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Aim: The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) provides an innovation leap in the use of fertilized chicken eggs (in ovo model) in preclinical imaging as PET/MRI enables the investigation of the chick embryonal organ-specific distribution of PET-tracers. However, hybrid PET/MRI inheres technical challenges in quantitative in ovo PET such as attenuation correction (AC) for the object as well as for additional hardware parts present in the PET field-of-view, which potentially contribute to quantification biases in the PET images if not accounted for. This study aimed to investigate the influence of the different sources of attenuation on in ovo PET/MRI and assess the accuracy of MR-based AC for in ovo experiments. Method: An in-house made chicken egg phantom was used to investigate the magnitude of self-attenuation and the influence of the MRI hardware on the PET signal. The phantom was placed in a preclinical PET/MRI system and PET acquisitions were performed without, and after subsequently adding the different hardware parts to the setup. Reconstructions were performed without any AC for the different setups and with subsequently incorporating the hardware parts into the AC. In addition, in ovo imaging was performed using [18F]FDG and [68Ga]Ga-Pentixafor, and PET data was reconstructed with the different AC combinations. Quantitative accuracy was assessed for the phantom and the in ovo measurements. Results: In general, not accounting for the self-attenuation of the egg and the hardware parts caused an underestimation of the PET signal of around 49% within the egg. Accounting for all sources of attenuation allowed a proper quantification with global offsets of 2% from the true activity. Quantification based on % injected dose per cc (%ID/cc) was similar for the in ovo measurements, regardless of whether hardware parts were included in AC or not, when the injected activity was extracted from the PET images. However, substantial quantification biases were found when the self-attenuation of the egg was not taken into account. Conclusion: Self-attenuation of the egg and PET signal attenuation within the hardware parts of the MRI substantially influence quantitative accuracy in in ovo measurements. However, when compensating for the self-attenuation of the egg by a respective AC, a reliable quantification using %ID/cc can be performed even if not accounting for the attenuation of the hardware parts. [ABSTRACT FROM AUTHOR]

Background: Poly (ADP-ribose) polymerase (PARP) enzymes are crucial for the repair of DNA single-strand breaks and have become key therapeutic targets in homologous recombination-deficient cancers, including prostate cancer. To enable non-invasive monitoring of PARP-1 expression, several PARP-1-targeting positron emission tomography (PET) tracers have been developed. Here, we aimed to preclinically investigate [carbonyl-11C]DPQ as an alternative PARP-1 PET tracer as it features a strongly distinct chemotype compared to the frontrunners [18F]FluorThanatrace and [18F]PARPi. Results: [carbonyl-11C]DPQ was synthesised in a GE TracerLab FXC2 module, yielding sufficient activity (940 ± 410 MBq), molar activity (53 ± 16 GBq/µmol) and radiochemical purity (> 97%) for subsequent preclinical evaluation. [carbonyl-11C]DPQ showed high stability in formulation, in human plasma, and when incubated with human liver microsomes. In vitro, similar specific uptake was observed in both PC3 prostate cancer cells and CHO-K1 Chinese hamster ovary cells. However, in vivo studies using fertilised chicken eggs (in ovo model) revealed poor and non-displaceable tumour accumulation in PC3-derived xenografts, despite confirmed vascularisation and PARP-1 expression. Rapid uptake was observed in the liver (10 min), with less than 30% of the intact compound remaining in the liver 70 min post-injection. Conclusions: Although [carbonyl-11C]DPQ demonstrated metabolic stability and specific binding in vitro, suboptimal tumour-targeting properties and pronounced liver metabolism were observed in ovo. Therefore, further animal experiments with mammalian models were not indicated. [ABSTRACT FROM AUTHOR]

In vitro therapeutic efficacy studies are commonly conducted in cell monolayers. However, three-dimensional (3D) tumor spheroids are known to better represent in vivo tumors. This study used [177Lu]Lu-PSMA-I&T, an already clinically applied radiopharmaceutical for targeted radionuclide therapy against metastatic castrate-resistant prostate cancer, to demonstrate the differences in the radiobiological response between 2D and 3D cell culture models of the prostate cancer cell lines PC-3 (PSMA negative) and LNCaP (PSMA positive). After assessing the target expression in both models via Western Blot, cell viability, reproductive ability, and growth inhibition were assessed. To investigate the geometric effects on dosimetry for the 2D vs. 3D models, Monte Carlo simulations were performed. Our results showed that PSMA expression in LNCaP spheroids was highly preserved, and target specificity was shown in both models. In monolayers of LNCaP, no short-term (48 h after treatment), but only long-term (14 days after treatment) radiobiological effects were evident, showing decreased viability and reproductive ability with the increasing activity. Further, LNCaP spheroid growth was inhibited with the increasing activity. Overall, treatment efficacy was higher in LNCaP spheroids compared to monolayers, which can be explained by the difference in the resulting dose, among others. [ABSTRACT FROM AUTHOR]

The first-in-class ruthenium-based chemotherapeutic agent BOLD-100 (formerly IT-139, NKP-1339, KP1339) is currently the subject of clinical evaluation for the treatment of gastric, pancreatic, colorectal and bile duct cancer. A radiolabeled version of the compound could present a helpful diagnostic tool. Thus, this study investigated the pharmacokinetics of BOLD-100 in more detail to facilitate the stratification of patients for the therapy. The synthesis of [103Ru]BOLD-100, radiolabeled with carrier added (c.a.) ruthenium-103, was established and the product was characterized by HPLC and UV/Vis spectroscopy. In order to compare the radiolabeled and non-radioactive versions of BOLD-100, both complexes were fully evaluated in vitro and in vivo. The cytotoxicity of the compounds was determined in two colon carcinoma cell lines (HCT116 and CT26) and biodistribution studies were performed in Balb/c mice bearing CT26 allografts over a time period of 72 h post injection (p.i.). We report herein preclinical cytotoxicity and pharmacokinetic data for BOLD-100, which were found to be identical to those of its radiolabeled analog [103Ru]BOLD-100. [ABSTRACT FROM AUTHOR]

Simple Summary: The high mortality rate of colorectal cancer (CRC) is associated with metastasis to the liver, which is related to an increased expression of the C-X-C chemokine receptor 4 (CXCR4). We hereby report the first preclinical evaluation of [68Ga]Ga-Pentixafor, a radiotracer specifically targeting human CXCR4, for CRC imaging. We established the chorioallantoic membrane (CAM)-xenograft model for two different human colon cancer cell lines (HT29 and HCT116) in our facility and conducted a thorough histological characterisation of the obtained xenograft tissues. The subsequently performed simultaneous positron emission tomography and magnetic resonance (µPET/MR) scans demonstrated [68Ga]Ga-Pentixafor uptake in CAM-xenografts and provided novel insights into the radiotracer distribution in the chick embryonal organism. Colorectal cancer is one of the leading causes of cancer-related deaths worldwide. Increased expression of CXCR4 has been associated with liver metastasis, disease progression, and shortened survival. Using in vitro cell binding studies and the in ovo model, we aimed to investigate the potential of [68Ga]Ga-Pentixafor, a radiotracer specifically targeting human CXCR4, for CRC imaging. Specific membrane binding and internalisation of [68Ga]Ga-Pentixafor was shown for HT29 cells, but not for HCT116 cells. Accordingly, [68Ga]Ga-Pentixafor accumulated specifically in CAM-xenografts derived from HT29 cells, but not in HCT116 xenografts, as determined by µPET/MRI. The CAM-grown xenografts were histologically characterised, demonstrating vascularisation of the graft, preserved expression of human CXCR4, and viability of the tumour cells within the grafts. In vivo viability was further confirmed by µPET/MRI measurements using 2-[18F]FDG as a surrogate for glucose metabolism. [68Ga]Ga-Pentixafor µPET/MRI scans showed distinct radiotracer accumulation in the chick embryonal heart, liver, and kidneys, whereas 2-[18F]FDG uptake was predominantly found in the kidneys and joints of the chick embryos. Our findings suggest that [68Ga]Ga-Pentixafor is an interesting novel radiotracer for CRC imaging that is worth further investigation. Moreover, this study further supports the suitability of the CAM-xenograft model for the initial preclinical evaluation of targeted radiopharmaceuticals. [ABSTRACT FROM AUTHOR]

Androgen deprivation therapy (ADT) remains a key approach in the treatment of prostate cancer (PCa). However, PCa inevitably relapses and becomes ADT resistant. Besides androgens, there is evidence that thyroid hormone thyroxine (T4) and its active form 3,5,3′‐triiodo‐L‐thyronine (T3) are involved in the progression of PCa. Epidemiologic evidences show a higher incidence of PCa in men with elevated thyroid hormone levels. The thyroid hormone binding protein μ‐Crystallin (CRYM) mediates intracellular thyroid hormone action by sequestering T3 and blocks its binding to cognate receptors (TRα/TRβ) in target tissues. We show in our study that low CRYM expression levels in PCa patients are associated with early biochemical recurrence and poor prognosis. Moreover, we found a disease stage‐specific expression of CRYM in PCa. CRYM counteracted thyroid and androgen signaling and blocked intracellular choline uptake. CRYM inversely correlated with [18F]fluoromethylcholine (FMC) levels in positron emission tomography/magnetic resonance imaging of PCa patients. Our data suggest CRYM as a novel antagonist of T3‐ and androgen‐mediated signaling in PCa. The role of CRYM could therefore be an essential control mechanism for the prevention of aggressive PCa growth. What's new? Thyroid hormones may play a role in the progression of prostate cancer (PCa). In this study, the authors found that PCa cells had decreased expression of the thyroid‐hormone‐binding protein μ‐Crystallin (CRYM). Lower CRYM was also associated with poor prognosis in men with PCa. In addition, CRYM inhibited thyroid‐hormone and androgen signaling, as well as 18F‐fluoromethylcholine uptake by PCa cells. These results suggest that CRYM may act as a novel antagonist against factors that fuel PCa progression, and therefore thyroid signalling may offer a new therapeutic target in slowing aggressive prostate cancer. [ABSTRACT FROM AUTHOR]

Purpose: The melanin-concentrating hormone receptor 1 (MCHR1) has become an important pharmacological target, since it may be involved in various diseases, such as diabetes, insulin resistance, and obesity. Hence, a suitable positron emission tomography radiotracer for the in vivo assessment of the MCHR1 pharmacology is imperative. The current paper contrasts the extensive in vitro, in vivo, and ex vivo assessments of the radiotracers [18F]FE@SNAP and [11C]SNAP-7941 and provides comprehensive information about their biological and physicochemical properties. Furthermore, it examines their suitability for first-in-man imaging studies.Procedures: Kinetic real-time cell-binding studies with [18F]FE@SNAP and [11C]SNAP-7941 were conducted on adherent Chines hamster ovary (CHO-K1) cells stably expressing the human MCHR1 and MCHR2. Small animal imaging studies on mice and rats were performed under displacement and baseline conditions, as well as after pretreatment with the P-glycoprotein/breast cancer resistant protein inhibitor tariquidar. After the imaging studies, detailed analyses of the ex vivo biodistribution were performed. Ex vivo metabolism was determined in rat blood and brain and analyzed at various time points using a quantitative radio-HPLC assay.Results: [11C]SNAP-7941 demonstrates high uptake on CHO-K1-hMCHR1 cells, whereas no uptake was detected for the CHO-K1-hMCHR2 cells. In contrast, [18F]FE@SNAP evinced binding to CHO-K1-hMCHR1 and CHO-K1-hMCHR2 cells. Imaging studies with [18F]FE@SNAP and [11C]SNAP-7941 showed an increased brain uptake after tariquidar pretreatment in mice, as well as in rats, and exhibited a significant difference between the time-activity curves of the baseline and blocking groups. Biodistribution of both tracers demonstrated a decreased uptake after displacement. [11C]SNAP-7941 revealed a high metabolic stability in rats, whereas [18F]FE@SNAP was rapidly metabolized.Conclusions: Both radiotracers demonstrate appropriate imaging properties for the MCHR1. However, the pronounced metabolic stability as well as superior selectivity and affinity of [11C]SNAP-7941 underlines the decisive superiority over [18F]FE@SNAP. [ABSTRACT FROM AUTHOR]

The glucose derivative 2-[18F]fluoro-2-deoxy-D-glucose (2-[18F]FDG) is still the most used radiotracer for positron emission tomography, as it visualizes glucose utilization and energy demand. In general, 2-[18F]FDG is said to be trapped intracellularly as 2-[18F]FDG-6-phosphate, which cannot be further metabolized. However, increasingly, this dogma is being questioned because of publications showing metabolism beyond 2-[18F]FDG-6-phosphate and even postulating 2-[18F]FDG imaging to depend on the enzyme hexose-6-phosphate dehydrogenase in the endoplasmic reticulum. Therefore, we aimed to study 2-[18F]FDG metabolism in the human cancer cell lines HT1080, HT29 and Huh7 applying HPLC. We then compared 2-[18F]FDG metabolism with intracellular tracer accumulation, efflux and the cells' metabolic state and used a graphical Gaussian model to visualize metabolic patterns. The extent of 2-[18F]FDG metabolism varied considerably, dependent on the cell line, and was significantly enhanced by glucose withdrawal. However, the metabolic pattern was quite conserved. The most important radiometabolites beyond 2-[18F]FDG-6-phosphate were 2-[18F]FDMannose-6-phosphate, 2-[18F]FDG-1,6-bisphosphate and 2-[18F]FD-phosphogluconolactone. Enhanced radiometabolite formation under glucose reduction was accompanied by reduced efflux and mirrored the cells' metabolic switch as assessed via extracellular lactate levels. We conclude that there can be considerable metabolism beyond 2-[18F]FDG-6-phosphate in cancer cell lines and a comprehensive understanding of 2-[18F]FDG metabolism might help to improve cancer research and tumor diagnosis. [ABSTRACT FROM AUTHOR]

Background: Diffuse hemispheric glioma, H3G34R/V-mutant (DHG-H3G34) is characterized by poor prognosis and lack of effective treatment options. DHG-H3G34R further harbor deactivation of Alpha-Thalassemia/Mental Retardation Syndrome X-linked protein (ATRX; DHG-H3G34R_ATRX) suggesting a unique interaction of these two oncogenic alterations. In this study, we dissect their cell biological interplay, investigate the impact on telomere stabilization and, consequently, validate a targeted therapy approach., Methods: We characterized patient-derived primary pediatric high-grade glioma (pHGG) models for telomere-maintenance mechanisms, DNA damage stress (including protein expression, pH2AX/Rad51 foci, cell-cycle arrest) and their sensitivity towards poly-ADP polymerase inhibitor (PARPi) combinations. Human induced pluripotent stem cells (iPSCs) were used for modelling the disease. The anticancer activity of PARPi combinations in vivo was studied in Chorioallantoic Membrane (CAM) and orthotopic in vivo experiments. Finally, we treated a DHG-H3G34R_ATRX patient with a PARPi combination therapy., Results: We elaborate that alternative lengthening of telomeres (ALT) is a key characteristic of DHG-H3G34R_ATRX. A dominant cooperative effect between H3G34R and ATRX loss in ALT activation also became apparent in iPSCs, which endogenously exert telomerase activity. In both, patient-derived DHG-H3G34R_ATRX models and H3G34R+/ATRX- iPSCs, the ALT phenotype was associated with increased basal DNA damage stress, mediating synergistic susceptibility towards PARPi (talazoparib, niraparib) combinations with topoisomerase-I inhibitors (topotecan, irinotecan). In a first-of-its-kind case, treatment of a DHG-H3G34R_ATRX patient with the brain-penetrant PARP inhibitor niraparib and topotecan resulted in a significant tumor reduction., Conclusion: Our preclinical and clinical data strongly support the further development of PARPis together with DNA damage stress-inducing treatment regimens for DHG-H3G34R_ATRX., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Neuro-Oncology.)