Ultrasensitive dynamic light scattering immunodetection of alpha-fetoprotein using heptamer-amplified nanoparticle crosslinking aggregation

A novel construction strategy is introduced for an ultrasensitive dynamic light scattering (DLS) immunosensor targeting alpha fetoprotein (AFP). This approach relies on a self-assembled heptamer fusion protein (A1-C4bpα), incorporating the dual functions of multivalent recognition and crosslinking aggregation amplification due to the presence of seven AFP-specific A1 nanobodies on the A1-C4bpα heptamer. Leveraging antibody-functionalized magnetic nanoparticles for target AFP capture and DLS signal output, the proposed heptamer-assisted DLS immunosensor offers high sensitivity, strong specificity, and ease of operation. Under the optimized conditions, the designed DLS immunosensor demonstrates excellent linear detection of AFP in the concentration range 0.06 ng mL-1 to 512 ng mL-1, with a detection limit of 15 pg mL-1. The selectivity, accuracy, precision, practicability, and reliability of this newly developed method were further validated through an assay of AFP levels in spiked and actual human serum samples. This work introduces a novel approach for constructing ultrasensitive DLS immunosensors, easily extendable to the sensitive determination of other targets via simply replacing the nanobody sequence, holding great promise in various applications, particularly in disease diagnosis.

Development of Shark Single Domain Antibodies Specific for Human α-Fetoprotein and the Multimerization Strategy in Serum Detection

Sensitive detection of cancer biomarkers can contribute to the timely diagnosis and treatment of diseases. In this study, the whitespotted bamboo sharks were immunized with human α-fetoprotein (AFP), and a phage-displayed variable new antigen receptor (VNAR) single domain antibody library was constructed. Then four unique VNARs (VNAR1, VNAR11, VNAR21, and VNAR25) against AFP were isolated from the library by biopanning for the first time. All of the sequences belong to type II of VNAR, and the VNAR11 was much different from the rest of the three sequences. Then VNAR1 and VNAR11 were selected to fuse with the C4-binding protein α chain (C4bpα) sequence and efficiently expressed in the Escherichia coli system. Furthermore, a VNAR-C4bpα-mediated sandwich chemiluminescence immunoassay (VSCLIA) was developed for the detection of AFP in human serum samples. After optimization, the VSCLIA showed a limit of detection of 0.74 ng/mL with good selectivity and accuracy. Moreover, the results of clinical serum samples detected by the VSCLIA were confirmed by an automatic immunoanalyzer in the hospital, indicating its practical application in actual samples. In conclusion, the novel antibody element VNAR exhibits great potential for immunodiagnosis, and this study also provides a new direction and experimental basis for AFP detection.

Enhanced Non-Toxic Immunodetection of Alternaria Mycotoxin Tenuazonic Acid Based on Ferritin-Displayed Anti-Idiotypic Nanobody-Nanoluciferase Multimers

The non-toxic immunoassay for mycotoxins is being paid more attention due to its advantages of higher safety and cost savings by using anti-idiotype antibodies to substitute toxins. In this study, with tenuazonic acid (TeA), a kind of highly toxic Alternaria mycotoxin as the target, an enhanced non-toxic immunoassay was developed based on the ferritin-displayed anti-idiotypic nanobody-nanoluciferase multimers. First, three specific β-type anti-idiotype nanobodies (AId-Nbs) bearing the internal image of TeA mycotoxin were selected from an immune phage display library. Then, the AId-Nb 2D with the best performance was exploited to generate a nanoluciferase (Nluc)-functionalized fusion monomer, by which a one-step non-toxic immunodetection format for TeA was established and proven to be effective. To further improve the affinity of the monomer, a ferritin display strategy was used to prepare 2D-Nluc fusion multimers. Finally, an enhanced bioluminescent enzyme immunoassay (BLEIA) was established in which the half maximal inhibitory concentration (IC₅₀) for TeA was 6.5 ng/mL with a 10.5-fold improvement of the 2D-based enzyme-linked immunosorbent assay (ELISA). The proposed assay exhibited high selectivities and good recoveries of 80.0-95.2%. The generated AId-Nb and ferritin-displayed AId-Nb-Nluc multimers were successfully extended to the application of TeA in food samples. This study brings a new strategy for production of multivalent AId-Nbs and non-toxic immunoassays for trace toxic contaminants.

Nanobodies targeting immune checkpoint molecules for tumor immunotherapy and immunoimaging (Review)

The immune checkpoint blockade is an effective strategy to enhance the anti-tumor T cell effector activity, thus becoming one of the most promising immunotherapeutic strategies in the history of cancer treatment. Several immune checkpoint inhibitor have been approved by the FDA, such as anti-CTLA-4, anti-PD-1, anti-PD-L1 monoclonal antibodies. Most tumor patients benefitted from these antibodies, but some of the patients did not respond to them. To increase the effectiveness of immunotherapy, including immune checkpoint blockade therapies, miniaturization of antibodies has been introduced. A single-domain antibody, also known as nanobody, is an attractive reagent for immunotherapy and immunoimaging thanks to its unique structural characteristic consisting of a variable region of a single heavy chain antibody. This structure confers to the nanobody a light molecular weight, making it smaller than conventional antibodies, although remaining able to bind to a specific antigen. Therefore, this review summarizes the production of nanobodies targeting immune checkpoint molecules and the application of nanobodies targeting immune checkpoint molecules in immunotherapy and immunoimaging.

Construction of Immunomagnetic Particles with High Stability in Stringent Conditions by Site-Directed Immobilization of Multivalent Nanobodies onto Bacterial Magnetic Particles for the Environmental Detection of Tetrabromobisphenol-A

Bacterial magnetic particles (BMPs) are an attractive carrier material for immunoassays because of their nanoscale size, dispersal ability, and membrane-bound structure. Antitetrabromobisphenol-A (TBBPA) nanobodies (Nbs) in the form of monovalence (Nb1), bivalence (Nb2), and trivalence (Nb3) were biotinylated and immobilized onto streptavidin (SA)-derivatized BMPs to construct the complexes of BMP-SA-Biotin-Nb1, -Nb2, and -Nb3, respectively. An increasing order of binding capability of BMP-SA-Biotin-Nb1, -Nb2, and -Nb3 to TBBPA was observed. These complexes showed high resilience to temperature (90 °C), methanol (100%), high pH (12), and strong ionic strength (1.37 M NaCl). A BMP-SA-Biotin-Nb3-based enzyme linked immunosorbent assay (ELISA) for TBBPA dissolved in methanol was developed, showing a half-maximum inhibition concentration (IC₅₀) of 0.42 ng mL^-1. TBBPA residues in landfill leachate, sewage, and sludge samples determined by this assay were in a range of <LOD-1.17 ng mL^-1, <LOD-0.75 ng mL^-1, and <LOD-3.65 ng g^-1 (dw), respectively, correlating well with the results by liquid chromatography tandem mass spectrometry. The BMP-SA-Biotin-Nb3 was reusable at least three times without significant loss of the binding capability. The BMP-SA-Biotin-Nb3-based ELISA, with a total assay time of less than 30 min, is promising for the rapid monitoring of TBBPA in the environment.

Single-Domain Antibodies and the Promise of Modular Targeting in Cancer Imaging and Treatment

Monoclonal antibodies and their fragments have significantly changed the outcome of cancer in the clinic, effectively inhibiting tumor cell proliferation, triggering antibody-dependent immune effector cell activation and complement mediated cell death. Along with a continued expansion in number, diversity, and complexity of validated tumor targets there is an increasing focus on engineering recombinant antibody fragments for lead development. Single-domain antibodies (sdAbs), in particular those engineered from the variable heavy-chain fragment (VHH gene) found in Camelidae heavy-chain antibodies (or IgG2 and IgG3), are the smallest fragments that retain the full antigen-binding capacity of the antibody with advantageous properties as drugs. For similar reasons, growing attention is being paid to the yet smaller variable heavy chain new antigen receptor (VNAR) fragments found in Squalidae. sdAbs have been selected, mostly from immune VHH libraries, to inhibit or modulate enzyme activity, bind soluble factors, internalize cell membrane receptors, or block cytoplasmic targets. This succinct review is a compilation of recent data documenting the application of engineered, recombinant sdAb in the clinic as epitope recognition “modules” to build monomeric, dimeric and multimeric ligands that target, tag and stall solid tumor growth in vivo. Size, affinity, specificity, and the development profile of sdAbs drugs are seemingly consistent with desirable clinical efficacy and safety requirements. But the hepatotoxicity of the tetrameric anti-DR5-VHH drug in patients with pre-existing anti-drug antibodies halted the phase I clinical trial and called for a thorough pre-screening of the immune and poly-specific reactivities of the sdAb leads.

(99m) Tc-labeled tetramer and pentamer of single-domain antibody for targeting epidermal growth factor receptor in xenografted tumors

The single-domain antibody EG2 can be fused with right-handed coiled-coil (RHCC) and human cartilage oligomeric matrix protein (COMP), to form the multivalent antibodies EG2-RHCC and EG2-COMP. We labeled these two antibodies with (99m) Tc and assessed their targeting efficiency for epidermal growth factor receptor (EGFR). Cell binding, uptake, efflux, and blocking studies were performed with EGFR high- and/or low-expressing cells with (99m) Tc-labeled EG2-RHCC or EG2-COMP. Single photon-emission computed tomography (SPECT) imaging and biodistribution studies were further carried out. Both (99m) Tc-EG2-RHCC and (99m) Tc-EG2-COMP can specially bind to EGFR in vitro. SPECT imaging showed that A431, which expresses high levels of EGFR, was clearly visible 6 h after (99m) Tc-EG2-COMP injection; however, it was not detectable after administration of (99m) Tc-EG2-RHCC. Uptake of both antibodies by the non-EGFR-secreting OCM-1 tumors was low. EG2-COMP shows promise in identifying EGFR over-expression in tumors; however, EG2-RHCC may not be suitable for targeting EGFR in vivo.

Bacterial secretion of soluble and functional trivalent scFv-based N-terminal trimerbodies

Recombinant antibodies are used with great success in many different diagnostic and therapeutic applications. A variety of protein expression systems are available, but nowadays almost all therapeutic antibodies are produced in mammalian cell lines due to their complex structure and glycosylation requirements. However, production of clinical-grade antibodies in mammalian cells is very expensive and time-consuming. On the other hand, Escherichia coli (E. coli) is known to be the simplest, fastest and most cost-effective recombinant expression system, which usually achieves higher protein yields than mammalian cells. Indeed, it is one of the most popular host in the industry for the expression of recombinant proteins. In this work, a trivalent single-chain fragment variable (scFv)-based N-terminal trimerbody, specific for native laminin-111, was expressed in human embryonic kidney 293 cells and in E. coli. Mammalian and bacterially produced anti-laminin trimerbody molecules display comparable functional and structural properties, although importantly the yield of trimerbody expressed in E. coli was considerably higher than in human cells. These results demonstrated that E. coli is a versatile and efficient expression system for multivalent trimerbody-based molecules that is suitable for their industrial production.

A novel multivalent (99m)Tc-labeled EG2-C4bpα antibody for targeting the epidermal growth factor receptor in tumor xenografts

INTRODUCTION

The C4b binding protein (C4bp) α/β-chain C-terminal effectively induces polymerization during protein synthesis. Using this fragment and the single-domain antibody EG2, which targets the epidermal growth factor receptor (EGFR), we generated the novel multimeric antibody EG2-C4bpα. We radiolabeled EG2-C4bpα with (99m)Tc and evaluated its targeting efficiency and pharmacokinetics in tumor xenografts.

METHODS

EGFR expression and EGFR-EG2-C4bpα binding was evaluated in A431 and OCM-1 cells by Western blotting and flow cytometry, respectively. EG2-C4bpα was radiolabeled with [(99m)Tc(CO)3(OH2)3](+) using a tricarbonyl vial followed by purification on a PD-10 column. In vitro studies with (99m)Tc-EG2-C4bpα were performed in A431 and/or OCM-1 cells. Single photon emission computed tomography (SPECT) imaging and biodistribution studies were carried out in (99m)Tc-EG2-C4bpα-injected mice bearing A431- and OCM-1-derived tumors. EGFR immunofluorescent staining in A431 and OCM-1 tumors was performed.

RESULTS

A431 cells showed higher EGFR expression levels than OCM-1 cells, and flow cytometry confirmed EG2-C4bpα bound more A431 cells than OCM-1 cells. (99m)Tc-EG2-C4bpα was successfully prepared with radiochemical yields of 30.3-50.4%. The binding affinity of (99m)Tc-EG2-C4bpα to A431 cells was approximately 20 nM. (99m)Tc-EG2-C4bpα specifically bound A431 cells and this binding was blocked by 41% in the presence of 50 nM excess unlabeled EG2-C4bpα. In vivo radioactivity uptake in A431 tumors was detected 2h after (99m)Tc-EG2-C4bpα administration and sustained up to 18h. The highest ratio of A431 tumor-to-muscle and tumor-to-blood was 3.69 ± 0.48 at 10h and 0.77 ± 0.14 at 20 h, respectively. Excess unlabeled EG2-C4bpα blocked radioactivity uptake in A431 tumors by 55% at 10h. (99m)Tc-EG2-C4bpα was barely detectable in OCM-1 tumors, and biodistribution analysis confirmed that radioactivity uptake was significantly lower than in A431 tumors.

CONCLUSIONS

(99m)Tc-EG2-C4bpα specifically and efficiently targets EGFR over-expressing tumors suggesting that EG2-C4bpα may be a promising antibody alternative for future diagnostic application and potential radioimmunotherapy. However, the high activity in the blood and liver, and the relative low ratio of tumor-to-blood should be noticed and improved.

Ionizing-radiation induced DNA double-strand breaks: a direct and indirect lighting up

The occurrence of DNA double-strand breaks (DSBs) induced by ionizing radiation has been extensively studied by biochemical or cell imaging techniques. Cell imaging development relies on technical advances as well as our knowledge of the cell DNA damage response (DDR) process. The DDR involves a complex network of proteins that initiate and coordinate DNA damage signaling and repair activities. As some DDR proteins assemble at DSBs in an established spatio-temporal pattern, visible nuclear foci are produced. In addition, post-translational modifications are important for the signaling and the recruitment of specific partners at damaged chromatin foci. We briefly review here the most widely used methods to study DSBs. We also discuss the development of indirect methods, using reporter expression or intra-nuclear antibodies, to follow the production of DSBs in real time and in living cells.