia coli inclusion bodies

The human interferon alpha2b (hu-IFNalpha2b) gene was cloned in Escherichia coli JM109(DE3) and the recombinant protein was expressed as cytoplasmic inclusion bodies (IB). The present work discusses the recovery of hu-IFNalpha2b IB from the E. coli cells. An optimized protocol is proposed based on the sequential evaluation of recovery steps and parameters: (i) cell disruption, (ii) IB recovery and separation from cell debris, (iii) IB washing, and (iv) IB solubilization. Parameters such as hu-IFNalpha2b purity and recovery yield were measured after each step. The optimized recovery protocol yielded 60% of hu-IFNalpha2b with a purity of up to 80%. The protein was renatured at high concentration after recovery and it was found to display biological activity.

Protein engineering of interferon alphas

Interferon (IFN)-alphas constitute a family of proteins exhibiting high degree of homology in primary, secondary, and tertiary structure and display a high level of species specificity in their biological properties. However, small structural differences in these proteins may be responsible for a significant variety of biological actions. Understanding the structure and function of human IFN-alpha is very important. Recombinant techniques are important tools for the production and modification of IFN proteins. The first IFN hybrid, IFN-alpha1/alpha2 was constructed using recombinant technology in 1981. Subsequently, a number of IFN hybrids and mutants have been constructed, expressed and characterized. These hybrids and mutants have resulted in novel IFNs that either combine different biological properties from the parental proteins or have significantly different biological activity. Therefore, IFN hybrids and mutants have provided a powerful tool for studying the structure and function of these molecules. Also, these engineered IFNs may have important new therapeutic applications and may provide greater sights into understanding of the clinical activities of these molecules.

Antiproliferative Properties of Chemically Modified Recombinant IFN-α2b

The antiproliferative activity of aconitylated (AIFN) and succinylated (SIFN) derivatives of recombinant interferon- alpha2b (IFN-alpha2b) was examined. Acylation of IFN-alpha2b was performed by succinic and cis-aconitic anhydrides. Antiproliferative properties of AIFN and SIFN were studied in vitro on the CaOv cell line, highly sensitive to IFN, and on the SW-480 cell line, with low sensitivity to IFN-alpha2b. Acylation of one lysine in the IFN-alpha2b molecule with cis-aconitic or succinic anhydride resulted in a 3-3.5-fold increase of its antiproliferative activity on CaOv cells. The highest antiproliferative activity of acylated IFN-alpha2b on SW-480 cells was observed for both AIFNs and SIFNs with three modified lysine residues. In conclusion, aconitylated and succinylated IFNs may be useful antiproliferative agents for cancer treatment.

Synthesis and biological properties of chimeric interferon-alpha2b peptides

We have previously reported the antiproliferative activity of synthetic sequences 29-35 and 122-139 of the interferon-alpha2b (IFN-alpha2b), both probably representing a common receptor recognition domain. In the search of new peptidic agonists, we designed and synthesized the linear peptide (Gly)2-122-137-Gly138-Gly29-30-35-(Gly)2, in which Gly residues replaced the 138 and 29 Cys bound through a disulfide bridge in the native cytokine. Additionally, a cyclic analog was obtained by reaction of the N- and C-terminal ends of the linear fragment. Thus, the distance that separates residues 122 and 35 in the crystalline structure of the IFN-alpha2b was maintained through a (Gly)4 bridge. When the influence of chimeric peptides on the proliferation of WISH cells was studied, it was shown that both derivatives significantly diminished cell growth. A more evident inhibitory effect on (125)I-IFN-alpha2b binding to WISH cell-membrane receptors was observed for both peptides. Results indicated that chimeric IFN-alpha2b peptides behaved as partial agonists of the IFN-alpha2b molecule and may be of interest for drug design purposes.

Pegylated IFNs for chronic hepatitis C: an update

For over a decade, IFN-alpha(2) has been the standard treatment for chronic hepatitis C. However, the drug's rapid clearance and short half-life have led to low rates of sustained virological response. Pegylation is a well-established method of modifying the pharmacological properties of IFNs, causing significant improvements in pharmacokinetics, which in turn lead to improved efficacy. Two pegylated forms of IFN-alpha(2) have been developed: PEG-IFN-alpha(2b) and PEG-IFN-alpha(2a), and their efficacy has been established in randomised, controlled trials. However, the two differ significantly in structure, in vitro activity and pharmacological properties, and this may translate into -differences in clinical efficacy. Comparative trials have been initiated that will provide insight into relative importance of pharmacokinetics, bioactivity and dosing regimen.

Structural, Kinetic, and Thermodynamic Analysis of the Binding of the 40 kDa PEG−Interferon-α2aand Its Individual Positional Isomers to the Extracellular Domain of the Receptor IFNAR2

Type-I Interferons exert antiviral and antiproliferative activities through the binding to a common cell surface receptor comprising two subunits, IFNAR1 and IFNAR2. Human recombinant Interferon-alpha(2a) (IFNalpha(2a)) is a potent drug (Roferon-A) used to treat various cancers and viral diseases including Hepatitis B/C infections. To significantly improve the pharmacological properties of the drug, a pegylated form of IFNalpha(2a) was developed (PEGASYS). This 40 kDa PEG-conjugated IFNalpha(2a) ((40)PEG-IFNalpha(2a)) is obtained by the covalent binding of one 40 kDa branched PEG-polymer to a lysine side-chain of IFNalpha(2a). Here, we report the detailed structural, kinetic, and thermodynamic analysis of the binding to the extracellular domain of the receptor IFNAR2 of (40)PEG-IFNalpha(2a) and its isolated positional isomers modified at K31, K134, K131, K121, K164, and K70, respectively, in comparison with unmodified IFNalpha(2a). Our binding studies, using the surface plasmon resonance technique, show that the pegylation does not abolish the binding to the receptor, but significantly reduces the affinity mainly due to a change of the association rate. The results are supported by modeling and simulation of the binding, using Self-Avoiding-Walk calculations for the polymer conformations. A correlation between the structural parameters and the kinetic and thermodynamic parameters of the binding of the positional isomers could be established. For the Isomer-K31 and -K164, the PEG-polymer attachment point is located in proximity to the binding interface, and the isomers display affinity in the range 150-520 nM in an enthalpy-driven binding process. In contrast for the Isomer-K134, -K131, -K121, and -K70, the PEG-polymer is attached remotely from the binding interface, and the isomers exhibit a higher affinity (32-76 nM) in an entropy-driven binding process. This study constitutes an essential collection of knowledge on which the interaction of (40)PEG-IFNalpha(2a) and its positional isomers with its cellular receptors can be better understood.

Structural and Biophysical Characterization of the 40 kDa PEG−Interferon-α2aand Its Individual Positional Isomers

The human recombinant Interferon-alpha(2a) (IFNalpha(2a)) is a potent drug (Roferon-A) to treat various types of cancer and viral diseases including Hepatitis B/C infections. To improve the pharmacological properties of the drug, a new pegylated form of IFNalpha(2a) was developed (PEGASYS). This 40 kDa PEG-conjugated IFNalpha(2a) ((40)PEG-IFNalpha(2a)) is obtained by the covalent binding of one 40 kDa branched PEG-polymer to a lysine side chain of IFNalpha(2a). (40)PEG-IFNalpha(2a) is a mixture of mainly six monopegylated positional isomers modified at K31, K134, K131, K121, K164, and K70, respectively. Here we report the detailed structural and biophysical characterization of (40)PEG-IFNalpha(2a) and its positional isomers, in comparison with IFNalpha(2a), using NMR spectroscopy, analytical ultracentrifugation, circular dichroism, fluorescence spectroscopy, and differential scanning calorimetry. Our results show that the three-dimensional structure of IFNalpha(2a) is not modified by the presence of the polymer in all positional isomers constituting (40)PEG-IFNalpha(2a). Regardless of where the PEG-polymer is attached, it adopts a very mobile and flexible random coil conformation, producing a shield for the protein without a permanent coverage of the protein surface. Hydrodynamic data indicate that the protein-attached PEG has a slightly more compact random-coil structure than the free PEG-polymer. Our results also provide evidence of significant structural and physicochemical advantages conferred by the pegylation: increase of the effective hydrodynamic volume and modification of the molecular shape, higher temperature stability, and reduced tendency for aggregation. These results are of tremendous pharmacological interest and benefit as was clinically shown with PEGASYS. This study constitutes a new standard for the characterization of pegylated proteins and enables an important step toward the understanding on a molecular level of the binding of (40)PEG-IFNalpha(2a) and its positional isomers to its cellular receptors.

[Effect of surface modification on surface energy of lactose and performance of dry powder inhalations]

AIM

To investigate the effects of surface modification of lactose carrier on performance of dry powder inhalations (DPIs).

METHODS

Modified lactose surface was prepared using a "particle smoothing" process to obtain smooth carrier surface and low surface energy with the presence of magnesium stearate, colloidal silica dioxide and talc. Inverse gas chromatography (IGC) was used to assess the surface energy of treated lactose, and the in vitro deposition of carrier-based IFNa-2b DPIs was evaluated with twin stage impinger.

RESULTS

The flowing property of lactose was greatly improved and the surface energy decreased by the "particle smoothing" process. Decreasing surface energy resulted in greater aspiration fraction of IFNa-2b.

CONCLUSION

IGC is a potentially useful tool for rapid formulation design and screening.

Microcalorimetric studies of the effects on the interactions of human recombinant interferon-alpha2a

The applicability of the physical stability of protein solution monitored by isothermal titration calorimetry (ITC) was evaluated. The second virial coefficient, b2, derived from the dilution enthalpies of protein solution measured by ITC under various experimental conditions was studied. The protein applied in this work is human recombinant interferon-alpha2a (hrIFN-alpha2a), which is a commercial drug applied for the treatment of virus-infected diseases. The results obtained were used to predict the possibility of hrIFN-alpha2a aggregation, and the prediction can be further confirmed by size-exclusion chromatography (SEC). Various factors affecting the stability of protein solution were investigated, for example, temperature, salts, surfactants, and mechanical stress. Specifically, the results show that the dilution enthalpy of hrIFN-alpha2a increased with increasing temperature and NaCl concentration, while b2 decreased, indicating that the attraction between hrIFN-alpha2a molecules was enhanced under these conditions. On studying the effect of mechanical stress, the data obtained reveals that the introduction of centrifugal or vortex force strengthened the attractive forces between hrIFN-alpha2a molecules. These implications were supported by SEC data, demonstrating that the amount of aggregated hrIFN-alpha2a was increased. As a consequence, the methodologies presented in this investigation offer a possibility of monitoring the physical stability of protein solution at various stages of recovery, purification as well as the development of appropriate drug storage formulations.

The development of a modified human IFN-alpha2b linked to the Fc portion of human IgG1 as a novel potential therapeutic for the treatment of hepatitis C virus infection

Interferon-alpha (IFN-alpha), in conjunction with ribavirin, is the current standard for the treatment of chronic hepatitis C virus (HCV) infection. This treatment requires frequent dosing, with a significant risk of the development of anti-IFN-alpha neutralizing antibodies that correlates with lack of efficacy or relapse. We have developed an IFN-alpha linked to the Fc region of human IgG1 for improved half-life and less frequent dosing. We have also identified, using a human T cell proliferation assay, three regions of IFN-alpha2b that are potentially immunogenic, and a variant containing a total of six mutations within these regions was made. This variant was made as a fusion to Fc either with or without a flexible linker between the fusion partners. Both configurations of the variant were less active than native IFN-alpha alone, although the variant containing the flexible linker had in vitro antiviral activity within the range of other modified IFN-alphas currently in clinical use. Peptides spanning the modified regions were tested in T cell proliferation assays and found to be less immunogenic than native controls when using peripheral blood mononuclear cells (PBMCs) from both healthy individuals and HCV-infected patients who had been treated previously with IFN-alpha2b.

Site of Pegylation and Polyethylene Glycol Molecule Size Attenuate Interferon-α Antiviral and Antiproliferative Activities through the JAK/STAT Signaling Pathway

Therapeutic pegylated interferon-alphas (IFN-alpha) are mixtures of positional isomers that have been monopegylated at specific sites on the core IFN-alpha molecule. The pegylation results in lower in vitro specific activity associated with the core IFN-alpha molecule that is related to the site of pegylation and size of polyethylene glycol (PEG) attached. We prepared purified, homogeneous, positional pegylation isomers of IFN-alpha2b that were monopegylated using 5-30-kDa linear PEG molecules attached at 7 primary reactive amino acid residues: Cys(1), His(34), Lys(31), Lys(83), Lys(121), Lys(131), and Lys(134). The isomers were evaluated for STAT translocation and antiviral and antiproliferative activity. The site of pegylation strongly influenced activity relative to an IFN-alpha2b control. The highest residual activity was observed with the His(34) positional isomers, and the lowest was observed with the Cys(1) positional isomers. The Lys positional isomers demonstrated intermediate activity, with a general order of Lys(134) > Lys(83) approximately Lys(131) approximately Lys(121) > Lys(31). The progressive relationship between decreased activity and increased PEG size suggests that pegylation may interfere with interaction and binding of IFN-alpha to the IFNAR1-IFNAR2 heterodimeric receptor. The higher specific activity associated with the His(34) positional isomer suggests that this site may be favorable for pegylating IFN-alpha2b molecules.

A Long-Acting, Highly Potent Interferon α-2 Conjugate Created Using Site-Specific PEGylation

Recombinant interferon alpha-2 (IFN-alpha2) is used clinically to treat a variety of viral diseases and cancers. IFN-alpha2 has a short circulating half-life, which necessitates frequent administration to patients. Previous studies showed that it is possible to extend the circulating half-life of IFN-alpha2 by modifying lysine residues of the protein with amine-reactive poly(ethylene glycol) (PEG) reagents. However, amine-PEGylated IFN-alpha2 comprises a heterogeneous product mixture with low specific activity due to the large number and critical locations of lysine residues in IFN-alpha2. In an effort to overcome these problems we determined the feasibility of creating site-specific, mono-PEGylated IFN-alpha2 analogues by introducing a free (unpaired) cysteine residue into the protein, followed by modification of the added cysteine residue with a maleimide-PEG reagent. IFN-alpha2 cysteine analogues were expressed in Escherichia coli and purified, and their in vitro bioactivities were measured in the human Daudi cell line growth inhibition assay. Several cysteine analogues were identified that do not significantly affect in vitro biological activity of IFN-alpha2. Certain of the cysteine analogues, but not wild-type IFN-alpha2, reacted with maleimide-PEG to produce mono-PEGylated proteins. The PEG-Q5C analogue retained high in vitro bioactivity (within 3- to 4-fold of wild-type IFN-alpha2) even when modified with 20- and 40-kDa PEGs. Pharmacokinetic experiments indicated that the 20-kDa PEG-Q5C and 40-kDa PEG-Q5C proteins have 20-fold and 40-fold longer half-lives, respectively, than IFN-alpha2 following subcutaneous administration to rats. These studies demonstrate the feasibility of using site-specific PEGylation technology to create a long-acting, mono-PEGylated IFN-alpha2 protein with high specific activity.

Identification of proteins regulated by interferon-? in resistant and sensitive malignant melanoma cell lines

Treatment of patients with malignant melanoma with interferon-alpha achieves a response in a small but significant subset of patients. Currently, although much is known about interferon biology, little is known about either the particular mechanisms of interferon-alpha activity that are crucial for response or why only some patients respond to interferon-alpha therapy. Two melanoma cell lines (MeWo and MM418) that are known to differ in their response to the antiproliferative activity of interferon-alpha, have been used as a model system to investigate interferon-alpha action. Using a proteomics approach based on two-dimensional polyacrylamide gel electrophoresis and mass spectrometry, several proteins induced in response to interferon-alpha have been identified. These include a number of gene products previously known to be type I interferon responsive (tryptophanyl tRNA synthetase, leucine aminopeptidase, ubiquitin cross-reactive protein, gelsolin, FUSE binding protein 2 and hPNPase) as well as a number of proteins not previously reported to be induced by type I interferon (cathepsin B, proteasomal activator 28alpha and alpha-SNAP). Although the proteins upregulated by interferon-alpha were common between the cell lines when examined at the level of Western blotting, the disparity in the basal level of cathepsin B was striking, raising the possibility that the higher level in MM418 may contribute to the sensitivity of this cell line to interferon-alpha treatment.

Pharmacokinetics of pegylated interferons: what is misleading?

Available pegylated interferon (PEG-IFN) products confer enhanced therapeutic efficacy when compared with their IFN counterparts, and the added convenience of once-weekly dosing with no novel toxicities. PEG optimises the action of the IFNs by decreasing clearance rates, thereby allowing serum concentrations to remain constant over the dosing period. The length and shape of each PEG moiety are crucial in determining the effect on pharmacokinetic and pharmacodynamic properties. In vitro activity decreases with increasing PEG size, therefore the reduction of potency at the molecular receptor should be compensated by the prolonged residence in blood, or by the higher total drug exposure. Moreover, in hepatitis C, viral suppression in blood alone may not be enough, HCV reservoirs outside the blood may play a role in HCV persistence, therefore drugs with a low volume of distribution offer much less chance for infiltrating extravascular tissue and may explain its higher relapse rate. The case of PEG-IFNs for use in the treatment of chronic hepatitis C clearly demonstrates the potential for different characteristics among PEG conjugates.

Review article: pegylated interferons: chemical and clinical differences

Pegylated interferon therapy for the treatment of chronic hepatitis C virus provides significant increases in sustained virological response rates compared with standard interferons. Two pegylated interferons are now available and are used in conjunction with ribavirin to maximize response rates in infected patients. The two pegylated interferons, peginterferonalpha-2a and peginterferonalpha-2b, differ substantially in terms of their chemical and structural characteristics, pharmacokinetic and pharmacodynamic properties, and dosing and administration. A full understanding of the differences between the two drugs is important to maximize the clinical benefits. Controlled studies designed to characterize the effects of the two drugs on viral kinetics and sustained virological response rates are emerging and may help to shed additional light on the use of these compounds in patients with chronic hepatitis C.