Franklin I. Aigbirhio

The angiotensin-converting enzyme 2 (ACE2) is pivotal as the cellular receptor for SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), the virus responsible for COVID-19. This study presents a novel synthetic route for four analogues of MLN-4760, a known inhibitor of ACE2, guided by in silico docking predictions. These synthetic advances enabled in vitro pIC₅₀ assays confirming the inhibitory potency of the synthesized analogues. Lastly, this route was applied to the synthesis of novel ¹⁸F-labeled ACE2 inhibitors for PET imaging applications.

Background: In recent years, the development of the [¹⁸F]difluoromethyl radical ([¹⁸F]2-((difluoromethyl)sulfonyl)benzo[d]thiazole, [¹⁸F]4), and [¹⁸F]difluorocarbene ([¹⁸F]1-chloro-4-((difluoromethyl)sulfonyl)benzene, [¹⁸F]10) prosthetic groups, has paved the way towards direct ¹⁸F-difluoromethylation in routine PET tracer synthesis with high molar activity. However, limitations in their syntheses may be hindering their widespread adoption by the radiochemistry community. Firstly, the synthesis of the precursors 2-((bromofluoromethyl)thio)benzo[d]thiazole (3) and (bromofluoromethyl)(4-chlorophfenyl)sulfane (8) requires the use of the ozone-depleting dibromofluoromethane, a reagent that is not-commercially available. Secondly, the reported syntheses of [¹⁸F]4 and [¹⁸F]10 are lengthy and require semi-preparative HPLC purification prior to the ¹⁸F-difluoromethylation step. Finally, in the case of [¹⁸F]10, very large amounts of precursor material (200 μmol) are required for difluorocarbene insertion. The aim of this work was to develop a halofluorocarbon-free radiosynthesis of [¹⁸F]4 and [¹⁸F]10 on the GE TRACERlab FX_FN module. Additionally, another aim was to develop a chromatography-free, fully-automated synthesis of [¹⁸F]10 on the GE FX_FN module. Results: Precursors 3 and 8 were synthesised in 21% and 54% yield via decarboxylative bromination, which circumvented the need for ozone-depleting dibromofluoromethane. Difluoromethyl reagents [¹⁸F]4 and [¹⁸F]10 were synthesised on a GE FX_FN module with semi-prep HPLC purification in 4% and 3% RCY (decay-corrected), respectively. The synthesis of [¹⁸F]10 was further simplified through elimination of the semi-prep HPLC purification in favour of a cartridge-based solid-phase extraction (SPE) trapping and elution approach (on an alumina SPE cartridge loaded in series with a C18 Sep-Pak plus SPE cartridge) to give [¹⁸F]10 in 10.1% ± 1.9% (n = 6, decay-corrected) RCY (97% ± 3% RCP, 1.5–11 GBq/μmol). Finally, a fully automated ¹⁸F-difluoromethylation radiosynthesis with [¹⁸F]10 was developed on two GE FX_FN modules linked together to yield the model ¹⁸F-difluoromethylated compound in adequate amounts for biological studies, in under two hours (99.0 MBq, 0.8% RCY {decay-corrected}, 1.5 GBq/μmol, 103 min total synthesis time). Therefore, we have established a path forward for routine automated synthesis of radiotracers via [¹⁸F]difluorocarbene insertion with [¹⁸F]10. Conclusions: A halofluorocarbon, chromatography-free synthesis on the GE FX_FN module afforded difluorocarbene reagent [¹⁸F]10 in 10.1% ± 1.9% RCY (decay-corrected). Additionally, a fully-automated three-step [¹⁸F]difluorocarbene insertion radiosynthesis using two tandem FX_FNs is described for the first time, providing a path forward to the full automation of [¹⁸F]difluorocarbene insertion on two-reactor systems. Graphical

Purpose: Positron Emission Tomography (PET) scans with radioligands targeting tau neurofibrillary tangles (NFT) have accelerated our understanding of the role of misfolded tau in neurodegeneration. While intended for human research, applying these radioligands to small animals establishes a vital translational link. Transgenic animal models of dementia, such as the tau rat SHR24, play a crucial role in enhancing our understanding of these disorders. This study aims to evaluate the utility of SHR24 rat model for PET studies. Procedures: Dynamic PET scans were conducted in male SHR24 rats and their wild-type SHR (SHRwt) littermates using [¹⁸F]AV1451. Rapid blood sampling and metabolite analysis were performed to acquire input curves. Time activity curves were obtained from various brain regions over 60 min. Blood-based, 2-Tissue Compartment Model (2-TCM) and Logan graphical analysis were used to obtain kinetic modelling parameters. The ability of reference tissue models to predict the binding potential (BP_ND) were assessed. Autoradiography studies were performed to corroborate the scan data. Results: Total distribution volume (V_T) was the best predicted parameter which revealed significantly higher uptake of [¹⁸F]AV1451 in the cortex (5.8 ± 1.1 vs 4.6 ± 0.7, P < 0.05) of SHR24 rats compared to SHRwt rats. Binding potential obtained from 2-TCM was variable, however BP_ND from reference tissue models detected significantly higher binding in cortex (0.28 ± 0.07 vs 0.20 ± 0.04, P < 0.01 by SRTM) and brainstem (0.14 ± 0.04 vs 0.08 ± 0.02, P < 0.01, by SRTM). Conclusions: With the ability to detect binding of established radioligand [¹⁸F]AV1451 in these rats, we have demonstrated the utility of this model for assessing aggregated tau neurobiology by PET, with reference tissue models providing potential for longitudinal studies.

Aggregation of β-amyloid protein is a hallmark pathology of the neurodegenerative disorder Alzheimer's disease and proceeds from monomers to insoluble misfolded fibril forms via soluble and highly toxic oligomeric intermediates. Given the dual feature of being the most toxic form of the Aβ aggregate proteome and an early marker of pathogenesis, there is a need for sensitive methods that can be used to detect Aβ oligomers and investigate the dynamics of aggregation. Herein, we describe a method based on the application of an oligomer-sensitive fluorescent chemical probe pTP-TFE combined with the use of a QIAD (Quantitative determination of Interference with Aβ Aggregate Size Distribution) assay to correctly identify Aβ oligomers in high sensitivity. pTP-TFE was evaluated and compared to thioflavin T and pFTAA, the two most widely used amyloid fibril dyes, and shown to be the only probe capable of detecting significant differences across all oligomeric species of β-amyloid. Furthermore, by observing changes in pTP-TFE fluorescence emission over time, we could track the dynamics of oligomer populations and thereby obtain kinetic information on the Aβ42 dynamic aggregation model. Therefore, we have established a highly sensitive, readily available, and simple method for studying β-amyloid protein aggregation dynamics.

Positron Emission Tomography (PET) is an important part of the medical imaging field which is continually exploring novel biological targets as exemplified by PET imaging of neuroinflammation. Due to limitations stemming from either sub‐optimal biological targets or a lack of available selective radiotracers, alternative biomarkers and PET imaging agent candidates are considered. One such possible target is microRNA (miRNA) and herein, we discuss the potential of miRNA for PET imaging. With the aim of addressing key strategies for imaging miRNA with PET, we identify three distinct approaches as follows: small molecules directly targeting miRNA, small molecules indirectly targeting Argonaute 2 (AGO2)‐protein complexes, and direct chemical modification of antisense oligonucleotides. The radiosynthetic approaches are based on the methods of direct radiolabelling of respective antisense oligonucleotides and several examples are described herein, showcasing the potential of miRNA in PET imaging. Whilst these approaches offer different radiolabelling strategies, application of these radiolabelled molecules towards PET imaging of miRNA are scarce with only one, limited example applied to bone remodeling reported in the literature.

Positron emission tomography imaging of misfolded proteins with high‐affinity and selective radioligands has played a vital role in expanding our knowledge of neurodegenerative diseases such as Parkinson's and Alzheimer's disease. The pathogenesis of Huntington's disease, a CAG trinucleotide repeat disorder, is similarly linked to the presence of protein fibrils formed from mutant huntingtin (mHTT) protein. Development of mHTT fibril–specific radioligands has been limited by the lack of structural knowledge around mHTT and a dearth of available hit compounds for medicinal chemistry refinement. Over the past decade, the CHDI Foundation, a non‐for‐profit scientific management organisation has orchestrated a large‐scale screen of small molecules to identify high affinity ligands of mHTT, with lead compounds now reaching clinical maturity. Here we describe the mHTT radioligands developed to date and opportunities for further improvement of this radiotracer class.

Neuroinflammation is an important pathogenic mechanism in many neurodegenerative diseases, including those caused by frontotemporal lobar degeneration (FTLD). There is a pressing need for scalable and mechanistically relevant blood markers of inflammation to facilitate drug development and experimental medicine. We assessed inflammatory profiles of serum cytokines from 214 patients with FTLD-associated syndromes (behavioural and language variants of frontotemporal dementia, progressive supranuclear palsy, corticobasal syndrome). We tested the association with brain microglial activation (by positron emission tomography) and survival. A pro-inflammatory profile across the FTLD spectrum (including TNF-α, TNF-R1, M-CSF, IL-17A, IL-12, IP-10 and IL-6) differentiated patients (all syndromes) from controls. A higher pro-inflammatory profile scores was associated with higher microglial activation in frontal and brainstem regions, and with lower survival. Blood-based markers of inflammation could increase the scalability and access to neuroinflammatory assessment of people with dementia, to facilitate clinical trials and experimental medicine studies.

Background: There is growing evidence for early and extensive synaptic loss in frontotemporal lobar degeneration syndromes from in vivo and post‐mortem studies. We proposed that synaptic loss would affect behaviour, in relation to changes in functional connectivity.Method: We recruited 29 participants with progressive supranuclear palsy, 16 participants with amyloid‐negative corticobasal syndrome, 8 participants with behavioural variant frontotemporal dementia and 24 similarly‐aged healthy volunteers. All participants underwent resting‐state functional 3T MRI and positron emission tomography with [¹¹C]UCB‐J, that binds synaptic vesicle 2A. We compared the connectivity metrics of nodal weighted degree and voxelwise regional homogeneity with [¹¹C]UCB‐J non‐displaceable binding potential (BP_ND), in associative and commonality analyses. We then used independent component analysis to extract [¹¹C]UCB‐J BP_ND signal variance across participants, followed by derivation of participant‐specific scores of functional spatial covariance with the [¹¹C]UCB‐J components. We applied model selection to assess whether connectivity scores would improve prediction of and moderate the effect of synaptic loss on clinical severity.Result: Reduced [¹¹C]UCB‐J BP_ND was associated with reduced connectivity, with synaptic density predicting both measures of connectivity over and above grey matter volume (Figure 1). The anatomical distribution of synaptic loss partially overlapped in PSP, bvFTD and CBS, but there were also disease‐specific effects (Figure 2). The effect of synaptic loss on functional connectivity was expressed local to the regions of severe synaptic loss, and in remote regions. Moreover, functional connectivity explained additional variance and moderated the relationship between synaptic density and clinical severity (Figure 3).Conclusion: In vivo synaptic loss is associated with reduced connectivity, and changes in behaviour, with implications for modelling disease pathogenesis and translational studies.

Background: Neuroinflammation is an important pathogenic mechanism in frontotemporal dementia (FTD) and related disorders. Postmortem and in vivo imaging studies have shown brain inflammation early in these conditions, and as proportionate to symptom severity and rate of progression. However, data on inflammation blood markers of inflammation and their relationship with central inflammation are limited. Here we assess inflammatory patterns of 41 serum cytokines from patients with FTD and related conditions, and their association with regional microglial activation (TSPO PET).Method: Blood samples were obtained from 29 healthy controls, and 214 patients with a clinical diagnosis of behavioural variant FTD (bvFTD = 52), primary progressive aphasia (PPA = 51), progressive supranuclear palsy (PSP = 58) and corticobasal syndrome (CBS = 53). Serum assays used the MesoScale Discovery V‐Plex‐Human Cytokine 36 plex panel plus five additional cytokine assays. A Principal Component Analysis (PCA) across all participants was used to reduce dimensionality of cytokine data. A sub‐group of patients (bvFTD = 10, PPA = 17, PSP = 17) underwent PET imaging with [¹¹C]PK11195 PET, as index of microglial activation. Kruskal‐Wallis and pairwise t‐tests were performed on the resulting components to compare each patient cohort to controls. [¹¹C]PK11195 non‐displaceable binding potential (BP_ND) was calculated in 83 regions of interest (ROIs) across the whole brain. Spearman correlations tested associations between cytokine components and regional [¹¹C]PK11195 BP_ND.Result: Sixteen cytokines were undetectable in >50% of participants and thus excluded. The first component identified by the PCA on the remaining 25 cytokines (explaining 19.7%) was strongly loaded by pro‐inflammatory cytokines (Figure 1, left). Kruskal–Wallis one‐way analyses of variance on detected significant differences across the groups (χ²(4) = 11.0, p = 0.027), and the pairwise t‐tests identified significant differences between each patient cohort and controls (Figure 1, right). Spearman correlations identified regional positive associations between individual cytokine‐component scores and microglial activation in frontal and brainstem regions across the whole group (R≥0.25), and syndrome‐specific regional patterns (Figure 2).Conclusion: This data‐driven approach identified a pro‐inflammatory profile across FTD and related conditions, which is positively associated with higher levels of microglial activation in syndrome‐related key brain regions. Blood‐based tests could greatly increase the scalability and access to neuroinflammatory assessment in dementia and experimental medicine studies.

Background: Neuroinflammation is an important pathogenic mechanism in frontotemporal dementia (FTD) and related disorders. Postmortem and in vivo imaging studies have shown brain inflammation early in these conditions, and as proportionate to symptom severity and rate of progression. However, data on inflammation blood markers of inflammation and their relationship with central inflammation are limited. Here we assess inflammatory patterns of 41 serum cytokines from patients with FTD and related conditions, and their association with regional microglial activation (TSPO PET).Method: Blood samples were obtained from 29 healthy controls, and 214 patients with a clinical diagnosis of behavioural variant FTD (bvFTD = 52), primary progressive aphasia (PPA = 51), progressive supranuclear palsy (PSP = 58) and corticobasal syndrome (CBS = 53). Serum assays used the MesoScale Discovery V‐Plex‐Human Cytokine 36 plex panel plus five additional cytokine assays. A Principal Component Analysis (PCA) across all participants was used to reduce dimensionality of cytokine data. A sub‐group of patients (bvFTD = 10, PPA = 17, PSP = 17) underwent PET imaging with [11C]PK11195 PET, as index of microglial activation. Kruskal‐Wallis and pairwise t‐tests were performed on the resulting components to compare each patient cohort to controls. [11C]PK11195 non‐displaceable binding potential (BPND) was calculated in 83 regions of interest (ROIs) across the whole brain. Spearman correlations tested associations between cytokine components and regional [11C]PK11195 BPND.Result: Sixteen cytokines were undetectable in >50% of participants and thus excluded. The first component identified by the PCA on the remaining 25 cytokines (explaining 19.7%) was strongly loaded by pro‐inflammatory cytokines (Figure 1, left). Kruskal–Wallis one‐way analyses of variance on detected significant differences across the groups (χ2(4) = 11.0, p = 0.027), and the pairwise t‐tests identified significant differences between each patient cohort and controls (Figure 1, right). Spearman correlations identified regional positive associations between individual cytokine‐component scores and microglial activation in frontal and brainstem regions across the whole group (R≥0.25), and syndrome‐specific regional patterns (Figure 2).Conclusion: This data‐driven approach identified a pro‐inflammatory profile across FTD and related conditions, which is positively associated with higher levels of microglial activation in syndrome‐related key brain regions. Blood‐based tests could greatly increase the scalability and access to neuroinflammatory assessment in dementia and experimental medicine studies.