Recombinant antibodies: a novel approach to cancer diagnosis and therapy

Continuous biomarker monitoring by particle mobility sensing with single molecule resolution

Healthcare is in demand of technologies for real-time sensing in order to continuously guard the state of patients. Here we present biomarker-monitoring based on the sensing of particle mobility, a concept wherein particles are coupled to a substrate via a flexible molecular tether, with both the particles and substrate provided with affinity molecules for effectuating specific and reversible interactions. Single-molecular binding and unbinding events modulate the Brownian particle motion and the state changes are recorded using optical scattering microscopy. The technology is demonstrated with DNA and protein as model biomarkers, in buffer and in blood plasma, showing sensitivity to picomolar and nanomolar concentrations. The sensing principle is direct and self-contained, without consuming or producing any reactants. With its basis in reversible interactions and single-molecule resolution, we envisage that the presented technology will enable biosensors for continuous biomarker monitoring with high sensitivity, specificity, and accuracy.

Protein-based tumor molecular imaging probes

Molecular imaging is an emerging discipline which plays critical roles in diagnosis and therapeutics. It visualizes and quantifies markers that are aberrantly expressed during the disease origin and development. Protein molecules remain to be one major class of imaging probes, and the option has been widely diversified due to the recent advances in protein engineering techniques. Antibodies are part of the immunosystem which interact with target antigens with high specificity and affinity. They have long been investigated as imaging probes and were coupled with imaging motifs such as radioisotopes for that purpose. However, the relatively large size of antibodies leads to a half-life that is too long for common imaging purposes. Besides, it may also cause a poor tissue penetration rate and thus compromise some medical applications. It is under this context that various engineered protein probes, essentially antibody fragments, protein scaffolds, and natural ligands have been developed. Compared to intact antibodies, they possess more compact size, shorter clearance time, and better tumor penetration. One major challenge of using protein probes in molecular imaging is the affected biological activity resulted from random labeling. Site-specific modification, however, allows conjugation happening in a stoichiometric fashion with little perturbation of protein activity. The present review will discuss protein-based probes with focus on their application and related site-specific conjugation strategies in tumor imaging.

Recent advances in recognition elements of food and environmental biosensors: a review

A sensitive monitoring of contaminants in food and environment, such as chemical compounds, toxins and pathogens, is essential to assess and avoid risks for both, human and environmental health. To accomplish this, there is a high need for sensitive, robust and cost-effective biosensors that make real time and in situ monitoring possible. Due to their high sensitivity, selectivity and versatility, affinity-based biosensors are interesting for monitoring contaminants in food and environment. Antibodies have long been the most popular affinity-based recognition elements, however recently a lot of research effort has been dedicated to the development of novel recognition elements with improved characteristics, like specificity, stability and cost-efficiency. This review discusses three of these innovative affinity-based recognition elements, namely, phages, nucleic acids and molecular imprinted polymers and gives an overview of biosensors for food and environmental applications where these novel affinity-based recognition elements are applied.

Gene therapy for carcinoma of the breast

In view of the limited success of available treatment modalities for breast cancer, alternative and complementary strategies need to be developed. The delineation of the molecular basis of breast cancer provides the possibility of specific intervention by gene therapy through the introduction of genetic material for therapeutic purposes. In this regard, several gene therapy approaches for carcinoma of the breast have been developed. These approaches can be divided into six broad categories: (1) mutation compensation, (2) molecular chemotherapy, (3) proapoptotic gene therapy, (4) antiangiogenic gene therapy, (5) genetic immunopotentiation, and (6) genetic modulation of resistance/sensitivity. Clinical trials for breast cancer have been initiated to evaluate safety, toxicity, and efficacy. Combined modality therapy with gene therapy and chemotherapy or radiation therapy has shown promising results. It is expected that as new therapeutic targets and approaches are identified and advances in vector design are realized, gene therapy will play an increasing role in clinical breast cancer treatment.

Gene transfer approaches in cancer immunotherapy

The idea of enhancing or establishing effective immune response against endogenously developed tumor cells is not novel. More than a hundred years ago, bacterial components were used to develop antitumor immune response. Later, when a number of immune system-effecting cytokines had been discovered, they were used for systemic treatment of cancer patients. However, systemic treatment often resulted in even negative outcome. Recent developments of genetic approaches of cell modifications allowed developing of modern techniques of targeted tumor cell elimination. In the present paper, we review modern trends of the antitumor response enhancement based on immunoregulatory gene transfer into different cell types both in vivo and in vitro. Almost all these approaches are based on the activation of the adaptive arm of the immune system in response to tumor cells. However, recent studies indicate that the innate arm of the immune system, as well as adaptive arm, is involved in tumor suppression. The innate immune system uses nonrearranging germline receptors, which could trigger cellular effector responses that are conditional (or instructive) to the subsequent adaptive immune response. Last years' viewpoints on 'self' and 'non-self' recognition and primary induction of the immune response have changed. The key role of lymphocytes is pathogen recognition and, following immune response induction, switched on the central role of dendritic cells in 'non-self' recognition and induction of both innate and adaptive responses. Moreover, innate response is supposed to be an essential starting point in induction of successful and effective acquired response. Most cancer vaccines do not have 'non-self' marks presentation due to their endogenous origin, thus lacking their effectiveness in the induction of the specific long-lasting immune response. Taking this point into consideration, we can conclude that to make cancer vaccine more effective we have to present tumor antigens, together with the molecules that can potentially activate downstream 'non-self' recognition events not in parallel, but as a consequence of tumor antigen processing and presentation.

Identification of the antigenic epitopes in staphylococcal enterotoxins A and E and design of a superantigen for human cancer therapy

Monoclonal antibodies have a potential for cancer therapy that may be further improved by linking them to effector molecules such as superantigens. Tumor targeting of a superantigen leads to a powerful T cell attack against the tumour tissue. Encouraging results have been observed preclinically and in patients using the superantigen staphylococcal enterotoxin A, SEA. To further improve the concept, we have reduced the reactivity to antibodies against superantigens, which is found in all individuals. Using epitope mapping, antibody binding sites in SEA and SEE were found around their MHC class II binding sites. These epitopes were removed genetically and a large number of synthetic superantigens were produced in an iterative engineering procedure. Properties such as decreased binding to anti-SEA as well as higher selectivity to induce killing of tumour cells compared to MHC class II expressing cells, were sequentially improved. The lysine residues 79, 81, 83 and 84 are all part of major antigenic epitopes, Gln204, Lys74, Asp75 and Asn78 are important for optimal killing of tumour cells while Asp45 affects binding to MHC class II. The production properties were optimised by further engineering and a novel synthetic superantigen, SEA/E-120, was designed. It is recognised by approximately 15% of human anti-SEA antibodies and have more potent tumour cell killing properties than SEA. SEA/E-120 is likely to have a low toxicity due to its reduced capacity to mediate killing of MHC class II expressing cells. It is produced as a Fab fusion protein at approximately 35 mg/l in Escherichia coli.

Optical imaging of metastatic tumors using a folate-targeted fluorescent probe

We describe the use of a tumor targeting ligand, the vitamin folic acid, to deliver an attached fluorescent probe to both primary and metastatic tumors overexpressing the folate receptor. Upon laser excitation, derived images of normal tissues generally show little or no fluorescence, whereas images of folate receptor-expressing tumors display bright fluorescence that can be easily distinguished from adjacent normal tissue. Furthermore, metastatic tumor loci of submillimeter size can also be visualized without the aid of image processing or enhancement. The sharp distinction between tumor and normal tissues provided by this technique could find application in the localization and resection of tumor tissue during surgery or in the enhanced endoscopic detection and staging of cancers.

Biomarkers, yesterday, today and tomorrow: the basis for health claims

The development of useful and accurate biomarkers for predicting outcomes of food based interventions is becoming more and more important, given the emphasis being placed on ingredients in foods contributing to disease risk reduction and optimal health promotion. With the human genome now laid bare, opportunities abound to barcode individuals with their risk profiles. The massive increase in DNA sequence information together with the development of new technologies such as genomics, proteomics and bioinformatics, has resulted in a much greater capacity to determine individual risk profiles. Screening for biomarkers at the gene or protein expression level using microarray technology has the potential to identify new biomarkers for disease diagnosis. Whether these techniques will enable a better understanding of food-gene interactions to permit health claims rather than better therapeutic treatment (at high economic cost) remains to be demonstrated.

Bispecific antibody conjugates in therapeutics

Bispecific monoclonal antibodies have drawn considerable attention from the research community due to their unique structure against two different antigens. The two-arm structure of bsMAb allows researchers to place a therapeutic agent on one arm while allowing the other to specifically target the disease site. The therapeutic agent can be a drug, toxin, enzyme, DNA, radionuclide, etc. Furthermore, bsMAb may redirect the cytotoxicity of immune effector cells towards the diseased cells or induce a systemic immune response against the target. BsMAb holds great promise for numerous therapeutic needs in the light of: (1) recent breakthroughs in recombinant DNA technology, (2) the increased number of identified disease targets as the result of the completion of human genomic map project, and (3) a better understanding of the mechanism of human immune system. This review focuses on therapeutic applications and production of bsMAb while providing the up-to-date clinical trial information.

Pharmacokinetics and biodistribution of genetically engineered antibodies

The engineering of monoclonal antibodies has created a new generation of pharmaceuticals with the desired pharmacokinetics and biodistribution properties. For radioimmunotherapy and radioscintigraphy, optimum tumor targeting can be achieved using engineered constructs that provide high antigen affinity and specificity, effective tumor penetration, circulation properties that allow high tumor uptake with acceptable doses to the normal tissues, and fast clearance allowing low background. Recent advances have made possible the development of antibodies with these properties.

The intracellular antibody capture technology (IACT): towards a consensus sequence for intracellular antibodies

We describe the application of an intracellular antibody capture technology (IACT) as a generic in vivo selection procedure for isolating intracellular antibodies or ICAbs. IACT was applied to the de novo selection of functional ICAbs against the microtubule-associated protein TAU, found in neurofibrillary lesions of Alzheimer's disease brains. A panel of 17 different ICAbs was created which bind TAU inside cells and the epitopes recognized by the selected ICAbs have been determined by an in vivo epitope mapping procedure. Finally, sequence analysis showed that the IACT-derived ICAbs are characterized by a common signature of conserved amino acid residues, suggesting that the IACT naturally selects a sort of "captured consensus sequence" for intracellular antibodies. The development of IACT, together with the possibility of scaling up in a high throughput and automated format, makes IACT a new enabling tool for target validation in functional genomics and global proteomics.

Effective single chain antibody (scFv) concentrations in vivo via adenoviral vector mediated expression of secretory scFv

Single chain antibodies (scFv) represent powerful interventional agents for the achievement of targeted therapeutics. The practical utility of these agents have been limited, however, by difficulties related to production of recombinant scFv and the achievement of effective and sustained levels of scFv in situ. To circumvent these limitations, we have developed an approach to express scFv in vivo. An anti-erbB2 scFv was engineered for secretion by eukaryotic cells. The secreted scFv could bind to its target and specifically suppress cell growth of erbB2-positive cells in vitro. Adenoviral vectors expressing the cDNA for the secretory scFv likewise could induce target cells to produce an anti-tumor anti-erbB2 scFv. In vivo gene transfer via the anti-erbB2 scFv encoding adenovirus also showed anti-tumor effects. Thus, by virtue of engineering a secreted version of the anti-tumor anti-erbB-2 scFv, and in vivo expression via adenoviral vector, effective concentrations of scFv were achieved. In vivo gene transfer clearly represents a powerful means to realize effective scFv-based approaches. This method will likely have applicability for a range of disorders amenable to targeted therapeutic approaches.

Dimeric and trimeric antibodies: high avidity scFvs for cancer targeting

Recombinant antibody fragments can be engineered to assemble into stable multimeric oligomers of high binding avidity and specificity to a wide range of target antigens and haptens. This review describes the design and expression of diabodies (dimers), triabodies (trimers) and tetrabodies (tetramers). In particular we discuss the role of linker length between V-domains and the orientation of the V-domains to direct the formation of either diabodies (60 kDa), triabodies (90 kDa) or tetrabodies (120 kDa), and how the size, flexibility and valency of each molecules is suited to different applications for in vivo imaging and therapy. Single chain Fv antibody fragments joined by polypeptide linkers of at least 12 residues irrespective of V-domains orientation predominantly form monomers with varying amounts of dimer and higher molecular mass oligomers in equilibrium. A scFv molecule with a linker of 3-12 residues cannot fold into a functional Fv domain and instead associates with a second scFv molecule to form a bivalent dimer (diabody, approximately 60 kDa). Reducing the linker length below three residues can force scFv association into trimers (triabodies, approximately 90 kDa) or tetramers ( approximately 120 kDa) depending on linker length, composition and V-domain orientation. A particular advantage for tumour targeting is that molecules of 60-100 kDa have increased tumour penetration and fast clearance rates compared with the parent Ig (150 kDa). We highlight a number of cancer-targeting scFv diabodies that have undergone successful pre-clinical trials for in vivo stability and efficacy. We also briefly review the design of multi-specific Fv modules suited to cross-link two or more different target antigens. Bi-specific diabodies formed by association of different scFv molecules have been designed as cross-linking reagents for T-cell recruitment into tumours (immunotherapy), viral retargeting (gene therapy) and as red blood cell agglutination reagents (immunodiagnostics). The more challenging trispecific multimers (triabodies) remain to be described.

Recombinant antibodies for cancer diagnosis and therapy

Recombinant antibodies now represent over 30% of biopharmaceuticals in clinical trials, highlighted by the recent approvals for cancer immunotherapy from the FDA which has awoken the biotechnology industry. Sales of these antibodies are increasing very rapidly to a predicted US$ 3 billion per annum worldwide by 2002. Since the development of new therapeutic reagent into commercial product takes 10 years, the recent FDA-approved antibodies are based on early antibody designs which are now considered primitive. Emerging technologies have created a vast range of novel, recombinant, antibody-based reagents which specifically target clinical biomarkers of disease. In the past year, radiolabelling of antibodies has increased their potential for cancer imaging and targeting. Recombinant antibodies have also been reduced in size and rebuilt into multivalent molecules for higher affinity. In addition, antibodies have been fused with many molecules including toxins, enzymes and viruses for prodrug therapy, cancer treatment and gene delivery. Recombinant antibody technology has enabled clever manipulations in the construction of complex antibody library repertoires for the selection of high-affinity reagents against refractory targets. Although phage display remains the most extensively used method, this year high affinity reagents have been isolated using alternative display and selection systems such as ribosome display and yeast display confirming the emergence of new display methods. Furthermore, innovative affinity maturation strategies have been developed to obtain high affinity reagents. This review focuses on developments in the last 12 months and describes the latest developments in the design, production and clinical use of recombinant antibodies for cancer diagnosis and therapy.

Design and application of diabodies, triabodies and tetrabodies for cancer targeting

Multivalent recombinant antibody fragments provide high binding avidity and unique specificity to a wide range of target antigens and haptens. This review describes the design and expression of diabodies, triabodies and tetrabodies using examples of scFv molecules that target viruses (influenza neuraminidase) and cancer (Ep-CAM; epithelial cell adhesion molecule). We discuss the preferred choice of linker length between V-domains to direct the formation of either diabodies (60 kDa), triabodies (90 kDa) or tetrabodies (120 kDa), each with size, flexibility and valency suited to different applications for in vivo imaging and therapy. The increased binding valency of these scFv multimers results in high avidity (low off-rates). A particular advantage for tumour targeting is that molecules of 60-100 kDa have increased tumour penetration and fast clearance rates compared to the parent Ig (150 kDa). We highlight a number of cancer-targeting scFv multimers that have recently successfully undergone pre-clinical trials for in vivo stability and efficacy. We also review the design of multi-specific Fv modules suited to cross-link two or more different target antigens. These bi- and tri-specific multimers can be formed by association of different scFv molecules and, in the first examples, have been designed as cross-linking reagents for T-cell recruitment into tumours (immunotherapy), viral retargeting (gene therapy) and as red blood cell agglutination reagents (immunodiagnostics).