A nanobody-based fluorescent reporter reveals human α-synuclein in the cell cytosol

Nanobodies against the myelin enzyme CNPase as tools for structural and functional studies

2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is an abundant constituent of central nervous system non-compact myelin, frequently used as a marker antigen for myelinating cells. The catalytic activity of CNPase, the 3'-hydrolysis of 2',3'-cyclic nucleotides, is well characterised in vitro, but the in vivo function of CNPase remains unclear. CNPase interacts with the actin cytoskeleton to counteract the developmental closure of cytoplasmic channels that travel through compact myelin; its enzymatic activity may be involved in adenosine metabolism and RNA degradation. We developed a set of high-affinity nanobodies recognizing the phosphodiesterase domain of CNPase, and the crystal structures of each complex show that the five nanobodies have distinct epitopes. One of the nanobodies bound deep into the CNPase active site and acted as an inhibitor. Moreover, the nanobodies were characterised in imaging applications and as intrabodies, expressed in mammalian cells, such as primary oligodendrocytes. Fluorescently labelled nanobodies functioned in imaging of teased nerve fibers and whole brain tissue sections, as well as super-resolution microscopy. These anti-CNPase nanobodies provide new tools for structural and functional biology of myelination, including high-resolution imaging of nerve tissue.

The Spreading and Effects of Human Recombinant α-Synuclein Preformed Fibrils in the Cerebrospinal Fluid of Mice

Parkinson's disease (PD) patients harbor seeding-competent α-synuclein (α-syn) in their cerebrospinal fluid (CSF), which is mainly produced by the choroid plexus (ChP). Nonetheless, little is known about the role of the CSF and the ChP in PD pathogenesis. To address this question, we used an intracerebroventricular (icv) injection mouse model to assess CSF α-syn spreading and its short- and long-term consequences on the brain. Hereby, we made use of seeding-competent, recombinant α-syn preformed fibrils (PFF) that are known to induce aggregation and subsequent spreading of endogenous α-syn in stereotactic tissue injection models. Here, we show that icv-injected PFF, but not monomers (Mono), are rapidly removed from the CSF by interaction with the ChP. Additionally, shortly after icv injection both Mono and PFF were detected in the olfactory bulb and striatum. This spreading was associated with increased inflammation and complement activation in these tissues as well as leakage of the blood-CSF barrier. Despite these effects, a single icv injection of PFF didn't induce a decline in motor function. In contrast, daily icv injections over the course of 5 days resulted in deteriorated grip strength and formation of phosphorylated α-syn inclusions in the brain 2 months later, whereas dopaminergic neuron levels were not affected. These results point toward an important clearance function of the CSF and the ChP, which could mediate removal of PFF from the brain, whereby chronic exposure to PFF in the CSF may negatively impact blood-CSF barrier functionality and PD pathology.

Advancing cell biology with nanoscale fluorescence imaging: essential practical considerations

Recently, biologists have gained access to several far-field fluorescence nanoscopy (FN) technologies that allow the observation of cellular components with ~20 nm resolution. FN is revolutionizing cell biology by enabling the visualization of previously inaccessible subcellular details. While technological advances in microscopy are critical to the field, optimal sample preparation and labeling are equally important and often overlooked in FN experiments. In this review, we provide an overview of the methodological and experimental factors that must be considered when performing FN. We present key concepts related to the selection of affinity-based labels, dyes, multiplexing, live cell imaging approaches, and quantitative microscopy. Consideration of these factors greatly enhances the effectiveness of FN, making it an exquisite tool for numerous biological applications.

Engineering paralog-specific PSD-95 recombinant binders as minimally interfering multimodal probes for advanced imaging techniques

Despite the constant advances in fluorescence imaging techniques, monitoring endogenous proteins still constitutes a major challenge in particular when considering dynamics studies or super-resolution imaging. We have recently evolved specific protein-based binders for PSD-95, the main postsynaptic scaffold proteins at excitatory synapses. Since the synthetic recombinant binders recognize epitopes not directly involved in the target protein activity, we consider them here as tools to develop endogenous PSD-95 imaging probes. After confirming their lack of impact on PSD-95 function, we validated their use as intrabody fluorescent probes. We further engineered the probes and demonstrated their usefulness in different super-resolution imaging modalities (STED, PALM, and DNA-PAINT) in both live and fixed neurons. Finally, we exploited the binders to enrich at the synapse genetically encoded calcium reporters. Overall, we demonstrate that these evolved binders constitute a robust and efficient platform to selectively target and monitor endogenous PSD-95 using various fluorescence imaging techniques.

Selective Targeting of Nanobody-Modified Gold Nanoparticles to Distinct Cell Types

Nanobody-modified gold nanoparticles were used to explore their ability to achieve selective targeting in vitro and in vivo to distinct cell type(s), based on the specificity of the nanobody that was installed. We developed conjugation methods that exploit click chemistry for octahedral ∼50 nm gold nanoparticles and chiral ∼180 nm gold nanoparticles. We determined that each of these particles could be modified with ∼75 and ∼330 nanobodies, respectively. Particle-bound nanobodies retain their antigen binding capacity. After conjugation of the mouse Class II MHC-specific nanobody VHH7 to chiral gold nanoparticles, selective targeting of Class II MHC-positive cell types was observed in vitro by fluorometric assays and by dark-field microscopy. Upon installation of the positron emission tomography (PET) isotopes 89Zr or 64Cu on nanobody-modified gold nanoparticles and retro-orbital injection of the radiolabeled particles, we observed accumulation predominantly in the liver and to a far lesser extent in the spleen, regardless of the size of the gold nanoparticles and the identity of the attached nanobody. We observed a striking difference in the distribution of radioisotope-labeled gold nanoparticles by changing the route of administration to intraperitoneal delivery. Significantly reduced accumulation in the liver and spleen was observed by intraperitoneal injection of nanoparticles. In the case of nanobody-modified gold nanoparticles injected intraperitoneally, prominent and persistent signals from the parathymic lymph nodes were observed in the PET/computed tomography images.

Protein nanobarcodes enable single-step multiplexed fluorescence imaging

Multiplexed cellular imaging typically relies on the sequential application of detection probes, as antibodies or DNA barcodes, which is complex and time-consuming. To address this, we developed here protein nanobarcodes, composed of combinations of epitopes recognized by specific sets of nanobodies. The nanobarcodes are read in a single imaging step, relying on nanobodies conjugated to distinct fluorophores, which enables a precise analysis of large numbers of protein combinations. Fluorescence images from nanobarcodes were used as input images for a deep neural network, which was able to identify proteins with high precision. We thus present an efficient and straightforward protein identification method, which is applicable to relatively complex biological assays. We demonstrate this by a multicell competition assay, in which we successfully used our nanobarcoded proteins together with neurexin and neuroligin isoforms, thereby testing the preferred binding combinations of multiple isoforms, in parallel.

Self-Assembly Multivalent Fluorescence-Nanobody Coupled Multifunctional Nanomaterial with Colorimetric Fluorescence and Photothermal to Enhance Immunochromatographic Assay

The multimodal lateral flow immunoassay (LFIA) has provided accurate and reliable results for fast and immediate detection. Nonetheless, multimodal LFIA remains challenging to develop biosensors with high sensitivity and tolerance to matrix interference in agro-food. In this study, we developed a self-assembled multivalent fluorescence-nanobody (Nb26-EGFP-H6) with 16.5-fold and 30-fold higher affinity and sensitivity than a monovalent nanobody (Nb26). Based on the Nb26-EGFP-H6, we synthesized enhanced immune-probes Zn-CN@Nb26-EGFP-H6 by pyrolyzing and oxidizing an imidazolating zeolite framework-8 (ZIF-8) to obtain photothermal metal-carbon nanomaterials (Zn-CN) for immobilizing Nb26-EGFP-H6. The rough and porous structure of Zn-CN with a large surface area facilitates the enrichment and immobilization of antibodies. A trimodal lateral flow immunoassay (tLFIA) with colorimetric, fluorescent, and photothermal triple signal outputs was constructed for the detection of aflatoxin B1 (AFB1) in maize. Attractively, the Zn-CN-based tLFIA's multiplex guarantees accurate and sensitive detection of AFB1, with triple signal detection limits of 0.0012 ng/mL (colorimetric signals), 0.0094 ng/mL (fluorescent signals), and 0.252 ng/mL (photothermal signals). The sensitivity of the trimode immunosensor was 628-fold and 42-fold higher than that of the original Nb26-based ELISA (IC50) and the unimodal LFIA (LOD). This work provides an idea for constructing a sensitive, tolerant matrix and efficient and accurate analytical platform for rapidly detecting AFB1 in food.

A Versatile Synaptotagmin-1 Nanobody Provides Perturbation-Free Live Synaptic Imaging And Low Linkage-Error in Super-Resolution Microscopy

Imaging of living synapses has relied for over two decades on the overexpression of synaptic proteins fused to fluorescent reporters. This strategy alters the stoichiometry of synaptic components and ultimately affects synapse physiology. To overcome these limitations, here a nanobody is presented that binds the calcium sensor synaptotagmin-1 (NbSyt1). This nanobody functions as an intrabody (iNbSyt1) in living neurons and is minimally invasive, leaving synaptic transmission almost unaffected, as suggested by the crystal structure of the NbSyt1 bound to Synaptotagmin-1 and by the physiological data. Its single-domain nature enables the generation of protein-based fluorescent reporters, as showcased here by measuring spatially localized presynaptic Ca2+ with a NbSyt1- jGCaMP8 chimera. Moreover, the small size of NbSyt1 makes it ideal for various super-resolution imaging methods. Overall, NbSyt1 is a versatile binder that will enable imaging in cellular and molecular neuroscience with unprecedented precision across multiple spatiotemporal scales.

α-Synuclein fibril and synaptic vesicle interactions lead to vesicle destruction and increased lipid-associated fibril uptake into iPSC-derived neurons

Monomeric alpha-synuclein (aSyn) is a well characterised protein that importantly binds to lipids. aSyn monomers assemble into amyloid fibrils which are localised to lipids and organelles in insoluble structures found in Parkinson's disease patient's brains. Previous work to address pathological aSyn-lipid interactions has focused on using synthetic lipid membranes, which lack the complexity of physiological lipid membranes. Here, we use physiological membranes in the form of synaptic vesicles (SV) isolated from rodent brain to demonstrate that lipid-associated aSyn fibrils are more easily taken up into iPSC-derived cortical i3Neurons. Lipid-associated aSyn fibril characterisation reveals that SV lipids are an integrated part of the fibrils and while their fibril morphology differs from aSyn fibrils alone, the core fibril structure remains the same, suggesting the lipids lead to the increase in fibril uptake. Furthermore, SV enhance the aggregation rate of aSyn, yet increasing the SV:aSyn ratio causes a reduction in aggregation propensity. We finally show that aSyn fibrils disintegrate SV, whereas aSyn monomers cause clustering of SV using small angle neutron scattering and high-resolution imaging. Disease burden on neurons may be impacted by an increased uptake of lipid-associated aSyn which could enhance stress and pathology, which in turn may have fatal consequences for neurons.

Simple and Highly Efficient Detection of PSD95 Using a Nanobody and Its Recombinant Heavy-Chain Antibody Derivatives

The post-synaptic density protein 95 (PSD95) is a crucial scaffolding protein participating in the organization and regulation of synapses. PSD95 interacts with numerous molecules, including neurotransmitter receptors and ion channels. The functional dysregulation of PSD95 as well as its abundance and localization has been implicated with several neurological disorders, making it an attractive target for developing strategies able to monitor PSD95 accurately for diagnostics and therapeutics. This study characterizes a novel camelid single-domain antibody (nanobody) that binds strongly and with high specificity to rat, mouse, and human PSD95. This nanobody allows for more precise detection and quantification of PSD95 in various biological samples. We expect that the flexibility and unique performance of this thoroughly characterized affinity tool will help to further understand the role of PSD95 in normal and diseased neuronal synapses.

Targeting the Brain with Single-Domain Antibodies: Greater Potential Than Stated So Far?

Treatments for central nervous system diseases with therapeutic antibodies have been increasingly investigated over the last decades, leading to some approved monoclonal antibodies for brain disease therapies. The detection of biomarkers for diagnosis purposes with non-invasive antibody-based imaging approaches has also been explored in brain cancers. However, antibodies generally display a low capability of reaching the brain, as they do not efficiently cross the blood-brain barrier. As an alternative, recent studies have focused on single-domain antibodies (sdAbs) that correspond to the antigen-binding fragment. While some reports indicate that the brain uptake of these small antibodies is still low, the number of studies reporting brain-penetrating sdAbs is increasing. In this review, we provide an overview of methods used to assess or evaluate brain penetration of sdAbs and discuss the pros and cons that could affect the identification of brain-penetrating sdAbs of therapeutic or diagnostic interest.

Modeling native and seeded Synuclein aggregation and related cellular dysfunctions in dopaminergic neurons derived by a new set of isogenic iPSC lines with SNCA multiplications

Triplication of the SNCA gene, encoding the protein alpha-Synuclein (αSyn), is a rare cause of aggressive and early-onset parkinsonism. Herein, we generated iPSCs from two siblings with a recently described compact SNCA gene triplication and suffering from severe motor impairments, psychiatric symptoms, and cognitive deterioration. Using CRISPR/Cas9 gene editing, each SNCA copy was inactivated by targeted indel mutations generating a panel of isogenic iPSCs with a decremental number from 4 down to none of functional SNCA gene alleles. We differentiated these iPSC lines in midbrain dopaminergic (DA) neuronal cultures to characterize αSyn aggregation in native and seeded conditions and evaluate its associated cellular dysfunctions. Utilizing a new nanobody-based biosensor combined with super-resolved imaging, we were able to visualize and measure αSyn aggregates in early DA neurons in unstimulated conditions. Calcium dysregulation and mitochondrial alterations were the first pathological signs detectable in early differentiated DA neuronal cultures. Accelerated αSyn aggregation was induced by exposing neurons to structurally well-characterized synthetic αSyn fibrils. 4xSNCA DA neurons showed the highest vulnerability, which was associated with high levels of oxidized DA and amplified by TAX1BP1 gene disruption. Seeded DA neurons developed large αSyn deposits whose morphology and internal constituents resembled Lewy bodies commonly observed in Parkinson's disease (PD) patient brain tissues. These findings provide strong evidence that this isogenic panel of iPSCs with SNCA multiplications offers a remarkable cellular platform to investigate mechanisms of PD and validate candidate inhibitors of native and seeded αSyn aggregation.

Nanobody-based RFP-dependent Cre recombinase for selective anterograde tracing in RFP-expressing transgenic animals

Transgenic animals expressing fluorescent proteins are widely used to label specific cells and proteins. By using a split Cre recombinase fused with mCherry-binding nanobodies or designed ankyrin repeat proteins, we created Cre recombinase dependent on red fluorescent protein (RFP) (Cre-DOR). Functional binding units for monomeric RFPs are different from those for polymeric RFPs. We confirmed selective target RFP-dependent gene expression in the mouse cerebral cortex using stereotaxic injection of adeno-associated virus vectors. In estrogen receptor-beta (Esr2)-mRFP1 mice and gastrin-releasing peptide receptor (Grpr)-mRFP1 rats, we confirmed that Cre-DOR can be used for selective tracing of the neural projection from RFP-expressing specific neurons. Cellular localization of RFPs affects recombination efficiency of Cre-DOR, and light and chemical-induced nuclear translocation of an RFP-fused protein can modulate Cre-DOR efficiency. Our results provide a method for manipulating gene expression in specific cells expressing RFPs and expand the repertory of nanobody-based genetic tools.

α-Synuclein in the Synaptic Vesicle Liquid Phase: Active Player or Passive Bystander?

The protein α-synuclein, which is well-known for its links to Parkinson’s Disease, is associated with synaptic vesicles (SVs) in nerve terminals. Despite intensive studies, its precise physiological function remains elusive. Accumulating evidence indicates that liquid-liquid phase separation takes part in the assembly and/or maintenance of different synaptic compartments. The current review discusses recent data suggesting α-synuclein as a component of the SV liquid phase. We also consider possible implications of these data for disease.

Deciphering the Structure and Formation of Amyloids in Neurodegenerative Diseases With Chemical Biology Tools

Protein aggregation into highly ordered, regularly repeated cross-β sheet structures called amyloid fibrils is closely associated to human disorders such as neurodegenerative diseases including Alzheimer's and Parkinson's diseases, or systemic diseases like type II diabetes. Yet, in some cases, such as the HET-s prion, amyloids have biological functions. High-resolution structures of amyloids fibrils from cryo-electron microscopy have very recently highlighted their ultrastructural organization and polymorphisms. However, the molecular mechanisms and the role of co-factors (posttranslational modifications, non-proteinaceous components and other proteins) acting on the fibril formation are still poorly understood. Whether amyloid fibrils play a toxic or protective role in the pathogenesis of neurodegenerative diseases remains to be elucidated. Furthermore, such aberrant protein-protein interactions challenge the search of small-molecule drugs or immunotherapy approaches targeting amyloid formation. In this review, we describe how chemical biology tools contribute to new insights on the mode of action of amyloidogenic proteins and peptides, defining their structural signature and aggregation pathways by capturing their molecular details and conformational heterogeneity. Challenging the imagination of scientists, this constantly expanding field provides crucial tools to unravel mechanistic detail of amyloid formation such as semisynthetic proteins and small-molecule sensors of conformational changes and/or aggregation. Protein engineering methods and bioorthogonal chemistry for the introduction of protein chemical modifications are additional fruitful strategies to tackle the challenge of understanding amyloid formation.

Development of nanobody-horseradish peroxidase-based sandwich ELISA to detect Salmonella Enteritidis in milk and in vivo colonization in chicken

Background

Salmonella Enteritidis (S. Enteritidis) being one of the most prevalent foodborne pathogens worldwide poses a serious threat to public safety. Prevention of zoonotic infectious disease and controlling the risk of transmission of S. Enteriditidis critically requires the evolution of rapid and sensitive detection methods. The detection methods based on nucleic acid and conventional antibodies are fraught with limitations. Many of these limitations of the conventional antibodies can be circumvented using natural nanobodies which are endowed with characteristics, such as high affinity, thermal stability, easy production, especially higher diversity. This study aimed to select the special nanobodies against S. Enteriditidis for developing an improved nanobody-horseradish peroxidase-based sandwich ELISA to detect S. Enteritidis in the practical sample. The nanobody-horseradish peroxidase fusions can help in eliminating the use of secondary antibodies labeled with horseradish peroxidase, which can reduce the time of the experiment. Moreover, the novel sandwich ELISA developed in this study can be used to detect S. Enteriditidis specifically and rapidly with improved sensitivity.

Results

This study screened four nanobodies from an immunized nanobody library, after four rounds of screening, using the phage display technology. Subsequently, the screened nanobodies were successfully expressed with the prokaryotic and eukaryotic expression systems, respectively. A sandwich ELISA employing the SE-Nb9 and horseradish peroxidase-Nb1 pair to capture and to detect S. Enteritidis, respectively, was developed and found to possess a detection limit of 5 × 10⁴ colony forming units (CFU)/mL. In the established immunoassay, the 8 h-enrichment enabled the detection of up to approximately 10 CFU/mL of S. Enteriditidis in milk samples. Furthermore, we investigated the colonization distribution of S. Enteriditidis in infected chicken using the established assay, showing that the S. Enteriditidis could subsist in almost all parts of the intestinal tract. These results were in agreement with the results obtained from the real-time PCR and plate culture. The liver was specifically identified to be colonized with quite a several S. Enteriditidis, indicating the risk of S. Enteriditidis infection outside of intestinal tract.

Conclusions

This newly developed a sandwich ELISA that used the SE-Nb9 as capture antibody and horseradish peroxidase-Nb1 to detect S. Enteriditidis in the spike milk sample and to analyze the colonization distribution of S. Enteriditidis in the infected chicken. These results demonstrated that the developed assay is to be applicable for detecting S. Enteriditidis in the spiked milk in the rapid, specific, and sensitive way. Meanwhile, the developed assay can analyze the colonization distribution of S. Enteriditidis in the challenged chicken to indicate it as a promising tool for monitoring S. Enteriditidis in poultry products. Importantly, the SE-Nb1-vHRP as detection antibody can directly bind S. Enteritidis captured by SE-Nb9, reducing the use of commercial secondary antibodies and shortening the detection time. In short, the developed sandwich ELISA ushers great prospects for monitoring S. Enteritidis in food safety control and further commercial production.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01376-y.

Development and Validation of Arc Nanobodies: New Tools for Probing Arc Dynamics and Function

Activity-regulated cytoskeleton-associated (Arc) protein plays key roles in long-term synaptic plasticity, memory, and cognitive flexibility. However, an integral understanding of Arc mechanisms is lacking. Arc is proposed to function as an interaction hub in neuronal dendrites and the nucleus, yet Arc can also form retrovirus-like capsids with proposed roles in intercellular communication. Here, we sought to develop anti-Arc nanobodies (ArcNbs) as new tools for probing Arc dynamics and function. Six ArcNbs representing different clonal lines were selected from immunized alpaca. Immunoblotting with recombinant ArcNbs fused to a small ALFA-epitope tag demonstrated binding to recombinant Arc as well as endogenous Arc from rat cortical tissue. ALFA-tagged ArcNb also provided efficient immunoprecipitation of stimulus-induced Arc after carbachol-treatment of SH-SY5Y neuroblastoma cells and induction of long-term potentiation in the rat dentate gyrus in vivo. Epitope mapping showed that all Nbs recognize the Arc C-terminal region containing the retroviral Gag capsid homology domain, comprised of tandem N- and C-lobes. ArcNbs E5 and H11 selectively bound the N-lobe, which harbors a peptide ligand binding pocket specific to mammals. Four additional ArcNbs bound the region containing the C-lobe and C-terminal tail. For use as genetically encoded fluorescent intrabodies, we show that ArcNbs fused to mScarlet-I are uniformly expressed, without aggregation, in the cytoplasm and nucleus of HEK293FT cells. Finally, mScarlet-I-ArcNb H11 expressed as intrabody selectively bound the N-lobe and enabled co-immunoprecipitation of full-length intracellular Arc. ArcNbs are versatile tools for live-cell labeling and purification of Arc, and interrogation of Arc capsid domain specific functions.

α-Synuclein in Parkinson's disease and advances in detection

Parkinson's disease (PD) is a threatening neurodegenerative disorder that seriously affects patients' life quality. Substantial evidence links the overexpression and abnormal aggregation of alpha-synuclein (α-Syn) to PD. α-Syn has been identified as a characteristic biomarker of PD, which indicates its great value of diagnosis and designing effective therapeutic strategy. This article systematically summarizes the pathogenic process of α-Syn based on recent researches, outlines and compares commonly used analysis and detection technologies of α-Syn. Specifically, the detection of α-Syn by new electrochemical, photochemical, and crystal biosensors is mainly examined. Furthermore, the speculation of future study orientation is discussed, which provides reference for the further research and application of α-Syn as biomarker.

Emerging fluorescence tools for the study of proteostasis in cells

Understanding how cells maintain the functional proteome and respond to stress conditions is critical for deciphering molecular pathogenesis and developing treatments for conditions such as neurodegenerative diseases. Efforts towards finer quantification of cellular proteostasis machinery efficiency, phase transitions and local environment changes remain a priority. Herein, we describe recent developments in fluorescence-based strategy and methodology, building on the experimental toolkit, for the study of proteostasis (protein homeostasis) in cells. We hope this review can assist in bridging gaps between a multitude of research disciplines and promote interdisciplinary collaboration to address the crucial topic of proteostasis.

Research Progress and Applications of Multivalent, Multispecific and Modified Nanobodies for Disease Treatment

Recombinant antibodies such as nanobodies are progressively demonstrating to be a valid alternative to conventional monoclonal antibodies also for clinical applications. Furthermore, they do not solely represent a substitute for monoclonal antibodies but their unique features allow expanding the applications of biotherapeutics and changes the pattern of disease treatment. Nanobodies possess the double advantage of being small and simple to engineer. This combination has promoted extremely diversified approaches to design nanobody-based constructs suitable for particular applications. Both the format geometry possibilities and the functionalization strategies have been widely explored to provide macromolecules with better efficacy with respect to single nanobodies or their combination. Nanobody multimers and nanobody-derived reagents were developed to image and contrast several cancer diseases and have shown their effectiveness in animal models. Their capacity to block more independent signaling pathways simultaneously is considered a critical advantage to avoid tumor resistance, whereas the mass of these multimeric compounds still remains significantly smaller than that of an IgG, enabling deeper penetration in solid tumors. When applied to CAR-T cell therapy, nanobodies can effectively improve the specificity by targeting multiple epitopes and consequently reduce the side effects. This represents a great potential in treating malignant lymphomas, acute myeloid leukemia, acute lymphoblastic leukemia, multiple myeloma and solid tumors. Apart from cancer treatment, multispecific drugs and imaging reagents built with nanobody blocks have demonstrated their value also for detecting and tackling neurodegenerative, autoimmune, metabolic, and infectious diseases and as antidotes for toxins. In particular, multi-paratopic nanobody-based constructs have been developed recently as drugs for passive immunization against SARS-CoV-2 with the goal of impairing variant survival due to resistance to antibodies targeting single epitopes. Given the enormous research activity in the field, it can be expected that more and more multimeric nanobody molecules will undergo late clinical trials in the next future. Systematic Review Registration.

Nanobodies - Little helpers unravelling intracellular signaling

The identification of diagnostic and therapeutic targets requires a comprehensive understanding of cellular processes, for which advanced technologies in biomedical research are needed. The emergence of nanobodies (Nbs) derived from antibody fragments of camelid heavy chain-only antibodies as intracellular research tools offers new possibilities to study and modulate target antigens in living cells. Here we summarize this rapidly changing field, beginning with a brief introduction of Nbs, followed by an overview of how target-specific Nbs can be generated, and introduce the selection of intrabodies as research tools. Intrabodies, by definition, are intracellular functional Nbs that target ectopic or endogenous intracellular antigens within living cells. Such binders can be applied in various formats, e.g. as chromobodies for live cell microscopy or as biosensors to decipher complex intracellular signaling pathways. In addition, protein knockouts can be achieved by target-specific Nbs, while modulating Nbs have the potential as future therapeutics. The development of fine-tunable and switchable Nb-based systems that simultaneously provide spatial and temporal control has recently taken the application of these binders to the next level.

Camelid Single-Domain Antibodies for the Development of Potent Diagnosis Platforms

The distinct biophysical and pharmaceutical properties of camelid single-domain antibodies, referred to as VHHs or nanobodies, are associated with their nanometric dimensions, elevated stability, and antigen recognition capacity. These biomolecules can circumvent a number of diagnostic system limitations, especially those related to the size and stability of conventional immunoglobulins currently used in enzyme-linked immunosorbent assays and point-of-care, electrochemical, and imaging assays. In these formats, VHHs are directionally conjugated to different molecules, such as metallic nanoparticles, small peptides, and radioisotopes, which demonstrates their comprehensive versatility. Thus, the application of VHHs in diagnostic systems range from the identification of cancer cells to the detection of degenerative disease biomarkers, viral antigens, bacterial toxins, and insecticides. The improvements of sensitivity and specificity are among the central benefits resulting from the use of VHHs, which are indispensable parameters for high-quality diagnostics. Therefore, this review highlights the main biotechnological advances related to camelid single-domain antibodies and their use in in vitro and in vivo diagnostic approaches for human health.

Nanobodies for Medical Imaging: About Ready for Prime Time?

Recent advances in medical treatments have been revolutionary in shaping the management and treatment landscape of patients, notably cancer patients. Over the last decade, patients with diverse forms of locally advanced or metastatic cancer, such as melanoma, lung cancers, and many blood-borne malignancies, have seen their life expectancies increasing significantly. Notwithstanding these encouraging results, the present-day struggle with these treatments concerns patients who remain largely unresponsive, as well as those who experience severely toxic side effects. Gaining deeper insight into the cellular and molecular mechanisms underlying these variable responses will bring us closer to developing more effective therapeutics. To assess these mechanisms, non-invasive imaging techniques provide valuable whole-body information with precise targeting. An example of such is immuno-PET (Positron Emission Tomography), which employs radiolabeled antibodies to detect specific molecules of interest. Nanobodies, as the smallest derived antibody fragments, boast ideal characteristics for this purpose and have thus been used extensively in preclinical models and, more recently, in clinical early-stage studies as well. Their merit stems from their high affinity and specificity towards a target, among other factors. Furthermore, their small size (~14 kDa) allows them to easily disperse through the bloodstream and reach tissues in a reliable and uniform manner. In this review, we will discuss the powerful imaging potential of nanobodies, primarily through the lens of imaging malignant tumors but also touching upon their capability to image a broader variety of nonmalignant diseases.

Fluorescent Probe for Selective Imaging of α-Synuclein Fibrils in Living Cells

Plaques of amyloid fibrils composed of neuronal protein α-synuclein are one of the hallmarks of Parkinson's disease, and their selective imaging is crucial to study the mechanism of its pathogenesis. However, the existing fluorescent probes for amyloids are efficient only in solution and tissue systems, and they are not selective enough for the visualization of amyloid fibrils in living cells. In this study, we present two molecular rotor-based probes RB1 and RB2. These thiazolium probes show affinity to α-synuclein fibrils and turn-on fluorescence response upon interactions. Because of its extended π-conjugation and high rotational degree of freedom, RB1 exhibits a 76 nm red-shift of absorption maxima and 112-fold fluorescence enhancement upon binding to amyloid fibrils. Owing to its strong binding affinity to α-synuclein fibrils, RB1 can selectively stain them in the cytoplasm of living HeLa and SH-SY5Y cells with high optical contrast. RB1 is a cell-permeable and noncytotoxic probe. Taken together, we have demonstrated that RB1 is an amyloid probe with an outstanding absorption red-shift that can be used for intracellular imaging of α-synuclein fibrils.

Fluorescent probes for bioimaging of potential biomarkers in Parkinson's disease

This review comprehensively summarizes various types of fluorescent probes for PD and their applications for detection of various PD biomarkers.

Nanobodies against the metal binding domains of ATP7B as tools to study copper transport in the cell

Nanobodies are genetically engineered single domain antibodies derived from the unusual heavy-chain only antibodies found in llamas and camels. The small size of the nanobodies and flexible selection schemes make them uniquely versatile tools for protein biochemistry and cell biology. We have developed a panel of nanobodies against the metal binding domains of the human copper transporter ATP7B, a multidomain membrane protein with a complex regulation of enzymatic activity and intracellular localization. To enable the use of the nanobodies as tools to investigate copper transport in the cell, we characterized their binding sites and affinity by isothermal titration calorimetry and NMR. We have identified nanobodies against each of the first four metal binding domains of ATP7B, with a wide affinity range, as evidenced by dissociation constants from below 10-9 to 10-6 M. We found both the inhibitory and activating nanobodies among those tested. The diverse properties of the nanobodies make the panel useful for the structural studies of ATP7B, immunoaffinity purification of the protein, modulation of its activity in the cell, protein dynamics studies, and as mimics of copper chaperone ATOX1, the natural interaction partner of ATP7B.

Nanobodies as Versatile Tool for Multiscale Imaging Modalities

Molecular imaging is constantly growing in different areas of preclinical biomedical research. Several imaging methods have been developed and are continuously updated for both in vivo and in vitro applications, in order to increase the information about the structure, localization and function of molecules involved in physiology and disease. Along with these progresses, there is a continuous need for improving labeling strategies. In the last decades, the single domain antigen-binding fragments nanobodies (Nbs) emerged as important molecular imaging probes. Indeed, their small size (~15 kDa), high stability, affinity and modularity represent desirable features for imaging applications, providing higher tissue penetration, rapid targeting, increased spatial resolution and fast clearance. Accordingly, several Nb-based probes have been generated and applied to a variety of imaging modalities, ranging from in vivo and in vitro preclinical imaging to super-resolution microscopy. In this review, we will provide an overview of the state-of-the-art regarding the use of Nbs in several imaging modalities, underlining their extreme versatility and their enormous potential in targeting molecules and cells of interest in both preclinical and clinical studies.