Capturing transient antibody conformations with DNA origami epitopes.

Revealing antibody-antigen interactions at the single-molecule level will deepen our understanding of immunology. However, structural determination under crystal or cryogenic conditions does not provide temporal resolution for resolving transient, physiologically or pathologically relevant functional antibody-antigen complexes. Here, we develop a triangular DNA origami framework with site-specifically anchored and spatially organized artificial epitopes to capture transient conformations of immunoglobulin Gs (IgGs) at room temperature. The DNA origami epitopes (DOEs) allows programmed spatial distribution of epitope spikes, which enables direct imaging of functional complexes with atomic force microscopy (AFM). We establish the critical dependence of the IgG avidity on the lateral distance of epitopes within 3-20 nm at the single-molecule level. High-speed AFM imaging of transient conformations further provides structural and dynamic evidence for the IgG avidity from monovalent to bivalent in a single event, which sheds light on various applications including virus neutralization, diagnostic detection and cancer immunotherapy.

Comparative evaluation of affibody- and antibody fragments-based CAIX imaging probes in mice bearing renal cell carcinoma xenografts.

Carbonic anhydrase IX (CAIX) is a cancer-associated molecular target for several classes of therapeutics. CAIX is overexpressed in a large fraction of renal cell carcinomas (RCC). Radionuclide molecular imaging of CAIX-expression might offer a non-invasive methodology for stratification of patients with disseminated RCC for CAIX-targeting therapeutics. Radiolabeled monoclonal antibodies and their fragments are actively investigated for imaging of CAIX expression. Promising alternatives are small non-immunoglobulin scaffold proteins, such as affibody molecules. A CAIX-targeting affibody ZCAIX:2 was re-designed with the aim to decrease off-target interactions and increase imaging contrast. The new tracer, DOTA-HE3-ZCAIX:2, was labeled with 111In and characterized in vitro. Tumor-targeting properties of [111In]In-DOTA-HE3-ZCAIX:2 were compared head-to-head with properties of the parental variant, [99mTc]Tc(CO)3-HE3-ZCAIX:2, and the most promising antibody fragment-based tracer, [111In]In-DTPA-G250(Fab')2, in the same batch of nude mice bearing CAIX-expressing RCC xenografts. Compared to the 99mTc-labeled parental variant, [111In]In-DOTA-HE3-ZCAIX:2 provides significantly higher tumor-to-lung, tumor-to-bone and tumor-to-liver ratios, which is essential for imaging of CAIX expression in the major metastatic sites of RCC. [111In]In-DOTA-HE3-ZCAIX:2 offers significantly higher tumor-to-organ ratios compared with [111In]In-G250(Fab')2. In conclusion, [111In]In-DOTA-HE3-ZCAIX:2 can be considered as a highly promising tracer for imaging of CAIX expression in RCC metastases based on our results and literature data.

An amino-modified metal-organic framework (type UiO-66-NH2) loaded with cadmium(II) and lead(II) ions for simultaneous electrochemical immunosensing of triazophos and thiacloprid.

A method is described for simultaneous voltammetric determination of the pesticides triazophos (TRS) and thiacloprid (THD). A glassy carbon electrode (GCE) was modified with a metal-organic framework (type UiO-66-NH2) which has a large specific surface (1018 m2·g-1) and contains large amounts of Cd(II) and Pb(II) ions, with adsorption capacities of 230 and 271 mg·g-1, respectively. The antigen-loaded particles were then bound to antibody, magnetically separated, and analyzed by square wave voltammetry to give signals for Cd(II) and Pb(II) at -0.82 and - 0.56 V (vs. Ag/AgCl) for TRS and THD, respectively. Under optimized conditions, the method has a wide linear range (0.2-750 ng·mL-1) and low detection limits (0.07 and 0.1 ng·mL-1 at a S/N of 3 for TRS and THD, respectively). It is perceived that this assay represents a useful tool for simultaneous determination of multiple pesticide residues. The method has a wide scope in that may be extended to monitoring of other small organic pollutants by changing the types of metal ions and by using other antibodies. Graphical abstract Schematic presentation of an amino-modified metal-organic framework (type UiO-66-NH2) loaded with Cd(II) and Pb(II) ions for simultaneous electrochemical immunosensing of triazophos (TRS) and thiacloprid (THD). It is based on the fabrication of antigen (Ab)-immobilized UiO-66-NH2-based signal tags (a), and of an antibody (Ab)-immobilized magnetic bead (MB-COOH)-based capture probes (b).

Molecular probing of TNF: From identification of therapeutic target to guidance of therapy in inflammatory diseases.

Therapy by blocking tumor necrosis factor (TNF) activity is highly efficacious and profoundly changed the paradigm of several inflammatory diseases. However, a significant proportion of patients with inflammatory diseases do not respond to TNF inhibitors (TNFi). Prediction of therapeutic response is required for TNFi therapy. Isotope labeled anti-TNF antibodies or TNF receptor have been investigated to localize TNF production at inflammatory tissue in animal models and in patients with inflammatory diseases. The in vivo detection of TNF has been associated with treatment response. Recently, fluorophore labeled anti-TNF antibody in combination with confocal laser endomicroscopy in patients with Crohn's disease yielded more accurate and quantitative in vivo detection of TNF in the diseased mucosa. More importantly, this method demonstrated high therapeutic predication value. Fluorophore labeled TNF binding aptamers in combination with modern imaging technology offers additional tools for in vivo TNF probing.

Molecular Imaging of P-glycoprotein in Chemoresistant Tumors Using a Dual-Modality PET/Fluorescence Probe.

Overexpression of P-glycoprotein (Pgp) has been considered a primary cause for multidrug resistance in a variety of cancers for three decades. However, clinical translation of Pgp targeted therapeutics has been hindered by lack of patient preselection based on the Pgp presence in tumors. We aim to develop a molecularly targeted probe for imaging tumoral Pgp in vivo with positron emission tomography (PET) and fluorescence, and to provide a tool for preselecting the patients with tumoral Pgp expression. Thus, a Pgp monoclonal antibody 15D3 was chemically modified with IRDye800 (IR800) and DOTA chelator. The specificity of the antibody conjugates DOTA-Pab-IR800 was verified in Pgp-expressing 3T3-MDR1 and control 3T3 cells. After radiolabeling with 64Cu, the probe was applied in small animal PET imaging of Pgp in a mouse xenograft model of NCI/ADR-Res cells, which are chemoresistant through overexpression of Pgp. Quantification analysis of the PET images demonstrated that the tumor uptake of the radioactive probe was 9.9 ± 1.4, 12.1 ± 1.2, and 10.5 ± 1.0%ID/g at 4, 24, and 48 h post injection. The tumor-to-muscle ratio was 20.9 at 48 h post injection based on biodistribution studies. Fluorescence imaging was performed following PET experiments, and it demonstrated excellent tumor accumulation of this dual-modality probe in the NCI/ADR-Res tumors. Further, an image-guided surgery was successfully performed using the fluorescence modality of the probe, demonstrating potential utility of this probe in image-guided surgical removal of Pgp-positive drug resistant tumors in the patients. In conclusion, this study clearly demonstrated that the Pgp-targeted antibody probe, 64Cu-DOTA-Pab-IR800, could provide a promising diagnosis tool for detection of Pgp-expressing tumors in vivo.

Accelerated cellular on- and off-target screening of bioactive compounds using microarrays.

In situ proteome labeling was carried out with 9 drug-like probes in live mammalian cells, with the corresponding cellular targets captured on microarrays and simultaneously screened using a diverse set of antibodies, revealing potential on- and off-targets.

A scanometric antibody probe for facile and sensitive immunoassays.

We have developed a novel scanometric antibody probe for rapid, sensitive, and naked-eye-visible immunoassays. Using this probe, we clearly demonstrated the successful scanometric detection and identification of influenza A viruses on a microarray. In addition, the sensitivity of the scanometric immunoassay was comparable to that of the fluorescence-based method.

Site-specific labeling of cysteine-tagged camelid single-domain antibody-fragments for use in molecular imaging.

Site-specific labeling of molecular imaging probes allows the development of a homogeneous tracer population. The resulting batch-to-batch reproducible pharmacokinetic and pharmacodynamic properties are of great importance for clinical translation. Camelid single-domain antibody-fragments (sdAbs)-the recombinantly produced antigen-binding domains of heavy-chain antibodies, also called Nanobodies-are proficient probes for molecular imaging. To safeguard their intrinsically high binding specificity and affinity and to ensure the tracer's homogeneity, we developed a generic strategy for the site-specific labeling of sdAbs via a thio-ether bond. The unpaired cysteine was introduced at the carboxyl-terminal end of the sdAb to eliminate the risk of antigen binding interference. The spontaneous dimerization and capping of the unpaired cysteine required a reduction step prior to conjugation. This was optimized with the mild reducing agent 2-mercaptoethylamine in order to preserve the domain's stability. As a proof-of-concept the reduced probe was subsequently conjugated to maleimide-DTPA, for labeling with indium-111. A single conjugated tracer was obtained and confirmed via mass spectrometry. The specificity and affinity of the new sdAb-based imaging probe was validated in a mouse xenograft tumor model using a modified clinical lead compound targeting the human epidermal growth factor receptor 2 (HER2) cancer biomarker. These data provide a versatile and standardized strategy for the site-specific labeling of sdAbs. The conjugation to the unpaired cysteine results in the production of a homogeneous group of tracers and is a multimodal alternative to the technetium-99m labeling of sdAbs.

Development of a universal anti-polyethylene glycol reporter gene for noninvasive imaging of PEGylated probes.

UNLABELLED: A reporter gene can provide important information regarding the specificity and efficacy of gene or cell therapies. Although reporter genes are increasingly used in experimental and clinical studies, a highly specific yet nonimmunogenic reporter that can track genes and cells in vivo by multiple imaging technologies still awaits development. In this study, we constructed a versatile and nonimmunogenic reporter gene to noninvasively image gene expression or cell delivery by optical imaging, MRI, and small-animal PET. METHODS: We cloned and expressed a membrane-anchored anti-polyethylene glycol (PEG) reporter that consists of the Fab fragment of a mouse anti-PEG monoclonal antibody, AGP3, fused to the C-like extracellular-transmembrane-cytosolic domains of the mouse B7-1 receptor. Binding of PEGylated probes (PEG-NIR797 for optical imaging, PEG-superparamagnetic iron oxide for MRI, and (124)I-PEG for small-animal PET) were examined in vitro and in vivo. In addition, we compared the specificity, immunogenicity, and probe toxicity of the anti-PEG reporter with the gold standard reporter gene, type 1 herpes simplex virus thymidine kinase (HSV-tk). Finally, we derived a humanized anti-PEG reporter and evaluated its imaging function in vivo with subcutaneous and metastatic tumor models in mice. RESULTS: The cells or tumors that stably expressed anti-PEG reporters selectively accumulated various PEGylated imaging probes and could be detected by optical imaging, MRI, and small-animal PET. Importantly, the anti-PEG reporter displayed an imaging specificity comparable to the HSV-tk reporter but did not provoke immune responses or cause toxicity to the host. Furthermore, the humanized anti-PEG reporter retained high imaging specificity in vivo. CONCLUSION: The highly specific and nonimmunogenic anti-PEG reporter may be paired with PEGylated probes to provide a valuable system to image gene expression or cell delivery in experimental and clinical studies.

Rates and equilibria for probe capture by an antibody with infinite affinity.

Probe-capture systems based on proteins and synthetic ligands have become important for new analytical and imaging applications. We have used kinetic measurements of luminescence and measurements of binding by isothermal calorimetry to determine essential rate and equilibrium constants for a system that permanently captures modified DOTA chelates for positron imaging. We used that information along with previous results to quantitatively characterize the behavior of this system in vitro and in vivo. Under physiological conditions at 37 degrees C, the equilibrium dissociation constant for yttrium S-2-(4-aminobenzyl)-1,4,7,10-tetraazacyclododecanetetraacetate from antibody 2D12.5 is 2.0 (+/- 0.4) x 10(-9) M and the dissociation rate constant is 7.0 (+/- 0.7) x 10(-3) s(-1), leading to an inferred association rate constant of 3.5 x 10(6) M(-1) s(-1). Using these values to interpret data from earlier experiments leads to the rate constant 2.5 x 10(-2) s(-1) for covalent attachment of bound yttrium S-2-(4-acrylamidobenzyl)-1,4,7,10-tetraazacyclododecanetetraacetate to the G54C mutant of antibody 2D12.5. These values lead to a model for the detailed behavior of the latter system for tumor imaging in vivo that is consistent with experimental observations.

Non-natural and photo-reactive amino acids as biochemical probes of immune function.

Wilms tumor protein (WT1) is a transcription factor selectively overexpressed in leukemias and cancers; clinical trials are underway that use altered WT1 peptide sequences as vaccines. Here we report a strategy to study peptide-MHC interactions by incorporating non-natural and photo-reactive amino acids into the sequence of WT1 peptides. Thirteen WT1 peptides sequences were synthesized with chemically modified amino acids (via fluorination and photo-reactive group additions) at MHC and T cell receptor binding positions. Certain new non-natural peptide analogs could stabilize MHC class I molecules better than the native sequences and were also able to elicit specific T-cell responses and sometimes cytotoxicity to leukemia cells. Two photo-reactive peptides, also modified with a biotin handle for pull-down studies, formed covalent interactions with MHC molecules on live cells and provided kinetic data showing the rapid clearance of the peptide-MHC complex. Despite "infinite affinity" provided by the covalent peptide bonding to the MHC, immunogenicity was not enhanced by these peptides because the peptide presentation on the surface was dominated by catabolism of the complex and only a small percentage of peptide molecules covalently bound to the MHC molecules. This study shows that non-natural amino acids can be successfully incorporated into T cell epitopes to provide novel immunological, biochemical and kinetic information.

High-resolution immunophenotyping of subcellular compartments in tissue microarrays by enzyme metallography.

Ultrasensitive bright field in situ hybridization assays using enzyme metallography (EnzMet) have been developed and validated, but little is known regarding the applicability of EnzMet for immunophenotypic detection of protein via IHC. Superior resolution via discrete metallographic deposits offers the potential for enhancing high-resolution immunophenotyping. Using high-complexity tissue microarrays (TMAs), 88 common solid tumors were evaluated by automated EnzMet (Nanoprobes and Ventana). Targets were chosen to assess the ability of EnzMet to specifically localize encoded antigens in the nucleus (estrogen receptor), cytoplasm (cytokeratins), and cytoplasmic membrane (HER2) in TMAs. Results were compared with conventional IHC diaminobenzidine (DAB) immunostaining. There was full concordance between the EnzMet and conventional IHC results. Furthermore, the EnzMet reaction products did not appreciably diffuse, were dense and sharply defined, and provided excellent high-resolution differentiation of cellular compartments in paraffin sections for the nuclear, cytoplasmic, and cell membrane-localized antigens evaluated. The higher density of elemental silver deposited during enzyme metallography permitted evaluation of core immunophenotypes at a relatively low magnification, allowing more tissue to be screened in an efficient manner. This preliminary study shows the utility of using enzyme metallography for high-resolution immunophenotyping in TMAs.

Producción de anticuerpos policlonales monoespecíficos contra la droga antileucemica L-asparaginasa / Production of monospecific polyclonal antibodies against the antileucemic drug L-asparaginase

Los anticuerpos han sido ampliamente utilizados como marcadores en la detección y localización de moléculas específicas. En base al método de Cevenini et al. (1991) y utilizando bajas dosis del inmunógeno L-Asparaginasa, se obtuvieron anticuerpos policlonales desde tumores ascíticos inducidos en ratón. El fluído ascítico se sometió a fraccionamiento con sulfato de amonio y a diálisis. Por Western Blot se evidenció un enriuecimiento en inmunoglobulinas y mediante Dot Blot se determinó la especificidad del anticuerpo frente al antígeno. El abundante pool de anticuerpos obtenidos tiene alta snsibilidad por el antígeno ya que no presenta relación cruzada con los epítopes probados

Monoclonal anti-TNF alpha antibody as a probe of pathogenesis and therapy of rheumatoid disease.

Rheumatoid arthritis is a common cause of chronic disability for which current therapies are of limited value in controlling the disease process and outcome. Our initial approach to understanding the pathogenesis of RA and defining a novel therapeutic target was to investigate the role of cytokines by blocking their action with antibodies on cultured synovial-derived mononuclear cells in vitro. These investigations suggested that neutralization of TNF alpha with antibodies significantly inhibited the generation of other pro-inflammatory cytokines also over-produced, such as, IL-1, GM-CSF, IL-6 and IL-8. The implication that blockade of a single cytokine, TNF alpha might have far-reaching effects on multiple cytokines and thereby exert significant anti-inflammatory and protective effects on cartilage and bone of joints, was tested in arthritic DBA/1 mice immunized with collagen II. Impressive amelioration of joint swelling and joint erosions in this model encouraged clinical trials with a monoclonal anti-TNF alpha antibody. The cA2 chimeric anti-TNF alpha high-affinity antibody was initially tested in an open-label study at a dose of 20 mg/kg on 20 patients, with substantial and universal benefit. Subsequently, a randomized placebo-controlled double-blind trial was performed on 73 patients comparing a single intravenous injection of placebo (0.1% human serum albumin) with two doses of cA2. Using a composite disease activity index, at 4 weeks post infusion, 8% of patients receiving placebo improved compared with 44% receiving 1 mg/kg cA/2 and 79% receiving 10 mg/kg. Between 2 to 4 repeated cycles of cA2 were administered to 7 patients and all patients showed improvement of a similar magnitude with each cycle. These data support our proposition that TNF alpha is implicated in the pathogenesis of RA, and is thus a key therapeutic target. Monoclonal anti-TNF alpha antibodies control disease flares and are candidate agents for longer-term control of RA, although repeated therapy with cA2 is associated with anti-idiotypic responses in 50% of patients and a trend toward shortening of the duration of response. In the DBA/1 arthritic mice, synergy of action of anti-TNF and anti-CD4 is observed together with suppression of an anti-globulin response, indicating one way in which benefit might be augmented in the future.