Nanobody: the "magic bullet" for molecular imaging?

Streamlined on-column refolding and purification of nanobodies from inclusion bodies expressed as fusion proteins

This study introduces an efficient on-column refolding and purification method for preparing nanobodies (Nbs) expressed as inclusion bodies and fusion proteins. The HisTrapTM FF system was successfully employed for the purification of the fusion protein FN1-ΔI-CM-2D5. The intein ΔI-CM cleavage activity was activated at 42 °C, followed by incubation for 4 h. Leveraging the remarkable thermal stability of Nbs, 2D5 was further purified through heat treatment at 80 °C for 1h. This method yielded up to 107.2 mg of pure 2D5 with a purity of 99.2 % from just 1L of bacterial culture grown in a shaker flask. Furthermore, this approach successfully restored native secondary structure and affinity of 2D5. Additionally, the platform was effectively applied to the refolding and purification of a polystyrene-binding nanobody (B2), which exhibited limited expression in the periplasmic and cytoplasmic spaces of E. coli. This endeavor resulted in the isolation of 53.2 mg of pure B2 Nb with a purity exceeding 99.5 % from the same volume of bacterial culture. Significantly, this approach restored the native secondary structure of the Nbs, highlighting its potential for addressing challenges associated with expressing complex Nbs in E. coli. Overall, this innovative platform provides a scientifically rigorous and reproducible method for the efficient preparation of Nbs, offering a valuable tool for antibody research and development.

Unlocking the Gates: Therapeutic Agents for Noninvasive Drug Delivery Across the Blood-Brain Barrier

The blood-brain barrier (BBB) is a highly selective network of various cell types that acts as a filter between the blood and the brain parenchyma. Because of this, the BBB remains a major obstacle for drug delivery to the central nervous system (CNS). In recent years, there has been a focus on developing various modifiable platforms, such as monoclonal antibodies (mAbs), nanobodies (Nbs), peptides, and nanoparticles, as both therapeutic agents and carriers for targeted drug delivery to treat brain cancers and diseases. Methods for bypassing the BBB can be invasive or noninvasive. Invasive techniques, such as transient disruption of the BBB using low pulse electrical fields and intracerebroventricular infusion, lack specificity and have numerous safety concerns. In this review, we will focus on noninvasive transport mechanisms that offer high levels of biocompatibility, personalization, specificity and are regarded as generally safer than their invasive counterparts. Modifiable platforms can be designed to noninvasively traverse the BBB through one or more of the following pathways: passive diffusion through a physio-pathologically disrupted BBB, adsorptive-mediated transcytosis, receptor-mediated transcytosis, shuttle-mediated transcytosis, and somatic gene transfer. Through understanding the noninvasive pathways, new applications, including Chimeric Antigen Receptors T-cell (CAR-T) therapy, and approaches for drug delivery across the BBB are emerging.

A Nanobody of PEDV S1 Protein: Screening and Expression in Escherichia coli

Porcine epidemic diarrhea virus (PEDV) has caused significant economic losses to the pig farming industry in various countries for a long time. Currently, there are no highly effective preventive or control measures available. Research into the pathogenic mechanism of PEDV has shown that it primarily causes infection by binding the S protein to the CD13 (APN) receptor on the membrane of porcine intestinal epithelial cells. The S1 region contains three neutralization epitopes and multiple receptor-binding domains, which are closely related to viral antigenicity and ad-sorption invasion. Nanobodies are a type of single-domain antibody that have been discovered in recent years. They can be expressed on a large scale through prokaryotic expression systems, which makes them cost-effective, stable, and less immunogenic. This study used a phage display library of nanobodies against the PEDV S1 protein. After three rounds of selection and enrichment, the DNA sequence of the highly specific nanobody S1Nb1 was successfully obtained. To obtain soluble nanobody S1Nb1, its DNA sequence was inserted into the vector Pcold and a solubility-enhancing SUMO tag was added. The resulting recombinant vector, Pcold-SUMO-S1Nb1, was then transformed into E. coli BL21(DE3) to determine the optimal expression conditions for the nanobody. Following purification using Ni-column affinity chromatography, Western blot analysis confirmed the successful purification of S1Nb1 carrying the solubility-enhancing tag. ELISA results demonstrated a strong affinity between the S1Nb1 nanobody and PEDV S1 protein.

Engineering and characterization of GFP-targeting nanobody: Expression, purification, and post-translational modification analysis

Nanobodies are single-variable domain antibodies with excellent properties, which are evolving as versatile tools to guide cognate antigens in vitro and in vivo for biological research, diagnosis, and treatment. Given their simple structure, nanobodies are readily produced in multiple systems. However, selecting an appropriate expression system is crucial because different conditions might cause proteins to produce different folds or post-translational modifications (PTMs), and these differences often result in different functions. At present, the strategies of PTMs are rarely reported. The GFP nanobody can specifically target the GFP protein. Here, we engineered a GFP nanobody fused with 6 × His tag and Fc tag, respectively, and expressed in bacteria and mammalian cells. The 6 × His-GFP-nanobody was produced from Escherichia coli at high yields and the pull-down assay indicated that it can precipitate the GFP protein. Meanwhile, the Fc-GFP-nanobody can be expressed in HEK293T cells, and the co-immunoprecipitation experiment can trace and target the GFP-tagged protein in vivo. Furthermore, some different PTMs in antigen-binding regions have been identified after using mass spectrometry (MS) to analyze the GFP nanobodies, which are expressed in prokaryotes and eukaryotes. In this study, a GFP nanobody was designed, and its binding ability was verified by using the eukaryotic and prokaryotic protein expression systems. In addition, this GFP nanobody was transformed into a useful instrument for more in-depth functional investigations of GFP fusion proteins. MS was further used to explore the reason for the difference in binding ability, providing a novel perspective for the study of GFP nanobodies and protein expression purification.

Generation and Characterization of Novel Pan-Cancer Anti-uPAR Fluorescent Nanobodies as Tools for Image-Guided Surgery

Fluorescence molecular imaging plays a vital role in image-guided surgery. In this context, the urokinase plasminogen activator receptor (uPAR) is an interesting biomarker enabling the detection and delineation of various tumor types due to its elevated expression on both tumor cells and the tumor microenvironment. In this study, anti-uPAR Nanobodies (Nbs) are generated through llama immunization with human and murine uPAR protein. Extensive in vitro characterization and in vivo testing with radiolabeled variants are conducted to assess their pharmacokinetics and select lead compounds. Subsequently, the selected Nbs are converted into fluorescent agents, and their application for fluorescence-guided surgery is evaluated in various subcutaneous and orthotopic tumor models. The study yields a panel of high-affinity anti-uPAR Nbs, showing specific binding across multiple types of cancer cells in vitro and in vivo. Lead fluorescently-labeled compounds exhibit high tumor uptake with high contrast at 1 h after intravenous injection across all assessed uPAR-expressing tumor models, outperforming a non-targeting control Nb. Additionally, rapid and accurate tumor localization and demarcation are demonstrated in an orthotopic human glioma model. Utilizing these Nbs can potentially enhance the precision of surgical tumor resection and, consequently, improve survival rates in the clinic.

Preclinical research progress in HER2-targeted small-molecule probes for breast cancer

Breast cancer is a malignant tumor that has the highest morbidity and mortality in women worldwide. Human epidermal growth factor receptor 2 (HER2) is a key driver of breast cancer development. Therefore, accurate assessment of HER2 expression in cancer patients and timely initiation or termination of anti-HER2 treatment are crucial for the prognosis of breast cancer patients. The emergence of radiolabeled molecular probes targeting HER2 makes this assessment possible. This article describes different types of small-molecule probes that target HER2 and are used in current preclinical applications and summarizes their advantages and disadvantages.

Single-domain antibodies as therapeutics for solid tumor treatment

Single-domain antibodies (sdAbs), initially identified in camelids or sharks and commonly referred to as nanobodies or VNARs, have emerged as a promising alternative to conventional therapeutic antibodies. These sdAbs have many superior physicochemical and pharmacological properties, including small size, good solubility and thermostability, easier accessible epitopes, and strong tissue penetration. However, the inherent challenges associated with the animal origin of sdAbs limit their clinical use. In recent years, various innovative humanization technologies, including complementarity-determining region (CDR) grafting or complete engineering of fully human sdAbs, have been developed to mitigate potential immunogenicity issues and enhance their compatibility. This review provides a comprehensive exploration of sdAbs, emphasizing their distinctive features and the progress in humanization methodologies. In addition, we provide an overview of the recent progress in developing drugs and therapeutic strategies based on sdAbs and their potential in solid tumor treatment, such as sdAb-drug conjugates, multispecific sdAbs, sdAb-based delivery systems, and sdAb-based cell therapy.

Nanobody engineering: computational modelling and design for biomedical and therapeutic applications

Nanobodies, the smallest functional antibody fragment derived from camelid heavy-chain-only antibodies, have emerged as powerful tools for diverse biomedical applications. In this comprehensive review, we discuss the structural characteristics, functional properties, and computational approaches driving the design and optimisation of synthetic nanobodies. We explore their unique antigen-binding domains, highlighting the critical role of complementarity-determining regions in target recognition and specificity. This review further underscores the advantages of nanobodies over conventional antibodies from a biosynthesis perspective, including their small size, stability, and solubility, which make them ideal candidates for economical antigen capture in diagnostics, therapeutics, and biosensing. We discuss the recent advancements in computational methods for nanobody modelling, epitope prediction, and affinity maturation, shedding light on their intricate antigen-binding mechanisms and conformational dynamics. Finally, we examine a direct example of how computational design strategies were implemented for improving a nanobody-based immunosensor, known as a Quenchbody. Through combining experimental findings and computational insights, this review elucidates the transformative impact of nanobodies in biotechnology and biomedical research, offering a roadmap for future advancements and applications in healthcare and diagnostics.

68Ga-NC-BCH Whole-Body PET Imaging Rapidly Targets Claudin18.2 in Lesions in Gastrointestinal Cancer Patients

68Ga-labeled nanobody (68Ga-NC-BCH) is a single-domain antibody-based PET imaging agent. We conducted a first-in-humans study of 68Ga-NC-BCH for PET to determine its in vivo biodistribution, metabolism, radiation dosimetry, safety, and potential for quantifying claudin-18 isoform 2 (CLDN18.2) expression in gastrointestinal cancer patients. Methods: Initially, we synthesized the probe 68Ga-NC-BCH and performed preclinical evaluations on human gastric adenocarcinoma cell lines and xenograft mouse models. Next, we performed a translational study with a pilot cohort of patients with advanced gastrointestinal cancer on a total-body PET/CT scanner. Radiopharmaceutical biodistribution, radiation dosimetry, and the relationship between tumor uptake and CLDN18.2 expression were evaluated. Results: 68Ga-NC-BCH was stably prepared and demonstrated good radiochemical properties. According to preclinical evaluation,68Ga-NC-BCH exhibited rapid blood clearance, high affinity for CLDN18.2, and high specific uptake in CLDN18.2-positive cells and xenograft mouse models. 68Ga-NC-BCH displayed high uptake in the stomach and kidney and slight uptake in the pancreas. Compared with 18F-FDG, 68Ga-NC-BCH showed significant differences in uptake in lesions with different levels of CLDN18.2 expression. Conclusion: A clear correlation was detected between PET SUV and CLDN18.2 expression, suggesting that 68Ga-NC-BCH PET could be used as a companion diagnostic tool for optimizing treatments that target CLDN18.2 in tumors.

Antibody design using deep learning: from sequence and structure design to affinity maturation

Deep learning has achieved impressive results in various fields such as computer vision and natural language processing, making it a powerful tool in biology. Its applications now encompass cellular image classification, genomic studies and drug discovery. While drug development traditionally focused deep learning applications on small molecules, recent innovations have incorporated it in the discovery and development of biological molecules, particularly antibodies. Researchers have devised novel techniques to streamline antibody development, combining in vitro and in silico methods. In particular, computational power expedites lead candidate generation, scaling and potential antibody development against complex antigens. This survey highlights significant advancements in protein design and optimization, specifically focusing on antibodies. This includes various aspects such as design, folding, antibody-antigen interactions docking and affinity maturation.

Molecular and functional insight into anti-EGFR nanobody: Theranostic implications for malignancies

Targeted therapy and imaging are the most popular techniques for the intervention and diagnosis of cancer. A potential therapeutic target for the treatment of cancer is the epidermal growth factor receptor (EGFR), primarily for glioblastoma, lung, and breast cancer. Over-production of ligand, transcriptional up-regulation due to autocrine/paracrine signalling, or point mutations at the genomic locus may contribute to the malfunction of EGFR in malignancies. This exploit makes use of EGFR, an established biomarker for cancer diagnostics and treatment. Despite considerable development in the last several decades in making EGFR inhibitors, they are still not free from limitations like toxicity and a short serum half-life. Nanobodies and antibodies share similar binding properties, but nanobodies have the additional advantage that they can bind to antigenic epitopes deep inside the target that conventional antibodies are unable to access. For targeted therapy, anti-EGFR nanobodies can be conjugated to various molecules such as drugs, peptides, toxins and photosensitizers. These nanobodies can be designed as novel immunoconjugates using the universal modular antibody-based platform technology (UniCAR). Furthermore, Anti-EGFR nanobodies can be expressed in neural stem cells and visualised by effective fluorescent and radioisotope labelling.

Non-Invasive Delivery of Negatively Charged Nanobodies by Anodal Iontophoresis: When Electroosmosis Dominates Electromigration

Iontophoresis enables the non-invasive transdermal delivery of moderately-sized proteins and the needle-free cutaneous delivery of antibodies. However, simple descriptors of protein characteristics cannot accurately predict the feasibility of iontophoretic transport. This study investigated the cathodal and anodal iontophoretic transport of the negatively charged M7D12H nanobody and a series of negatively charged variants with single amino acid substitutions. Surprisingly, M7D12H and its variants were only delivered transdermally by anodal iontophoresis. In contrast, transdermal permeation after cathodal iontophoresis and passive diffusion was Collapse

Key Words

• anti-EGFR 7D12 nanobody
• electroosmosis
• iontophoresis
• nanobodies
• protein expression and purification
• skin topical and transdermal delivery

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Affiliation(s)

Phedra Firdaws Sahraoui School of Pharmaceutical Sciences, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland; Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland
Oscar Vadas Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland;
Yogeshvar N. Kalia School of Pharmaceutical Sciences, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland; Institute of Pharmaceutical Sciences of Western Switzerland, University of Geneva, CMU-1 Rue Michel Servet, 1211 Geneva, Switzerland

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Preclinical development of novel PD-L1 tracers and first-in-human study of [68Ga]Ga-NOTA-RW102 in patients with lung cancers

BACKGROUND

The programmed cell death protein-1 (PD-1)/programmed death receptor ligand 1 (PD-L1) axis critically facilitates cancer cells' immune evasion. Antibody therapeutics targeting the PD-1/PD-L1 axis have shown remarkable efficacy in various tumors. Immuno-positron emission tomography (ImmunoPET) imaging of PD-L1 expression may help reshape solid tumors' immunotherapy landscape.

METHODS

By immunizing an alpaca with recombinant human PD-L1, three clones of the variable domain of the heavy chain of heavy-chain only antibody (VHH) were screened, and RW102 with high binding affinity was selected for further studies. ABDRW102, a VHH derivative, was further engineered by fusing RW102 with the albumin binder ABD035. Based on the two targeting vectors, four PD-L1-specific tracers ([68Ga]Ga-NOTA-RW102, [68Ga]Ga-NOTA-ABDRW102, [64Cu]Cu-NOTA-ABDRW102, and [89Zr]Zr-DFO-ABDRW102) with different circulation times were developed. The diagnostic efficacies were thoroughly evaluated in preclinical solid tumor models, followed by a first-in-human translational investigation of [68Ga]Ga-NOTA-RW102 in patients with non-small cell lung cancer (NSCLC).

RESULTS

While RW102 has a high binding affinity to PD-L1 with an excellent KD value of 15.29 pM, ABDRW102 simultaneously binds to human PD-L1 and human serum albumin with an excellent KD value of 3.71 pM and 3.38 pM, respectively. Radiotracers derived from RW102 and ABDRW102 have different in vivo circulation times. In preclinical studies, [68Ga]Ga-NOTA-RW102 immunoPET imaging allowed same-day annotation of differential PD-L1 expression with specificity, while [64Cu]Cu-NOTA-ABDRW102 and [89Zr]Zr-DFO-ABDRW102 enabled longitudinal visualization of PD-L1. More importantly, a pilot clinical trial shows the safety and diagnostic value of [68Ga]Ga-NOTA-RW102 immunoPET imaging in patients with NSCLCs and its potential to predict immune-related adverse effects following PD-L1-targeted immunotherapies.

CONCLUSIONS

We developed and validated a series of PD-L1-targeted tracers. Initial preclinical and clinical evidence indicates that immunoPET imaging with [68Ga]Ga-NOTA-RW102 holds promise in visualizing differential PD-L1 expression, selecting patients for PD-L1-targeted immunotherapies, and monitoring immune-related adverse effects in patients receiving PD-L1-targeted treatments.

TRIAL REGISTRATION NUMBER

NCT06165874.

Molecular probes targeting HER2 PET/CT and their application in advanced breast cancer

PURPOSE

Human epidermal growth factor receptor 2 (HER2)-positive breast cancer cases are among the most aggressive breast tumor subtypes. Accurately assessing HER2 expression status is vital to determining whether patients will benefit from targeted anti-HER2 treatment. HER2-targeted positron emission tomography (PET/CT) is noninvasive, enabling the real-time evaluation of breast cancer patient HER2 status with accuracy.

METHODS

We summarize the research progress of PET/CT targeting HER2 in breast cancer, focusing on PET/CT molecular probes targeting HER2 and their clinical application in the management of advanced breast cancer.

RESULTS

At present, a variety of different HER2 targeted molecular probes for PET/CT imaging have been developed, including nucleolin-labeled antibodies, antibody fragments, nanobodies, and peptides of various affinities, among others. HER2-targeted PET/CT can relatively accurately evaluate HER2 expression status in advanced breast cancer patients. It has good performance in the early detection of small HER2-positive lesions, evaluation of HER2 status in lesions that cannot be readily biopsied, evaluation of the heterogeneity of multiple metastases, identification of lesions with altered HER2 status, and evaluation of the efficacy of anti-HER2 drugs.

CONCLUSION

HER2-targeted PET/CT offers a promising noninvasive approach for real-time assessment of HER2 status，which can be guide targeted treatment for HER2-positive breast cancer patients. Future prospective clinical studies will be invaluable for fully evaluating the importance of HER2-targeted molecular imaging in the management of breast cancer.

Detection of HER2 expression using 99mTc-NM-02 nanobody in patients with breast cancer: a non-randomized, non-blinded clinical trial

BACKGROUND

99mTc radiolabeled nanobody NM-02 (99mTc-NM-02) is a novel single photon emission computed tomography (SPECT) probe with a high affinity and specificity for human epidermal growth factor receptor 2 (HER2). In this study, a clinical imaging trial was conducted to investigate the relationship between 99mTc-NM-02 uptake and HER2 expression in patients with breast cancer.

METHODS

Thirty patients with pathologically confirmed breast cancer were recruited and imaged with both 99mTc-NM-02 SPECT/computed tomography (CT) and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/CT. According to the treatment conditions before recruitment, patients were divided into two groups, the newly diagnosed group (n = 24) and the treated group (n = 6). The maximal standard uptake value (SUVmax) of 18F-FDG and SUVmax and mean SUV (SUVmean) of 99mTc-NM-02 in the lesions were determined to analyze the relationship with HER2 expression.

RESULTS

No meaningful relationship was observed between 18F-FDG uptake and HER2 expression in 30 patients with breast cancer. 99mTc-NM-02 uptake was positively correlated with HER2 expression in the newly diagnosed group, but no correlation was observed in the treated group. 99mTc-NM-02 uptake in HER2-positive lesions was lower in those with effective HER2-targeted therapy compared with the newly diagnosed group. 99mTc-NM-02 SPECT/CT detected brain and bone metastases of breast cancer with a different imaging pattern from 18F-FDG PET/CT. 99mTc-NM-02 showed no non-specific uptake in inflamed tissues and revealed intra- and intertumoral HER2 heterogeneity by SPECT/CT imaging in 9 of the 30 patients with breast cancer.

CONCLUSIONS

99mTc-NM-02 SPECT/CT has the potential for visualizing whole-body HER2 overexpression in untreated patients, making it a promising method for HER2 assessment in patients with breast cancer.

TRIAL REGISTRATION

NCT04674722, Date of registration: December 19, 2020.

NanoLAS: a comprehensive nanobody database with data integration, consolidation and application

Nanobodies, a unique subclass of antibodies first discovered in camelid animals, are composed solely of a single heavy chain's variable region. Their significantly reduced molecular weight, in comparison to conventional antibodies, confers numerous advantages in the treatment of various diseases. As research and applications involving nanobodies expand, the quantity of identified nanobodies is also rapidly growing. However, the existing antibody databases are deficient in type and coverage, failing to satisfy the comprehensive needs of researchers and thus impeding progress in nanobody research. In response to this, we have amalgamated data from multiple sources to successfully assemble a new and comprehensive nanobody database. This database has currently included the latest nanobody data and provides researchers with an excellent search and data display interface, thus facilitating the progression of nanobody research and their application in disease treatment. In summary, the newly constructed Nanobody Library and Archive System may significantly enhance the retrieval efficiency and application potential of nanobodies. We envision that Nanobody Library and Archive System will serve as an accessible, robust and efficient tool for nanobody research and development, propelling advancements in the field of biomedicine. Database URL: https://www.nanolas.cloud.

Promising Diagnostic and Therapeutic Approaches Based on VHHs for Cancer Management

The discovery of the distinctive structure of heavy chain-only antibodies in species belonging to the Camelidae family has elicited significant interest in their variable antigen binding domain (VHH) and gained attention for various applications, such as cancer diagnosis and treatment. This article presents an overview of the characteristics, advantages, and disadvantages of VHHs as compared to conventional antibodies, and their usage in diverse applications. The singular properties of VHHs are explained, and several strategies that can augment their utility are outlined. The preclinical studies illustrating the diagnostic and therapeutic efficacy of distinct VHHs in diverse formats against solid cancers are summarized, and an overview of the clinical trials assessing VHH-based agents in oncology is provided. These investigations demonstrate the enormous potential of VHHs for medical research and healthcare.

A Universal Aptamer for Influenza A Viruses: Selection, Recognition, and Infection Inhibition

It is crucial to develop universal inhibitors for viral inhibition due to the rapid mutation of viruses. Herein, a universal aptamer inhibitor was developed that enabled a single DNA molecule to recognize several hemeagglutinin (HA) protein subtypes, inducing broad neutralization against influenza A viruses (IAVs). Through a multi-channel enrichment (MCE) strategy, a high-affinity aptamer named UHA-2 was obtained, with its dissociation constants (Kd) for three different HA proteins being 1.5 ± 0.2 nM (H5N1), 3.7 ± 0.4 nM (H7N9), and 10.1 ± 1.1 nM (H9N2). The UHA-2 aptamer had a universal inhibition effect, by which it could broadly neutralize influenza A H5N1, H7N9, H9N2, H1N1, and H3N2 viruses. Universal aptamer inhibitors have the advantages of acquisition in vitro, stability, simple structure, small size, etc. This study not only develops a novel universal aptamer to achieve a broad inhibition effect on various IAVs, but also opens up an efficient strategy for the development of universal inhibitors against viruses.

Anti-CTLA-4 nanobody as a promising approach in cancer immunotherapy

Cancer is one of the most common diseases and causes of death worldwide. Since common treatment approaches do not yield acceptable results in many patients, developing innovative strategies for effective treatment is necessary. Immunotherapy is one of the promising approaches that has been highly regarded for preventing tumor recurrence and new metastases. Meanwhile, inhibiting immune checkpoints is one of the most attractive methods of cancer immunotherapy. Cytotoxic T lymphocyte-associated protein-4 (CTLA-4) is an essential immune molecule that plays a vital role in cell cycle modulation, regulation of T cell proliferation, and cytokine production. This molecule is classically expressed by stimulated T cells. Inhibition of overexpression of immune checkpoints such as CTLA-4 receptors has been confirmed as an effective strategy. In cancer immunotherapy, immune checkpoint-blocking drugs can be enhanced with nanobodies that target immune checkpoint molecules. Nanobodies are derived from the variable domain of heavy antibody chains. These small protein fragments have evolved entirely without a light chain and can be used as a powerful tool in imaging and treating diseases with their unique structure. They have a low molecular weight, which makes them smaller than conventional antibodies while still being able to bind to specific antigens. In addition to low molecular weight, specific binding to targets, resistance to temperature, pH, and enzymes, high ability to penetrate tumor tissues, and low toxicity make nanobodies an ideal approach to overcome the disadvantages of monoclonal antibody-based immunotherapy. In this article, while reviewing the cellular and molecular functions of CTLA-4, the structure and mechanisms of nanobodies' activity, and their delivery methods, we will explain the advantages and challenges of using nanobodies, emphasizing immunotherapy treatments based on anti-CTLA-4 nanobodies.

Characterization of novel CD19-specific VHHs isolated from a camelid immune library by phage display

BACKGROUND

Monoclonal antibody (mAb)-based immunotherapies have achieved promising outcomes in the treatment of immunological and oncological indications. CD19 is considered one of the most qualified antigens in the treatment of B-cell neoplasms. VHHs (nanobodies) are known for their physicochemical advantages over conventional mAbs rendering them suitable therapeutics and diagnostic tools. Herein, we aimed to isolate CD19-specific VHHs from a novel immune library using phage display.

METHODS

An immune VHH gene library was constructed. Using phage display and after five biopanning rounds, two monoclonal CD19-specific VHHs were isolated. The selected VHHs were expressed, purified, and characterized in terms of their affinity, specificity, sensitivity, and ability to target CD19-positive cell lines. Moreover, in silico analyses were employed for further characterization.

RESULTS

A VHH library was developed, and because the outputs of the 4th biopanning round exhibited the most favorable characteristics, a panel of random VHHs was selected from them. Ultimately, two of the most favorable VHHs were selected and DNA sequenced (designated as GR37 and GR41). Precise experiments indicated that GR37 and GR41 exhibited considerable specificity, sensitivity, and affinity (1.15 × 107 M-1 and 2.08 × 107 M-1, respectively) to CD19. Flow cytometric analyses revealed that GR37 and GR41 could bind CD19 on the surface of cell lines expressing the antigen. Moreover, in silico experiments predicted that both VHHs target epitopes that are distinct from that targeted by the CD19-specific single-chain variable fragment (scFv) FMC63.

CONCLUSION

The selected VHHs can be used as potential targeting tools for the development of CD19-based immunotherapeutics.

Screening and Preclinical Evaluation of Novel Radiolabeled Anti-Fibroblast Activation Protein-α Recombinant Antibodies

Background: Fibroblast activation protein-α (FAPα) is selectively overexpressed in tumor-associated fibroblasts in more than 90% of epithelial tumors, and may be a good target for anticancer treatment, for example, using an anti-FAPα recombinant antibody (rAb) labeled with radionuclides. In the present report, the radiolabeling and preclinical evaluation of novel anti-FAPα rAbs were investigated. Materials and Methods: Two novel anti-FAPα VHHs (AMS002-1 and AMS002-2) with high binding affinity to FAPα were selected from an antibody phage library. The anti-FAPα VHHs were then fused with the Fc fragment of human IgG4 to create two VHH-Fc rAbs. The VHH-Fc rAbs were radiolabeled with 89Zr and 177Lu. The radiolabeled products were evaluated by radioligand-binding assays using FAPα-expressing cells. The biodistribution and tumor-targeting properties were investigated by small-animal PET/CT. AMS002-1-Fc, which showed promising tumor-targeting properties in 89Zr-microPET imaging, was radiolabeled with 177Lu for efficacy study on HT1080 tumor-bearing mice and monitored with SPECT/CT imaging. Results: The two VHH-Fc rAbs with good affinity with KD values in low nanomolar range were identified. Both PET/CT imaging with 89Zr-AMS002-1-Fc rAb and SPECT/CT imaging with 177Lu-AMS002-1-Fc rAb demonstrated highest tumor uptakes at 72 h p.i. and long tumor retention in the preclinical models. Furthermore, ex vivo biodistribution analysis revealed high tumor uptake of 89Zr-AMS002-1-Fc at 48 h p.i. with the value of 6.91% ± 2.08% ID/g. Finally, radioimmunotherapy with 177Lu-AMS002-1-Fc rAb delayed the tumor growth without significant weight loss in mice with HT1080 xenografts. The tumor size of untreated control group was 2.59 times larger compared with the treatment group with 177Lu-AMS002-1-Fc at day 29. Conclusion: 89Zr/177Lu-AMS002-1-Fc represent a pair of promising radiopharmaceuticals for theranostics on FAPα-expressing tumors.

Mirror-Image Single-Domain Antibody for a Novel Nonimmunogenic Drug Scaffold

Immunogenic responses by protein therapeutics often lead to reduced therapeutic effects and/or adverse effects via the generation of neutralizing antibodies and/or antidrug antibodies (ADA). Mirror-image proteins of the variable domain of the heavy chain of the heavy chain antibody (VHH) are potential novel protein therapeutics with high-affinity binding to target proteins and reduced immunogenicity because these mirror-image VHHs (d-VHHs) are less susceptible to proteolytic degradation in antigen-presenting cells (APCs). In this study, we investigated the preparation protocols of d-VHHs and their biological properties, including stereoselective target binding and immunogenicity. Initially, we established a facile synthetic process of two model VHHs [anti-GFP VHH and PMP12A2h1 (monomeric VHH of caplacizumab)] and their mirror-image proteins by three-step native chemical ligations (NCLs) from four peptide segments. The folded synthetic VHHs (l-anti-GFP VHH and l-PMP12A2h1) bound to the target proteins (EGFP and vWF-A1 domain, respectively), while their mirror-image proteins (d-anti-GFP VHH and d-PMP12A2h1) showed no binding to the native proteins. For biodistribution studies, l-VHH and d-VHH with single radioactive indium diethylenetriamine-pentaacid (111In-DTPA) labeling at the C-terminus were designed and synthesized by the established protocol. The distribution profiles were essentially similar between l-VHH and d-VHH, in which the probes accumulated in the kidney within 15 min after intravenous administration in mice, because of the small molecular size of VHHs. Comparative assessment of the immunogenicity responses revealed that d-VHH-induced levels of ADA generation were significantly lower than those of native VHH, regardless of the peptide sequences and administration routes. The resulting scaffold investigated should be applicable in the design of d-VHHs with various C-terminal CDR3 sequences, which can be identified by screening using display technologies.

30 years of nanobodies - an ongoing success story of small binders in biological research

A milestone in the field of recombinant binding molecules was achieved 30 years ago with the discovery of single-domain antibodies from which antigen-binding variable domains, better known as nanobodies (Nbs), can be derived. Being only one tenth the size of conventional antibodies, Nbs feature high affinity and specificity, while being highly stable and soluble. In addition, they display accessibility to cryptic sites, low off-target accumulation and deep tissue penetration. Efficient selection methods, such as (semi-)synthetic/naïve or immunized cDNA libraries and display technologies, have facilitated the isolation of Nbs against diverse targets, and their single-gene format enables easy functionalization and high-yield production. This Review highlights recent advances in Nb applications in various areas of biological research, including structural biology, proteomics and high-resolution and in vivo imaging. In addition, we provide insights into intracellular applications of Nbs, such as live-cell imaging, biosensors and targeted protein degradation.

Site-Specific Modification of Single Domain Antibodies by Enzyme-Immobilized Magnetic Beads

Nanobodies as imaging agents and drug conjugates have shown great potential for cancer diagnostics and therapeutics. However, site-specific modification of a nanobody with microbial transglutaminase (mTGase) encounters problems in protein separation and purification. Here, we describe a facile yet reliable strategy of immobilizing mTGase onto magnetic beads for site-specific nanobody modification. The mTGase immobilized on magnetic beads (MB-mTGase) exhibits catalytic activity nearly equivalent to that of the free mTGase, with good reusability and universality. Magnetic separation simplifies the protein purification step and reduces the loss of nanobody bioconjugates more effectively than size exclusion chromatography. Using MB-mTGase, we demonstrate site-specific conjugation of nanobodies with fluorescent dyes and polyethylene glycol molecules, enabling targeted immunofluorescence imaging and improved circulation dynamics and tumor accumulation in vivo. The combined advantages of MB-mTGase method, including high conjugation efficiency, quick purification, less protein loss, and recycling use, are promising for site-specific nanobody functionalization and biomedical applications.

Radiotracer Development for Fungal-Specific Imaging: Past, Present, and Future

Invasive fungal infections have become a major challenge for public health, mainly due to the growing numbers of immunocompromised patients, with high morbidity and mortality. Currently, conventional imaging modalities such as computed tomography and magnetic resonance imaging contribute largely to the noninvasive diagnosis and treatment evaluation of those infections. These techniques, however, often fall short when a fast, noninvasive and specific diagnosis of fungal infection is necessary. Molecular imaging, especially using nuclear medicine-based techniques, aims to develop fungal-specific radiotracers that can be tested in preclinical models and eventually translated to human applications. In the last few decades, multiple radioligands have been developed and tested as potential fungal-specific tracers. These include radiolabeled peptides, antifungal drugs, siderophores, fungal-specific antibodies, and sugars. In this review, we provide an overview of the pros and cons of the available radiotracers. We also address the future prospects of fungal-specific imaging.

In Vitro Affinity Maturation of Nanobodies against Mpox Virus A29 Protein Based on Computer-Aided Design

Mpox virus (MPXV), the most pathogenic zoonotic orthopoxvirus, caused worldwide concern during the SARS-CoV-2 epidemic. Growing evidence suggests that the MPXV surface protein A29 could be a specific diagnostic marker for immunological detection. In this study, a fully synthetic phage display library was screened, revealing two nanobodies (A1 and H8) that specifically recognize A29. Subsequently, an in vitro affinity maturation strategy based on computer-aided design was proposed by building and docking the A29 and A1 three-dimensional structures. Ligand-receptor binding and molecular dynamics simulations were performed to predict binding modes and key residues. Three mutant antibodies were predicted using the platform, increasing the affinity by approximately 10-fold compared with the parental form. These results will facilitate the application of computers in antibody optimization and reduce the cost of antibody development; moreover, the predicted antibodies provide a reference for establishing an immunological response against MPXV.

Shark IgNAR: The Next Broad Application Antibody in Clinical Diagnoses and Tumor Therapies?

Antibodies represent a relatively mature detection means and serve as therapeutic drug carriers in the clinical diagnosis and treatment of cancer-among which monoclonal antibodies (mAbs) currently occupy a dominant position. However, the emergence and development of small-molecule monodomain antibodies are inevitable due to the many limitations of mAbs, such as their large size, complex structure, and sensitivity to extreme temperature, and tumor microenvironments. Thus, since first discovered in Chondroid fish in 1995, IgNAR has become an alternative therapeutic strategy through which to replace monoclonal antibodies, thus entailing that this novel type of immunoglobulin has received wide attention with respect to clinical diagnoses and tumor therapies. The variable new antigen receptor (VNAR) of IgNAR provides an advantage for the development of new antitumor drugs due to its small size, high stability, high affinity, as well as other structural and functional characteristics. In that respect, a better understanding of the unique characteristics and therapeutic potential of IgNAR/VNAR in clinical and anti-tumor treatment is needed. This article reviews the advantages of its unique biochemical conditions and molecular structure for clinical diagnoses and novel anti-tumor drugs. At the same time, the main advantages of the existing conjugated drugs, which are based on single-domain antibodies, are introduced here, thereby providing new ideas and methods for the development of clinical diagnoses and anti-tumor therapies in the future.

Degradation of extracellular and membrane proteins in targeted therapy: Status quo and quo vadis

Targeted protein degradation (TPD) strategies, such as proteolysis-targeting chimeras (PROTACs) only work for intracellular protein degradation because they involve the intracellular protein degradation machinery. Several new technologies have emerged in recent years for TPD of extracellular and membrane proteins. Even though some progress has been demonstrated in the extracellular and membrane protein degradation field, the application of these technologies is still in its infancy. In this review, we survey the therapeutic potential of existing technologies by summarizing and reviewing discoveries and hurdles in extracellular and membrane protein-of-interest (POI) degradation.

Selection, identification and crystal structure of shark-derived single-domain antibodies against a green fluorescent protein

Shark variable domain of new antigen receptors (VNARs) are the smallest naturally occurring binding domains with properties of low complexity, small size, cytoplasmic expression, and ease of engineering. Green fluorescent protein (GFP) molecules have been analyzed in conventional microscopy, but their spectral characteristics preclude their use in techniques offering substantially higher resolution. Besides, the GFP molecules can be quenched in acidic environment, which makes it necessary to develop anti-GFP antibody to solve these problems. In view of the diverse applications of GFP and unique physicochemical features of VNAR, the present study aims to generate VNARs against GFP. Here, we identified 36 VNARs targeting eCGP123, an extremely stable GFP, by phage display from three immunized sharks. These VNARs bound to eCGP123 with affinity constant KD values ranging from 6.76 to 605 nM. Among them, two lead VNARs named aGFP-14 and aGFP-15 with nanomolar eCGP123-binding affinity were selected for in-depth characterization. aGFP-14 and aGFP-15 recognized similar epitopes on eCGP123. X-ray crystallography studies clarified the mechanism by which aGFP14 interacts with eCGP123. aGFP-14 also showed cross-reaction with EGFP, with KD values of 47.2 nM. Finally, immunostaining analyses demonstrated that aGFP-14 was able to bind effectively to the EGFP expressed in both cultured cells and mouse brain tissues, and can be used as a fluorescence amplifier for EGFP. Our research demonstrates a feasible idea for the screening and production of shark-derived VNARs. The two high-affinity VNARs developed in the study contribute to the diversity of GFP sdAbs and may enhance the applications of GFP.

The role of protein corona on nanodrugs for organ-targeting and its prospects of application

Nowadays, nanodrugs become a hotspot in the high-end medical field. They have the ability to deliver drugs to reach their destination more effectively due to their unique properties and flexible functionalization. However, the fate of nanodrugs in vivo is not the same as those presented in vitro, which indeed influenced their therapeutic efficacy in vivo. When entering the biological organism, nanodrugs will first come into contact with biological fluids and then be covered by some biomacromolecules, especially proteins. The proteins adsorbed on the surface of nanodrugs are known as protein corona (PC), which causes the loss of prospective organ-targeting abilities. Fortunately, the reasonable utilization of PC may determine the organ-targeting efficiency of systemically administered nanodrugs based on the diverse expression of receptors on cells in different organs. In addition, the nanodrugs for local administration targeting diverse lesion sites will also form unique PC, which plays an important role in the therapeutic effect of nanodrugs. This article introduced the formation of PC on the surface of nanodrugs and summarized the recent studies about the roles of diversified proteins adsorbed on nanodrugs and relevant protein for organ-targeting receptor through different administration pathways, which may deepen our understanding of the role that PC played on organ-targeting and improve the therapeutic efficacy of nanodrugs to promote their clinical translation.

Radiochemistry for positron emission tomography

Positron emission tomography (PET) constitutes a functional imaging technique that is harnessed to probe biological processes in vivo. PET imaging has been used to diagnose and monitor the progression of diseases, as well as to facilitate drug development efforts at both preclinical and clinical stages. The wide applications and rapid development of PET have ultimately led to an increasing demand for new methods in radiochemistry, with the aim to expand the scope of synthons amenable for radiolabeling. In this work, we provide an overview of commonly used chemical transformations for the syntheses of PET tracers in all aspects of radiochemistry, thereby highlighting recent breakthrough discoveries and contemporary challenges in the field. We discuss the use of biologicals for PET imaging and highlight general examples of successful probe discoveries for molecular imaging with PET - with a particular focus on translational and scalable radiochemistry concepts that have been entered to clinical use.

Reviving a Classic Antigen with a Cutting-Edge Approach: Nanobodies for HER2+ Breast Cancer

The serendipitous discovery of nanobodies (NBs) around two decades ago opened the door to new possibilities for innovative strategies, particularly in cancer treatment. These antigen-binding fragments are derived from heavy-chain-only antibodies naturally found in the serum of camelids and sharks. NBs are an appealing agent for the progress of innovative therapeutic strategies because they combine the advantageous assets of smaller molecules and conventional monoclonal antibodies (mAbs). Moreover, the possibility to produce NBs using bacterial systems reduces manufacturing expenses and speeds up the production process, making them a feasible option for the development of new bio-drugs. Several NBs have been developed over the past 10 years and are currently being tested in clinical trials for various human targets. Here, we provide an overview of the notable structural and biochemical characteristics of NBs, particularly in their application against HER2, an extracellular receptor that often gets aberrantly activated during breast cancer tumorigenesis. The focus is on the recent advancements in diagnostic and therapeutic research up to the present date.

The Role of Molecular Imaging in Personalized Medicine

The concept of personalized medicine refers to the tailoring of medical treatment to each patient's unique characteristics. Scientific advancements have led to a better understanding of how a person's unique molecular and genetic profile makes them susceptible to certain diseases. It provides individualized medical treatments that will be safe and effective for each patient. Molecular imaging modalities play an essential role in this aspect. They are used widely in screening, detection and diagnosis, treatment, assessing disease heterogeneity and progression planning, molecular characteristics, and long-term follow-up. In contrast to conventional imaging approaches, molecular imaging techniques approach images as the knowledge that can be processed, allowing for the collection of relevant knowledge in addition to the evaluation of enormous patient groups. This review presents the fundamental role of molecular imaging modalities in personalized medicine.

Screening and epitope characterization of diagnostic nanobody against total and activated Bacteroides fragilis toxin

Enterotoxigenic Bacteroides fragilis (ETBF) can rapidly secrete an enterotoxin termed B. fragilis toxin (BFT), which is thought to be the only recognized virulence factor in ETBF. ETBF can cause acute diarrhea, inflammatory bowel disease (IBD), colorectal cancer, and breast cancer. BFT is divided into three subtypes, BFT1, BFT2, and BFT3. BFT1 is the most widely distributed in human B. fragilis isolates. BFT can be used as a biomarker for predicting the inflammation-cancer transformation of intestine and breast. Nanobodies have the advantages of small structure, complete antigen recognition capacity, rapid selection via phage display technology, and can be massively produced in microbial expression systems. Nanobodies have become a powerful tool for medical diagnosis and treatment. This study focuses on screening and structural characterization of nanobodies targeting full length and active BFT. By constructing prokaryotic expression systems to obtain recombinant BFT1 protein, high purity BFT1 protein was used to immunize alpacas. Phage display technology was used to construct a phage display library. The positive clones were selected by bio-panning, and the isothermal titration calorimetry was used to select high-affinity nanobodies. Then the three-dimensional structures of BFT1:Nb2.82 and BFT1:Nb3.27 were solved by crystal X-ray diffraction. We got two kinds of nanobodies, Nb2.82 targeting the BFT1 prodomain and Nb3.27 recognizing the BFT1 catalytic domain. This study provides a new strategy for the early diagnosis of ETBF and the possibility for BFT as a biomarker for diagnosing diseases.

Isolation and Characterization of Single-Domain Antibodies from Immune Phage Display Libraries

Naturally occurring heavy chain antibodies (HCAbs) in Camelidae species were a surprise discovery in 1993 by Hamers et al. Since that time, antibody fragments derived from HCAbs have garnered considerable attention by researchers and biotechnology companies. Due to their biophysico-chemical advantages over conventional antibody fragments, camelid single-domain antibodies (sdAbs, VHHs, nanobodies) are being increasingly utilized as viable immunotherapeutic modalities. Currently there are multiple VHH-based therapeutic agents in different phases of clinical trials in various formats such as bi- and multivalent, bi- and multi-specific, CAR-T, and antibody-drug conjugates. The first approved VHH, a bivalent humanized VHH (caplacizumab), was approved for treating rare blood clotting disorders in 2018 by the EMA and the FDA in 2019. This was followed by the approval of an anti-BCMA VHH-based CAR-T cell product in 2022 (ciltacabtagene autoleucel; CARVYKTI™) and more recently a trivalent antitumor necrosis factor alpha-based VHH drug (ozoralizumab; Nanozora®) in Japan for the treatment of rheumatoid arthritis. In this chapter we provide protocols describing the latest developments in isolating antigen-specific VHHs including llama immunization, construction of phage-displayed libraries, phage panning and screening of the soluble VHHs by ELISA, affinity measurements by surface plasmon resonance, functional cell binding by flow cytometry, and additional validation by immunoprecipitation. We present and discuss comprehensive, step-by-step methods for isolating and characterization of antigen-specific VHHs. This includes protocols for expression, biotinylation, purification, and characterization of the isolated VHHs. To demonstrate the feasibility of the entire strategy, we present examples of VHHs previously isolated and characterized in our laboratory.

Isolation and Mass Spectrometry Identification of K48 and K63 Ubiquitin Proteome Using Chain-Specific Nanobodies

Protein ubiquitylation is an essential mechanism regulating almost all cellular functions in eukaryotes. The understanding of the role of distinct ubiquitin chains in different cellular processes is essential to identify biomarkers for disease diagnosis and prognosis but also to open new therapeutic possibilities. The high complexity of ubiquitin chains complicates this analysis, and multiple strategies have been developed over the last decades. Here, we report a protocol for the isolation and identification of K48 and K63 ubiquitin chains using chain-specific nanobodies associated to mass spectrometry. Different steps were optimized to increase the purification yield and reduce the binding on nonspecific proteins. The resulting protocol allows the enrichment of ubiquitin chain-specific targets from mammalian cells.

Molecular imaging of HER2 receptor: Targeting HER2 for imaging and therapy in nuclear medicine

Targeting HER 2 for imaging and therapy in nuclear medicine has been used with a special emphasis on developing more powerful radiopharmaceuticals. Zirconium-89 plays an essential role in immune PET imaging so was used labeled with anti-HER2 antibody (Trastuzumab and Pertuzumab). Also there were attempts with other PET tracers as Cuprum-64 and Galium-68, as well as SPECT radiopharmaceuticals Indium-111 and Technetium- 99m. Regarding antibody pharmacokinetic that is not quite appropriate for imaging acquisition, several smaller molecules with shorter residence times have been developed. These molecules called nanobody, affibody, minibody do not compromize HER2 receptor affinity and specificity. Excess of Trastuzumab do not block the affinity of labeled affibodies. Silica nanoparticles have been conjugated to anti-HER2 antibodies to enable targeting of HER2 expressing cells with potential of drug delivery carry for antitumor agents and b(beta) or a(alfa) emitting radioisotopes commonly used for radionuclide therapy, as Iodine-131, Lutetium-177, Yttrium-90, Rhenium-188 and Thorium-277.

High in-vivo stability in preclinical and first-in-human experiments with [18F]AlF-RESCA-MIRC213: a 18F-labeled nanobody as PET radiotracer for diagnosis of HER2-positive cancers

PURPOSE

[18F]AlF-RESCA was introduced as a core particularly useful for 18F-labeling of heat-sensitive biomolecules. However, no translational studies have been reported up to now. Herein, we reported the first-in-human evaluation of an 18F-labeled anti-HER2 nanobody MIRC213 as a PET radiotracer for imaging HER2-positive cancers.

METHODS

MIRC213 was produced by E. coli and conjugated with ( ±)-H3RESCA-Mal. [18F]AlF-RESCA-MIRC213 was prepared at room temperature. Its radiochemical purity and stability of were determined by radio-HPLC with the size-exclusion chromatographic column. Cell uptake was performed in NCI-N87 (HER2 +) and MCF-7 (HER2-) cells and the cell-binding affinity was verified in SK-OV-3 (HER2 +) cells. Small-animal PET/CT was performed using SK-OV-3, NCI-N87, and MCF-7 tumor-bearing mice at 30 min, 1 h, and 2 h post-injection. For blocking experiment, excess MIRC213 was co-injected with radiotracer. Biodistribution were performed on SKOV-3 and MCF-7 tumor-bearing mice at 2 h post-injection. For clinical study, PET/CT images were acquired at 2 h and 4 h after injection of [18F]AlF-RESCA-MIRC213 (1.85-3.7 MBq/kg) in six breast cancer patients (3 HER2-positive and 3 HER2-negative). All patients underwent [18F]-FDG PET/CT within a week for tissue selection purpose. Distribution and dosimetry were calculated. Standardized uptake values (SUV) were measured in tumors and normal organs.

RESULTS

MIRC213 was produced with > 95% purity and modified with RESCA to obtain RESCA-MIRC213. [18F]AlF-RESCA-MIRC213 was prepared within 20 min at room temperature with the radiochemical yield of 50.48 ± 7.6% and radiochemical purity of > 98% (n > 10), and remained stable in both PBS (88%) and 5% HSA (92%) after 6 h. The 2 h cellular uptake of [18F]AlF-RESCA-MIRC213 in NCI-N87 cells was 11.22 ± 0.60 AD%/105 cells. Its binding affinity Kd value was determined to be 1.23 ± 0.58 nM. Small-animal PET/CT with [18F]AlF-RESCA-MIRC213 can clearly differentiate SK-OV-3 and NCI-N87 tumors from MCF-7 tumors and background with a high uptake of 4.73 ± 1.18 ID%/g and substantially reduced to 1.70 ± 0.13 ID%/g for the blocking group (p < 0.05) in SK-OV-3 tumors at 2 h post-injection. No significant bone radioactivity was seen in the tumor-bearing animals. In all six breast cancer patients, there was no adverse reaction during study. The uptake of [18F]AlF-RESCA-MIRC213 was mainly in lacrimal gland, parotid gland, submandibular gland, thyroid gland, gallbladder, kidneys, liver, and intestines. There was no significant bone radioactivity accumulation in cancer patients. [18F]AlF-RESCA-MIRC213 had significantly higher tumor uptake in lesions from HER2-positive patients than that lesions from HER2-negative patients (SUVmax of 3.62 ± 1.56 vs. 1.41 ± 0.41, p = 0.0012) at 2 h post-injection. The kidneys received the highest radiation dose of 2.42 × 10-1 mGy/MBq, and the effective dose was 1.56 × 10-2 mSv/MBq.

CONCLUSIONS

[18F]AlF-RESCA-MIRC213 could be prepared with high radiolabeling yield under mild conditions. [18F]AlF-RESCA-MIRC213 has relatively high stability both in vitro and in vivo. The results from clinical transformation suggest that [18F]AlF-RESCA-MIRC213 PET/CT is a safe procedure with favorable pharmacokinetics and dosimetry profile, and it is a promising new PET radiotracer for noninvasive diagnosis of HER2-positive cancers.

Development of anti-membrane type 1-matrix metalloproteinase nanobodies as immunoPET probes for triple negative breast cancer imaging

Triple-negative breast cancer (TNBC) is characterized by aggressiveness and high rates of metastasis. The identification of relevant biomarkers is crucial to improve outcomes for TNBC patients. Membrane type 1-matrix metalloproteinase (MT1-MMP) could be a good candidate because its expression has been reported to correlate with tumor malignancy, progression and metastasis. Moreover, single-domain variable regions (VHHs or Nanobodies) derived from camelid heavy-chain-only antibodies have demonstrated improvements in tissue penetration and blood clearance, important characteristics for cancer imaging. Here, we have developed a nanobody-based PET imaging strategy for TNBC detection that targets MT1-MMP. A llama-derived library was screened against the catalytic domain of MT1-MMP and a panel of specific nanobodies were identified. After a deep characterization, two nanobodies were selected to be labeled with gallium-68 (⁶⁸Ga). ImmunoPET imaging with both ([⁶⁸Ga]Ga-NOTA-3TPA14 and [⁶⁸Ga]Ga-NOTA-3CMP75) in a TNBC mouse model showed precise tumor-targeting capacity in vivo with high signal-to-background ratios. (⁶⁸Ga)Ga-NOTA-3CMP75 exhibited higher tumor uptake compared to (⁶⁸Ga)Ga-NOTA-3TPA14. Furthermore, imaging data correlated perfectly with the immunohistochemistry staining results. In conclusion, we found a promising candidate for nanobody-based PET imaging to be further investigated as a diagnostic tool in TNBC.

Development and evaluation of an 18F-labeled nanobody to target SARS-CoV-2's spike protein

COVID-19, caused by the SARS-CoV-2 virus, has become a global pandemic that is still present after more than two years. COVID-19 is mainly known as a respiratory disease that can cause long-term consequences referred to as long COVID. Molecular imaging of SARS-CoV-2 in COVID-19 patients would be a powerful tool for studying the pathological mechanisms and viral load in different organs, providing insights into the disease and the origin of long-term consequences and assessing the effectiveness of potential COVID-19 treatments. Current diagnostic methods used in the clinic do not allow direct imaging of SARS-CoV-2. In this work, a nanobody (NB) - a small, engineered protein derived from alpacas - and an Fc-fused NB which selectively target the SARS-CoV-2 Spike protein were developed as imaging agents for positron emission tomography (PET). We used the tetrazine ligation to 18F-label the NB under mild conditions once the NBs were successfully modified with trans-cyclooctenes (TCOs). We confirmed binding to the Spike protein by SDS-PAGE. Dynamic PET scans in rats showed excretion through the liver for both constructs. Future work will evaluate in vivo binding to the Spike protein with our radioligands.

Rhenium Radioisotopes for Medicine, a Focus on Production and Applications

In recent decades, the use of alpha; pure beta; or beta/gamma emitters in oncology, endocrinology, and interventional cardiology rheumatology, has proved to be an important alternative to the most common therapeutic regimens. Among radionuclides used for therapy in nuclear medicine, two rhenium radioisotopes are of particular relevance: rhenium-186 and rhenium-188. The first is routinely produced in nuclear reactors by direct neutron activation of rhenium-186 via 185Re(n,γ)186Re nuclear reaction. Rhenium-188 is produced by the decay of the parent tungsten-188. Separation of rhenium-188 is mainly performed using a chromatographic 188W/188Re generator in which tungsten-188 is adsorbed on the alumina column, similar to the 99Mo/99mTc generator system, and the radionuclide eluted in saline solution. The application of rhenium-186 and rhenium-188 depends on their specific activity. Rhenium-186 is produced in low specific activity and is mainly used for labeling particles or diphosphonates for bone pain palliation. Whereas, rhenium-188 of high specific activity can be used for labeling peptides or bioactive molecules. One of the advantages of rhenium is its chemical similarity with technetium. So, diagnostic technetium analogs labeled with radiorhenium can be developed for therapeutic applications. Clinical trials promoting the use of 186/188Re-radiopharmaceuticals is, in particular, are discussed.

Imaging of Clear Cell Renal Carcinoma with Immune Checkpoint Targeting Aptamer-Based Probe

Immune checkpoint targeting immunotherapy has revolutionized the treatment of certain cancers in the recent years. Determination of the status of immune checkpoint expression in particular cancers may assist decision making. Here, we describe the development of a single-stranded aptamer-based molecular probe specifically recognizing human PD-L1. Target engaging aptamers are selected by iterative enrichment from a random ssDNA pool and the binding is characterized biochemically. Specificity and dose dependence is demonstrated in vitro in the cell culture using human kidney tumor cells (786-0), human melanoma cells (WM115 and WM266.4) and human glioblastoma LN18 cancer cells. The utility of the probe in vivo is demonstrated using two mouse tumor models, where we show that the probe exhibits excellent potential in imaging. We postulate that further development of the probe may allow universal imaging of different types of tumors depending on their PD-L1 status, which may find utility in cancer diagnosis.

SARS-CoV-2 Delta Variant Decreases Nanobody Binding and ACE2 Blocking Effectivity

The Delta variant spreads more rapidly than previous variants of SARS-CoV-2. This variant comprises several mutations on the receptor-binding domain (RBD_Delta) of its spike glycoprotein, which binds to the peptidase domain (PD) of angiotensin-converting enzyme 2 (ACE2) receptors in host cells. The RBD-PD interaction has been targeted by antibodies and nanobodies to prevent viral infection, but their effectiveness against the Delta variant remains unclear. Here, we investigated RBD_Delta-PD interactions in the presence and absence of nanobodies H11-H4, H11-D4, and Ty1 by performing 21.8 μs of all-atom molecular dynamics simulations. Unbiased simulations revealed that Delta variant mutations strengthen RBD binding to ACE2 by increasing the hydrophobic interactions and salt bridge formation, but weaken interactions with H11-H4, H11-D4, and Ty1. Among these nanobodies H11-H4 and H11-D4 bind RBD without overlapping ACE2. They were unable to dislocate ACE2 from RBD_Delta when bound side by side with ACE2 on RBD. Steered molecular dynamics simulations at comparable loading rates to high-speed atomic force microscopy (AFM) experiments estimated lower rupture forces of the nanobodies from RBD_Delta compared to ACE2. Our results suggest that existing nanobodies are less effective to inhibit RBD_Delta-PD interactions and a new generation of nanobodies is needed to neutralize the Delta variant.

Camelid Single-Domain Antibodies: Promises and Challenges as Lifesaving Treatments

Since the discovery of camelid heavy-chain antibodies in 1993, there has been tremendous excitement for these antibody domains (VHHs/sdAbs/nanobodies) as research tools, diagnostics, and therapeutics. Commercially, several patents were granted to pioneering research groups in Belgium and the Netherlands between 1996–2001. Ablynx was established in 2001 with the aim of exploring the therapeutic applications and development of nanobody drugs. Extensive efforts over two decades at Ablynx led to the first approved nanobody drug, caplacizumab (Cablivi) by the EMA and FDA (2018–2019) for the treatment of rare blood clotting disorders in adults with acquired thrombotic thrombocytopenic purpura (TPP). The relatively long development time between camelid sdAb discovery and their entry into the market reflects the novelty of the approach, together with intellectual property restrictions and freedom-to-operate issues. The approval of the first sdAb drug, together with the expiration of key patents, may open a new horizon for the emergence of camelid sdAbs as mainstream biotherapeutics in the years to come. It remains to be seen if nanobody-based drugs will be cheaper than traditional antibodies. In this review, I provide critical perspectives on camelid sdAbs and present the promises and challenges to their widespread adoption as diagnostic and therapeutic agents.

Engineering nanobodies for next-generation molecular imaging

In recent years, nanobodies have emerged as ideal imaging agents for molecular imaging. Molecular nanobody imaging combines the specificity of nanobodies with the sensitivity of state-of-the-art molecular imaging modalities, such as positron emission tomography (PET). Given that modifications of nanobodies alter their pharmacokinetics (PK), the engineering strategies that combine nanobodies with radionuclides determine the effectiveness, reliability, and safety of the molecular imaging probes. In this review, we introduce conjugation strategies that have been applied to nanobodies, including random conjugation, ^99mTc tricarbonyl chemistry, sortase A-mediated site-specific conjugation, maleimide-cysteine chemistry, and click chemistries. We also summarize the latest advances in nanobody tracers, emphasizing their preclinical and clinical use. In addition, we elaborate on nanobody-based near-infrared fluorescence (NIRF) imaging and image-guided surgery.

Emerging Novel Combined CAR-T Cell Therapies

Simple Summary

As a result of FDA approval of CAR-T cell treatments in the last few years, this immunotherapy has provided further direction to precision medicine through its combination with other therapeutic approaches. In the past year, several review articles have been published focusing on advances in this fast-developing field, especially with respect to efforts to overcome hurdles associated with applying CAR-T cells in solid tumors. This review paper focuses on combining CAR-T cell therapy with small molecule drugs, up-to-date progress in CAR-T cell therapy research, and advances in combined CAR-T immunotherapy with other treatments targeting solid tumors.

Abstract

Chimeric antigen receptors (CAR) T cells are T cells engineered to express membrane receptors with high specificity to recognize specific target antigens presented by cancer cells and are co-stimulated with intracellular signals to increase the T cell response. CAR-T cell therapy is emerging as a novel therapeutic approach to improve T cell specificity that will lead to advances in precision medicine. CAR-T cells have had impressive outcomes in hematological malignancies. However, there continue to be significant limitations of these therapeutic responses in targeting solid malignancies such as heterogeneous antigens in solid tumors, tumor immunosuppressive microenvironment, risk of on-target/off-tumor, infiltrating CAR-T cells, immunosuppressive checkpoint molecules, and cytokines. This review paper summarizes recent approaches and innovations through combination therapies of CAR-T cells and other immunotherapy or small molecule drugs to counter the above disadvantages to potentiate the activity of CAR-T cells.

Design and Preparation of Photobodies: Light-Activated Single-Domain Antibody Fragments

Nanobodies are single-domain antibody fragments that have found widespread use in basic research, therapy, and diagnostics. Like other antibody formats, nanobodies can be developed with high affinity and specificity for desired antigens. A photobody is a light-activatable nanobody, obtained by incorporating a photo-labile caging group into the paratope region. The caging group prevents antigen binding until removed with light (365 nm), thereby rendering the binding controllable with high temporal and spatial resolution. Thus far photocaged tyrosine residues have been used for this purpose, as tyrosine is a frequent residue at critical positions of nanobody paratopes. Nanobodies without a tyrosine residue at the antigen-binding interface may require a different strategy. In this chapter, we describe methods to design and prepare photobodies by recombinant expression in Escherichia coli in combination with genetic code expansion technology to incorporate ortho-nitrobenzyl-tyrosine residues. We use the conversion of the anti-green fluorescent protein enhancer nanobody into a photobody as an example. These protocols should be applicable to many other nanobodies.