Background/Objectives: The chemokine receptor CXCR4 plays a pivotal role in tumor progression, metastasis, and therapy resistance and is frequently overexpressed in hematologic malignancies, including multiple myeloma and lymphoma. This study investigates a CXCR4-targeted theranostic platform comprising a PET imaging agent and two therapeutic radioconjugates derived from the high-affinity CXCR4 antagonist LY2510924. Methods: The PET tracer [18F]AlF-NOTA-SC and therapeutic radioconjugates [177Lu]Lu-BL02 and [161Tb]Tb-BL02 were synthesized and evaluated. Radiolabeling efficiency, molar activity, and in vitro binding affinity were assessed. Specificity and uptake were evaluated in CXCR4-expressing U87.CD4.CXCR4 and MM.1S cells, with cytotoxic potential being analyzed via clonogenic survival assays. In vivo biodistribution and pharmacokinetics were evaluated in MM.1S xenograft mouse models, supported by longitudinal SPECT imaging. Results: All radioconjugates were obtained with high radiochemical purity (>98%). The constructs showed nanomolar affinity for human CXCR4; in vitro assays confirmed specific uptake in CXCR4-positive cells, and both therapeutic agents demonstrated dose-dependent cytotoxicity. In vivo, all compounds displayed comparable tumor uptake with low off-target accumulation. Co-injection studies confirmed consistent pharmacokinetics across agents, while SPECT/CT imaging demonstrated gradual tumor clearance of [177Lu]Lu-BL02 over seven days. Conclusions: The radiopharmaceutical trio [18F]AlF-NOTA-SC, [177Lu]Lu-BL02, and [161Tb]Tb-BL02 demonstrates the feasibility of a CXCR4-targeted theranostic approach for imaging and treating hematologic malignancies. The observed tumor washout highlights the need for further structural optimization to enhance tumor retention and therapeutic efficacy, providing a clear direction for future development toward clinical translation.

Heat shock protein 90 (Hsp90) is a critical chaperone in the protein quality control system, essential for maintaining cellular proteostasis. Aberrant Hsp90 function has been implicated in cancer and neurodegenerative disorders, making it an attractive therapeutic target and a potential biomarker for disease characterisation and progression using PET imaging. In this study, we aimed to develop the first fluorine-18 labelled brain permeable PET imaging agent, [18F]FEHSP990, suitable for imaging Hsp90 in both brain and tumour tissue. The radiosynthesis of [18F]FEHSP990 was achieved with a radiochemical yield of 48 ± 29%, high radiochemical purity of > 99% and a molar activity of 213 ± 101 GBq/μmol at the end of synthesis. Competition binding studies in healthy mouse brain homogenate samples indicated a Ki value of approximately 200 nM. In vitro tracer binding to rodent brain and glioblastoma tumour tissue slices was high and deemed Hsp90-specific, as demonstrated by autoradiography blocking studies, whereas binding to living glioblastoma U87 cells was notably low. Ex vivo biodistribution and in vivo PET imaging studies in healthy rodents demonstrated limited brain exposure of the tracer, potentially due to insufficient affinity for Hsp90 and/or restricted blood-brain barrier permeability. Further development of fluorine-18 labelled Hsp90 tracers is warranted.

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPA-R) are the primary determinants of synaptic strength in most glutamatergic neurons. Inhibition or negative modulation of AMPA-Rs is an attractive strategy for therapeutic intervention in central nervous system (CNS) disorders characterized by excessive neuronal activity. We report the clinical qualification of a AMPA-R associated TARP-γ8 specific PET ligand [18F]JNJ-64511070 in healthy volunteers including biodistribution, dosimetry and kinetic modelling. Whole body dosimetry was performed in 3 healthy male subjects (22-41y). Upon estimation of the normalized cumulated activity (NCA), the effective dose (ED) was calculated using OLINDA v1.1. In a second part, 120-minute dynamic brain scanning with arterial blood sampling was done in five healthy males (25-53y) to determine the appropriate kinetic model and evaluate time stability of total distribution volume (VT). Both 1- and 2-tissue compartment models (1-2TCM) as well as Logan graphical analysis (LGA) were considered to assess regional VT. The average ED (± SD) was 15.6 ± 1.0 µSv/MBq. Brain uptake of [18F]JNJ-64511070 was fast and showed slow clearance from brain. The intact parent tracer fraction was 80

Fibroblast activation protein inhibitor (FAPI)-based positron emission tomography (PET) radiopharmaceuticals have shown promise for imaging cancer-associated fibroblasts (CAFs), a key component of the tumor microenvironment. FAPI radiopharmaceuticals offer high tumor-to-background contrast and are not influenced by hyperglycemia. Among these, [18F]AlF-FAPI-74, labeled using the Al18F-method, offers logistical advantages over 68Ga-labeled radiopharmaceuticals, including a longer physical half-life and suitability for large-scale, centralized production. This study reports a fully automated, efficient, and GMP-compliant synthesis of [18F]AlF-FAPI-74 using the Trasis AllInOne® platform, alongside a refined isocratic radio-HPLC method that enhances fluorine-18 recovery and impurity resolution. Additionally, the impact of molar dose on [18F]AlF-FAPI-74 biodistribution is evaluated in a preclinical model and a clinical case-study highlighting the performance of [18F]AlF-FAPI-74 produced at high apparent molar activity is provided. The automated GMP-compliant production was validated in three independent runs, with an average decay-corrected yield and apparent molar activity of 50 ± 10

[68Ga]PentixaFor detects C-X-C chemokine receptor type 4 (CXCR4) overexpression in various malignancies, such as multiple myeloma and non-Hodgkin lymphomas, as well as in endocrine and inflammatory disorders. This study aimed to develop an Al18F-labeled radiotracer derived from LY2510924 for CXCR4-targeted imaging, leveraging the physical and logistical advantages of fluorine-18. We designed a CXCR4-specific radioprobe, [18F]AlF-NOTA-SC, based on LY2510924 by incorporating a triglutamate linker and NOTA chelator to enable Al18F-labeling. The in vitro CXCR4 affinity was assessed using cell-based binding assays. Subsequently, in vivo pharmacokinetics and tumor uptake of [18F]AlF-NOTA-SC were assessed in naïve mice and mice with xenografts derived from U87.CD4/U87.CD4.CXCR4 and MM.1 S cells. Finally, biodistribution was determined in a non-human primate using PET-MR. Compared to Ga-PentixaFor, AlF-NOTA-SC demonstrated similar in vitro affinity for human CXCR4. [18F]AlF-NOTA-SC was produced with a decay-corrected radiochemical yield of 21.0 ± 7.1

Multimodal imaging provides rich biological information, which can be exploited to study drug activity, disease associated phenotypes, and pharmacological responses. Here we show discovery and validation of a new probe targeting the endocannabinoid α/β-hydrolase domain 6 (ABHD6) enzyme by utilizing positron emission tomography (PET) and matrix-assisted laser desorption/ionization (MALDI) imaging. [18F]JZP-MA-11 as the first PET ligand for in vivo imaging of the ABHD6 is reported and specific uptake in ABHD6-rich peripheral tissues and major brain regions was demonstrated using PET. A proof-of-concept study in nonhuman primate confirmed brain uptake. In vivo pharmacological response upon ABHD6 inhibition was observed by MALDI imaging. These synergistic imaging efforts used to identify biological information cannot be obtained by a single imaging modality and hold promise for improving the understanding of ABHD6-mediated endocannabinoid metabolism in peripheral and central nervous system disorders.

Despite its limitations, [123I]MIBG scintigraphy has been the standard for human norepinephrine transporter (hNET) imaging for several decades. Recently, [18F]MFBG has emerged as a promising PET alternative. This prospective trial aimed to evaluate safety, biodistribution, tumour lesion pharmacokinetics, and lesion targeting of [18F]MFBG and perform a head-to-head comparison with [123I]MIBG in neural crest tumour patients. Six neural crest tumour patients (4 phaeochromocytoma, 1 paraganglioma, 1 neuroblastoma) with a recent routine clinical [123I]MIBG scintigraphy (interval: − 37–75 days) were included. Adult patients (n = 5) underwent a 30-min dynamic PET, followed by 3 whole-body PET/CT scans at 60, 120, and 180 min after injection of 4 MBq/kg [18F]MFBG. One minor participant underwent a single whole-body PET/CT at 60 min after administration of 2 MBq/kg [18F]MFBG. Normal organ uptake (SUVmean) and lesion uptake (SUVmax; tumour-to-background ratio (TBR)) were measured. Regional distribution volumes (VT) were estimated using a Logan graphical analysis in up to 6 lesions per patient. A lesion-by-lesion analysis was performed to compare detection ratios (DR), i.e. fraction of detected lesions, between [18F]MFBG and [123I]MIBG. [18F]MFBG was safe and well tolerated. Its biodistribution was overall similar to that of [123I]MIBG, with prominent uptake in the salivary glands, liver, left ventricle wall and adrenals, and mainly urinary excretion. In the phaeochromocytoma subgroup, the median VT was 37.4 mL/cm3 (range: 18.0–144.8) with an excellent correlation between VT and SUVmean at all 3 time points (R2: 0.92–0.94). Mean lesion SUVmax and TBR at 1 h after injection were 19.3 ± 10.7 and 23.6 ± 8.4, respectively. All lesions detected with [123I]MIBG were also observed with [18F]MFBG. The mean DR with [123I]MIBG was significantly lower than with [18F]MFBG (61.0% ± 26.7% vs. 99.8% ± 0.5% at 1 h; p = 0.043). [18F]MFBG is a promising hNET imaging agent with favourable imaging characteristics and improved lesion targeting compared with [123I]MIBG scintigraphy. Clinicaltrials.gov : NCT04258592 (Registered: 06 February 2020), EudraCT: 2019-003872-37A.

INTRODUCTION:Cabozantinib is a tyrosine kinase inhibitor (TKI) approved for the treatment of medullary thyroid cancer, renal cell carcinoma and hepatocellular carcinoma, and is currently in clinical trials for the treatment of prostate cancer and others. It exerts its therapeutic effect mainly through inhibition of the tyrosine kinases MET (hepatocyte growth factor receptor) and VEGFR2 (vascular endothelial growth factor receptor 2), in addition to several other kinases involved in cancer. PET imaging with TKIs such as [18F]cabozantinib could potentially aid in cancer diagnosis and guide treatment. This study aims to evaluate the utility of [18F]cabozantinib as a PET imaging probe in PC3 tumor xenografted mice. METHODS:[18F]cabozantinib was evaluated in non-tumor and tumor bearing (PC3 xenografted) male mice by ex vivo biodistribution studies and in vivo μPET imaging. Pretreatment studies were performed in the tumor bearing mice with the MET inhibitor PF04217903. Mouse plasma was analyzed with HPLC to quantify radiometabolites. To further evaluate the binding specificity of [18F]cabozantinib, in vitro autoradiography studies on heart and PC3 tumor sections were performed in the presence of authentic cabozantinib or specific MET and VEGFR2 inhibitors. RESULTS:Tissue distribution studies in non-tumor bearing mice revealed slow blood clearance, absence of brain uptake and a high myocardial uptake. In the tumor bearing mice, tumor uptake was low (0.58 ± 0.20% ID/g at 30 min post tracer injection), which was confirmed by μPET imaging. No differences in tissue distribution and kinetics were observed in both biodistributions and μPET studies after pretreatment with the MET inhibitor PF04217903. At 30 min post tracer injection, 60 ± 3% of the recovered radioactivity in plasma in non-tumor bearing mice was present as intact tracer. [18F]cabozantinib binding in vitro to heart and tumor tissues was partly blocked in the presence of selective MET and VEGFR2 inhibitors (up to 40% block). The fraction of non-specific binding was relatively high for both tissues (66% for heart and 39% for tumor). CONCLUSION:[18F]cabozantinib exhibits non-favorable properties as a PET imaging probe, demonstrated by slow excretion kinetics along with low tumor uptake and high non-specific binding in tumor and heart tissue. The results reflect cabozantinibs multi-kinase activity, making PET imaging of tumor specific kinase expression with [18F]cabozantinib challenging.

Histone deacetylase 6 (HDAC6) is a multifunctional cytoplasmic enzyme involved in diverse cellular processes such as intracellular transport and protein quality control. Inhibition of HDAC6 can alleviate defects in cell and rodent models of certain diseases, particularly neurodegenerative disorders, including Alzheimer's disease and amyotrophic lateral sclerosis. However, while HDAC6 represents a potentially powerful therapeutic target, development of effective brain-penetrant HDAC6 inhibitors remains challenging. Recently, [18F]EKZ-001 ([18F]Bavarostat), a brain-penetrant positron emission tomography (PET) radioligand with high affinity and selectivity toward HDAC6, was developed and evaluated preclinically for its ability to bind HDAC6. Herein, we describe the efficient and robust fully automated current Good Manufacturing Practices (cGMP) compliant production method. [18F]EKZ-001 quantification methods were validated in nonhuman primates (NHP) using full kinetic modeling, and [18F]EKZ-001 PET was applied to compare dose-occupancy relationships between two HDAC6 inhibitors, EKZ-317 and ACY-775. [18F]EKZ-001 is cGMP produced with an average decay-corrected radiochemical yield of 14% and an average molar activity of 204 GBq/μmol. We demonstrate that a two-tissue compartmental model and Logan graphical analysis are appropriate for [18F]EKZ-001 PET quantification in NHP brain. Blocking studies show that the novel compound EKZ-317 achieves higher target occupancy than ACY-775. This work supports the translation of [18F]EKZ-001 PET for first-in-human studies.

Histone 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. Biodistribution 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. The 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. [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.

[18F]THK5351 as well as [18F]AV1451 tau-PET consistently shows high anterior temporal lobe retention in primary progressive aphasia semantic variant (PPA SV). This syndrome is however most commonly associated with TDP-43 type C proteinopathy. Cases were selected from the UZ/KU Leuven Brain-BioBank: five PPA SV (3 FTLD-TDP-43 type C, 1 Alzheimer's disease (AD), 1 Pick's disease (PiD)), one frontotemporal dementia behavioral variant (FTDbv) (FTLD-TDP-43 type C), two cases with a clinical diagnosis of AD with underlying AD pathology, and two healthy controls. An in vitro autoradiography binding study was performed according to the method of Xia et al. with some minor modifications: Each 20 μm cryosection of the right anterior part of the inferior temporal gyrus was incubated with 7–15 kBq [18F]AV1451 or [18F]THK5351 in presence/absence of 10 μM authentic reference material (cold compound) or 10 μM R-deprenyl (MAO-B inhibitor) at room temperature for 60 minutes. Four of the same cases were also studied with [18F]THK5351 (one typical AD, one SV with AD and two SV with FTLD-TDP-43 type C). Autoradiograms were obtained by overnight exposure to a phosphor-storage screen and read by a Cyclone Plus system. Semiquantitative analyses were performed using Optiquant software. None of two tracers showed specific binding to any of the PPA SV FTLD-TDP-43 type C brain slices. Neither was there any binding in the FTDbv FTLD-TDP-43 type C case. Accordingly, binding was not affected by R-deprenyl. In contrast, PPA SV due to PiD showed strong cortical [18F]AV1451 binding, which was displaceable by the cold compound. The two typical AD cases as well as SV due to AD showed strong cortical binding for both tracers, which could be blocked by co-incubation with the cold compound. No specific tracer binding was observed to brain slices of two healthy controls. In vitro, no specific binding to non-tau aggregates was observed in contrast to the consistently strong signal of these tau-PET tracers in PPA SV in vivo. We propose that the binding in vivo reflects an interaction with a component of the reactive astrocytic or microglial system, which is not picked up by in vitro autoradiography.

Vitamin B-12 (cobalamin) deficiency in humans is a worldwide problem emanating from varied causes such as insufficient dietary intake or malabsorption of the micronutrient due to an underlying condition (absence or failure of intrinsic factor, atrophic gastritis, post-operative bariatric surgery, inflammatory bowel disease, cobalt deficiency etc.). As oral supplementation is limited by its bioavailability due to the absorptive property of intrinsic factor, clinicians often prescribe parenteral forms of administration to replenish diminished levels rapidly. The gold standard in parenteral delivery of cobalamin is subcutaneous and/or intramuscular injections. The relatively large molecular size of cobalamin (1355.39 Da) makes passive transdermal patch-based delivery via the stratum corneum quite challenging. Hence, the primary goal of this study is to investigate the feasibility of intradermal (ID) delivery of Vitamin B-12 via an almost painless microneedle injection and subsequent comparison with standard subcutaneous (SC) delivery. This work reports on a custom-made microneedle device built from a commercial insulin needle and it’s use to perform ID delivery of Co-57 radiolabeled Vitamin B-12 in-vivo in rabbits. The pharmacokinetic profile and bioavailability were studied and compared with SC delivery. It is the first comprehensive study, to our best knowledge, that compares a micronutrient (eg. Vitamin B-12) delivery via ID and SC routes in-vivo. While the bioavailability for the SC route is found to be slightly higher compared to the ID route (99% vs. 96%), the T max for both are almost identical. Thus, ID delivery of Vitamin B-12 using a microneedle injection could be a viable and minimally invasive alternative to existing parenteral options.

The P2X7 receptor (P2X7R) is an adenosine triphosphate-gated ion channel that is predominantly expressed on microglial cells in the central nervous system. We report the clinical qualification of P2X7-specific PET ligand F-18-JNJ-64413739 in healthy volunteers, including dosimetry, kinetic modeling, test-retest variability, and blocking by the P2X7 antagonist JNJ-54175446. Methods: Whole-body dosimetry was performed in 3 healthy male subjects by consecutive whole-body PET/CT scanning, estimation of the normalized cumulated activity, and calculation of the effective dose using OLINDA (v1.1). Next, 5 healthy male subjects underwent a 120-min dynamic F-18-JNJ-64413739 PET/MRI scan with arterial blood sampling to determine the appropriate kinetic model. For this purpose, 1- and 2-tissue compartment models and Logan graphic analysis (LGA) were evaluated for estimating regional volumes of distribution (VT). PET/MRI scanning was repeated in 4 of these subjects to evaluate medium-term test-retest variability (interscan interval, 26-97 d). For the single-dose occupancy study, 8 healthy male subjects underwent baseline and postdose F-18-JNJ-64413739 PET/MRI scans 46 h after the administration of a single oral dose of JNJ-54175446 (dose range, 5-300 mg). P2X7 occupancies were estimated using a Lassen plot and regional baseline and postdose VT. Results: The average (mean +/- SD) effective dose was 22.0 +/- 1.0 mu Sv/MBq. The 2-tissue compartment model was the most appropriate kinetic model, with LGA showing very similar results. Regional 2-tissue compartment model VT values were about 3 and were rather homogeneous across all brain regions, with slightly higher estimates for the thalamus, striatum, and brain stem. Between-subject VT variability was relatively high, with cortical VT showing an approximate 3-fold range across subjects. As for time stability, the acquisition time could be reduced to 90 min. The average regional test-retest variability values were 10.7% +/- 2.2% for 2-tissue compartment model VT and 11.9% +/- 2.2% for LGA VT. P2X7 occupancy approached saturation for single doses of JNJ-54175446 higher than 50 mg, and no reference region could be identified. Conclusion: F-18-JNJ-64413739 is a suitable PET ligand for the quantification of P2X7R expression in the human brain. It can be used to provide insight into P2X7R expression in health and disease, to evaluate target engagement by P2X7 antagonists, and to guide dose selection.