Intracerebroventricular delivery of vascular endothelial growth factor in patients with amyotrophic lateral sclerosis, a phase I study.

We studied the feasibility, safety, tolerability and pharmacokinetics of intracerebroventricular delivery of recombinant human vascular endothelial growth factor in patients with amyotrophic lateral sclerosis. In this phase I study in patients with amyotrophic lateral sclerosis, the study drug was delivered using an implantable programmable pump connected to a catheter inserted in the frontal horn of the lateral cerebral ventricle. A first cohort received open label vascular endothelial growth factor (0.2, 0.8 and 2 µg/day), a second cohort received placebo, 0.8 or 2 µg/day of study dug. After the 3-month study period, all patients could participate in an open label extension study. In total, 18 patients with amyotrophic lateral sclerosis, seen at the University Hospitals in Leuven were included. The surgical procedure was well tolerated in most patients. One patient had transient postoperative seizures, due to an ischemic lesion along the catheter tract. The first 3-month study period was completed by 15/18 patients. Administration of 2 µg/day vascular endothelial growth factor resulted in sustained detectable levels in cerebrospinal fluid. A pulmonary embolus occurred in 3 patients, in 1 patient in the first 3-month study, and in 2 patients during the open label extension study. The study drug was well tolerated in the other patients, for up to 6 years in the open label extension study. Our study shows that intracerebroventricular administration of 2 µg/day of vascular endothelial growth factor to patients with amyotrophic lateral sclerosis is feasible, results in detectable cerebrospinal fluid levels and is well tolerated in most patients. The most common serious adverse event was a pulmonary embolus.

Generation of tumour-necrosis-factor-alpha-specific affibody molecules capable of blocking receptor binding in vitro.

Affibody molecules specific for human TNF-alpha (tumour necrosis factor-alpha) were selected by phage-display technology from a library based on the 58-residue Protein A-derived Z domain. TNF-alpha is a proinflammatory cytokine involved in several inflammatory diseases and, to this day, four TNF-alpha-blocking protein pharmaceuticals have been approved for clinical use. The phage selection generated 18 unique cysteine-free affibody sequences of which 12 were chosen, after sequence cluster analysis, for characterization as proteins. Biosensor binding studies of the 12 Escherichia coli-produced and IMAC (immobilized-metal-ion affinity chromatography)-purified affibody molecules revealed three variants that demonstrated the strongest binding to human TNF-alpha. These three affibody molecules were subjected to kinetic binding analysis and also tested for their binding to mouse, rat and pig TNF-alpha. For ZTNF-alpha:185, subnanomolar affinity (KD=0.1-0.5 nM) for human TNF-alpha was demonstrated, as well as significant binding to TNF-alpha from the other species. Furthermore, the binding site was found to overlap with the binding site for the TNF-alpha receptor, since this interaction could be efficiently blocked by the ZTNF-alpha:185 affibody. When investigating six dimeric affibody constructs with different linker lengths, and one trimeric construct, it was found that the inhibition of the TNF-alpha binding to its receptor could be further improved by using dimers with extended linkers and/or a trimeric affibody construct. The potential implication of the results for the future design of affibody-based reagents for the diagnosis of inflammation is discussed.

Engineering of a femtomolar affinity binding protein to human serum albumin.

We describe the development of a novel serum albumin binding protein showing an extremely high affinity (K(D)) for HSA in the femtomolar range. Using a naturally occurring 46-residue three-helix bundle albumin binding domain (ABD) of nanomolar affinity for HSA as template, 15 residues were targeted for a combinatorial protein engineering strategy to identify variants showing improved HSA affinities. Sequencing of 55 unique phage display-selected clones showed a strong bias for wild-type residues at nine positions, whereas various changes were observed at other positions, including charge shifts. Additionally, a few non-designed substitutions appeared. On the basis of the sequences of 12 variants showing high overall binding affinities and slow dissociation rate kinetics, a set of seven 'second generation' variants were constructed. One variant denoted ABD035 displaying wild-type-like secondary structure content and excellent thermal denaturation/renaturation properties showed an apparent affinity for HSA in the range of 50-500 fM, corresponding to several orders of magnitude improvement compared with the wild-type domain. The ABD035 variant also showed an improved affinity toward serum albumin from a number of other species, and a capture experiment involving human serum indicated that the selectivity for serum albumin had not been compromised from the affinity engineering.

Generation of Affibody ligands binding interleukin-2 receptor alpha/CD25.

Affibody molecules specific for human IL-2Ralpha, the IL-2 (interleukin-2) receptor alpha subunit, also known as CD25, were selected by phage-display technology from a combinatorial protein library based on the 58-residue Protein A-derived Z domain. The IL-2R system plays a major role in T-cell activation and the regulation of cellular immune responses. Moreover, CD25 has been found to be overexpressed in organ rejections, a number of autoimmune diseases and T-cell malignancies. The phage-display selection using Fc-fused target protein generated 16 unique Affibody molecules targeting CD25. The two most promising binders were characterized in more detail using biosensor analysis and demonstrated strong and selective binding to CD25. Kinetic biosensor analysis revealed that the two monomeric Affibody molecules bound to CD25 with apparent affinities of 130 and 240 nM respectively. The Affibody molecules were, on biosensor analysis, found to compete for the same binding site as the natural ligand IL-2 and the IL-2 blocking monoclonal antibody 2A3. Hence the Affibody molecules were assumed to have an overlapping binding site with IL-2 and antibodies targeting the IL-2 blocking Tac epitope (for example, the monoclonal antibodies Daclizumab and Basiliximab, both of which have been approved for therapeutic use). Furthermore, immunofluorescence microscopy and flow-cytometric analysis of CD25-expressing cells demonstrated that the selected Affibody molecules bound to CD4+ CD25+ PMBCs (peripheral-blood mononuclear cells), the IL-2-dependent cell line NK92 and phytohaemagglutinin-activated PMBCs. The potential use of the CD25-binding Affibody molecules as targeting agents for medical imaging and for therapeutic applications is discussed.

Selection and characterization of Affibody ligands binding to Alzheimer amyloid beta peptides.

Affibody (Affibody) ligands specific for human amyloid beta (Abeta) peptides (40 or 42 amino acid residues in size), involved in the progress of Alzheimer's disease, were selected by phage display technology from a combinatorial protein library based on the 58-amino acid residue staphylococcal protein A-derived Z domain. Post-selection screening of 384 randomly picked clones, out of which 192 clones were subjected to DNA sequencing and clustering, resulted in the identification of 16 Affibody variants that were produced and affinity purified for ranking of their binding properties. The two most promising Affibody variants were shown to selectively and efficiently bind to Abeta peptides, but not to the control proteins. These two Affibody ligands were in dimeric form (to gain avidity effects) coupled to affinity resins for evaluation as affinity devices for capture of Abeta peptides from human plasma and serum. It was found that both ligands could efficiently capture Abeta that were spiked (100 microgml(-1)) to plasma and serum samples. A ligand multimerization problem that would yield suboptimal affinity resins, caused by a cysteine residue present at the binding surface of the Affibody ligands, could be circumvented by the generation of second-generation Affibody ligands (having cysteine to serine substitutions). In an epitope mapping effort, the preferred binding site of selected Affibody ligands was mapped to amino acids 30-36 of Abeta, which fortunately would indicate that the Affibody molecules should not bind the amyloid precursor protein (APP). In addition, a significant effort was made to analyze which form of Abeta (monomer, dimer or higher aggregates) that was most efficiently captured by the selected Affibody ligand. By using Western blotting and a dot blot assay in combination with size exclusion chromatography, it could be concluded that selected Affibody ligands predominantly bound a non-aggregated form of analyzed Abeta peptide, which we speculate to be dimeric Abeta. In conclusion, we have successfully selected Affibody ligands that efficiently capture Abeta peptides from human plasma and serum. The potential therapeutic use of these optimized ligands for extracorporeal capture of Abeta peptides in order to slow down or reduce amyloid plaque formation, is discussed.

Design of an optimized scaffold for affibody molecules.

Affibody molecules are non-immunoglobulin-derived affinity proteins based on a three-helical bundle protein domain. Here, we describe the design process of an optimized Affibody molecule scaffold with improved properties and a surface distinctly different from that of the parental scaffold. The improvement was achieved by applying an iterative process of amino acid substitutions in the context of the human epidermal growth factor receptor 2 (HER2)-specific Affibody molecule Z(HER2:342). Replacements in the N-terminal region, loop 1, helix 2 and helix 3 were guided by extensive structural modeling using the available structures of the parent Z domain and Affibody molecules. The effect of several single substitutions was analyzed followed by combination of up to 11 different substitutions. The two amino acid substitutions N23T and S33K accounted for the most dramatic improvements, including increased thermal stability with elevated melting temperatures of up to +12 degrees C. The optimized scaffold contains 11 amino acid substitutions in the nonbinding surface and is characterized by improved thermal and chemical stability, as well as increased hydrophilicity, and enables generation of identical Affibody molecules both by chemical peptide synthesis and by recombinant bacterial expression. A HER2-specific Affibody tracer, [MMA-DOTA-Cys61]-Z(HER2:2891)-Cys (ABY-025), was produced by conjugating MMA-DOTA (maleimide-monoamide-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) to the peptide produced either chemically or in Escherichia coli. ABY-025 showed high affinity and specificity for HER2 (equilibrium dissociation constant, K(D), of 76 pM) and detected HER2 in tissue sections of SKOV-3 xenograft and human breast tumors. The HER2-binding capacity was fully retained after three cycles of heating to 90 degrees C followed by cooling to room temperature. Furthermore, the binding surfaces of five Affibody molecules targeting other proteins (tumor necrosis factor alpha, insulin, Taq polymerase, epidermal growth factor receptor or platelet-derived growth factor receptor beta) were grafted onto the optimized scaffold, resulting in molecules with improved thermal stability and a more hydrophilic nonbinding surface.