Exogenous administration of protease-resistant, non-matrix-binding IGFBP-2 inhibits tumour growth in a murine model of breast cancer.

BACKGROUND: Insulin-like growth factors (IGF-I and IGF-II) signal via the type 1 IGF receptor (IGF-1R) and IGF-II also activates the insulin receptor isoform A (IR-A). Signalling via both receptors promotes tumour growth, survival and metastasis. In some instances IGF-II action via the IR-A also promotes resistance to anti-IGF-1R inhibitors. This study assessed the efficacy of two novel modified IGF-binding protein-2 (IGFBP-2) proteins that were designed to sequester both IGFs. The two modified IGFBP-2 proteins were either protease resistant alone or also lacked the ability to bind extracellular matrix (ECM). METHODS: The modified IGFBP-2 proteins were tested in vitro for their abilities to inhibit cancer cell proliferation and in vivo to inhibit MCF-7 breast tumour xenograft growth. RESULTS: Both mutants retained low nanomolar affinity for IGF-I and IGF-II (0.8-2.1-fold lower than IGFBP-2) and inhibited cancer cell proliferation in vitro. However, the combined protease resistant, non-matrix-binding mutant was more effective in inhibiting MCF-7 tumour xenograft growth and led to inhibition of angiogenesis. CONCLUSIONS: By removing protease cleavage and matrix-binding sites, modified IGFBP-2 was effective in inhibiting tumour growth and reducing tumour angiogenesis.

Targeting of acute myeloid leukemia in vitro and in vivo with an anti-CD123 mAb engineered for optimal ADCC.

Acute myeloid leukemia (AML) is a biologically heterogeneous group of related diseases in urgent need of better therapeutic options. Despite this heterogeneity, overexpression of the interleukin (IL)-3 receptor α-chain (IL-3 Rα/CD123) on both the blast and leukemic stem cell (LSC) populations is a common occurrence, a finding that has generated wide interest in devising new therapeutic approaches that target CD123 in AML patients. We report here the development of CSL362, a monoclonal antibody to CD123 that has been humanized, affinity-matured and Fc-engineered for increased affinity for human CD16 (FcγRIIIa). In vitro studies demonstrated that CSL362 potently induces antibody-dependent cell-mediated cytotoxicity of both AML blasts and CD34(+)CD38(-)CD123(+) LSC by NK cells. Importantly, CSL362 was highly effective in vivo reducing leukemic cell growth in AML xenograft mouse models and potently depleting plasmacytoid dendritic cells and basophils in cynomolgus monkeys. Significantly, we demonstrated CSL362-dependent autologous depletion of AML blasts ex vivo, indicating that CSL362 enables the efficient killing of AML cells by the patient's own NK cells. These studies offer a new therapeutic option for AML patients with adequate NK-cell function and warrant the clinical development of CSL362 for the treatment of AML.

Protein engineering and preclinical development of a GM-CSF receptor antibody for the treatment of rheumatoid arthritis.

BACKGROUND AND PURPOSE: For antibody therapies against receptor targets, in vivo outcomes can be difficult to predict because of target-mediated clearance or antigen 'sink' effects. The purpose of this work was to engineer an antibody to the GM-CSF receptor α (GM-CSFRα) with pharmacological properties optimized for chronic, s.c. treatment of rheumatoid arthritis (RA) patients. EXPERIMENTAL APPROACH: We used an in silico model of receptor occupancy to guide the target affinity and a combinatorial phage display approach for affinity maturation. Mechanism of action and internalization assays were performed on the optimized antibody in vitro before refining the modelling predictions of the eventual dosing in man. Finally, in vivo pharmacology studies in cynomolgus monkeys were carried out to inform the predictions and support future clinical development. KEY RESULTS: Antibody potency was improved 8600-fold, and the target affinity was reached. The refined model predicted pharmacodynamic effects at doses as low as 1 mg kg(-1) and a study in cynomolgus monkeys confirmed in vivo efficacy at 1 mg kg(-1) dosing. CONCLUSIONS AND IMPLICATIONS: This rational approach to antibody drug discovery enabled the isolation of a potent molecule compatible with chronic, s.c. self-administration by RA patients. We believe this general approach enables the development of optimal biopharmaceuticals.

Human vascular endothelial growth factor B: characterization of recombinant isoforms and generation of neutralizing monoclonal antibodies.

1. The vascular endothelial growth factor (VEGF) family is a focus of interest with respect to novel therapies for cardiovascular disease. Members of this family bind differentially to three receptor tyrosine kinases, namely VEGF-R1, -R2 and -R3, and to the semaphorin receptors neuropilin 1 and 2. The role of VEGF-R1 and the factors that interact exclusively with this receptor (VEGF-B and placenta growth factor) has remained controversial. 2. To further elucidate the role of VEGF-B in blood vessel formation and function, we have expressed, purified and refolded both naturally occurring VEGF-B isoforms and a truncated amino acid 10-108 form. All refolded proteins have been demonstrated to bind to VEGF-R1 with appropriate kinetics in biosensor-based analysis. 3. Robust cell assays for VEGF-R1 ligands, such as VEGF-B, have been problematic. We have developed an assay based on a chimeric receptor consisting of extracellular domains 1-4 of VEGF-R1 and the transmembrane and intracellular domains of gp130. The cell line expresses luciferase to high levels 24 h after exposure to VEGF-A and both refolded VEGF-B167 and the short 10-108 isoform have been demonstrated to be active in this assay. 4. The novel cell-based assay, in combination with a variety of immunochemical approaches, has been used to identify and characterize monoclonal antibodies that neutralize VEGF-B activity.

Rapid microscale enzymic semisynthesis of epidermal growth factor (EGF) analogues.

Epidermal Growth Factor (EGF) is a small growth factor containing 53 amino acid residues capable of stimulating the proliferation of both mesenchymal and epithelial cells. Comparison of the amino acid sequences of EGF from several species, and related proteins that can bind to the EGF receptor (e.g. TGFalpha, VGF, heparin-binding EGF, and betacellulin), suggests that Leu47, which is highly conserved, is important for biological function. Additionally, we have shown previously, using a combination of trypsin and carboxypeptidase Y digestion of native murine EGF, that removal of Leu47 results in more than 100-fold decrease in both receptor binding and mitogenic activity. We now describe a micromethod for the rapid generation of C-terminally modified EGFs to investigate further the role of C-terminal residues in determining functional activity. These analogues have been generated by digesting native murine EGF with trypsin, purifying the biologically inactive, but structurally intact, EGF1-45 core by micropreparative RP-HPLC, and then reversing the action of trypsin to couple synthetic peptides (e.g. DL, DI, DF, EL, DLLW) onto the C-terminus of the EGF1-45 core. This enzymic semisynthesis method allows multiple derivatives to be generated rapidly from microgram quantities of EGF1-45 in sufficient quantities for sensitive biological and physicochemical analysis. We have validated the method by regenerating EGF1-47 from EGF1-45 with equivalent mitogenic and receptor binding activity to EGF1-47 generated from wild type EGF by digestion with trypsin and carboxypeptidase Y. We have also investigated the effect of substituting alternative normal or nonphysiological amino acids (e.g. allo-Ile) for Asp46, Leu47 or Arg48. Even small changes in these C-terminal residues reduce the mitogenic potency of the analogue.

Purification and refolding of vascular endothelial growth factor-B.

Vascular endothelial growth factor (VEGF)-A interacts with the receptor tyrosine kinases VEGF-R1 and R2, and the importance of this interaction in endothelial cell (EC) function and blood vessel development has been well documented. Other ligands that interact differentially with these receptors and that are structurally related to VEGF-A include VEGF-B, VEGF-C, VEGF-D, and placenta growth factor (PLGF). Compared with VEGF-A, relatively little is known about the biological role of the VEGF-R1 specific ligand, VEGF-B. Two splice variant isoforms that differ at the COOH-terminus and which retain unique solubility characteristics are widely expressed throughout embryonic and postnatal development. Recent analysis of mice with a targeted deletion of the VEGF-B gene has revealed a defect in heart development and function consistent with an important role in vascularization of the myocardium (Bellomo D et al., 2000, Circ Res 86:E29-E35). To facilitate further characterization of VEGF-B, we have developed a protocol for expression and purification of refolded recombinant protein from Escherichia coli inclusion bodies (IBs). The approach developed resolves a number of significant issues associated with VEGF-B, including the ability to heterodimerize with endogenous VEGF-A when co-expressed in mammalian cells, a complex secondary structure incorporating inter- and intrachain disulfide bonds and hydrophobic characteristics that preclude the use of standard chromatographic resins. The resulting purified disulfide-linked homodimer was demonstrated to bind to VEGF-R1 and to compete with VEGF-A for binding to this receptor.

Stoichiometry, kinetic and binding analysis of the interaction between epidermal growth factor (EGF) and the extracellular domain of the EGF receptor.

The kinetics, binding equilibria and stoichiometry of the interaction between epidermal growth factor and the soluble extracellular domain of the epidermal growth factor receptor (sEGFR), produced in CHO cells using a bioreactor, have been studied by three methods: analytical ultracentrifugation, biosensor analysis using surface plasmon resonance detection (BIAcore 2000) and fluorescence anisotropy. These studies were performed with an sEGFR preparation purified in the absence of detergent using a mild two step chromatographic procedure employing anion exchange and size exclusion HPLC. The fluorescence anisotropy and analytical ultracentrifugation data indicated a 1:1 molar binding ratio between EGF and the sEGFR. Analytical ultracentrifugation further indicated that the complex comprised 2EGF:2sEGFR, consistent with the model proposed recently by Lemmon et al. (1997). Global analysis of the BIAcore binding data showed that a simple Langmuirian interaction does not adequately describe the EGF:sEGFR interaction and that more complex interaction mechanisms are operative. Furthermore, analysis of solution binding data using either fluorescence anisotropy or the biosensor, to determine directly the concentration of free sEGFR in solution competition experiments, yielded Scatchard plots which were biphasic and Hill coefficients of less than unity. Taken together our data indicate that in solution there are two sEGFR populations; one which binds EGF with a KD of 2-20 nM and the other with a KD of 400-550 nM.

Suppressor of cytokine signaling-3 preferentially binds to the SHP-2-binding site on the shared cytokine receptor subunit gp130.

Suppressor of cytokine signaling-3 (SOCS-3) is one member of a family of intracellular inhibitors of signaling pathways initiated by cytokines that use, among others, the common receptor subunit gp130. The SH2 domain of SOCS-3 has been shown to be essential for this inhibitory activity, and we have used a quantitative binding analysis of SOCS-3 to synthetic phosphopeptides to map the potential sites of interaction of SOCS-3 with different components of the gp130 signaling pathway. The only high-affinity ligand found corresponded to the region of gp130 centered around phosphotyrosine-757 (pY757), previously shown to be a docking site for the tyrosine phosphatase SHP-2. By contrast, phosphopeptides corresponding to other regions within gp130, Janus kinase, or signal transducer and activator of transcription proteins bound to SOCS-3 with weak or undetectable affinity. The significance of pY757 in gp130 as a biologically relevant SOCS-3 docking site was investigated by using transfected 293T fibroblasts. Although SOCS-3 inhibited signaling in cells transfected with a chimeric receptor containing the wild-type gp130 intracellular domain, inhibition was considerably impaired for a receptor carrying a Y-->F point mutation at residue 757. Taken together, these data suggest that the mechanism by which SOCS-3 inhibits the gp130 signaling pathway depends on recruitment to the phosphorylated gp130 receptor, and that some of the negative regulatory roles previously attributed to the phosphatase SHP-2 might in fact be caused by the action of SOCS-3.

The N-terminus of gp130 is critical for the formation of the high-affinity interleukin-6 receptor complex.

Interleukin-6 (IL-6) mediates its activity through binding to two cell-surface receptors. The high-affinity human IL-6 receptor complex consists of two transmembrane anchored subunits: a ligand-specific, low-affinity IL-6 receptor and the high-affinity converter and signal transducing, gp130. Previously, using recombinant forms of human IL-6 and the extracellular ('soluble') domains of the IL-6 receptor (sIL-6R) and gp130 (sgp130), we have shown that the high-affinity IL-6R complex is hexameric, consisting of two molecules each of IL-6, sIL-6R and sgp130 (Ward et al., 1994, J. Biol. Chem. 269: 23286-23289). This paper investigates the role of the N-terminal region of gp130 in the formation of the high-affinity IL-6R complex. Using recombinant sgp130 produced with a FLAG octapeptide epitope (DYKDDDDK) at the N-terminus (sgp130-FLAG), we demonstrate, using biosensor analysis and size-exclusion chromatography, that modification of the N-terminus of sgp130 interferes with the in vitro in solution formation of the stable hexameric IL-6 receptor complex. Rather, sgp130-FLAG interacts with IL-6 and sIL-6R with a much lower affinity and forms a stable lower-order ternary complex. However, this lower-order complex is inconsistent with the solution molecular weight of a trimeric complex, as measured by size-exclusion chromatography. In contrast, N-terminal modification of the sgp130 with the FLAG epitope did not interfere with the binding of leukemia inhibitory factor or oncostatin-M (other cytokines that signal through gp130) to sgp130. These data support our model of the hexameric IL-6 receptor complex, which is biased towards the association of two IL-6.IL-6R.gp130 trimers, and postulates the critical involvement of the N-terminal Ig-like domain of gp130 in tethering the two trimers to form the stable hexamer (Simpson et al., 1997, Prot. Sci. 6: 929-955).

Suckling defect in mice lacking the soluble haemopoietin receptor NR6.

Cytokines control a variety of cellular responses including proliferation, differentiation, survival and functional activation, via binding to specific receptors expressed on the surface of target cells [1]. The cytokine receptors of the haemopoietin family are defined by the presence of a conserved 200 amino acid extracellular domain known as the haemopoietin domain [2]. We report here the isolation of NR6, a haemopoietin receptor that, like the p40 subunit of interleukin-12 (IL-12) [3] and the EBI3 gene induced by Epstein-Barr virus infection in lymphocytes [4], contains a typical haemopoietin domain but lacks transmembrane and cytoplasmic domains. Although in situ hybridisation revealed NR6 expression at multiple sites in the developing embryo, mice lacking NR6 did not display obvious abnormalities and were born in the expected numbers. Neonatal NR6(-/-) mice failed to suckle, however, and died within 24 hours of birth, suggesting that NR6 is necessary for the recognition or processing of pheromonal signals or for the mechanics of suckling itself. In addition, NR6(-/-) mice had reduced numbers of haemopoietic progenitor cells, suggesting a potential role in the regulation of primitive haemopoiesis.

DAN is a secreted glycoprotein related to Xenopus cerberus.

We report that DAN, a potential cell cycle regulator and tumour suppressor, is a secreted glycoprotein related to Xenopus cerberus. DAN, cerberus, its mouse relative Cer-1/cer-l/Cerberus-like/Cerr1, and the recently described factor DRM/Gremlin, appear to be members of the cystine knot superfamily, which includes TGFbetas and BMPs. Like cerberus and mCer-1, DAN-induced cement glands as well as markers of anterior neural tissue and endoderm in Xenopus animal cap assays, features of BMP signalling blockade. During mouse embryogenesis, Dan was expressed from E8.5 in cranial mesenchyme and somites, then later in limb and facial mesenchyme. The pattern in somites was highly dynamic, with transcripts initially localized to the caudal half of the nascent epithelial somite, then, after maturation, to sclerotomal cells adjacent to the neural tube. Dan was also expressed in the developing myotome. The expression domains include sites in which BMP inhibition is known to be important for development. Thus, DAN appears to be a secreted factor belonging to the cystine knot superfamily, and one of a growing number of antagonists acting to modulate BMP signalling during development.

Murine cerberus homologue mCer-1: a candidate anterior patterning molecule.

Xenopus cerberus (Xcer) is a cytokine expressed in anterior mesendoderm overlapping and surrounding Spemann's gastrula organiser. When misexpressed in blastomeres, Xcer can induce ectopic heads with well-defined brain, cement gland, olfactory placodes, cyclopic eye, and occasionally liver and heart. We report here the identification of mCer-1, a murine gene related to cerberus. Both mCer-1 and Xcer appear to belong to the cystine knot superfamily, which includes TGF beta s and BMPs. In Xenopus animal cap assays, mCer-1 and Xcer induced cement glands and markers of anterior neural tissue and endoderm, characteristic of BMP inhibition. Furthermore, both antagonised the ventrolateral mesoderm-inducing activity of coexpressed BMP4. In mouse embryos, mCer-1 was expressed at early gastrulation in a stripe of primitive endoderm along the future anterior side of the egg cylinder, a region essential for anterior patterning. A second phase of expression was detected in anterior embryonic mesendoderm, and by late-streak stages most of the anterior half of the embryo was positive, except for the node and cardiac progenitors. Expression was later seen in the cranial portion of the two most-recently formed somites and in two stripes within presomitic mesoderm. In embryos lacking Otx2, a homeogene with a demonstrated role in anterior patterning, mCer-1 was still expressed in an anterior zone, although often abnormally. The data suggest that mCer-1 shares structural, functional, and expression characteristics with Xcer and may participate in patterning the anterior of the embryo and nascent somite region, in part, through a BMP-inhibitory mechanism.

Evidence for the formation of a heterotrimeric complex of leukaemia inhibitory factor with its receptor subunits in solution.

Leukaemia inhibitory factor (LIF) is a polyfunctional cytokine that is known to require at least two distinct receptor components (LIF receptor alpha-chain and gp130) in order to form a high-affinity, functional, receptor complex. Human LIF binds with unusually high affinity to a naturally occurring mouse soluble LIF receptor alpha-chain, and this property was used to purify a stable complex of human LIF and mouse LIF receptor alpha-chain from pregnant-mouse serum. Recombinant soluble human gp130 was expressed, with a FLAG(R) epitope (DYKDDDDK) at the N-terminus, in the methylotropic yeast Pichia pastoris and purified using affinity chromatography. The formation of a trimeric complex in solution was established by native gel electrophoresis, gel-filtration chromatography, sedimentation equilibrium analysis, surface plasmon resonance spectroscopy and chemical cross-linking. The stoichiometry of this solution complex was 1:1:1, in contrast with that of the complex of interleukin-6, the interleukin-6-specific low-affinity receptor subunit and gp130, which is 2:2:2.

Influence of interleukin-6 (IL-6) dimerization on formation of the high affinity hexameric IL-6.receptor complex.

The high affinity interleukin-6 (IL-6) signaling complex consists of IL-6 and two membrane-associated receptor components: a low affinity but specific IL-6 receptor and the affinity converter/signal transducing protein gp130. Monomeric (IL-6M) and dimeric (IL-6D) forms of Escherichia coli-derived human IL-6 and the extracellular ("soluble") portions of the IL-6 receptor (sIL-6R) and gp130 have been purified in order to investigate the effect of IL-6 dimerization on binding to the receptor complex. Although IL-6D has a higher binding affinity for immobilized sIL-6R, as determined by biosensor analysis employing surface plasmon resonance detection, IL-6M is more potent than IL-6D in a STAT3 phosphorylation assay. The difference in potency is significantly less pronounced when measured in the murine 7TD1 hybridoma growth factor assay and the human hepatoma HepG2 bioassay due to time-dependent dissociation at 37 degrees C of IL-6 dimers into active monomers. The increased binding affinity of IL-6D appears to be due to its ability to cross-link two sIL-6R molecules on the biosensor surface. Studies of the IL-6 ternary complex formation demonstrated that the reduced biological potency of IL-6D resulted from a decreased ability of the IL-6D (sIL-6R)2 complex to couple with the soluble portion of gp130. These data imply that IL-6-induced dimerization of sIL-6R is not the driving force in promoting formation of the hexameric (IL-6 IL-6R gp130)2 complex. A model is presented whereby the trimeric complex of IL-6R, gp130, and IL-6M forms before the functional hexamer. Due to its increased affinity for the IL-6R but its decreased ability to couple with gp130, we suggest that a stable IL-6 dimer may be an efficient IL-6 antagonist.

Platelet-derived growth factor stimulates the release of protein kinase A from the cell membrane.

The mitogenic action of growth factors involves the stimulation of intracellular protein kinases. In this report we have characterized the major protein kinase released from Balb/c 3T3 and normal rat kidney plasma membranes by the action of platelet-derived growth factor (PDGF). PDGF appears to stimulate the release of approximately 10 proteins, at least one of which is a kinase capable of phosphorylating proteins on Ser or Thr (as determined by the lability of the phosphate to alkali treatment). More than 90% of the Ser/Thr kinase activity was inhibited by PKI5-22, a specific peptide inhibitor of the cAMP-dependent protein kinase (PKA). We used immunoblotting to confirm that the kinase released in response to PDGF was PKA. cAMP also stimulated the release of PKA, and the set of protein substrates phosphorylated was similar following PDGF or cAMP stimulation. Interestingly, in the presence of a cAMP analogue ((Rp)-cAMPS), cAMP could not induce dissociation of PKA from the membranes, whereas stimulation by PDGF increased the level of PKA activation. Furthermore, unlike Swiss 3T3 cells, neither Balb/c 3T3 fibroblasts nor normal rat kidney cells accumulate cAMP in response to PDGF, yet the level of PKA in the cytosol of these intact cells increases in response to PDGF. Thus, it appears as though PDGF activation of the membrane-associated form of the PKA holoenzyme occurs by a mechanism independent of an elevation in cAMP levels.

Synergies between micropreparative high-performance liquid chromatography and an instrumental optical biosensor.

The recent development of an automated surface plasmon resonance technology for the measurement of biomolecular interactions (Pharmacia BIAcore) has provided new opportunities for the detection and analysis of protein-protein interactions. In the BIAcore, detection is based on changes in surface plasmon resonance which are monitored optically. Changes in surface plasmon resonance correspond to changes in surface concentration of macromolecules and can be monitored in real time. We have found that the detection sensitivity obtainable with this technology (ng/ml concentrations of specific ligands are readily detectable for many applications) is complementary "in a bidirectional manner" to micropreparative HPLC. Thus micropreparative HPLC may be used to purify and characterise reagents for the biosensor, whilst the biosensor may be used to define chromatographic parameters such as elution conditions for affinity chromatography or serve as an affinity detector for fractions obtained during chromatographic purification. Examples of such applications, including the potential of the biosensor to search for and monitor the purification of unknown ligands for which the target molecule has been identified, are shown. In particular, the use of the biosensor to monitor the purification of soluble epidermal growth factor receptor from A431 cell conditioned media is demonstrated.

Structural characterisation of native and recombinant forms of the neurotrophic cytokine MK.

The retinoic acid (RA)-inducible midkine (MK) gene encodes a heparin-binding protein which can induce neurite outgrowth in cultured mammalian embryonic brain cells. This cytokine shares 65% amino acid sequence identity with another RA-inducible cytokine, pleiotropin (PTN). Both proteins contain 10 conserved cysteine residues, all of which appear to be disulphide linked. MK and PTN are also rich in lysine and arginine residues rendering them susceptible to proteolysis during purification, and making large-scale preparation of these molecules inherently difficult. Recombinant MK has been expressed as a fusion protein using a pGEX vector transfected into E. coli. To enable refolding of MK, the fusion protein was stored in solution at 4 degrees C for 14 days in the presence of dithiothreitol (DTT). Thrombin cleavage of the fusion protein, post storage, typically generated 5 mg of MK per litre of bacterial pellet. To establish the structural integrity of the recombinant product, we have analysed the refolding kinetics and compared the disulphide bond assignment of recombinant MK with that of native MK and native PTN. The synergistic use of micropreparative HPLC, to separate and recover in small eluant volumes enzymatically derived peptide fragments, with matrix assisted laser desorption mass spectrometry (MALD-MS) and N-terminal sequence analysis has allowed the unambiguous identification of the disulphide bonded fragments of native and recombinant MK. The disulphide bond assignment of MK is C12-C36, C20-C45, C27-C49, C59-C91 and C69-C101, and is equivalent to that of PTN.

Mapping of the antibody- and receptor-binding domains of granulocyte colony-stimulating factor using an optical biosensor. Comparison with enzyme-linked immunosorbent assay competition studies.

An automated optical biosensor instrument for measuring molecular interactions (Pharmacia BIAcore) has been used to characterise the epitopes recognised by 15 monoclonal antibodies raised against recombinant human granulocyte colony-stimulating factor (G-CSF). The BIAcore combines an autosampler and integrated microfluidic cartridge for the introduction and transportation of samples to the sensor chip surface, with surface plasmon resonance to detect binding events. A rabbit anti-mouse Fc antibody, coupled to the sensor surface in situ using conventional protein chemistry techniques, was used to capture an anti-G-CSF monoclonal antibody. G-CSF was bound to this antibody by injection over the sensor surface. Multi-site binding experiments were then performed in which other anti-G-CSF monoclonal antibodies were injected sequentially over the surface, and their ability to bind to the G-CSF in a multimolecular complex monitored in real time. Results obtained using the biosensor have been compared with data obtained by cross competition studies using biotinylated antibodies or antibody binding studies using chemically or enzymatically derived G-CSF peptide fragments or synthetic peptides. The results of these studies are in excellent agreement with the data from the BIAcore, although modification of the antibody or G-CSF occasionally altered the epitope affinity.

Micropreparative ion exchange high performance liquid chromatography: applications to microsequence analysis.

Data on the characterization of anion and cation micropreparative (50 x 1.6 mm i.d.) HPLC columns is presented. It is shown how subnanomole quantities of protein can be efficiently recovered from such columns, rendering them compatible for use in multidimensional chromatographic strategies for the purification of trace biological samples. By selection of appropriate solvent systems (e.g., buffer-free sodium chloride solutions), the small eluant peak volumes can be loaded directly onto the gas phase sequencer, and N-terminal sequence data obtained. The potential of the technique is illustrated for the purification of a GTPase activating protein (GAP-3).