Engineered antibodies

Human anti-ErbB2 immunoagents--immunoRNases and compact antibodies

Immunotherapy, based on mAbs specifically directed against cancer cells, is considered a precious strategy in the fight against cancer because of its selectivity and lack of multidrug resistant effects. However, there are obstacles to the complete success of current immunotherapy such as immune responses to nonhuman or even humanized antibodies and the large size of the antibodies, which hinders their diffusion into bulky tumors. Fully human, small immunoagents, capable of inhibiting tumor growth may overcome these problems and provide safe, highly selective and effective antitumor drugs. An attractive target for immunotherapy is ErbB2, a transmembrane tyrosine kinase receptor, overexpressed on tumor cells of different origin, with a key role in the development of malignancy. An anti-ErbB2 humanized monoclonal (Herceptin) is currently used with success for breast cancer therapy; however, it can engender cardiotoxicity and a high proportion of breast cancer patients are resistant to Herceptin treatment. Anti-ErbB2 immunoagents of human origin, with potentially no or very low immunogenicity have been engineered to assemble 'compact', i.e. reduced size, antibodies, one consisting of a human single-chain antibody fragment (scFv) fused to a human RNase to construct an immunoRNase and the other made up of two human scFv molecules fused to the Fc region of a human IgG1. By choosing a human antibody fragment as the immune moiety and a human RNase as the effector moiety, an immunoRNase would be both nonimmunogenic and nontoxic, as it becomes toxic only when the scFv promotes its internalization by target cells. The alternative strategy of compact antibodies was aimed at producing therapeutic agents with an increased half-life, prolonged tumor retention and the ability to recruit host effector functions. Moreover, the bivalency of compact antibodies can be exploited to construct bispecific antibodies, as well as for other therapeutic applications.

Anti-vascular endothelial growth factor therapy for ocular neovascular disease

PURPOSE OF REVIEW

Recent research has shown that vascular endothelial growth factor (VEGF) is responsible for many ocular pathologies involving neovascularization. Over the past several years several new agents targeting VEGF have become commercially available for intraocular use. These agents have revolutionized the care of neovascular age related macular degeneration and have great potential for other blinding conditions such as diabetic retinopathy, retinopathy of prematurity, and neovascular glaucoma.

RECENT FINDINGS

The VEGF Inhibition Study in Ocular Neovascularization (VISION) trial first showed that an anti-VEGF agent (pegaptanib) was able to prevent vision loss in neovascular age related macular degeneration. The Minimally Classic/Occult Trial of Anti-VEGF Antibody Ranibizumab in the Treatment of Neovascular AMD (MARINA) and Anti-VEGF Antibody for the Treatment of Predominantly Classic Choroidal Neovascularization in AMD (ANCHOR) trials showed that ranibizumab prevented moderate vision loss in neovascular age related macular degeneration and for the first time that a substantial proportion of patients regained vision. Smaller case series have shown that bevacizumab can regress retinal, iris and disc neovascularization. Ongoing trials are investigating the utility of anti-VEGF therapy in retinopathy of prematurity, diabetic retinopathy, and neovascular glaucoma.

SUMMARY

Newer anti-VEGF therapies have shown unprecedented efficacy in treating age related macular degeneration with many patients experiencing improvement in vision. Ongoing trials will help guide their use in age related macular degeneration and expand their indications to many other blinding diseases.

Development and preclinical testing of a high-affinity single-chain antibody against (+)-methamphetamine

Chronic or excessive (+)-methamphetamine (METH) use often leads to addiction and toxicity to critical organs like the brain. With medical treatment as a goal, a novel single-chain variable fragment (scFv) against METH was engineered from anti-METH monoclonal antibody mAb6H4 (IgG, kappa light chain, K(d) = 11 nM) and found to have similar ligand affinity (K(d) = 10 nM) and specificity as mAb6H4. The anti-METH scFv (scFv6H4) was cloned, expressed in yeast, purified, and formulated as a naturally occurring mixture of monomer ( approximately 75%) and dimer ( approximately 25%). To test the in vivo efficacy of the scFv6H4, male Sprague-Dawley rats (n = 5) were implanted with 3-day s.c. osmotic pumps delivering 3.2 mg/kg/day METH. After reaching steady-state METH concentrations, an i.v. dose of scFv6H4 (36.5 mg/kg, equimolar to the METH body burden) was administered along with a [(3)H]scFv6H4 tracer. Serum pharmacokinetic analysis of METH and [(3)H]scFv6H4 showed that the scFv6H4 caused an immediate 65-fold increase in the METH concentrations and a 12-fold increase in the serum METH area under the concentration-time curve from 0 to 480 min after scFv6H4 administration. The scFv6H4 monomer was quickly cleared or converted to multivalent forms with an apparent t(1/2lambdaz) of 5.8 min. In contrast, the larger scFv6H4 multivalent forms (dimers, trimers, etc.) showed a much longer t(1/2lambdaz) (228 min), and the significantly increased METH serum molar concentrations correlated directly with scFv6H4 serum molar concentrations. Considered together, these data suggested that the scFv6H4 multimers (and not the monomer) were responsible for the prolonged redistribution of METH into the serum.

Directed evolution for drug and nucleic acid delivery

Directed evolution is a term used to describe a variety of related techniques to rapidly evolve peptides and proteins into new forms that exhibit improved properties for specific applications. In this process, molecular biology techniques allow the creation of up to billions of mutants in a single experiment, which are then subjected to high-throughput screening to identify those with enhanced activity. Applications of directed evolution to drug and gene delivery have been recently described, including those that improve the effectiveness of therapeutic enzymes, targeting peptides and antibodies, and the effectiveness or tropism of viral vectors for use in gene therapy. This review first introduces fundamental concepts of directed evolution, and then discusses emerging applications in the field of drug and gene delivery.

Internalization via Antennapedia protein transduction domain of an scFv antibody toward c-Myc protein

We constructed a single-chain variable fragment miniantibody (G11-scFv) directed toward the transactivation domain of c-Myc, which is fused with the internalization domain Int of Antennapedia at its carboxyl terminus (a cargo-carrier construct). In ELISA experiments, an EC(50) for binding saturation was achieved at concentrations of G11-scFv-Int(-) of approximately 10(-8) M. Internalization of a fluoresceinated Fl-G11-scFv-Int(+) construct was observed in intact human cultured cells with confocal microscopy. After 5 h of incubation in medium containing 1 microM Fl-G11-scFv-Int(+) or Fl-G11-scFv-Int(-), fluorescence intensity was determined in individual cells, both for cytoplasmic and nuclear compartments: concentration levels of Fl-G11-scFv-Int(+), relative to the extracellular culture medium concentration, were 4-5 times higher in the cytoplasm, 7-8 times higher in the nucleus, and 10 times higher in the nucleoli. In the same experimental conditions, the Fl-G11-scFv-Int(-) construct was 3-4 times more concentrated outside of the cells than inside. Cell membranes kept their integrity after 5 h of incubation. The antiproliferative activity of our miniantibody was studied on HCT116 cells. Incubation with 4 microM G11-scFv-Int(+) for 4 days induced very significant statistical and biological growth inhibition, whereas Int alone was completely inactive. Miniantibodies capable of penetrating cell membranes dramatically broaden the potential for innovative therapeutic agents and attack of new targets.

From Combinatorial Chemistry to Cancer-Targeting Peptides

Several monoclonal antibodies that target cell surface receptors have gained approval by the U.S. Food and Drug Administration and are widely used in the treatment of some cancers. These include but are not limited to the anti-CD20 antibody Rituximab, used in lymphoma treatment, as well as anti-HER-2 antibody for breast cancer therapy. The efficacy of this cancer immunotherapy modality is, however, limited by the large size of the antibody (160 kd) and its relatively nonspecific binding to the reticuloendothelial system. This latter property is particularly problematic if the antibody is used as a vehicle to deliver radionuclides, cytotoxic drugs, or toxins to the tumor site. Peptides, peptidomimetic, or small molecules are thus attractive as alternative cell surface targeting agents for cancer imaging and therapy. Cancer cell surface targeting peptides can be derived from known native peptide hormones such as somatostatin and bombesin, or they can be identified through screening combinatorial peptide libraries against unknown cell surface receptor targets. Phage-display peptide library and one-bead one-compound (OBOC) combinatorial library methods have been successfully used to discover peptides that target cancer cells or tumor blood vessel endothelial cells. The phage-display peptide library method, because of its biological nature, can only display l-amino acid peptides. In contrast, the OBOC combinatorial library method allows for bead-surface display of peptides that contain l-amino acids, d-amino acids, unnatural amino acids, or other organic moieties. We have successfully used the OBOC method to discover and optimize ligands against unique cell surface receptors of prostate cancer, T- and B-cell lymphoma, as well as ovarian and lung cancers, and we have used some of these peptides to image xenografts in nude mice with high specificity. Here, we (i) review the literature on the use of phage-display and OBOC combinatorial library methods to discover cancer and tumor blood vessel targeting ligands, and (ii) report on the use of an ovarian cancer targeting ligand, OA02, as an in vivo PET imaging probe in a xenograft model in nude mice.

The Thomsen-Friedenreich disaccharide as antigen for in vivo tumor targeting with multivalent scFvs

The Thomsen-Friedenreich disaccharide (TF(alpha)) is a promising antigen for tumor immunotargeting, since it is almost exclusively expressed on carcinoma tissues. So far, an obstacle preventing the exploitation of TF for immunotargeting has been the lack of suitable (non-IgM) antibodies with high affinity and specificity. Recently we reported on a novel strategy for generating antibodies toward small uncharged carbohydrates and the generation of recombinant antibodies toward TF. Among them, two multivalent scFv antibodies showed sub-micromolar functional affinities and appeared well suited for immunotargeting. In the present study, the trimeric scFv(1aa) and the tetrameric scFv(0aa) have been further developed for radioimmunotargeting. The scFvs were radiolabeled with (111)In using DTPA as chelator without losing binding activity or molecular stoichiometry. Binding affinities as high as 1 x 10(-7) M toward TF displayed on living cells were determined. Antibody biodistribution and tumor targeting efficacy were studied in TF-positive human breast cancer (ZR-75-1) bearing mice. TF was successfully targeted in vivo with tumor uptakes of approximately 11 and 8% ID/g after 24 h for the trimeric and tetrameric scFv, respectively. These results validate TF as a potent antigen for tumor targeting. The biodistribution of the scFvs was comparable to that reported for IgGs. In contrast to the IgGs, the serum clearance of the scFvs was very fast, which could be an advantage in a therapeutic setting. Furthermore, kidney uptake, which is often critical for small recombinant antibodies labeled with radio-metals, was low with the tetramer (11% ID/g). We conclude that the multimeric anti-TF scFvs are promising candidates to be further developed toward therapeutic application.

Intracellular Ribosome Display Via SecM Translation Arrest as a Selection for Antibodies with Enhanced Cytosolic Stability

Ribosome display is a powerful approach for affinity and stability maturation of recombinant antibodies. However, since ribosome display is performed entirely in vitro, there are several limitations to this approach including technical challenges associated with: (i) efficiently expressing and stalling antibodies on ribosomes using cell-free translation mixtures; and (ii) folding of antibodies in buffers where the concentration and composition of factors varies from that found in the intracellular milieu. We have developed a novel method for intracellular ribosome display that takes advantage of the recently discovered Escherichia coli SecM translation arrest mechanism. Specifically, we provide the first evidence that the encoding mRNA of SecM-stalled heterologous proteins remains stably attached to ribosomes, thereby enabling creation of stalled antibody-ribosome-mRNA (ARM) complexes entirely inside of living cells. Since ARM complexes faithfully maintain a genotype-phenotype link between the arrested antibody and its encoding mRNA, we demonstrate that this method is ideally suited for isolating stability-enhanced single-chain variable fragment (scFv) antibodies that are efficiently folded and functional in the bacterial cytoplasm.

Single-molecule selection and recovery of structure-specific antibodies using atomic force microscopy

Protein misfolding and aggregation are a common thread in numerous diseases including Alzheimer's, Parkinson's, Huntington's, amyotrophic lateral sclerosis, diabetes, and prion-related diseases. Elucidation of the role played by the various protein forms in these diseases requires reagents that can target specific protein forms. Here we present a method to isolate antibodies that bind to a specific protein form. We combined the imaging and nanomanipulation capabilities of atomic force microscopy (AFM) with the protein diversity of phage display antibody libraries to develop a technology that allows us to recover a single antibody molecule that is bound to a single protein molecular target. The target protein-antibody complex is first imaged by AFM, the AFM tip is then manipulated by nanolithography over the target antibody to recover the associated phage, and the antibody gene is recovered from the single phage particle by polymerase chain reaction.

The antibody-mediated targeted delivery of interleukin-15 and GM-CSF to the tumor neovasculature inhibits tumor growth and metastasis

Tumor-targeting immunocytokines represent a new class of anticancer pharmaceutical agents, which often display a superior therapeutic index compared with the corresponding unconjugated cytokines. In this article, we have studied the anticancer properties of interleukin-15 (IL-15) and granulocyte macrophage colony-stimulating factor (GM-CSF), fused to the human antibody fragment scFv(L19), specific to the EDB domain of fibronectin, a marker of angiogenesis. The immunocytokines L19-IL-15 and L19-GM-CSF were expressed in mammalian cells and purified to homogeneity, revealing no loss of cytokine activity in in vitro assays. Furthermore, the ability of the two immunocytokines to selectively localize to tumors in vivo was confirmed by biodistribution analysis with radioiodinated protein preparations. L19-IL-15 and L19-GM-CSF displayed a potent antitumor activity both in s.c. and in metastatic F9 and C51 murine models of cancer in immunocompetent mice. This therapeutic action was superior compared with IL-15-based and GM-CSF-based fusion proteins, containing antibodies of irrelevant specificity in the mouse, which were used as non-tumor-targeting controls. For both L19-IL-15 and L19-GM-CSF immunocytokines, CD8(+) T cells seemed to mostly contribute to the therapeutic action as shown by in vivo cell depletion experiments. The results presented in this article are of clinical significance, considering the fact that the sequence of EDB is identical in mouse and man and that the tumor-targeting ability of the L19 antibody has been extensively shown in clinical trials in patients with cancer.

Expression and detection strategies for an scFv fragment retaining the same high affinity than Fab and whole antibody: Implications for therapeutic use in prion diseases

Since antibodies currently constitute the most rapidly growing class of human therapeutics, the high-yield production of recombinant antibodies and antibody fragments is a real challenge. Using as model a monoclonal antibody directed against the human prion protein that we prepared previously and tested for its therapeutic value, we describe here experimental conditions allowing the production of large quantities (up to 35 mg/l of bacterial culture) of correctly refolded and totally functional single chain fragment variable (scFv). These quantities were sufficient to characterize the binding properties of this small recombinant fragment through in vitro and ex vivo approaches. Interestingly, this scFv retains full binding capacity for its antigen, i.e. the human prion protein, when compared with the corresponding Fab or whole antibody, and recognizes soluble, solid-phase-adsorbed, and membrane-bound prion protein. This strongly suggests that from the mAb cloning step to the refolding of the recombinant fragment, each stage is well controlled, leading to almost 100% functional scFv. These results are of interest not only in view of possible immunotherapy for prion diseases, but also more generally in emphasizing the great promise of these small recombinant molecules in the context of targeted therapies.

Role of monoclonal antibodies in tumor-specific immunity

Monoclonal antibodies, considered to be 'magic bullets' 20 years ago, may finally be realizing their full potential, particularly in the area of oncology, where > 10 monoclonal antibodies are approved for treatment. Monoclonal antibodies are being used to modulate tumor-specific immunity through several approaches: antibodies that direct cytotoxicity against the tumor through cellular or complement-mediated pathways; antibodies that directly modulate immune regulation; antibodies that alter tolerance to tumor antigens; and antibodies that act as antigen mimetics through the anti-idiotype network. Therapeutic progress in these areas is reviewed as well as the potential to combine these approaches with standard therapies.

An inductively coupled plasma mass spectrometry method for the quantification of yttrium-antibody based drugs using stable isotope tracing

Targeted radioimmunotherapy has been recently clinically validated and approved for the treatment of cancer by the US Food and Drug Administration. This therapeutic approach employs monoclonal antibodies directed to cancer-related, cell-surface antigens coupled to beta-emitting nuclides. 90Y is one of the most useful radioisotopes in the development of antibody based radioimmunotherapy and evaluation of the pharmacokinetic profile for 90Y-radiopharmaceuticals is usually performed by radiochemical methods. In this work we have developed an alternative radioactive-free approach to evaluate pharmacokinetic profiles based on the inductively coupled plasma mass spectrometric (ICP-MS) quantification of 89Y. A highly sensitive and rapid method for the determination of yttrium in urine is described and applied to evaluate the urinary clearance of antibody-based drugs labeled with the stable isotope of yttrium, 89Y. This approach overcomes some important limitations for pre-clinical radioanalytical methods such as radiation hazards and radioactive waste disposal. Method development was performed by determining detection and quantification limits, and precision as repeatability and trueness. These performance parameters fulfilled the acceptance criteria for bioanalytical methods.

Development and characterization of mouse hybridomas

Cell fusion protocols that were developed by Kohler and Milstein in the mid-1970s and aimed at producing and characterization of mouse monoclonal antibodies (MAbs) remain the gold standard of hybridoma development. Despite tremendous progress in using MAbs in multiple research, diagnostic, and therapeutic areas, major experimental flaws in designing and carrying out hybridoma experimentation often result in the production of hybridomas exhibiting poor growth parameters and secreting low-specificity and low-affinity antibodies. This methodology chapter is built around the conventional hybridoma protocol, with a special emphasis on tissue culture and biochemical techniques aimed at producing truly monospecific and highly active mouse MAbs.

Immunotoxins: a review of their use in cancer treatment

Abstract

Antibody therapies have become an important component in the management of malignant disease. Antibodies can block tumour growth factors or their receptors, activate immunological attack on the tumour, and are used to deliver payloads such as radioisotopes, cytotoxic drugs or toxins. Immunotoxins are a new class of antitumour agents consisting of tumour- selective ligands (generally monoclonal antibodies [MoAbs]) linked to highly toxic protein molecules and take the advantage of the exquisite specificity of antibodies to selectively target drug delivery and the potency of toxins to kill the target cells. Toxins are modified to remove their normal tissue-binding domains by genetic engineering. Analysis of the aminoacid sequence of the region specific for immunogenecity and the signal transduction mechanisms involved in the interaction of immunotoxins with tumour cells will give the clue for the development of most efficient immunotoxins.

Therapeutic Expression of an Anti-Death Receptor 5 Single-Chain Fixed-Variable Region Prevents Tumor Growth in Mice

The clinical use of the single-chain fixed-variable (scFv) fragments of recombinant monoclonal antibodies as credible alternatives for classic therapeutic antibodies has two limitations: rapid blood clearance and inefficient local expression of functional molecules. In attempt to address these issues, we have developed a novel gene therapy protocol in which the anti-death receptor 5 (DR5) scFv fragments were either in vitro expressed in several tumor cell lines, or in vivo expressed in mice, using recombinant adeno-associated virus (rAAV)-mediated gene transfer. Viral transduction using the rAAV-S3C construct, which encodes a scFv molecule (S3C scFv) specific to DR5, led to stable expression in tumor cell lines and showed apoptosis-inducing activity in vitro, which could be inhibited by recombinant DR5 but not by DR4. A single i.m. injection of rAAV-S3C virus in nude mice resulted in stable expression of DR5-binding S3C scFv proteins in mouse sera for at least 240 days. Moreover, the expression of S3C scFv was associated with significant suppression of tumor growth and the increase of tumor cell apoptosis in previously established s.c. human lung LTEP-sml and liver Hep3B tumor xenografts.

Suppression of human hepatoma growth in vivo by a monoclonal antibody against a Mr 45,000 protein

The monoclonal antibody T2-2 was originally raised against the colorectal carcinoma cell line LS174T and was found to bind to several other human carcinomas, including hepatoma and ovarian cancer. The goal of this study was to investigate the antitumor activity of mAb T2-2 in human tumor models and further characterize the antigen. mAb T2-2 inhibited the growth of human hepatocellular cell line SMMC 7721 in vivo and in vitro. Western blot analysis revealed that this mAb recognizes an unique Mr 45,000 band from tissue extracts of human hepatocellular carcinoma (HCC), which localizes to the cell periphery. In vitro cell assays indicate that T2-2 decreases cell adhesion to laminin, implying the functional role of T2-2 antigen in cell-matrix interaction and cell migration.

Vascular endothelial growth factor biology: clinical implications for ocular treatments

Decades of research on vascular endothelial growth factor (VEGF) have reached fruition with the recent development of intravitreal anti-VEGF treatments for exudative age-related macular degeneration. VEGF is a critical regulator of angiogenesis and vascular permeability with diverse roles, both pathological and physiological, during development and adulthood. The aim of this article is to review aspects of VEGF biology that may be relevant to the clinical use of anti-VEGF agents in ophthalmology: molecular characteristics and isoforms of VEGF; its roles in vasculogenesis, vascular maintenance and angiogenesis; systemic effects of VEGF inhibition; and properties of current anti-VEGF agents.

Novel proteins in emulsions using in vitro compartmentalization

IVC (in vitro compartmentalization) provides a complete cell-free approach for the production of novel targeted proteins. IVC uses aqueous droplets, which contain DNA and components for protein production, within water-in-oil emulsions. Recent advances in the composition and formation, as well as the detection, sorting and recovery, of the droplets enable the evolution of the encoded protein. Furthermore, IVC technology permits the step-wise addition of reagents into the droplets, making them suitable for high-throughput applications - where synthetic enzymes with substrate specificity are selected for catalytic activity, binding and regulation. In the broad field of in vitro display, developments such as the incorporation of unnatural amino acids and the production of cell toxic proteins expand the diverse spectrum of future applications for IVC.

A novel pentamer versus pentamer approach to generating neutralizers of verotoxin 1

Verotoxins (VTs), or shiga-like toxins, are produced by enterohemorrhagic Escherichia coli (EHEC), which cause hemorrhagic colitis and hemolytic uremic syndrome. VTs are the major virulence factors in EHEC infection due to their cytotoxicity to various types of cells. Here, we present a novel type of VT neutralizer based on pentavalent single-domain antibodies, or pentabodies. Two single-domain antibodies (sdAbs) specific for the receptor binding sites of the B subunit of VT1 (VT1B) were isolated from a naïve llama phage display library. These two sdAbs were pentamerized to generate pentameric VT neutralizers, VTI-1 and VTI-3. Both VT neutralizers bound wild type VT1B specifically with superior functional affinity. In vitro neutralization assays showed that VTI-1 and VTI-3 were able to neutralize 90% and 40%, respectively, of the cytotoxicity caused by VT1. This effort provides the basis of a novel type of VT neutralizer that can potentially be produced at a relatively low cost.

A comparative study of different vector designs for the mammalian expression of recombinant IgG antibodies

Monoclonal antibodies (Mab) are the fastest growing group of biopharmaceuticals in development. For production in mammalian cells, the four polypeptide chains of the immunoglobulin diheterotetramer must be assembled prior to exit from the endoplasmic reticulum. Various recombinant Mab expression vectors have been developed utilizing mono-and bicistronic expression cassettes encoded on one or two plasmids. However, there are only few studies providing information on the type of vector design optimal for stable or transient production of recombinant IgG. Consequently, in this study, we have constructed a series of mammalian expression vectors for the production of recombinant human or chimeric IgG antibodies with different expression cassette designs. Versions for monocistronic and bicistronic expression with different promoters and cistron arrangements were generated. Antibody production levels were evaluated in transiently transfected 293T and CHO-K1 cells. Furthermore, stable CHO cell lines were generated and analyzed for antibody production levels and stability. Our results indicate that compared to monocistronic expression, EMCV IRES-mediated bicistronic expression constructs yield similar antibody expression levels and show long-term stability in CHO cell lines. Addition of a third cistron encoding YFP was shown to facilitate screening and isolation of clones using a FACS sorter.

The use of immunoliposome for nutrient target regulation (a review)

Although research on the role of genetically engineered antibodies and liposomes in the immunology or the nutrition field is extensive, there is no case for immunoliposome to nutrient target regulation. It is known that liposomes are spherical particles that encapsulate a fraction of the solvent, in which they freely diffuse (float) into their interior. Therefore, identification of immunoliposomes in hypothalamic site or intestinal epithelial cells that are differentially regulated by liposomes encapsulating nutrients or drugs will be an important step toward understanding the role of immunoliposomes in nutrition regulation progression and ingredient stability. Consequently, a useful model (immunoliposomal nutrient delivery system, ILNDS) of nutrient target regulation via immunoliposomes is designed to regulate the endocrine system effectively. This review focuses on antibody libraries' construction, display and selection, a brief introduction of immunoliposome, and how to use ILNDS for nutrient target regulation.

Ranibizumab: treatment in patients with neovascular age-related macular degeneration

Vascular endothelial growth factor (VEGF)-A is a major regulator of angiogenesis and vascular permeability implicated in the development of diseases involving pathological angiogenesis and increased vascular permeability, such as neovascular age-related macular degeneration (AMD). LUCENTIS (ranibizumab), a humanized antigen-binding fragment (Fab) that neutralizes all VEGF-A isoforms and their biologically active degradation products, was recently approved by the FDA. Ranibizumab is the first FDA-approved treatment for neovascular AMD that maintains or improves vision in > or = 90% patients and provides a > or = 15-letter improvement in visual acuity for a quarter to a third of patients with all choroidal neovascularisation subtypes. Ranibizumab was associated with a < or = 1.7% rate of key serious ocular adverse events, such as endophthalmitis and uveitis, in two pivotal Phase III trials.

Established bioprocesses for producing antibodies as a basis for future planning

In the early years of monoclonal antibody production for human therapy and diagnosis the methods used were arrived at by individual organisations. However, there is now an accumulating body of information on antibodies and fragments that have been produced by processes approved for human use. This information is becoming available at a time when the number of potential antibody-based medicines is growing sharply. The review addresses the reported production routes, their scale and the titres achieved. It identifies the performances of fed-batch and perfusion culture versus batch culture, and compares processes for the production of antibodies for diagnosis and for antibody fragments. The analysis defines the likely routes of future production in a sector where demanding regulations constrain new technology. It also indicates what levels of performance new approaches will need to meet to be competitive.

Antivascular endothelial growth factor agents and their development: therapeutic implications in ocular diseases

PURPOSE

To provide an overview of angiogenesis and vascular endothelial growth factor (VEGF) and discusses the development approach, safety, and efficacy results of current and emerging anti-VEGF therapies for ocular diseases.

DESIGN

Analysis of literature and current clinical trials of antiangiogenic agents for age-related macular degeneration (AMD).

METHODS

Literature review.

RESULTS

There are several novel antiangiogenic molecules that target vascular endothelial growth factor and are being used in the management of AMD. Large scale, Phase III trials have shown promising results in improving vision in this devastating disease.

CONCLUSIONS

Therapies that target VEGF have shown tremendous promise as treatments for AMD.

Comparing antibody and small-molecule therapies for cancer

The 'magic bullet' concept of specifically targeting cancer cells at the same time as sparing normal tissues is now proven, as several monoclonal antibodies and targeted small-molecule compounds have been approved for cancer treatment. Both antibodies and small-molecule compounds are therefore promising tools for target-protein-based cancer therapy. We discuss and compare the distinctive properties of these two therapeutic strategies so as to provide a better view for the development of new drugs and the future direction of cancer therapy.

Latest technologies for the enhancement of antibody affinity

High affinity antibodies are crucial both for the discovery and validation of biomarkers for human health and disease and as clinical diagnostic and therapeutic reagents. This review describes some of the latest technologies for the design, mutation and selection of high affinity antibodies that provide a paradigm for molecular evolution of a far wider range of proteins including enzymes. Strategies include both in vivo and in vitro methods and embrace the latest concepts for antibody display and selection. Specifically, affinity enhancement can be tailored to the target-binding surface, typically the complementary determining region (CDR) loops in antibodies, whereas enhanced stability, expression or catalytic properties can be affected by selected changes to the core protein scaffold. Together, these technologies provide a rapid and powerful strategy to drive the next generation of protein-based reagents for numerous clinical, environmental and agribusiness applications.

Ligand-Targeted Delivery of Therapeutic siRNA

RNA interference (RNAi) is a post-transcriptional gene-silencing phenomenon that is triggered by double-stranded RNA (dsRNA). Since many diseases are associated with the inappropriate production of specific proteins, attempts are being made to exploit RNAi in a clinical settings. However, before RNAi can be exploited as therapeutically, several obstacles must be overcome. For example, small interfering RNA (siRNA) is unstable in the blood stream so any effects of injected siRNA are only transient. Accordingly, methods must be developed to prolong its activity. Furthermore, the efficient and safe delivery of siRNA into target tissues and cells is critical for successful therapy. Any useful delivery method should be designed to target siRNA to specific cells and to promote gene-silencing activity once the siRNA is inside the cells. Recent chemical modifications of siRNA have overcome problems associated with the instability of siRNA, and various ligands, including glycosylated molecules, peptides, proteins, antibodies and engineered antibody fragments, appear to be very useful or have considerable potential for the targeted delivery of siRNA. The use of such ligands improves the efficiency, specificity and, as a consequence, the safety of the corresponding delivery systems.

Targeting antigens to dendritic cells in vivo

Dendritic cells (DCs) play a key role in antigen-specific immune regulation. DCs take up and process antigens and present these as peptides through MHC molecules to T cells. Recent pre-clinical and clinical studies have exploited DCs as a means to improve vaccine efficiency. In these studies, monocyte-derived autologous DCs are loaded ex vivo with antigens and re-administered to the patient. These tailor-made vaccines are costly and labor intensive, and therefore less suitable for large-scale immunization programs. As a next step in the development of DC vaccines, it is proposed to load DCs with antigens in vivo. Drug delivery systems harboring antigens have been targeted to DCs via specific surface receptors preferentially expressed by DCs, resulting in priming of humoral and cellular immune responses. The present review focuses on the various antigen delivery systems that are currently in use and the DC surface receptors they target.

AHNP-streptavidin: a tetrameric bacterially produced antibody surrogate fusion protein against p185her2/neu

The anti-p185(her2/neu) peptidomimetic (AHNP) is a small exo-cyclic peptide derived from the anti-p185(her2/neu) rhumAb 4D5 (h4D5). AHNP mimics many but not all of the antitumor characteristics exhibited by h4D5. However, the pharmacokinetic profiles of AHNP are less than optimal for therapeutic or diagnostic purposes. To improve the binding affinity to p185(her2/neu) and the antitumor efficacy, we have engineered a fusion protein containing AHNP and a nonimmunoglobulin protein scaffold, streptavidin (SA). The recombinant protein, AHNP-SA (ASA) bound to p185(her2/neu) with high affinity, inhibited the proliferation of p185(her2/neu)-overexpressing cells, and reduced tumor growth induced by p185(her2/neu)-transformed cells. These data suggest that the bacterially produced tetrameric ASA can be used as an antibody-surrogate molecule. This class of molecule will play a role in the diagnosis and treatment of p185(her2/neu)-related tumors. Our studies establish a general principle by which a small biologically active synthetic exo-cyclic peptide can be engineered to enhance functional aspects by structured oligomerization and can be produced recombinantly using bacterial expression.

Affinity maturation of phage display antibody populations using ribosome display

A comparison has been performed, using phage display or ribosome display, of stringent selections on antibody populations derived from three rounds of phage display selection. Stringent selections were performed by reducing concentrations of the antigen, bovine insulin, down to 1 nM. Higher affinity antibodies were isolated using ribosome display in a process that introduces random mutations across the clone population. Whereas the highest affinity antibody produced by phage display, D3, has a K(d) of 5.8 nM as a scFv fragment, ribosome display generated higher affinity variants of this antibody with K(d) values of 189 pM and 152 pM, without or with the use of error prone mutagenesis, respectively. The affinities were further increased for each antibody on conversion of the scFv fragments to whole IgG format, to a K(d) of less than 21 pM for the highest affinity variant of D3. Mutation of VH D101 of antibody D3 to glycine or valine, removing the salt bridge between K94 and D101 at the base of VHCDR3, was responsible for the enhanced affinity observed. In addition to the variants of D3, other unrelated antibodies of comparable or higher affinity for insulin, were isolated by ribosome display, but not phage display, indicating that ribosome display can enrich for different populations of antibodies. Affinity maturation of phage antibody populations using ribosome display is a valuable method of rapidly generating diverse, high affinity antibodies to antigen and should be readily applicable to the isolation of antibodies for the detection and assay of biomarkers.

Ribosome display for improved biotherapeutic molecules

Ribosome display presents an innovative in vitro technology for the rapid isolation and evolution of high-affinity peptides or proteins. Displayed proteins are bound to and recovered from target molecules in multiple rounds of selection in order to enrich for specific binding proteins. No transformation step is necessary, which could lead to a loss of library diversity. A cycle of display and selection can be performed in one day, enabling the existing gene repertoire to be rapidly scanned. Proteins isolated from the panning rounds can be further modified through random or directed molecular evolution for affinity maturation, as well as selected for characteristics such as protein stability, folding and functional activity. Recently, the field of display technologies has become more prominent due to the generation of new scaffolds for ribosome display, isolation of high-affinity human antibodies by phage display, and their implementation in the discovery of novel protein-protein interactions. Applications for this technology extend into the broad field of antibody engineering, proteomics, and synthetic enzymes for diagnostics and therapeutics in cancer, autoimmune and infectious diseases, neurodegenerative diseases and inflammatory disorders. This review highlights the role of ribosome display in drug discovery, discusses advantages and disadvantages of the system, and attempts to predict the future impact of ribosome display technology on the development of novel engineered biopharmaceutical products for biological therapies.

Isolation of scFvs to in vitro produced extracellular domains of EGFR family members

The members of the epidermal growth factor receptor (EGFR) family are over expressed in a variety of malignancies and are frequently linked to aggressive disease and a poor prognosis. Although clinically effective monoclonal antibodies (MAbs) have been developed to target HER2 and EGFR, the remaining two family members, HER3 and HER4, have not been the subject of significant efforts. In this paper, we have taken the initial steps required to generate antibodies with potential clinically utility that target the members of the EGFR family. The genes for the extracellular domains (ECDs) of all four members of the EGFR family were cloned and used to stably transfect 293 (HEK) cells. Milligram quantities of each ECD were produced and characterized. The HER3, HER4, and EGFR ECDs were then employed as targets for the selection of antibodies from naïve human scFv (single-chain Fv) phage display libraries. Six unique scFv clones were isolated that bound specifically to HER3, 13 unique clones were isolated with specificity for HER4 and 52 unique anti-EGFR clones were isolated. These scFvs provide a valuable and potentially clinically relevant panel of agents to target the members of the EGFR family.

Mannose receptor-targeted vaccines

Targeting antigens to endocytic receptors on professional antigen-presenting cells (APCs) represents an attractive strategy to enhance the efficacy of vaccines. Such APC-targeted vaccines have an exceptional ability to guide exogenous protein antigens into vesicles that efficiently process the antigen for major histocompatibility complex class I and class II presentation. Efficient targeting not only requires high specificity for the receptor that is abundantly expressed on the surface of APCs, but also the ability to be rapidly internalised and loaded into compartments that contain elements of the antigen-processing machinery. The mannose receptor (MR) and related C-type lectin receptors are particularly designed to sample antigens (self and non-self), much like pattern recognition receptors, to integrate the innate with adaptive immune responses. In fact, a variety of approaches involving delivery of antigens to the MR have demonstrated effective induction of potent cellular and humoral immune responses. Yet, although several lines of evidence in diverse experimental systems attest to the efficacy of targeted vaccine strategies, it is becoming increasingly clear that additional signals, such as those afforded by adjuvants, may be critical to elicit sustained immunity. Therefore, MR-targeted vaccines are likely to be most efficacious in vivo when combined with agents that elicit complementary activation signals. Certainly, a better understanding of the mechanism associated with the induction of immune responses as a result of targeting antigens to the MR, will be important in exploiting MR-targeted vaccines not only for mounting immune defenses against cancer and infectious disease, but also for specific induction of tolerance in the treatment of autoimmune disease.

Nanobodies as novel agents for cancer therapy

Nanobodies are the smallest fragments of naturally occurring heavy-chain antibodies that have evolved to be fully functional in the absence of a light chain. As such, the cloning and selection of antigen-specific nanobodies obviate the need for construction and screening of large libraries, and for lengthy and unpredictable in vitro affinity maturation steps. The unique and well-characterised properties enable nanobodies to excel conventional therapeutic antibodies in terms of recognising uncommon or hidden epitopes, binding into cavities or active sites of protein targets, tailoring of half-life, drug format flexibility, low immunogenic potential and ease of manufacture. Moreover, the favourable biophysical and pharmacological properties of nanobodies, together with the ease of formatting them into multifunctional protein therapeutics, leaves them ideally placed as a new generation of antibody-based therapeutics. This review describes the state of the art on nanobodies and illustrates their potential as cancer therapeutic agents.

Ab-induced ectodomain shedding mediates hepatocyte growth factor receptor down-regulation and hampers biological activity

Targeting tyrosine kinase receptors (RTKs) with specific Abs is a promising therapeutic approach for cancer treatment, although the molecular mechanism(s) responsible for the Abs' biological activity are not completely known. We targeted the transmembrane RTK for hepatocyte growth factor (HGF) with a monoclonal Ab (DN30). In vitro, chronic treatment of carcinoma cell lines resulted in impairment of HGF-induced signal transduction, anchorage-independent growth, and invasiveness. In vivo, administration of DN30 inhibited growth and metastatic spread to the lung of neoplastic cells s.c. transplanted into immunodeficient nu/nu mice. This Ab efficiently down-regulates HGF receptor through a molecular mechanism involving a double proteolytic cleavage: (i) cleavage of the extracellular portion, resulting in "shedding" of the ectodomain, and (ii) cleavage of the intracellular domain, which is rapidly degraded by the proteasome. Interestingly, the "decoy effect" generated by the shed ectodomain, acting as a dominant negative molecule, enhanced the inhibitory effect of the Ab.

A new generation of protein display scaffolds for molecular recognition

Engineered antibodies and their fragments are invaluable tools for a vast range of biotechnological and pharmaceutical applications. However, they are facing increasing competition from a new generation of protein display scaffolds, specifically selected for binding virtually any target. Some of them have already entered clinical trials. Most of these nonimmunoglobulin proteins are involved in natural binding events and have amazingly diverse origins, frameworks, and functions, including even intrinsic enzyme activity. In many respects, they are superior over antibody-derived affinity molecules and offer an ever-extending arsenal of tools for, e.g., affinity purification, protein microarray technology, bioimaging, enzyme inhibition, and potential drug delivery. As excellent supporting frameworks for the presentation of polypeptide libraries, they can be subjected to powerful in vitro or in vivo selection and evolution strategies, enabling the isolation of high-affinity binding reagents. This article reviews the generation of these novel binding reagents, describing validated and advanced alternative scaffolds as well as the most recent nonimmunoglobulin libraries. Characteristics of these protein scaffolds in terms of structural stability, tolerance to multiple substitutions, ease of expression, and subsequent applications as specific targeting molecules are discussed. Furthermore, this review shows the close linkage between these novel protein tools and the constantly developing display, selection, and evolution strategies using phage display, ribosome display, mRNA display, cell surface display, or IVC (in vitro compartmentalization). Here, we predict the important role of these novel binding reagents as a toolkit for biotechnological and biomedical applications.

Antibody- and Fc-receptor-based therapeutics for malaria

Abs (antibodies) are complex glycoproteins that play a crucial role in protective immunity to malaria, but their effectiveness in mediating resistance can be enhanced by genetically engineered modifications that improve on nature. These Abs also aid investigation of immune mechanisms operating to control the disease and are valuable tools in developing neutralization assays for vaccine design. This review explores how this might be achieved.

Improved antigen binding by a CD20-specific single-chain antibody fragment with a mutation in CDRH1

We have prepared single-chain immunoglobulin Fv fragments from the CD20-specific hybridoma HB13d. One scFv clone demonstrated strong binding to a CD20-derived peptide by ELISA and to CD20-positive cells by flow cytometry, a second had reduced binding, and a third clone did not bind the target antigen. Sequence analysis showed that all three constructs contained shared and unique amino acid changes when compared to the nearest germline match. Molecular modelling of the scFv variants revealed that several of the mutations are located in regions predicted to contact antigen, including a mutation in the heavy chain CDR1 of the strongest binding scFv construct. No similar mutation is present in the highly conserved protein sequences of a number of CD20-specific monoclonal antibodies. BIACORE analysis demonstrated that the mutated scFv had approximately three-fold greater antigen-binding activity than another clone. Competition studies showed that the scFv is able to compete with intact CD20 monoclonal antibody for binding to the target antigen. The improved antigen binding of this scFv will permit the construction of novel CD20-specific reagents for the therapy of lymphomas.

Chemistry in living systems

Dissecting complex cellular processes requires the ability to track biomolecules as they function within their native habitat. Although genetically encoded tags such as GFP are widely used to monitor discrete proteins, they can cause significant perturbations to a protein's structure and have no direct extension to other classes of biomolecules such as glycans, lipids, nucleic acids and secondary metabolites. In recent years, an alternative tool for tagging biomolecules has emerged from the chemical biology community--the bioorthogonal chemical reporter. In a prototypical experiment, a unique chemical motif, often as small as a single functional group, is incorporated into the target biomolecule using the cell's own biosynthetic machinery. The chemical reporter is then covalently modified in a highly selective fashion with an exogenously delivered probe. This review highlights the development of bioorthogonal chemical reporters and reactions and their application in living systems.

Artificial, non-antibody binding proteins for pharmaceutical and industrial applications

Using combinatorial chemistry to generate novel binding molecules based on protein frameworks ('scaffolds') is a concept that has been strongly promoted during the past five years in both academia and industry. Non-antibody recognition proteins derive from different structural families and mimic the binding principle of immunoglobulins to varying degrees. In addition to the specific binding of a pre-defined target, these proteins provide favourable characteristics such as robustness, ease of modification and cost-efficient production. The broad spectrum of potential applications, including research tools, separomics, diagnostics and therapy, has led to the commercial exploitation of this technology by various small- and medium-sized companies. It is predicted that scaffold-based affinity reagents will broaden and complement applications that are presently covered by natural or recombinant antibodies. Here, we provide an overview on current approaches in the biotech industry, considering both scientific and commercial aspects.

Opinion: antibody-based therapies for malaria

Antibodies are multifunctional glycoproteins that are found in blood and tissue fluids, and can protect against malaria by binding and neutralizing malaria parasites and preparing them for destruction by immune cells. Important technical advances mean that it is now possible to synthesize antibodies against important Plasmodium antigens that could be used for therapeutic purposes. These reagents could be designed to act like a drug and kill parasites directly, or could be used in vaccine strategies to protect individuals from infection. In this article, we discuss the possible therapeutic uses of antibodies in the treatment and prevention of malaria.

Development of Antibodies and Chimeric Molecules for Cancer Immunotherapy

Monoclonal antibodies are among the most rapidly expanding class of therapeutics for cancer treatment. Monoclonal antibodies targeting non-Hodgkin's lymphoma (NHL), Her-2/neu highly expressing metastatic breast cancer, colorectal cancer, acute myelogenous leukemia, and B-cell chronic lymphocytic leukemia (CLL) have received FDA approval. Promising new targets for antibody therapy include cellular growth factor receptors, mediators of tumor-driven neo-angiogenesis, as well as host negative immunoregulatory checkpoints that impede an effective immune response to neoplasia. Antibody efficacy has been increased by genetic engineering to humanize the antibodies and to increase their effector functions including antibody dependent cellular cytotoxicity. Furthermore, antibodies have been armed with cytokines, chemotherapeutic agents, toxins, and radionuclides to augment their efficacy as tumor cytotoxic agents. As a consequence of these advances, 30 years after their first development, monoclonal antibodies have become an important standard approach for the therapy of neoplasia with 19 therapeutic monoclonal antibodies now approved by the FDA including 8 for the treatment of cancer.

Engineered antibody fragments and the rise of single domains

With 18 monoclonal antibody (mAb) products currently on the market and more than 100 in clinical trials, it is clear that engineered antibodies have come of age as biopharmaceuticals. In fact, by 2008, engineered antibodies are predicted to account for >30% of all revenues in the biotechnology market. Smaller recombinant antibody fragments (for example, classic monovalent antibody fragments (Fab, scFv)) and engineered variants (diabodies, triabodies, minibodies and single-domain antibodies) are now emerging as credible alternatives. These fragments retain the targeting specificity of whole mAbs but can be produced more economically and possess other unique and superior properties for a range of diagnostic and therapeutic applications. Antibody fragments have been forged into multivalent and multi-specific reagents, linked to therapeutic payloads (such as radionuclides, toxins, enzymes, liposomes and viruses) and engineered for enhanced therapeutic efficacy. Recently, single antibody domains have been engineered and selected as targeting reagents against hitherto immunosilent cavities in enzymes, receptors and infectious agents. Single-domain antibodies are anticipated to significantly expand the repertoire of antibody-based reagents against the vast range of novel biomarkers being discovered through proteomics. As this review aims to show, there is tremendous potential for all antibody fragments either as robust diagnostic reagents (for example in biosensors), or as nonimmunogenic in vivo biopharmaceuticals with superior biodistribution and blood clearance properties.

Engineering Camel Single-Domain Antibodies and Immobilization Chemistry for Human Prostate-Specific Antigen Sensing

The specificity and affinity characteristics of antibodies make them excellent probes in biosensor applications. Unfortunately, their large size, unstable behavior, and random immobilization properties create numerous problems. The single-domain antigen-binding fragment derived from heavy-chain antibodies of camelids (termed VHH) offers special advantages in terms of size, stability, and ease of generating different antibody constructs. In this study, we show the potential of those VHHs in sensing human prostate-specific antigen (hPSA) by SPR technology. Different VHH constructs were immobilized onto commercial and custom-built sensor surfaces by metal chelation, biotin-streptavidin interaction, or covalent coupling. The detection of subnanogram per milliliter hPSA concentrations could be attained on a covalently coupled three-dimensional dextran surface. Moreover, the ratio of different hPSA isoform concentrations could be assessed via a sandwich assay and resulted in the detection of clinically significant antigen concentrations within 15 min. In addition, for the first time, the intrinsic protein stability is presented as an important probe design factor, since our results reveal that higher intrinsic stability offers higher resistance to harsh regeneration conditions. In conclusion, we present VHHs as a novel class of biosensor probes rivaling conventional antibodies and their derived antibody fragments.

Designing antibodies for oncology

The past five years have witnessed the emergence of monoclonal antibodies as important therapeutics for cancer treatment. Lower toxicity for antibodies versus small molecules, the potential for increased efficacy by conjugation to radioisotopes and cellular toxins, or the ability to exploit immune cell functions have led to clinical performances on par or superior to conventional drug therapies. This review outlines the various immunoglobulin design strategies currently available, techniques used to reduce Ig antigenicity and toxicity, and points to consider during the manufacture of antibodies for use in clinical oncology.