A few good reasons to use nanobodies for cancer treatment.

mAbs have been instrumental for targeted cancer therapies. However, their relatively large size and physicochemical properties result in a heterogenous distribution in the tumor microenvironment, usually restricted to the first cell layers surrounding blood vessels, and a limited ability to penetrate the brain. Nanobodies are tenfold smaller, resulting in a deeper tumor penetration and the ability to reach cells in poorly perfused tumor areas. Nanobodies are rapidly cleared from the circulation, which generates a fast target-to-background contrast that is ideally suited for molecular imaging purposes but may be less optimal for therapy. To circumvent this problem, nanobodies have been formatted to noncovalently bind albumin, increasing their serum half-life without majorly increasing their size. Finally, nanobodies have shown superior qualities to infiltrate brain tumors as compared to mAbs. In this review, we discuss why these features make nanobodies prime candidates for targeted therapy of cancer.

Dendritic Cell-Based Immunotherapy in Multiple Myeloma: Challenges, Opportunities, and Future Directions.

Immunotherapeutic approaches, including adoptive cell therapy, revolutionized treatment in multiple myeloma (MM). As dendritic cells (DCs) are professional antigen-presenting cells and key initiators of tumor-specific immune responses, DC-based immunotherapy represents an attractive therapeutic approach in cancer. The past years, various DC-based approaches, using particularly ex-vivo-generated monocyte-derived DCs, have been tested in preclinical and clinical MM studies. However, long-term and durable responses in MM patients were limited, potentially attributed to the source of monocyte-derived DCs and the immunosuppressive bone marrow microenvironment. In this review, we briefly summarize the DC development in the bone marrow niche and the phenotypical and functional characteristics of the major DC subsets. We address the known DC deficiencies in MM and give an overview of the DC-based vaccination protocols that were tested in MM patients. Lastly, we also provide strategies to improve the efficacy of DC vaccines using new, improved DC-based approaches and combination therapies for MM patients.

Novel half-life extended anti-MIF nanobodies protect against endotoxic shock.

Sepsis-leading to septic shock-is the leading cause of death in intensive care units. The systemic inflammatory response to infection, which is initiated by activated myeloid cells, plays a key role in the lethal outcome. Macrophage migration inhibitory factor (MIF) is an upstream immunoregulatory mediator, released by myeloid cells, that underlies a common genetic susceptibility to different infections and septic shock. Accordingly, strategies that are aimed at inhibiting the action of MIF have therapeutic potential. Here, we report the isolation and characterization of tailorable, small, affinity-matured nanobodies (Nbs; single-domain antigen-binding fragments derived from camelid heavy-chain Abs) directed against MIF. Of importance, these bioengineered Nbs bind both human and mouse MIFs with nanomolar affinity. NbE5 and NbE10 inhibit key MIF functions that can exacerbate septic shock, such as the tautomerase activity of MIF (by blocking catalytic pocket residues that are critical for MIF's conformation and receptor binding), the TNF-inducing potential, and the ability of MIF to antagonize glucocorticoid action. A lead NbE10, tailored to be a multivalent, half-life extended construct (NbE10-NbAlb8-NbE10), attenuated lethality in murine endotoxemia when administered via single injection, either prophylactically or therapeutically. Hence, Nbs, with their structural and pharmacologic advantages over currently available inhibitors, may be an effective, novel approach to interfere with the action of MIF in septic shock and other conditions of inflammatory end-organ damage.-Sparkes, A., De Baetselier, P., Brys, L., Cabrito, I., Sterckx, Y. G.-J., Schoonooghe, S., Muyldermans, S., Raes, G., Bucala, R., Vanlandschoot, P., Van Ginderachter, J. A., Stijlemans, B. Novel half-life extended anti-MIF nanobodies protect against endotoxic shock.

NIRF-Molecular Imaging with Synovial Macrophages-Targeting Vsig4 Nanobody for Disease Monitoring in a Mouse Model of Arthritis.

Nanobody against V-set and Ig domain-containing 4 (Vsig4) on tissue macrophages, such as synovial macrophages, could visualize joint inflammation in multiple experimental arthritis models via single-photon emission computed tomography imaging. Here, we further addressed the specificity and assessed the potential for arthritis monitoring using near-infrared fluorescence (NIRF) Cy7-labeled Vsig4 nanobody (Cy7-Nb119). In vivo NIRF-imaging of collagen-induced arthritis (CIA) was performed using Cy7-Nb119. Signals obtained with Cy7-Nb119 or isotope control Cy7-NbBCII10 were compared in joints of naive mice versus CIA mice. In addition, pathological microscopy and fluorescence microscopy were used to validate the arthritis development in CIA. Cy7-Nb119 accumulated in inflamed joints of CIA mice, but not the naive mice. Development of symptoms in CIA was reflected in increased joint accumulation of Cy7-Nb119, which correlated with the conventional measurements of disease. Vsig4 is co-expressed with F4/80, indicating targeting of the increasing number of synovial macrophages associated with the severity of inflammation by the Vsig4 nanobody. NIRF imaging with Cy7-Nb119 allows specific assessment of inflammation in experimental arthritis and provides complementary information to clinical scoring for quantitative, non-invasive and economical monitoring of the pathological process. Nanobody labelled with fluorescence can also be used for ex vivo validation experiments using flow cytometry and fluorescence microscopy.

The role of hepatic macrophages in liver metastasis.

The liver is a major target organ for metastasis of both gastrointestinal and extra-gastrointestinal cancers. Due to its frequently inoperable nature, liver metastasis represents a leading cause of cancer-associated death worldwide. In the past years, the pivotal role of the immune system in this process is being increasingly recognised. In particular, the role of the hepatic macrophages, both recruited monocyte-derived macrophages (Mo-Mfs) and tissue-resident Kupffer cells (KCs), has been shown to be more versatile than initially imagined. However, the lack of tools to easily distinguish between these two macrophage populations has hampered the assignment of particular functionalities to specific hepatic macrophage subsets. In this Review, we highlight the most remarkable findings regarding the origin and functions of hepatic macrophage populations, and we provide a detailed description of their distinct roles in the different phases of the liver metastatic process.

The transduction pattern of IL-12-encoding lentiviral vectors shapes the immunological outcome.

In situ modification of antigen-presenting cells garnered interest in cancer immunotherapy. Therefore, we developed APC-targeted lentiviral vectors (LVs). Unexpectedly, these LVs were inferior vaccines to broad tropism LVs. Since IL-12 is a potent mediator of antitumor immunity, we evaluated whether this proinflammatory cytokine could enhance antitumor immunity of an APC-targeted LV-based vaccine. Therefore, we compared subcutaneous administration of broad tropism LVs (VSV-G-LV) with APC-targeted LVs (DC2.1-LV)-encoding enhanced GFP and ovalbumin, or IL-12 and ovalbumin in mice. We show that codelivery of IL-12 by VSV-G-LVs or DC2.1-LVs augments CD4(+) or CD8(+) T-cell proliferation, respectively. Furthermore, we demonstrate that codelivery of IL-12 enhances the CD4(+) TH 1 profile irrespective of its delivery mode, while an increase in cytotoxic and therapeutic CD8(+) T cells was only induced upon VSV-G-LV injection. While codelivery of IL-12 by DC2.1-LVs did not enhance CD8(+) T-cell performance, it increased expression of inhibitory checkpoint markers Lag3, Tim3, and PD-1. Finally, the discrepancy between CD4(+) T-cell stimulation with and without functional CD8(+) T-cell stimulation by VSV-G- and DC2.1-LVs is partly explained by the observation that IL-12 relieves CD8(+) T cells from CD4(+) T-cell help, implying that a T(H)1 profile is of minor importance for antitumor immunotherapy if IL-12 is exogenously delivered.

MIF contributes to Trypanosoma brucei associated immunopathogenicity development.

African trypanosomiasis is a chronic debilitating disease affecting the health and economic well-being of many people in developing countries. The pathogenicity associated with this disease involves a persistent inflammatory response, whereby M1-type myeloid cells, including Ly6C(high) inflammatory monocytes, are centrally implicated. A comparative gene analysis between trypanosusceptible and trypanotolerant animals identified MIF (macrophage migrating inhibitory factor) as an important pathogenic candidate molecule. Using MIF-deficient mice and anti-MIF antibody treated mice, we show that MIF mediates the pathogenic inflammatory immune response and increases the recruitment of inflammatory monocytes and neutrophils to contribute to liver injury in Trypanosoma brucei infected mice. Moreover, neutrophil-derived MIF contributed more significantly than monocyte-derived MIF to increased pathogenic liver TNF production and liver injury during trypanosome infection. MIF deficient animals also featured limited anemia, coinciding with increased iron bio-availability, improved erythropoiesis and reduced RBC clearance during the chronic phase of infection. Our data suggest that MIF promotes the most prominent pathological features of experimental trypanosome infections (i.e. anemia and liver injury), and prompt considering MIF as a novel target for treatment of trypanosomiasis-associated immunopathogenicity.

Targeting of human antigen-presenting cell subsets.

Antigen-presenting cells are a heterogeneous group of cells that are characterized by their functional specialization. Consequently, targeting specific antigen-presenting cell subsets offers opportunities to induce distinct T cell responses. Here we report on the generation and use of nanobodies (Nbs) to target lentivectors specifically to human lymph node-resident myeloid dendritic cells, demonstrating that Nbs represent a powerful tool to redirect lentivectors to human antigen-presenting cell subsets.

Current status and future expectations of nanobodies in oncology trials.

INTRODUCTION: Monoclonal antibodies have revolutionized personalized medicine for cancer in recent decades. Despite their broad application in oncology, their large size and complexity may interfere with successful tumor targeting for certain applications of cancer diagnosis and therapy. Nanobodies have unique structural and pharmacological features compared to monoclonal antibodies and have successfully been used as complementary anti-cancer diagnostic and/or therapeutic tools. AREAS COVERED: Here, an overview is given of the nanobody-based diagnostics and therapeutics that have been or are currently being tested in oncological clinical trials. Furthermore, preclinical developments, which are likely to be translated into the clinic in the near future, are highlighted. EXPERT OPINION: Overall, the presented studies show the application potential of nanobodies in the field of oncology, making it likely that more nanobodies will be clinically approved in the upcoming future.

Development and evaluation of nanobody tracers for noninvasive nuclear imaging of the immune-checkpoint TIGIT.

Introduction: T cell Ig and ITIM domain receptor (TIGIT) is a next-generation immune checkpoint predominantly expressed on activated T cells and NK cells, exhibiting an unfavorable prognostic association with various malignancies. Despite the emergence of multiple TIGIT-blocking agents entering clinical trials, only a fraction of patients responded positively to anti-TIGIT therapy. Consequently, an urgent demand arises for noninvasive techniques to quantify and monitor TIGIT expression, facilitating patient stratification and enhancing therapeutic outcomes. Small antigen binding moieties such as nanobodies, are promising candidates for such tracer development. Methods: We generated a panel of anti-human or anti-mouse TIGIT nanobodies from immunized llamas. In addition, we designed a single-chain variable fragment derived from the clinically tested monoclonal antibody Vibostolimab targeting TIGIT, and assessed its performance alongside the nanobodies. In vitro characterization studies were performed, including binding ability and affinity to cell expressed or recombinant TIGIT. After Technetium-99m labeling, the nanobodies and the single-chain variable fragment were evaluated in vivo for their ability to detect TIGIT expression using SPECT/CT imaging, followed by ex vivo biodistribution analysis. Results: Nine nanobodies were selected for binding to recombinant and cell expressed TIGIT with low sub-nanomolar affinities and are thermostable. A six-fold higher uptake in TIGIT-overexpressing tumor was demonstrated one hour post- injection with Technetium-99m labeled nanobodies compared to an irrelevant control nanobody. Though the single-chain variable fragment exhibited superior binding to TIGIT-expressing peripheral blood mononuclear cells in vitro, its in vivo behavior yielded lower tumor-to-background ratios at one hour post- injection, indicating that nanobodies are better suited for in vivo imaging than the single-chain variable fragment. Despite the good affinity, high specificity and on-target uptake in mice in this setting, imaging of TIGIT expression on tumor- infiltrating lymphocytes within MC38 tumors remained elusive. This is likely due to the low expression levels of TIGIT in this model. Discussion: The excellent affinity, high specificity and rapid on-target uptake in mice bearing TIGIT- overexpressing tumors showed the promising diagnostic potential of nanobodies to noninvasively image high TIGIT expression within the tumor. These findings hold promise for clinical translation to aid patient selection and improve therapy response.

In vitro modelling of local gene therapy with IL-15/IL-15Rα and a PD-L1 antagonist in melanoma reveals an interplay between NK cells and CD4+ T cells.

Blockade of the immune checkpoint axis consisting of programmed death-1 (PD-1) and its ligand PD-L1 alleviates the functional inhibition of tumor-infiltrating lymphoid cells yet weakly induces their expansion. Exogenous cytokines could further expand lymphoid cells and thus synergize with αPD-L1 therapy. However, systemic delivery of most cytokines causes severe toxicity due to unspecific expansion of immune cells in the periphery. Here, we modelled local delivery of cytokines and αPD-L1 therapeutics to immune cell-containing in vitro melanoma tumors. Three-dimensional tumor models consisting of 624-MEL cells were co-cultured with human peripheral blood lymphoid cells (PBLs) in presence of the cytokines IL-2, IL-7, IL-15, IL-21 and IFN-γ. To model local gene therapy, melanoma tumors were modified with lentiviral vectors encoding IL-15 fused to IL-15Rα (IL-15/IL-15Rα) and K2-Fc, a fusion of a human PD-L1 specific single domain antibody to immunoglobulin (Ig)G1 Fc. To evaluate the interplay between PBL fractions, NK cells, CD4+ T cells or CD8+ T cells were depleted. Tumor cell killing was followed up using real time imaging and immune cell expansion and activation was evaluated with flow cytometry. Among the tested cytokines, IL-15 was the most potent cytokine in stimulating tumor cell killing and expanding both natural killer (NK) cells and CD8+ T cells. Gene-based delivery of IL-15/IL-15Rα to tumor cells, shows expansion of NK cells, activation of NK cells, CD4+ and CD8+ T cells, and killing of tumor spheroids. Both NK cells and CD8+ T cells are necessary for tumor cell killing and CD4+ T-cell activation was reduced without NK cells. Co-delivery of K2-Fc improved tumor cell killing coinciding with increased activation of NK cells, which was independent of bystander T cells. CD4+ or CD8+ T cells were not affected by the co-delivery of K2-Fc even though NK-cell activation impacted CD4+ T-cell activation. This study demonstrates that gene-based delivery of IL-15/IL-15Rα to tumor cells effectively mediates anti-tumor activity and sensitizes the tumor microenvironment for therapy with αPD-L1 therapeutics mainly by impacting NK cells. These findings warrant further investigation of gene-based IL-15 and K2-Fc delivery in vivo.

Phase I Study of [68Ga]Ga-Anti-CD206-sdAb for PET/CT Assessment of Protumorigenic Macrophage Presence in Solid Tumors (MMR Phase I).

Macrophages play an important role throughout the body. Antiinflammatory macrophages expressing the macrophage mannose receptor (MMR, CD206) are involved in disease development, ranging from oncology to atherosclerosis and rheumatoid arthritis. [68Ga]Ga-NOTA-anti-CD206 single-domain antibody (sdAb) is a PET tracer targeting CD206. This first-in-human study, as its primary objective, evaluated the safety, biodistribution, and dosimetry of this tracer. The secondary objective was to assess its tumor uptake. Methods: Seven patients with a solid tumor of at least 10 mm, an Eastern Cooperative Oncology Group score of 0 or 1, and good renal and hepatic function were included. Safety was evaluated using clinical examination and blood sampling before and after injection. For biodistribution and dosimetry, PET/CT was performed at 11, 90, and 150 min after injection; organs showing tracer uptake were delineated, and dosimetry was evaluated. Blood samples were obtained at selected time points for blood clearance. Metabolites in blood and urine were assessed. Results: Seven patients were injected with, on average, 191 MBq of [68Ga]Ga-NOTA-anti-CD206-sdAb. Only 1 transient adverse event of mild severity was considered to be possibly, although unlikely, related to the study drug (headache, Common Terminology Criteria for Adverse Events grade 1). The blood clearance was fast, with less than 20% of the injected activity remaining after 80 min. There was uptake in the liver, kidneys, spleen, adrenals, and red bone marrow. The average effective dose from the radiopharmaceutical was 4.2 mSv for males and 5.2 mSv for females. No metabolites were detected. Preliminary data of tumor uptake in cancer lesions showed higher uptake in the 3 patients who subsequently progressed than in the 3 patients without progression. One patient could not be evaluated because of technical failure. Conclusion: [68Ga]Ga-NOTA-anti-CD206-sdAb is safe and well tolerated. It shows rapid blood clearance and renal excretion, enabling high contrast-to-noise imaging at 90 min after injection. The radiation dose is comparable to that of routinely used PET tracers. These findings and the preliminary results in cancer patients warrant further investigation of this tracer in phase II clinical trials.

A novel promiscuous class of camelid single-domain antibody contributes to the antigen-binding repertoire.

It is well established that, in addition to conventional Abs, camelids (such as Camelus dromedarius and Lama glama) possess unique homodimeric H chain Abs (HCAbs) devoid of L chains. The Ag-binding site of these HCAbs consists of a single variable domain, referred to as VHH. It is widely accepted that these VHHs, with distinct framework-2 imprints evolved within the V(H) clan III-family 3, are exclusively present on HCAbs. In this study, we report the finding of a distinct leader signal sequence linked to variable genes displaying a high degree of homology to the clan II, human VH(4) family that contributes to the HCAb Ag-binding diversity. Although the VHH framework-2 imprints are clearly absent, their VH(4)-D-JH recombination products can be rearranged to the H chains of both classical and HCAbs. This suggests that for these V domains the presence of a L chain to constitute the Ag-binding site is entirely optional. As such, the capacity of this promiscuous VH(4) family to participate in two distinct Ab formats significantly contributes to the breadth of the camelid Ag-binding repertoire. This was illustrated by the isolation of stable, dendritic cell-specific VH(4) single domains from a VH(4)-HCAb phage display library. The high degree of homology with human VH(4) sequences is promising in that it may circumvent the need for "humanization" of such single-domain Abs in therapeutic applications.

Tolerance and M2 (alternative) macrophage polarization are related processes orchestrated by p50 nuclear factor kappaB.

Cells of the monocyte-macrophage lineage play a central role in the orchestration and resolution of inflammation. Plasticity is a hallmark of mononuclear phagocytes, and in response to environmental signals these cells undergo different forms of polarized activation, the extremes of which are called classic or M1 and alternative or M2. NF-kappaB is a key regulator of inflammation and resolution, and its activation is subject to multiple levels of regulation, including inhibitory, which finely tune macrophage functions. Here we identify the p50 subunit of NF-kappaB as a key regulator of M2-driven inflammatory reactions in vitro and in vivo. p50 NF-kappaB inhibits NF-kappaB-driven, M1-polarizing, IFN-beta production. Accordingly, p50-deficient mice show exacerbated M1-driven inflammation and defective capacity to mount allergy and helminth-driven M2-polarized inflammatory reactions. Thus, NF-kappaB p50 is a key component in the orchestration of M2-driven inflammatory reactions.

Applications of nanobodies in brain diseases.

Nanobodies are antibody fragments derived from camelids, naturally endowed with properties like low molecular weight, high affinity and low immunogenicity, which contribute to their effective use as research tools, but also as diagnostic and therapeutic agents in a wide range of diseases, including brain diseases. Also, with the success of Caplacizumab, the first approved nanobody drug which was established as a first-in-class medication to treat acquired thrombotic thrombocytopenic purpura, nanobody-based therapy has received increasing attention. In the current review, we first briefly introduce the characterization and manufacturing of nanobodies. Then, we discuss the issue of crossing of the brain-blood-barrier (BBB) by nanobodies, making use of natural methods of BBB penetration, including passive diffusion, active efflux carriers (ATP-binding cassette transporters), carrier-mediated influx via solute carriers and transcytosis (including receptor-mediated transport, and adsorptive mediated transport) as well as various physical and chemical methods or even more complicated methods such as genetic methods via viral vectors to deliver nanobodies to the brain. Next, we give an extensive overview of research, diagnostic and therapeutic applications of nanobodies in brain-related diseases, with emphasis on Alzheimer's disease, Parkinson's disease, and brain tumors. Thanks to the advance of nanobody engineering and modification technologies, nanobodies can be linked to toxins or conjugated with radionuclides, photosensitizers and nanoparticles, according to different requirements. Finally, we provide several perspectives that may facilitate future studies and whereby the versatile nanobodies offer promising perspectives for advancing our knowledge about brain disorders, as well as hopefully yielding diagnostic and therapeutic solutions.

In vivo Visualization of M2 Macrophages in the Myocardium After Myocardial Infarction (MI) Using 68 Ga-NOTA-Anti-MMR Nb: Targeting Mannose Receptor (MR, CD206) on M2 Macrophages.

Introduction and Objectives: Wound healing after myocardial infarction (MI) is a dynamic and complex multiple phase process, and a coordinated cellular response is required for proper scar formation. The current paradigm suggests that pro-inflammatory monocytes infiltrate the MI zone during the initial pro-inflammatory phase and differentiate into inflammatory macrophages, and then switch their phenotypes to anti-inflammatory during the reparative phase. Visualization of the reparative phase post-MI is of great interest because it may reveal delayed resolution of inflammation, which in turn predicts adverse cardiac remodeling. Imaging of anti-inflammatory macrophages may also be used to assess therapy approaches aiming to modulate the inflammatory response in order to limit MI size. Reparative macrophages can be distinguished from inflammatory macrophages by the surface marker mannose receptor (MR, CD206). In this study we evaluated the feasibility of 68Ga-NOTA-anti-MMR Nb for imaging of MR on alternatively activated macrophages in murine MI models. Methods: Wildtype and MR-knockout mice and Wistar rats were subjected to MI via permanent ligation of the left coronary artery. Non-operated or sham-operated animals were used as controls. MR expression kinetics on cardiac macrophages was measured in mice using flow cytometry. PET/CT scans were performed 1 h after intravenous injection of 68Ga-NOTA-anti-MMR Nb. Mice and rats were euthanized and hearts harvested for ex vivo PET/MRI, autoradiography, and staining. As a non-targeting negative control, 68Ga-NOTA-BCII10 was used. Results: In vivo-PET/CT scans showed focal radioactivity signals in the infarcted myocardium for 68Ga-NOTA-anti-MMR Nb which were confirmed by ex vivo-PET/MRI scans. In autoradiography images, augmented uptake of the tracer was observed in infarcts, as verified by the histochemistry analysis. Immunofluorescence staining demonstrated the presence and co-localization of CD206- and CD68-positive cells, in accordance to infarct zone. No in vivo or ex vivo signal was observed in the animals injected with control Nb or in the sham-operated animals. 68Ga-NOTA-anti-MMR Nb uptake in the infarcts of MR-knockout mice was negligibly low, confirming the specificity of 68Ga-NOTA-anti-MMR Nb to MR. Conclusion: This exploratory study highlights the potential of 68Ga-NOTA-anti-MMR Nb to image MR-positive macrophages that are known to play a pivotal role in wound healing that follows acute MI.

Myeloid-derived suppressor cells in parasitic infections.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells that share a common property of suppressing immune responses. Several helminth and protozoan parasite species have developed efficient strategies to increase the rate of medullary or extramedullary myelopoiesis and to induce the expansion and accumulation of immature myeloid cells such as MDSC. In this review, we examine current knowledge on the factors mediating enhanced myelopoiesis and MDSC induction and recruitment during parasitic infections and how the MDSC phenotype and mechanism of immune modulation and suppression depends on the factors they encounter within the host. Finally, we place MDSC expansion in the context of the critical balance between parasite elimination and pathogenicity to the host and suggest attractive avenues for future research.

Do-it-yourself: construction of a custom cDNA macroarray platform with high sensitivity and linear range.

BACKGROUND: Research involving gene expression profiling and clinical applications, such as diagnostics and prognostics, often require a DNA array platform that is flexibly customisable and cost-effective, but at the same time is highly sensitive and capable of accurately and reproducibly quantifying the transcriptional expression of a vast number of genes over the whole transcriptome dynamic range using low amounts of RNA sample. Hereto, a set of easy-to-implement practical optimisations to the design of cDNA-based nylon macroarrays as well as sample (33)P-labeling, hybridisation protocols and phosphor screen image processing were analysed for macroarray performance. RESULTS: The here proposed custom macroarray platform had an absolute sensitivity as low as 50,000 transcripts and a linear range of over 5 log-orders. Its quality of identifying differentially expressed genes was at least comparable to commercially available microchips. Interestingly, the quantitative accuracy was found to correlate significantly with corresponding reversed transcriptase - quantitative PCR values, the gold standard gene expression measure (Pearson's correlation test p < 0.0001). Furthermore, the assay has low cost and input RNA requirements (0.5 µg and less) and has a sound reproducibility. CONCLUSIONS: Results presented here, demonstrate for the first time that self-made cDNA-based nylon macroarrays can produce highly reliable gene expression data with high sensitivity and covering the entire mammalian dynamic range of mRNA abundances. Starting off from minimal amounts of unamplified total RNA per sample, a reasonable amount of samples can be assayed simultaneously for the quantitative expression of hundreds of genes in an easily customisable and cost-effective manner.

68Ga-Labeling: Laying the Foundation for an Anti-Radiolytic Formulation for NOTA-sdAb PET Tracers.

During the preparation of [68Ga]Ga-NOTA-sdAb at high activity, degradation of the tracers was observed, impacting the radiochemical purity (RCP). Increasing starting activities in radiolabelings is often paired with increased degradation of the tracer due to the formation of free radical species, a process known as radiolysis. Radical scavengers and antioxidants can act as radioprotectant due to their fast interaction with formed radicals and can therefore reduce the degree of radiolysis. This study aims to optimize a formulation to prevent radiolysis during the labeling of NOTA derivatized single domain antibody (sdAbs) with 68Ga. Gentisic acid, ascorbic acid, ethanol and polyvinylpyrrolidone were tested individually or in combination to find an optimal mix able to prevent radiolysis without adversely influencing the radiochemical purity (RCP) or the functionality of the tracer. RCP and degree of radiolysis were assessed via thin layer chromatography and size exclusion chromatography for up to three hours after radiolabeling. Individually, the radioprotectants showed insufficient efficacy in reducing radiolysis when using high activities of 68Ga, while being limited in amount due to negative impact on radiolabeling of the tracer. A combination of 20% ethanol (VEtOH/VBuffer%) and 5 mg ascorbic acid proved successful in preventing radiolysis during labeling with starting activities up to 1-1.2 GBq of 68Ga, and is able to keep the tracer stable for up to at least 3 h after labeling at room temperature. The prevention of radiolysis by the combination of ethanol and ascorbic acid potentially allows radiolabeling compatibility of NOTA-sdAbs with all currently available 68Ge/68Ga generators. Additionally, a design is proposed to allow the incorporation of the radioprotectant in an ongoing diagnostic kit development for 68Ga labeling of NOTA-sdAbs.

Decorating sdAbs with Chelators: Effect of Conjugation on Biodistribution and Functionality.

Single domain antibodies (sdAbs) have proven to be valuable probes for molecular imaging. In order to produce such probes, one strategy is the functionalization of the reactive amine side chain of lysines with a chelator, resulting in a mixture of compounds with a different degree of conjugation. In this study, we implemented anion exchange chromatography (AEX) to separate the different compounds or fractions that were further characterized and evaluated to study the impact of the conjugation degree on pharmacokinetic properties and functionality. Anti-HER2 and anti-MMR sdAbs were functionalized with NOTA or DTPA chelator. Anion exchange chromatography was performed using 0.02 mol/L Tris pH 7.5 as the first solvent and 0.25 M or 0.4 M NaCl (in case of NOTA chelator or DTPA chelator, respectively) as the second solvent applied as a gradient. The fractions were characterized via mass spectrometry (MS), surface plasmon resonance (SPR), and isoelectric focusing gel electrophoresis (IEF), while in vivo studies were performed after radiolabeling with either 68Ga (NOTA) or 111In (DTPA) to assess the impact of the conjugation degree on pharmacokinetics. AEX could successfully be applied to separate fractions of (chelator)n-anti-HER2 and (chelator)n-anti-MMR sdAb constructs. MS confirmed the identity of different peaks obtained in the separation process. SPR measurement suggests a small loss of affinity for (chelator)3-anti-sdAb, while IEF revealed a correlated decrease in isoelectric point (pI) with the number of conjugated chelators. Interestingly, both the reduction in affinity and in pI was stronger with the DTPA chelator than with NOTA for both sdAbs. In vivo data showed no significant differences in organ uptake for any construct, except for (DTPA)n-anti-MMR, which showed a significantly higher liver uptake for (DTPA)1-anti-MMR compared to (DTPA)2-anti-MMR and (DTPA)3-anti-MMR. For all constructs in general, high kidney uptake was observed, due to the typical renal clearance of sdAb-based tracers. The kidney uptake showed significant differences between fractions of a same construct and indicates that a higher conjugation degree improves kidney clearance. AEX allows the separation of sdAbs with a different degree of conjugation and provides the opportunity to further characterize individual fractions. The conjugation of a chelator to sdAbs can alter some properties of the tracers, such as pI; however, the impact on the general biodistribution profile and tumor targeting was minimal.