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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly spread around the globe after its emergence in Wuhan in December 2019. With no specific therapeutic and prophylactic options available, the virus has infected millions of people of which more than half a million succumbed to the viral disease, COVID-19. The urgent need for an effective treatment together with a lack of small animal infection models has led to clinical trials using repurposed drugs without preclinical evidence of their in vivo efficacy. We established an infection model in Syrian hamsters to evaluate the efficacy of small molecules on both infection and transmission. Treatment of SARS-CoV-2–infected hamsters with a low dose of favipiravir or hydroxychloroquine with(out) azithromycin resulted in, respectively, a mild or no reduction in virus levels. However, high doses of favipiravir significantly reduced infectious virus titers in the lungs and markedly improved lung histopathology. Moreover, a high dose of favipiravir decreased virus transmission by direct contact, whereas hydroxychloroquine failed as prophylaxis. Pharmacokinetic modeling of hydroxychloroquine suggested that the total lung exposure to the drug did not cause the failure. Our data on hydroxychloroquine (together with previous reports in macaques and ferrets) thus provide no scientific basis for the use of this drug in COVID-19 patients. In contrast, the results with favipiravir demonstrate that an antiviral drug at nontoxic doses exhibits a marked protective effect against SARS-CoV-2 in a small animal model. Clinical studies are required to assess whether a similar antiviral effect is achievable in humans without toxic effects.

Molecular imaging, where the location of molecules or nanoscale constructs can be tracked in the body to report on disease or biochemical processes, is rapidly expanding to include combined modality or multimodal imaging. No single imaging technique can offer the optimum combination of properties (e.g. resolution, sensitivity, cost, availability). The rapid technological advances in hardware to scan patients, and software to process and fuse images, are pushing the boundaries of novel medical imaging approaches, and hand-in-hand with this is the requirement for advanced and specific multimodal imaging agents. These agents can be detected using a selection from radioisotope, magnetic resonance and optical imaging, among others. Nanoparticles offer great scope in this area as they lend themselves, via facile modification procedures, to act as multifunctional constructs. They have relevance as therapeutics and drug delivery agents that can be tracked by molecular imaging techniques with the particular development of applications in optically guided surgery and as radiosensitizers. There has been a huge amount of research work to produce nanoconstructs for imaging, and the parameters for successful clinical translation and validation of therapeutic applications are now becoming much better understood. It is an exciting time of progress for these agents as their potential is closer to being realized with translation into the clinic. The coming 5-10 years will be critical, as we will see if the predicted improvement in clinical outcomes becomes a reality. Some of the latest advances in combination modality agents are selected and the progression pathway to clinical trials analysed. This article is part of the themed issue ‘Challenges for chemistry in molecular imaging’.

PurposeHistone deacetylase 6 (HDAC6) is a cytoplasmic enzyme that modulates intracellular transport and protein quality control. Inhibition of HDAC6 deacetylase activity has shown beneficial effects in disease models, including Alzheimer’s disease and amyotrophic lateral sclerosis. This first-in-human positron emission tomography (PET) study evaluated the brain binding of [18F]EKZ-001 ([18F]Bavarostat), a radiotracer selective for HDAC6, in healthy adult subjects.MethodsBiodistribution and radiation dosimetry studies were performed in four healthy subjects (2M/2F, 23.5 ± 2.4 years) using sequential whole-body PET/CT. The most appropriate kinetic model to quantify brain uptake was determined in 12 healthy subjects (6M/6F, 57.6 ± 3.7 years) from 120-min dynamic PET/MR scans using a radiometabolite-corrected arterial plasma input function. Four subjects underwent retest scans (2M/2F, 57.3 ± 5.6 years) with a 1-day interscan interval to determine test-retest variability (TRV). Regional volume of distribution (VT) was calculated using one-tissue and two-tissue compartment models (1-2TCM) and Logan graphical analysis (LGA), with time-stability assessed. VT differences between males and females were evaluated using volume of interest and whole-brain voxel-wise approaches.ResultsThe effective dose was 39.1 ± 7.0 μSv/MBq. Based on the Akaike information criterion, 2TCM was the preferred model compared to 1TCM. Regional LGA VT were in agreement with 2TCM VT, however demonstrated a lower absolute TRV of 7.7 ± 4.9%. Regional VT values were relatively homogeneous with highest values in the hippocampus and entorhinal cortex. Reduction of acquisition time was achieved with a 0 to 60-min scan followed by a 90 to 120-min scan. Males demonstrated significantly higher VT than females in the majority of cortical and subcortical brain regions. No relevant radiotracer related adverse events were reported.Conclusion[18F]EKZ-001 is safe and appropriate for quantifying HDAC6 expression in the human brain with Logan graphical analysis as the preferred quantitative approach. Males showed higher HDAC6 expression across the brain compared to females.

Background Many patients diagnosed with oesophageal adenocarcinoma (OAC) present with advanced disease and approximately half present with metastatic disease. Patients with localised disease, who are managed with curative intent, frequently undergo neoadjuvant chemoradiotherapy. Unfortunately, ~ 70% of patients have little or no response to chemoradiotherapy. We previously identified miR-330-5p as being the most significantly downregulated microRNA in the pre-treatment OAC tumours of non-responders to treatment, but that loss of miR-330-5p had a limited impact on sensitivity to chemotherapy and radiation in vitro. Here, we further examined the impact of miR-330-5p loss on OAC biology. Methods miR-330-5p was suppressed in OE33 OAC cells following stable transfection of a vector-driven anti-sense RNA. Whole transcriptome digital RNA-Seq was employed to identify miR-330-5p regulated genes, and qPCR was used for validation. Protein expression was assessed by protein array, Western blotting and zymography. Invasive potential was measured using a transwell assay system. Tumour xenograft growth profile studies were performed in immunocompromised CD1 mice. Results In OE33 cells, suppression of miR-330-5p significantly altered expression of 42 genes, and several secreted proteases. MMP1 gene expression and protein secretion was significantly enhanced with miR-330-5p suppression. This corresponded to enhanced collagen invasion in vitro. In vivo, OE33-derived tumour xenografts with miR-330-5p suppression grew faster than controls. Conclusions Loss of miR-330-5p expression in OAC tumours may influence tumour cell invasive capacity, tumour growth and therapeutic sensitivity via alterations to the tumour microenvironment.

Background Therapeutic antibodies for the treatment of neurological disease show great potential, but their applications are rather limited due to limited brain exposure. The most well-studied approach to enhance brain influx of protein therapeutics, is receptor-mediated transcytosis (RMT) by targeting nutrient receptors to shuttle protein therapeutics over the blood–brain barrier (BBB) along with their endogenous cargos. While higher brain exposure is achieved with RMT, the timeframe is short due to rather fast brain clearance. Therefore, we aim to increase the brain half-life of antibodies by binding to myelin oligodendrocyte glycoprotein (MOG), a CNS specific protein. Methods Alpaca immunization with mouse/human MOG, and subsequent phage selections and screenings for MOG binding single variable domain antibodies (VHHs) were performed to find mouse/human cross-reactive VHHs. Their ability to increase the brain half-life of antibodies was evaluated in healthy wild-type mice by coupling two different MOG VHHs (low/high affinity) in a mono- and bivalent format to a β-secretase 1 (BACE1) inhibiting antibody or a control (anti-SARS-CoV-2) antibody, fused to an anti-transferrin receptor (TfR) VHH for active transport over the BBB. Brain pharmacokinetics and pharmacodynamics, CNS and peripheral biodistribution, and brain toxicity were evaluated after intravenous administration to balb/c mice. Results Additional binding to MOG increases the C max and brain half-life of antibodies that are actively shuttled over the BBB. Anti-SARS-CoV-2 antibodies coupled with an anti-TfR VHH and two low affinity anti-MOG VHHs could be detected in brain 49 days after a single intravenous injection, which is a major improvement compared to an anti-SARS-CoV-2 antibody fused to an anti-TfR VHH which cannot be detected in brain anymore one week post treatment. Additional MOG binding of antibodies does not affect peripheral biodistribution but alters brain distribution to white matter localization and less neuronal internalization. Conclusions We have discovered mouse/human/cynomolgus cross-reactive anti-MOG VHHs which have the ability to drastically increase brain exposure of antibodies. Combining MOG and TfR binding leads to distinct PK, biodistribution, and brain exposure, differentiating it from the highly investigated TfR-shuttling. It is the first time such long brain antibody exposure has been demonstrated after one single dose. This new approach of adding a binding moiety for brain specific targets to RMT shuttling antibodies is a huge advancement for the field and paves the way for further research into brain half-life extension.

Background The extracellular localisation of the Heat shock protein 90 (Hsp90) is associated with the diseased state and wound healing and presents a promising opportunity for cancer targeting using Positron Emission Tomography (PET) imaging and molecularly targeted radiotherapy. The aim of this work is to develop a radiotracer with low nanomolar binding affinity to target the extracellular and particularly membrane pool of Hsp90, evaluate it in vitro, and conduct preliminary PET studies in vivo in mouse tumour models. Variable Heavy domain of Heavy chain antibodies, often referred to as Nanobodies, are suitable targeting vectors for the extracellular targets due to their favourable pharmacokinetic properties and low nanomolar target affinities. The main objective of the study is to target tumours expressing extracellular and membrane Hsp90 phenotype with minimal tracer accumulation in the non-target organs, which limited the translation of previously studied small molecule cytosolic Hsp90 tracers suffering from high non-Hsp90 specific background in the abdominal area. Results Six nanobodies were obtained after llama immunization with recombinant Hsp90α and ELISA biopanning, produced in E. coli and screened for stability and affinity. We selected one nanobody, 4DAM26, with good thermal stability, no aggregation at elevated temperatures, and low nanomolar affinity towards Hsp90α and Hsp90β isoforms for translation as a PET radiotracer. The nanobody was bioconjugated to p -NCS-NODAGA and radiolabeled with gallium-68 with 75 ± 11% radiochemical yield and > 99% radiochemical purity and remained stable up to 3 h in phosphate buffered saline and mouse serum. Pilot in vivo evaluation using µPET/CT and ex vivo biodistribution demonstrated a favourable pharmacokinetic profile, but the tumour uptake was non-distinguishable from the background tissue. Conclusion Compared to the small molecule Hsp90 tracers, the studied Nb-based tracer has improved pharmacokinetics properties including renal clearance and almost no accumulation in the non-target organs. Tumour uptake, on the other hand, was minimal and could not be differentiated from the background in µPET/CT. Our experiments indicate that in the studied models, membrane and extracellular expression of Hsp90 is majorly an artifact of cellular death, as only dead/dying cells had accessible pools of Hsp90 by flow cytometry, a consequence of a leaky membrane. More fundamental research is required to reassess the role of extracellular Hsp90 in cancer, and our future efforts will be focused on improving our inventory of cytosolic Hsp90 tracers with proven Hsp90-specific tumour accumulation.

Background/Objectives: NANOBODY® molecules (VHHs) are attractive vectors for radiopharmaceuticals due to their small size and high target affinity, but rapid clearance and pronounced kidney retention limit their therapeutic applicability. Binding to serum albumin is a widely used strategy to prolong circulation, yet the respective contributions of albumin-binding affinity and molecular format remain insufficiently defined. This study aimed to systematically evaluate how affinity and valency modulate VHH pharmacokinetics. Methods: Four monovalent albumin-binding VHHs spanning nanomolar to micromolar affinities and two bivalent constructs were engineered, generated by fusing an albumin-binding VHH to an irrelevant non-binding VHH. All constructs incorporated a site-specific cysteine for DFO* conjugation, enabling uniform zirconium-89 labeling with high radiochemical purity. Pharmacokinetics were assessed in healthy mice using serial blood sampling and positron emission tomography. Blood and kidney exposure were quantified by non-compartmental analysis. Results: All albumin-binding constructs showed increased systemic exposure and reduced kidney uptake relative to a non-binding control. Nanomolar-affinity binders reached maximal exposure, and further affinity increases (KD < ~100 nM) did not improve pharmacokinetics, suggesting a threshold. The micromolar binder showed intermediate exposure but still reduced renal retention compared with control. Valency effects were affinity-dependent. They were negligible at high affinity but pronounced at low affinity, where bivalency reduced systemic exposure and increased kidney uptake toward control levels. Conclusions: Albumin binding enables tuning of VHH pharmacokinetics in an affinity-dependent manner. Above an apparent affinity threshold, pharmacokinetics become format independent, whereas below this threshold, molecular format substantially influences systemic and renal disposition.

BackgroundMetastatic spread is responsible for the majority of cancer-associated deaths. The tumour microenvironment, including hypoxia, is a major driver of metastasis. The aim of this study was to investigate the role of the E3 ligase WSB-1 in breast cancer biology in the context of the hypoxic tumour microenvironment, particularly regarding metastatic spread.MethodsIn this study, WSB-1 expression was evaluated in breast cancer cell lines and patient samples. In silico analyses were used to determine the impact of WSB-1 expression on distant metastasis-free survival (DMFS) in patients, and correlation between WSB1 expression and hypoxia gene expression signatures. The role of WSB-1 on metastasis promotion was evaluated in vitro and in vivo.ResultsHigh WSB1 expression was associated with decreased DMFS in ER-breast cancer and PR-breast cancer patients. Surprisingly, WSB1 expression was not positively correlated with known hypoxic gene expression signatures in patient samples. Our study is the first to show that WSB-1 knockdown led to decreased metastatic potential in breast cancer hormone receptor-negative models in vitro and in vivo. WSB-1 knockdown was associated with decreased metalloproteinase (MMP) activity, vascular endothelial growth factor (VEGF) secretion, and angiogenic potential.ConclusionsOur data suggests that WSB-1 may be an important regulator of aggressive metastatic disease in hormone receptor-negative breast cancer. WSB-1 could therefore represent a novel regulator and therapeutic target for secondary breast cancer in these patients.

Background Gallium-68 labeled synthetic somatostatin analogs for PET/CT imaging are the current gold standard for somatostatin receptor imaging in neuroendocrine tumor patients. Despite good imaging properties, their use in clinical practice is hampered by the low production levels of 68 Ga eluted from a 68 Ge/ 68 Ga generator. In contrast, 18 F-tracers can be produced in large quantities allowing centralized production and distribution to distant PET centers. [ 18 F]AlF-NOTA-octreotide is a promising tracer that combines a straightforward Al 18 F-based production procedure with excellent in vivo pharmacokinetics and specific tumor uptake, demonstrated in SSTR2 positive tumor mice. However, advancing towards clinical studies with [ 18 F]AlF-NOTA-octreotide requires the development of an efficient automated GMP production process and additional preclinical studies are necessary to further evaluate the in vivo properties of [ 18 F]AlF-NOTA-octreotide. In this study, we present the automated GMP production of [ 18 F]AlF-NOTA-octreotide on the Trasis AllinOne® radio-synthesizer platform and quality control of the drug product in accordance with GMP. Further, radiometabolite studies were performed and the pharmacokinetics and biodistribution of [ 18 F]AlF-NOTA-octreotide were assessed in healthy rats using μPET/MR. Results The production process of [ 18 F]AlF-NOTA-octreotide has been validated by three validation production runs and the tracer was obtained with a final batch activity of 10.8 ± 1.3 GBq at end of synthesis with a radiochemical yield of 26.1 ± 3.6% (dc), high radiochemical purity and stability (96.3 ± 0.2% up to 6 h post synthesis) and an apparent molar activity of 160.5 ± 75.3 GBq/μmol. The total synthesis time was 40 ± 3 min. Further, the quality control was successfully implemented using validated analytical procedures. Finally, [ 18 F]AlF-NOTA-octreotide showed high in vivo stability and favorable pharmacokinetics with high and specific accumulation in SSTR2-expressing organs in rats. Conclusion This robust and automated production process provides high batch activity of [ 18 F]AlF-NOTA-octreotide allowing centralized production and shipment of the compound to remote PET centers. Further, the production process and quality control developed for [ 18 F]AlF-NOTA-octreotide is easily implementable in a clinical setting and the tracer is a potential clinical alternative for somatostatin directed 68 Ga labeled peptides obviating the need for a 68 Ge/ 68 Ga-generator. Finally, the favorable in vivo properties of [ 18 F]AlF-NOTA-octreotide in rats, with high and specific accumulation in SSTR2 expressing organs, supports clinical translation.

Background Array tomography (AT) is a high-resolution imaging method to resolve fine details at the organelle level and has the advantage that it can provide 3D volumes to show the tissue context. AT can be carried out in a correlative way, combing light and electron microscopy (LM, EM) techniques. However, the correlation between modalities can be a challenge and delineating specific regions of interest in consecutive sections can be time-consuming. Integrated light and electron microscopes (iLEMs) offer the possibility to provide well-correlated images and may pose an ideal solution for correlative AT. Here, we report a workflow to automate navigation between regions of interest. Results We use a targeted approach that allows imaging specific tissue features, like organelles, cell processes, and nuclei at different scales to enable fast, directly correlated in situ AT using an integrated light and electron microscope (iLEM-AT). Our workflow is based on the detection of section boundaries on an initial transmitted light acquisition that serves as a reference space to compensate for changes in shape between sections, and we apply a stepwise refinement of localizations as the magnification increases from LM to EM. With minimal user interaction, this enables autonomous and speedy acquisition of regions containing cells and cellular organelles of interest correlated across different magnifications for LM and EM modalities, providing a more efficient way to obtain 3D images. We provide a proof of concept of our approach and the developed software tools using both Golgi neuronal impregnation staining and fluorescently labeled protein condensates in cells. Conclusions Our method facilitates tracing and reconstructing cellular structures over multiple sections, is targeted at high resolution ILEMs, and can be integrated into existing devices, both commercial and custom-built systems.