Development and In Vivo Evaluation of Small-Molecule Ligands for Positron Emission Tomography of Immune Checkpoint Modulation Targeting Programmed Cell Death 1 Ligand 1.

A substantial portion of patients do not benefit from programmed cell death protein 1/programmed cell death 1 ligand 1 (PD-1/PD-L1) checkpoint inhibition therapies, necessitating a deeper understanding of predictive biomarkers. Immunohistochemistry (IHC) has played a pivotal role in assessing PD-L1 expression, but small-molecule positron emission tomography (PET) tracers could offer a promising avenue to address IHC-associated limitations, i.e., invasiveness and PD-L1 expression heterogeneity. PET tracers would allow for improved quantification of PD-L1 through noninvasive whole-body imaging, thereby enhancing patient stratification. Here, a large series of PD-L1 targeting small molecules were synthesized, leveraging advantageous substructures to achieve exceptionally low nanomolar affinities. Compound 5c emerged as a promising candidate (IC50 = 10.2 nM) and underwent successful carbon-11 radiolabeling. However, a lack of in vivo tracer uptake in xenografts and notable accumulation in excretory organs was observed, underscoring the challenges encountered in small-molecule PD-L1 PET tracer development. The findings, including structure-activity relationships and in vivo biodistribution data, stand to illuminate the path forward for refining small-molecule PD-L1 PET tracers.

Intramolecular Friedel-Crafts Acylation of [11C]Isocyanates Enabling the Radiolabeling of [carbonyl-11C]DPQ.

α,ß-aromatic lactams are highly abundant in biologically active molecules, yet so far they cannot be radiolabeled with short-lived (t1/2=20.3 min), ß+-decaying carbon-11, which has prevented their application as positron emission tomography tracers. Herein, we developed, optimized, and applied a widely applicable, one-pot, quick, robust and automatable radiolabeling method for α,ß-aromatic lactams starting from [11C]CO2 using the reagent POCl3⋅AlCl3. This method proceeds via intramolecular Friedel-Crafts acylation of in situ formed [11C]isocyanates and shows a broad substrate scope for the formation of five- and six-membered rings. We implemented our developed labeling method for the radiosynthesis of the potential PARP1 PET tracer [carbonyl-11C]DPQ in a clinical radiotracer production facility following the standards of the European Pharmacopoeia.

Microplastics role in cell migration and distribution during cancer cell division.

Amidst the global plastic pollution crisis, the gastrointestinal tract serves as the primary entry point for daily exposure to micro- and nanoplastics. We investigated the complex dynamics between polystyrene micro- and nanoplastics (PS-MNPs) and four distinct human colorectal cancer cell lines (HT29, HCT116, SW480, and SW620). Our findings revealed a significant size- and concentration dependent uptake of 0.25, 1, and 10 µm PS-MNPs across all cell lines, with HCT116 cells exhibiting the highest uptake rates. During cell division, particles were distributed between mother and daughter cells. Interestingly, we observed no signs of elimination from the cells. Short-term exposure to 0.25 µm particles significantly amplified cell migration, potentially leading to pro-metastatic effects. Particles demonstrated high persistence in 2D and 3D cultures, and accumulation in non-proliferating parts of spheroids, without interfering with cell proliferation or division. Our study unveils the disturbing fact of the persistence and bioaccumulation of MNPs in colorectal cancer cell lines, key toxicological traits under REACH (Regulation concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals). Our observations underscore the potential of MNPs as hidden catalysts for tumor progression, particularly through enhancing cell migration and possibly fueling metastasis - a finding that sheds light on a significant and previously underexplored area of concern.

Metabolic tumor volume and sites of organ involvement predict outcome in NSCLC immune-checkpoint inhibitor therapy.

PURPOSE: The purpose of this study was to assess the ability of pretreatment PET parameters and peripheral blood biomarkers to predict progression-free survival (PFS) and overall survival (OS) in NSCLC patients treated with ICIT. METHODS: We prospectively included 87 patients in this study who underwent pre-treatment [18F]-FDG PET/CT. Organ-specific and total metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were measured using a semiautomatic software. Sites of organ involvement (SOI) were assessed by PET/CT. The log-rank test and Cox-regression analysis were used to assess associations between clinical, laboratory, and imaging parameters with PFS and OS. Time dependent ROC were calculated and model performance was evaluated in terms of its clinical utility. RESULTS: MTV increased with the number of SOI and was correlated with neutrophil and lymphocyte cell count (Spearman's rho = 0.27 or 0.32; p =.02 or 0.003; respectively). Even after adjustment for known risk factors, such as PD-1 expression and neutrophil cell count, the MTV and the number of SOI were independent risk factors for progression (per 100 cm3; adjusted hazard ratio [aHR]: 1.13; 95% confidence interval [95%CI]: 1.01-1.28; p =.04; single SOI vs. ≥ 4 SOI: aHR: 2.26, 95%CI: 1.04-4.94; p =.04). MTV and the number of SOI were independent risk factors for overall survival (per 100 cm3 aHR: 1.11, 95%CI: 1.01-1.23; p =.03; single SOI vs. ≥ 4 SOI: aHR: 4.54, 95%CI: 1.64-12.58; p =.04). The combination of MTV and the number of SOI improved the risk stratification for PFS and OS (log-rank test p <.001; C-index: 0.64 and 0.67). CONCLUSION: The MTV and the number of SOI are simple imaging markers that provide complementary information to facilitate risk stratification in NSCLC patients scheduled for ICIT.

Quality Assurance Investigations and Impurity Characterization during Upscaling of [177Lu]Lu-PSMAI&T.

[177Lu]Lu-PSMAI&T is widely used for the radioligand therapy of metastatic castration-resistant prostate cancer (mCRPC). Since this kind of therapy has gained a large momentum in recent years, an upscaled production process yielding multiple patient doses in one batch has been developed. During upscaling, the established production method as well as the HPLC quality control were challenged. A major finding was a correlation between the specific activity and the formation of a pre-peak, presumably caused by radiolysis. Hence, nonradioactive reference standards were irradiated with an X-ray source and the formed pre-peak was subsequently identified as a deiodination product by UPLC-MS. To confirm the occurrence of the same deiodinated side product in the routine batch, a customized deiodinated precursor was radiolabeled and analyzed with the same HPLC setup, revealing an identical retention time to the pre-peak in the formerly synthesized routine batches. Additionally, further cyclization products of [177Lu]Lu-PSMAI&T were identified as major contributors to radiochemical impurities. The comparison of two HPLC methods showed the likelihood of the overestimation of the radiochemical purity during the synthesis of [177Lu]Lu-PSMAI&T. Finally, a prospective cost reduction through an optimization of the production process was shown.

On the Road towards Small-Molecule Programmed Cell Death 1 Ligand 1 Positron Emission Tomography Tracers: A Ligand-Based Drug Design Approach.

PD-1/PD-L1 immune checkpoint blockade for cancer therapy showed promising results in clinical studies. Further endeavors are required to enhance patient stratification, as, at present, only a small portion of patients with PD-L1-positive tumors (as determined by PD-L1 targeted immunohistochemistry; IHC) benefit from anti-PD-1/PD-L1 immunotherapy. This can be explained by the heterogeneity of tumor lesions and the intrinsic limitation of multiple biopsies. Consequently, non-invasive in vivo quantification of PD-L1 on tumors and metastases throughout the entire body using positron emission tomography (PET) imaging holds the potential to augment patient stratification. Within the scope of this work, six new small molecules were synthesized by following a ligand-based drug design approach supported by computational docking utilizing lead structures based on the (2-methyl-[1,1'-biphenyl]-3-yl)methanol scaffold and evaluated in vitro for potential future use as PD-L1 PET tracers. The results demonstrated binding affinities in the nanomolar to micromolar range for lead structures and newly prepared molecules, respectively. Carbon-11 labeling was successfully and selectively established and optimized with very good radiochemical conversions of up to 57%. The obtained insights into the significance of polar intermolecular interactions, along with the successful radiosyntheses, could contribute substantially to the future development of small-molecule PD-L1 PET tracers.

The QuADRANT study: Current status and recommendations for improving uptake and implementation of clinical audit of medical radiological procedures in Europe. The radiotherapy perspective.

BACKGROUND: QuADRANT was a research project funded by the European Commission to evaluate clinical audit uptake and implementation across Europe, with an emphasis on clinical audit as mandated within the BSSD (Basic Safety Standards Directive). AIM: Focusing on the QuADRANT objectives - to obtain an overview of European clinical audit activity; identify good practices, resources, barriers and challenges; provide guidance and recommendations going forwards; identify the potential for European Union action on quality and safety focusing on the field of radiotherapy. RESULTS: A pan-European survey, expert interviews and a literature review conducted within the framework of the QuADRANT project indicated that developments in national clinical audit infrastructure are required. While in radiotherapy, there is a strong tradition and high level of experience of dosimetry audits and well-established practice through the IAEA's QUATRO audits, few countries have a well-established comprehensive clinical audit programme or international/national initiatives on tumour specific clinical audits. Even if sparse, the experience from countries with established system of quality audits can be used as role-models for national professional societies to promote clinical audit implementation. However, resource allocation and national prioritisation of clinical audit are needed in many countries. National and international societies should take the initiative to promote and facilitate training and resources (guidelines, experts, courses) for clinical audits. Enablers used to enhance clinical audit participation are not widely employed. Development of hospital accreditation programmes can facilitate clinical audit uptake. An active and formalised role for patients in clinical audit practice and policy development is recommended. Because there is a persisting variation in European awareness of BSSD clinical audit requirements, work is needed to improve dissemination of information on the legislative requirements relating to clinical audit in the BSSD and in relation to inspection processes. The aim is to ensure these include clinical audit and that they encompass all clinics and specialties involved in medical applications using ionising radiation. CONCLUSION: QuADRANT provided an overarching view of clinical audit practice in Europe, with all its related aspects. Unfortunately, it showed that the awareness of the BSSD requirements for clinical audit are highly variable. Therefore, there is an urgent need to dedicate efforts towards ensuring that regulatory inspections also incorporate an assessment of clinical audit program(s), affecting all aspects of clinical work and specialties involved in patient exposure to ionising radiation.

Task-evoked metabolic demands of the posteromedial default mode network are shaped by dorsal attention and frontoparietal control networks.

External tasks evoke characteristic fMRI BOLD signal deactivations in the default mode network (DMN). However, for the corresponding metabolic glucose demands both decreases and increases have been reported. To resolve this discrepancy, functional PET/MRI data from 50 healthy subjects performing Tetris were combined with previously published data sets of working memory, visual and motor stimulation. We show that the glucose metabolism of the posteromedial DMN is dependent on the metabolic demands of the correspondingly engaged task-positive networks. Specifically, the dorsal attention and frontoparietal network shape the glucose metabolism of the posteromedial DMN in opposing directions. While tasks that mainly require an external focus of attention lead to a consistent downregulation of both metabolism and the BOLD signal in the posteromedial DMN, cognitive control during working memory requires a metabolically expensive BOLD suppression. This indicates that two types of BOLD deactivations with different oxygen-to-glucose index may occur in this region. We further speculate that consistent downregulation of the two signals is mediated by decreased glutamate signaling, while divergence may be subject to active GABAergic inhibition. The results demonstrate that the DMN relates to cognitive processing in a flexible manner and does not always act as a cohesive task-negative network in isolation.

QuADRANT: a study on uptake and implementation of clinical audit of medical radiological procedures in Europe-expert recommendations for improvement, endorsed by the ESR.

BACKGROUND: QuADRANT was a study funded by the European Commission to evaluate clinical audit uptake and implementation across Europe, with an emphasis on clinical audit as mandated within the BSSD (Basic Safety Standards Directive). AIMS: QuADRANT objectives-obtain an overview of European clinical audit activity; identify good practices and resources, barriers and challenges; provide guidance and recommendations going forwards; identify the potential for European Union action on quality and safety in the three core project specialties, radiology, radiotherapy and nuclear medicine. FINDINGS AND RECOMMENDATIONS: QuADRANT identified that developments in national clinical audit infrastructure are required. National professional societies can be pivotal in improving clinical audit implementation, but resource allocation and national prioritisation of clinical audit are needed in many countries. Lack of staff time and expertise are also barriers. Enablers to enhance clinical audit participation are not widely employed. Development of hospital accreditation programmes can facilitate clinical audit uptake. An active and formalised role for patients in clinical audit practice and policy development is recommended. There is persisting variation in European awareness of BSSD clinical audit requirements. Work is needed to improve dissemination of information on the legislative requirements relating to clinical audit in the BSSD and in relation to inspection processes to ensure these include clinical audit and that they encompass all clinics and specialties involved in medical applications using ionising radiation. CONCLUSION: QuADRANT provides an important step towards enhancing clinical audit uptake and implementation across Europe and improving patient safety and outcomes.

To Waste or Not to Waste: Questioning Potential Health Risks of Micro- and Nanoplastics with a Focus on Their Ingestion and Potential Carcinogenicity.

Micro- and nanoplastics (MNPs) are recognized as emerging contaminants, especially in food, with unknown health significance. MNPs passing through the gastrointestinal tract have been brought in context with disruption of the gut microbiome. Several molecular mechanisms have been described to facilitate tissue uptake of MNPs, which then are involved in local inflammatory and immune responses. Furthermore, MNPs can act as potential transporters ("vectors") of contaminants and as chemosensitizers for toxic substances ("Trojan Horse effect"). In this review, we summarize current multidisciplinary knowledge of ingested MNPs and their potential adverse health effects. We discuss new insights into analytical and molecular modeling tools to help us better understand the local deposition and uptake of MNPs that might drive carcinogenic signaling. We present bioethical insights to basically re-consider the "culture of consumerism." Finally, we map out prominent research questions in accordance with the Sustainable Development Goals of the United Nations.

Effects of bilateral sequential theta-burst stimulation on 5-HT1A receptors in the dorsolateral prefrontal cortex in treatment-resistant depression: a proof-of-concept trial.

Theta-burst stimulation (TBS) represents a brain stimulation technique effective for treatment-resistant depression (TRD) as underlined by meta-analyses. While the methodology undergoes constant refinement, bilateral stimulation of the dorsolateral prefrontal cortex (DLPFC) appears promising to restore left DLPFC hypoactivity and right hyperactivity found in depression. The post-synaptic inhibitory serotonin-1A (5-HT1A) receptor, also occurring in the DLPFC, might be involved in this mechanism of action. To test this hypothesis, we performed PET-imaging using the tracer [carbonyl-11C]WAY-100635 including arterial blood sampling before and after a three-week treatment with TBS in 11 TRD patients compared to sham stimulation (n = 8 and n = 3, respectively). Treatment groups were randomly assigned, and TBS protocol consisted of excitatory intermittent TBS to the left and inhibitory continuous TBS to the right DLPFC. A linear mixed model including group, hemisphere, time, and Hamilton Rating Scale for Depression (HAMD) score revealed a 3-way interaction effect of group, time, and HAMD on specific distribution volume (VS) of 5-HT1A receptor. While post-hoc comparisons showed no significant changes of 5-HT1A receptor VS in either group, higher 5-HT1A receptor VS after treatment correlated with greater difference in HAMD (r = -0.62). The results of this proof-of-concept trial hint towards potential effects of TBS on the distribution of the 5-HT1A receptor. Due to the small sample size, all results must, however, be regarded with caution.

Effect of MAOA DNA Methylation on Human in Vivo Protein Expression Measured by [11C]harmine Positron Emission Tomography.

BACKGROUND: Epigenetic modifications like DNA methylation are understood as an intermediary between environmental factors and neurobiology. Cerebral monoamine oxidase A (MAO-A) levels are altered in depression, as are DNA methylation levels within the MAOA gene, particularly in the promoter/exon I/intron I region. An effect of MAOA methylation on peripheral protein expression was shown, but the extent to which methylation affects brain MAO-A levels is not fully understood. METHODS: Here, the influence of MAOA promoter/exon I/intron I region DNA methylation on global MAO-A distribution volume (VT), an index of MAO-A density, was assessed via [11C]harmine positron emission tomography in 22 patients (14 females) suffering from seasonal affective disorder and 30 healthy controls (17 females). RESULTS: No significant influence of MAOA DNA methylation on global MAO-A VT was found, despite correction for health status, sex, season, and MAOA variable number of tandem repeat genotype. However, season affected average methylation in women, with higher levels in spring and summer (Puncorr = .03). We thus did not find evidence for an effect of MAOA DNA methylation on brain MAO-A VT. CONCLUSIONS: In contrast to a previous study demonstrating an effect of methylation of a MAOA promoter region located further 5' on brain MAO-A, MAOA methylation of the region assessed here appears to affect brain protein levels to a limited extent at most. The observed effect of season on methylation levels is in accordance with extensive evidence for seasonal effects within the serotonergic system. CLINICALTRIALS.GOV IDENTIFIER: NCT02582398 (https://clinicaltrials.gov/ct2/show/NCT02582398).

ABCB1 variants and sex affect serotonin transporter occupancy in the brain.

Strategies to personalize psychopharmacological treatment promise to improve efficacy and tolerability. We measured serotonin transporter occupancy immediately after infusion of the widely prescribed P-glycoprotein substrate citalopram and assessed to what extent variants of the ABCB1 gene affect drug target engagement in the brain in vivo. A total of 79 participants (39 female) including 31 patients with major depression and 48 healthy volunteers underwent two PET/MRI scans with the tracer [11C]DASB and placebo-controlled infusion of citalopram (8 mg) in a cross-over design. We tested the effect of six ABCB1 single nucleotide polymorphisms and found lower SERT occupancy in ABCB1 rs2235015 minor allele carriers (n = 26, MAF = 0.18) compared to major allele homozygotes (t73 = 2.73, pFWE < 0.05) as well as in men compared to women (t73 = 3.33, pFWE < 0.05). These effects were robust to correction for citalopram plasma concentration, age and diagnosis. From occupancy we derived the ratio of occupied to unoccupied SERT, because in theory this measure is equal to the product of drug affinity and concentration at target sites. A model combining genotype with basic clinical variables, predicted that, at the same dosage, occupied to unoccupied SERT ratio was -14.48 ± 5.38% lower in rs2235015 minor allele carriers, +19.10 ± 6.95% higher in women, -4.83 ± 2.70% lower per 10 kg bodyweight, and -2.68 ± 3.07% lower per 10 years of age. Our results support the exploration of clinical algorithms with adjustment of initial citalopram dosing and highlight the potential of imaging-genetics for precision pharmacotherapy in psychiatry.

Biodistribution and dosimetry of the GluN2B-specific NMDA receptor PET radioligand (R)-[11C]Me-NB1.

BACKGROUND: The NMDA receptor (NMDAR) plays a key role in the central nervous system, e.g., for synaptic transmission. While synaptic NMDARs are thought to have protective characteristics, activation of extrasynaptic NMDARs might trigger excitotoxic processes linked to neuropsychiatric disorders. Since extrasynaptic NMDARs are typically GluN2B-enriched, the subunit is an interesting target for drug development and treatment monitoring. Recently, the novel GluN2B-specific PET radioligand (R)-[11C]Me-NB1 was investigated in rodents and for the first time successfully translated to humans. To assess whether (R)-[11C]Me-NB1 is a valuable radioligand for (repeated) clinical applications, we evaluated its safety, biodistribution and dosimetry. METHODS: Four healthy subjects (two females, two males) underwent one whole-body PET/MR measurement lasting for more than 120 min. The GluN2B-specific radioligand (R)-[11C]Me-NB1 was administered simultaneously with the PET start. Subjects were measured in nine passes and six bed positions from head to mid-thigh. Regions of interest was anatomically defined for the brain, thyroid, lungs, heart wall, spleen, stomach contents, pancreas, liver, kidneys, bone marrow and urinary bladder contents, using both PET and MR images. Time-integrated activity coefficients were estimated to calculate organ equivalent dose coefficients and the effective dose coefficient. Additionally, standardized uptake values (SUV) were computed to visualize the biodistribution. RESULTS: Administration of the radioligand was safe without adverse events. The organs with the highest uptake were the urinary bladder, spleen and pancreas. Organ equivalent dose coefficients were higher in female in almost all organs, except for the urinary bladder of male. The effective dose coefficient was 6.0 µSv/MBq. CONCLUSION: The GluN2B-specific radioligand (R)-[11C]Me-NB1 was well-tolerated without reported side effects. Effective dose was estimated to 1.8 mSv when using 300 MBq of presented radioligand. The critical organ was the urinary bladder. Due to the low effective dose coefficient of this radioligand, longitudinal studies for drug development and treatment monitoring of neuropsychiatric disorders including neurodegenerative diseases are possible. Trial registration Registered on 11th of June 2019 at https://www.basg.gv.at (EudraCT: 2018-002933-39).

Autoradiography on deparaffinized tissue sections - A feasibility study with 68Ga-labeled PET-tracers.

Tissue available for retrospective research questions is often already paraffin-embedded for better preservation. However, in vitro autoradiography (AURA) is normally performed on cryopreserved tissue sections. We hypothesized a) that it would also be feasible with deparaffinized tissue sections, enabling the use of human paraffin-embedded tissue for in vitro AURA and b) that the results would be comparable to those obtained with corresponding cryosections. For that purpose, the clinically relevant oncological targets CXCR4, SSTR and PSMA were evaluated. In vitro AURA on deparaffinized tissue sections was feasible, but only with the two receptor ligands [68Ga]Ga-PentixaFor and [68Ga]Ga-DOTANOC. [68Ga]Ga-PSMA-11 did not show any binding on deparaffinized tissue sections, suggesting that native tissue is required for an interaction between this inhibitor and the enzyme.