Targeting of biotinylated compounds to its target tissue using a low-density lipoprotein receptor–avidin fusion protein

Biotin-Avidin-Mediated Capture of Microspheres on Polymer Fibers

Systems for efficient and selective capture of micro-scale objects and structures have application in many areas and are of particular relevance for selective isolation of mammalian cells. Systems for the latter should also not interfere with the biology of the cells. This study demonstrates the capture of microspheres through orthogonal coupling using biotin (ligand) and (strept)avidin (receptor). Fibrous poly(ethylene terephthalate) (PET) meshes were hydrolyzed under controlled alkaline conditions to obtain activated surfaces with COOH groups allowing for the functionalization of the PET with biotin of various spacer length. The system capture efficiency was optimized by varying the length of spacer presenting the biotin against streptavidin. In a proof of concept experiment, avidin-functionalized microspheres were used as surrogates for cells, and their capture under dynamic conditions including virous mixing and high-flow rate perfusion is demonstrated. Functionalization of PET meshes with biotin conjugated to longest spacer yielded the most efficient capture of microspheres. These preliminary results lay the foundation for the development of biosystems for capture of specific cells under physiologically relevant conditions, using biorthogonal avidin-biotin interactions.

Synthesis and characterization of pH-sensitive, biotinylated MRI contrast agents and their conjugates with avidin

Responsive or smart contrast agents (SCAs) provide new opportunities in magnetic resonance imaging (MRI) to examine a number of physiological and pathological events. However, their application in vivo remains challenging. Therefore, much research is focused on the optimization of their properties, to enable their use in additional imaging modalities, pre-targeted delivery, or to increase the local concentration of the agent. The key feature in the SCA synthetic modification is the retention of their physicochemical properties related to the specific MR response. Here, we report the preparation and characterization of pH sensitive SCAs appended with a phosphonate pendant arm and either an aliphatic (GdL(1)) or aromatic linker (GdL(2)). The longitudinal relaxivity of GdL(1) and GdL(2) increases by 146% and 31%, respectively, while the pH decreases from 9 to 5. These two SCAs were converted to the biotinylated systems GdL(3) and GdL(4) and their interaction with avidin was investigated. The binding affinity with avidin was assessed with a fluorescence displacement assay and with MRI phantom experiments in a 3T MRI scanner. The fluorometric assay and MRI E-titrations revealed a 3 : 1 binding mode of GdL(3-4) to avidin with the binding affinity as high as that of the parent avidin-biotin complex. The high binding affinity was confirmed with MRI by a competitive assay. The avidin-GdL(3-4) complexes thus obtained exhibit changes in both r(1) and r(2) that are pH dependent. The results reveal a new pathway for the modification and improvement of SCAs to make them more suitable for in vivo application.

Conditional expression of Lodavin, an avidin-tagged LDL receptor, for biotin-mediated applications in vivo

Lodavin represents an engineered fusion protein that consists of a cytoplasmic and a transmembrane domain of the human low-density lipoprotein receptor coupled to an extracellular avidin monomer. Biotinylated compounds have been successfully targeted to Lodavin-expressing cells that have been transduced by a Lodavin-containing virus, and the targeting is based on the high affinity between biotin and avidin. We engineered a Rosa26 (R26R) knock-in Lodavin mouse to develop biotin-based applications such as targeted drug delivery, cell purification, and tissue imaging in vivo. A cDNA encoding Lodavin was inserted downstream of a floxed βgeo resistance gene in the R26R locus in embryonic stem cells, and a germ line-derived R26RLodavin mouse line was generated. Efficient removal of the floxed βgeo cassette and conditional activation of Lodavin expression was achieved as a result of crossing the R26RLodavin mice with HoxB7-Cre, Wnt4-Cre, or Tie1-Cre mice. In summary, the R26RLodavin mouse line may provide a useful tool for testing and developing applications with the aid of avidin and biotin interaction.

Surface differentiation of ferritin and apoferritin with atomic force microscopic techniques

In the study reported herein, we differentiated the structure of ferritin from that of its demetalated counterpart, apoferritin, using field-effect-based atomic force microscopic (AFM) techniques. When ferritin was subjected to conductive-mode AFM analysis, the protein resembled a pancake with a diameter of 10 nm adsorbed on the indium-doped tin-oxide substrate with its fourfold channel perpendicular to the substrate, whereas a flat, empty cavity was revealed for apoferritin. We also attempted to verify the conformational difference with magnetic-mode AFM. However, the resulting phase images failed to differentiate the proteins due to interference from the fringe effect. Despite this, the ferritin analysis revealed a sound correlation between the surface conductivity profiles and the phase profiles. In contrast, apoferritin showed a chaotic relationship in this respect. These results not only suggest that the magnetic domain of ferritin is limited to the iron aggregate in the core, but also demonstrate that AFM is a useful tool for protein conformation analysis.

Retargeted clostridial neurotoxins as novel agents for treating chronic diseases

Botulinum neurotoxin (BoNT) A and B are used to treat neuropathic disorders; if retargeted, these agents could be used to treat medical conditions that involve secretion from nonneuronal cells. Here, we report novel strategies for successfully retargeting BoNTs, and also tetanus neurotoxin (TeNT), to primary human blood monocyte-derived macrophages where BoNT/B inhibited the release of tumor necrosis factor-α, a cytokine that plays a key role in inflammation. Furthermore, mice treated with retargeted BoNT/B exhibited a significant reduction in macrophage (MΦ) recruitment, indicating that these toxins can be used to treat chronic inflammation.

Avidin-biotin technology in targeted therapy

IMPORTANCE OF THE FIELD

The goal of drug targeting is to increase the concentration of the drug in the vicinity of the cells responsible for disease without affecting healthy cells. Many approaches in cancer treatment are limited because of their broad range of unwanted side effects on healthy cells. Targeting can reduce side effects and increase efficacy of drugs in the patient.

AREAS COVERED IN THIS REVIEW

Avidin, originally isolated from chicken eggs, and its bacterial analogue, streptavidin, from Streptomyces avidinii, have extremely high affinity for biotin. This unique feature is the basis of avidin-biotin technology. This article reviews the current status of avidin-biotin systems and their use for pretargeted drug delivery and vector targeting.

WHAT THE READER WILL GAIN

The reader will gain an understanding of the following approaches using the avidin-biotin system: i) targeting antibodies and therapeutic molecules are administered separately leading to a reduction of drug dose in normal tissues compared with conventional (radio)immunotherapies; ii) introducing avidin gene into specific tissues by local gene transfer, which subsequently can sequester and concentrate considerable amounts of therapeutic ligands; and iii) enabling transductional targeting of gene therapy vectors.

TAKE HOME MESSAGE

Avidin and biotin technology has proved to be an extremely versatile tool with broad applications, such as pretargeting, delivering avidin gene into cells enabling targeting of biotinylated compounds and targeting of viral vectors.

Avidin fusion protein-expressing lentiviral vector for targeted drug delivery

One of the main objectives of cancer therapy is to enhance the effectiveness of the drug by concentrating it at the target site and to minimize the undesired side effects to nontarget cells. We have previously constructed a fusion protein, Lodavin, consisting of avidin and the endocytotic part of the low-density lipoprotein receptor, and demonstrated its applicability to transient drug targeting in vivo. In this study we produced a lentiviral vector expressing this fusion protein and evaluated its safety and efficacy. The results showed that lentivirus-mediated gene transfer led to long-term avidin fusion protein expression on glioma cells and that the receptor was able to bind biotinylated compounds. Repeated administration was proven feasible and the optimal time frame(s) for administration of biotinylated therapeutic and/or imaging compounds was elucidated. Intravenous or intracranial injection of the virus into BDIX rats led to the production of antibodies against transgene (avidin), but repeated administration of the vector was unable to boost this effect. Neutralizing antibodies against the lentivirus were also detected. Furthermore, we showed that the anti-avidin antibodies did not significantly affect the ligand-binding capacity of the avidin fusion protein. The therapeutic efficacy of avidin fusion protein in tumor treatment was tested in vitro with biotinylated and nonbiotinylated nanoparticles loaded with paclitaxel. In vivo applicability of lentivirus was studied in the BDIX rat glioma model, in which high receptor expression was detected in the tumor area. The lentivirus-mediated delivery of the avidin fusion protein thus represents a potential approach for the repeated targeting of cytotoxic compounds to cancer cells.

Dynamic partitioning of a glycosyl-phosphatidylinositol-anchored protein in glycosphingolipid-rich microdomains imaged by single-quantum dot tracking

Recent experimental developments have led to a revision of the classical fluid mosaic model proposed by Singer and Nicholson more than 35 years ago. In particular, it is now well established that lipids and proteins diffuse heterogeneously in cell plasma membranes. Their complex motion patterns reflect the dynamic structure and composition of the membrane itself, as well as the presence of the underlying cytoskeleton scaffold and that of the extracellular matrix. How the structural organization of plasma membranes influences the diffusion of individual proteins remains a challenging, yet central, question for cell signaling and its regulation. Here we have developed a raft-associated glycosyl-phosphatidyl-inositol-anchored avidin test probe (Av-GPI), whose diffusion patterns indirectly report on the structure and dynamics of putative raft microdomains in the membrane of HeLa cells. Labeling with quantum dots (qdots) allowed high-resolution and long-term tracking of individual Av-GPI and the classification of their various diffusive behaviors. Using dual-color total internal reflection fluorescence (TIRF) microscopy, we studied the correlation between the diffusion of individual Av-GPI and the location of glycosphingolipid GM1-rich microdomains and caveolae. We show that Av-GPI exhibit a fast and a slow diffusion regime in different membrane regions, and that slowing down of their diffusion is correlated with entry in GM1-rich microdomains located in close proximity to, but distinct, from caveolae. We further show that Av-GPI dynamically partition in and out of these microdomains in a cholesterol-dependent manner. Our results provide direct evidence that cholesterol-/sphingolipid-rich microdomains can compartmentalize the diffusion of GPI-anchored proteins in living cells and that the dynamic partitioning raft model appropriately describes the diffusive behavior of some raft-associated proteins across the plasma membrane.

Post-transcriptional regulatory element boosts baculovirus-mediated gene expression in vertebrate cells

Baculoviruses can express transgenes in a wide range of vertebrate cells. However, in some cells transgene expression is weak. To enhance transgene expression, we studied the effect of the Woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) on baculovirus (BV)-mediated gene expression of several transgenes. A significant increase in BV-mediated gene expression was detected in several cell lines. A 10-fold increase in transgene expression was observed with the WPRE as determined by the percentage of positive cells and mean fluorescence intensity (MFI). Furthermore, a combination of optimized cell culture medium and WPRE virus led to more than a 60-fold increase in gene expression. In accordance, elevated mRNA and protein levels were detected in WPRE-virus transduced cells. In HepG2 and RaaSMC, WPRE-mediated enhancement was comparable to the previously shown positive effect of sodium butyrate on BV-mediated gene expression. Thus, inclusion of the WPRE into a baculovirus vector provides a simple means to improve BV-mediated gene expression in vertebrate cells.

Gene therapy for malignant glioma: current clinical status

Glioblastoma is an aggressive brain tumor with a dismal prognosis. Gene therapy may offer a new option for the treatment of these patients. Several gene therapy approaches have shown anti-tumor efficiency in experimental studies, and the first clinical trials for the treatment of malignant glioma were conducted in the 1990s. HSV-tk gene therapy has been the pioneering and most commonly used approach, but oncolytic conditionally replicating adenoviruses and herpes simplex virus mutant vectors, p53, interleukins, interferons, and antisense oligonucleotides have also been used. During the past few years, adenoviruses have become the most popular gene transfer vectors, and some recent randomized, controlled trials have shown significant anti-tumor efficacy in clinical use. However, efficient gene delivery into the brain still presents a major problem, and there is a lack of definitive phase III trials, which would avoid potential problems associated with a small number of patients, inadvertent patient selection, and overinterpretation of results based on a few long-time survivors. For clinical efficacy, median survival is one of the most rigorous endpoints. It is used here to evaluate the usefulness of various treatment approaches and current clinical status of gene therapy for malignant glioma.

Dual-affinity avidin molecules

A recently reported dual-chain avidin was modified further to contain two distinct, independent types of ligand-binding sites within a single polypeptide chain. Chicken avidin is normally a tetrameric glycoprotein that binds water-soluble d-biotin with extreme affinity (K(d) approximately 10(-15) M). Avidin is utilized in various applications and techniques in the life sciences and in the nanosciences. In a recent study, we described a novel avidin monomer-fusion chimera that joins two circularly permuted monomers into a single polypeptide chain. Two of these dual-chain avidins were observed to associate spontaneously to form a dimer equivalent to the wt tetramer. In the present study, we successfully used this scaffold to generate avidins in which the neighboring biotin-binding sites of dual-chain avidin exhibit two different affinities for biotin. In these novel avidins, one of the two binding sites in each polypeptide chain, the pseudodimer, is genetically modified to have lower binding affinity for biotin, whereas the remaining binding site still exhibits the high-affinity characteristic of the wt protein. The pseudotetramer (i.e., a dimer of dual-chain avidins) has two high and two lower affinity biotin-binding sites. The usefulness of these novel proteins was demonstrated by immobilizing dual-affinity avidin with its high-affinity sites. The sites with lower affinity were then used for affinity purification of a biotinylated enzyme. These "dual-affinity" avidin molecules open up wholly new possibilities in avidin-biotin technology, where they may have uses as novel bioseparation tools, carrier proteins, or nanoscale adapters.

Gene technology based therapies in the brain

Gene therapy potentially represents one of the most important developments in modern medicine. Gene therapy, especially of cancer, has created exciting and elusive areas of therapeutic research in the past decade. In fact, the first gene therapy performed in a human was not against cancer but was performed to a 14 year old child suffering from adenosine deaminase (ADA) deficiency. In addition to cancer gene therapy there are many other diseases and disorders where gene therapy holds exciting and promising opportunities. These include amongst others gene therapy within the central nervous system and the cardiovascular system. Improvements of the efficiency and safety of gene therapy is the major goal of gene therapy development. After the death of Jesse Gelsinger, the first patient in whom death could be directly linked to the viral vector used for the treatment, ethical doubts were raised about the feasibility of gene therapy in humans. Therefore, the ability to direct gene transfer vectors to specific target cells is also a crucial task to be solved and will be important not only to achieve a therapeutic effect but also to limit potential adverse effects.

Production of Hev b5 as a fluorescent biotin-binding tripartite fusion protein in insect cells

The presented green fluorescent protein and streptavidin core-based tripartite fusion system provides a simple and efficient way for the production of proteins fused to it in insect cells. This fusion protein forms a unique tag, which serves as a multipurpose device enabling easy optimization of production, one-step purification via streptavidin-biotin interaction, and visualization of the fusion protein during downstream processing and in applications. In the present study, we demonstrate the successful production, purification, and detection of a natural rubber latex allergen Hev b5 with this system. We also describe the production of another NRL allergen with the system, Hev b1, which formed large aggregates and gave small yields in purification. The aggregates were detected at early steps by microscopical inspection of the infected insect cells producing this protein. Therefore, this fusion system can also be utilized as a fast indicator of the solubility of the expressed fusion proteins and may therefore be extremely useful in high-throughput expression approaches.

Novel avidin-like protein from a root nodule symbiotic bacterium, Bradyrhizobium japonicum

Bradyrhizobium japonicum is an important nitrogenfixing symbiotic bacterium, which can form root nodules on soybeans. These bacteria have a gene encoding a putative avidin- and streptavidin-like protein, which bears an amino acid sequence identity of only about 30% over the core regions with both of them. We produced this protein in Escherichia coli both as the full-length wild type and as a C-terminally truncated core form and showed that it is indeed a high affinity biotin-binding protein that resembles (strept)avidin structurally and functionally. Because of the considerable dissimilarity in the amino acid sequence, however, it is immunologically very different, and polyclonal rabbit and human antibodies toward (strept)avidin did not show significant cross-reactivity with it. Therefore this new avidin, named bradavidin, facilitates medical treatments such as targeted drug delivery, gene therapy, and imaging by offering an alternative tool for use if (strept)avidin cannot be used, because of a deleterious patient immune response for example. In addition to its medical value, bradavidin can be used both in other applications of avidin-biotin technology and as a source of new ideas when creating engineered (strept)avidin forms by changing or combining the desired parts, interface patterns, or specific residues within the avidin protein family. Moreover, the unexpected discovery of bradavidin indicates that the group of new and undiscovered bacterial avidin-like proteins may be both more diverse and more common than hitherto thought.

Survey of the year 2003 commercial optical biosensor literature

In the year 2003 there was a 17% increase in the number of publications citing work performed using optical biosensor technology compared with the previous year. We collated the 962 total papers for 2003, identified the geographical regions where the work was performed, highlighted the instrument types on which it was carried out, and segregated the papers by biological system. In this overview, we spotlight 13 papers that should be on everyone's 'must read' list for 2003 and provide examples of how to identify and interpret high-quality biosensor data. Although we still find that the literature is replete with poorly performed experiments, over-interpreted results and a general lack of understanding of data analysis, we are optimistic that these shortcomings will be addressed as biosensor technology continues to mature.