Imaging Memory T-Cells Stratifies Response to Adjuvant Metformin Combined with αPD-1 Therapy.

The low response rates associated with immune checkpoint inhibitor (ICI) use has led to a surge in research investigating adjuvant combination strategies in an attempt to enhance efficacy. Repurposing existing drugs as adjuvants accelerates the pace of cancer immune therapy research; however, many combinations exacerbate the immunogenic response elicited by ICIs and can lead to adverse immune-related events. Metformin, a widely used type 2 diabetes drug is an ideal candidate to repurpose as it has a good safety profile and studies suggest that metformin can modulate the tumour microenvironment, promoting a favourable environment for T cell activation but has no direct action on T cell activation on its own. In the current study we used PET imaging with [18F]AlF-NOTA-KCNA3P, a radiopharmaceutical specifically targeting KV1.3 the potassium channel over-expressed on active effector memory T-cells, to determine whether combining PD1 with metformin leads to an enhanced immunological memory response in a preclinical colorectal cancer model. Flow cytometry was used to assess which immune cell populations infiltrate the tumours in response to the treatment combination. Imaging with [18F]AlF-NOTA-KCNA3P demonstrated that adjuvant metformin significantly improved anti-PD1 efficacy and led to a robust anti-tumour immunological memory response in a syngeneic colon cancer model through changes in tumour infiltrating effector memory T-cells.

Fluorine-18 Labeling of Difluoromethyl and Trifluoromethyl Groups via Monoselective C-F Bond Activation.

We report a general method for the labeling of both CF3 and CF2 H groups in a broad range of chemical settings (aryl, oxide, sulfide). The method utilizes frustrated Lewis pair mediated selective C-F activation to formally substitute fluorine-19 with fluorine-18 in a two-step defluorination/radiofluorination process, and as such can utilize the target compounds as starting materials. The radiotracer precursors can be isolated as stable salts prior to radiofluorination. The method delivers good radiochemical yields and molar activities (up to 35.2±6.5 % non-decay corrected isolated activity yields and 12.0±1.7 GBq µmol-1 molar activities) and is shown to be applicable to biologically relevant compounds. The ability to utilize the target compound as the starting material and the synthetic simplicity of the method coupled with the ever-increasing use of CF3 and CF2 H groups in pharmaceuticals makes this method attractive for drug and radiotracer development.

PET Imaging of Translocator Protein as a Marker of Malaria-Associated Lung Inflammation.

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is a severe complication of malaria that occurs despite effective antimalarial treatment. Currently, noninvasive imaging procedures such as chest X-rays are used to assess edema in established MA-ARDS, but earlier detection methods are needed to reduce morbidity and mortality. The early stages of MA-ARDS are characterized by the infiltration of leukocytes, in particular monocytes/macrophages; thus, monitoring of immune infiltrates may provide a useful indicator of early pathology. In this study, Plasmodium berghei ANKA-infected C57BL/6 mice, a rodent model of MA-ARDS, were longitudinally imaged using the 18-kDa translocator protein (TSPO) imaging agent [18F]FEPPA as a marker of macrophage accumulation during the development of pathology and in response to combined artesunate and chloroquine diphosphate (ART+CQ) therapy. [18F]FEPPA uptake was compared to blood parasitemia levels and to levels of pulmonary immune cell infiltrates by using flow cytometry. Infected animals showed rapid increases in lung retention of [18F]FEPPA, correlating well with increases in blood parasitemia and pulmonary accumulation of interstitial inflammatory macrophages and major histocompatibility complex class II (MHC-II)-positive alveolar macrophages. Treatment with ART+CQ abrogated this increase in parasitemia and significantly reduced both lung uptake of [18F]FEPPA and levels of macrophage infiltrates. We conclude that retention of [18F]FEPPA in the lungs is well correlated with changes in blood parasitemia and levels of lung-associated macrophages during disease progression and in response to ART+CQ therapy. With further development, TSPO biomarkers may have the potential to accurately assess the early onset of MA-ARDS.

Granzyme B PET Imaging Stratifies Immune Checkpoint Inhibitor Response in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is a notoriously difficult cancer to treat. The recent development of immune checkpoint inhibitors has revolutionised HCC therapy; however, successful response is only observed in a small percentage of patients. Biomarkers typically used to predict treatment response in other tumour types are ineffective in HCC, which arises in an immune-suppressive environment. However, imaging markers that measure changes in tumour infiltrating immune cells may supply information that can be used to determine which patients are responding to therapy posttreatment. We have evaluated [18F]AlF-mNOTA-GZP, a radiolabeled peptide targeting granzyme B, to stratify response to ICIs in a HEPA 1-tumours, a syngeneic model of HCC. Posttherapy, in vivo tumour retention of [18F]AlF-mNOTA-GZP was correlated to changes in tumour volume and tumour-infiltrating immune cells. [18F]AlF-mNOTA-GZP successfully stratified response to immune checkpoint inhibition in the syngeneic HEPA 1-6 model. FACS indicated significant changes in the immune environment including a decrease in immune suppressive CD4+ T regulatory cells and increases in tumour-associated GZB+ NK+ cells, which correlated well with tumour radiopharmaceutical uptake. While the immune response to ICI therapies differs in HCC compared to many other cancers, [18F]AlF-mNOTA-GZP retention is able to stratify response to ICI therapy associated with tumour infiltrating GZB+ NK+ cells in this complex tumour microenvironment.

Improved amyloid burden quantification with nonspecific estimates using deep learning.

PURPOSE: Standardized uptake value ratio (SUVr) used to quantify amyloid-ß burden from amyloid-PET scans can be biased by variations in the tracer's nonspecific (NS) binding caused by the presence of cerebrovascular disease (CeVD). In this work, we propose a novel amyloid-PET quantification approach that harnesses the intermodal image translation capability of convolutional networks to remove this undesirable source of variability. METHODS: Paired MR and PET images exhibiting very low specific uptake were selected from a Singaporean amyloid-PET study involving 172 participants with different severities of CeVD. Two convolutional neural networks (CNN), ScaleNet and HighRes3DNet, and one conditional generative adversarial network (cGAN) were trained to map structural MR to NS PET images. NS estimates generated for all subjects using the most promising network were then subtracted from SUVr images to determine specific amyloid load only (SAßL). Associations of SAßL with various cognitive and functional test scores were then computed and compared to results using conventional SUVr. RESULTS: Multimodal ScaleNet outperformed other networks in predicting the NS content in cortical gray matter with a mean relative error below 2%. Compared to SUVr, SAßL showed increased association with cognitive and functional test scores by up to 67%. CONCLUSION: Removing the undesirable NS uptake from the amyloid load measurement is possible using deep learning and substantially improves its accuracy. This novel analysis approach opens a new window of opportunity for improved data modeling in Alzheimer's disease and for other neurodegenerative diseases that utilize PET imaging.

Head-to-head comparison of amplified plasmonic exosome Aß42 platform and single-molecule array immunoassay in a memory clinic cohort.

BACKGROUND AND PURPOSE: Various blood biomarkers reflecting brain amyloid-ß (Aß) load have recently been proposed with promising results. However, to date, no comparative study amongst blood biomarkers has been reported. Our objective was to examine the diagnostic performance and cost effectiveness of three blood biomarkers on the same cohort. METHODS: Using the same cohort (n = 68), the performances of the single-molecule array (Simoa) Aß40, Aß42, Aß42/Aß40 and the amplified plasmonic exosome (APEX) Aß42 blood biomarkers were compared using amyloid positron emission tomography (PET) as the reference standard. The extent to which these blood tests can reduce the recruitment cost of clinical trials was also determined by identifying amyloid positive (Aß+) participants. RESULTS: Compared to Simoa biomarkers, APEX-Aß42 showed significantly higher correlations with amyloid PET retention values and excellent diagnostic performance (sensitivity 100%, specificity 93.3%, area under the curve 0.995). When utilized for clinical trial recruitment, our simulation showed that pre-screening with blood biomarkers followed by a confirmatory amyloid PET imaging would roughly half the cost (56.8% reduction for APEX-Aß42 and 48.6% for Simoa-Aß42/Aß40) compared to the situation where only PET imaging is used. Moreover, with 100% sensitivity, APEX-Aß42 pre-screening does not increase the required number of initial participants. CONCLUSIONS: With its high diagnostic performance, APEX is an ideal candidate for Aß+ subject identification, monitoring and primary care screening, and could efficiently enrich clinical trials with Aß+ participants whilst halving recruitment costs.

Plasma P-tau181 to Aß42 ratio is associated with brain amyloid burden and hippocampal atrophy in an Asian cohort of Alzheimer's disease patients with concomitant cerebrovascular disease.

INTRODUCTION: There is increasing evidence that phosphorylated tau (P-tau181) is a specific biomarker for Alzheimer's disease (AD) pathology, but its potential utility in non-White patient cohorts and patients with concomitant cerebrovascular disease (CeVD) is unknown. METHODS: Single molecule array (Simoa) measurements of plasma P-tau181, total tau, amyloid beta (Aß)40 and Aß42, as well as derived ratios were correlated with neuroimaging modalities indicating brain amyloid (Aß+), hippocampal atrophy, and CeVD in a Singapore-based cohort of non-cognitively impaired (NCI; n = 43), cognitively impaired no dementia (CIND; n = 91), AD (n = 44), and vascular dementia (VaD; n = 22) subjects. RESULTS: P-tau181/Aß42 ratio showed the highest area under the curve (AUC) for Aß+ (AUC = 0.889) and for discriminating between AD Aß+ and VaD Aß- subjects (AUC = 0.903). In addition, P-tau181/Aß42 ratio was associated with hippocampal atrophy. None of the biomarkers was associated with CeVD. DISCUSSION: Plasma P-tau181/Aß42 ratio may be a noninvasive means of identifying AD with elevated brain amyloid in populations with concomitant CeVD.

Improved quantification of amyloid burden and associated biomarker cut-off points: results from the first amyloid Singaporean cohort with overlapping cerebrovascular disease.

PURPOSE: The analysis of the [11C]PiB-PET amyloid images of a unique Asian cohort of 186 participants featuring overlapping vascular diseases raised the question about the validity of current standards for amyloid quantification under abnormal conditions. In this work, we implemented a novel pipeline for improved amyloid PET quantification of this atypical cohort. METHODS: The investigated data correction and amyloid quantification methods included motion correction, standardized uptake value ratio (SUVr) quantification using the parcellated MRI (standard method) and SUVr quantification without MRI. We introduced a novel amyloid analysis method yielding 2 biomarkers: AßL which quantifies the global Aß burden and ns that characterizes the non-specific uptake. Cut-off points were first determined using visual assessment as ground truth and then using unsupervised classification techniques. RESULTS: Subject's motion impacts the accuracy of the measurement outcome but has however a limited effect on the visual rating and cut-off point determination. SUVr computation can be reliably performed for all the subjects without MRI parcellation while, when required, the parcellation failed or was of mediocre quality in 10% of the cases. The novel biomarker AßL showed an association increase of 29.5% with the cognitive tests and increased effect size between positive and negative scans compared with SUVr. ns was found sensitive to cerebral microbleeds, white matter hyperintensity, volume, and age. The cut-off points for SUVr using parcellated MRI, SUVr without parcellation, and AßL were 1.56, 1.39, and 25.5. Finally, k-means produced valid cut-off points without the requirement of visual assessment. CONCLUSION: The optimal processing for the amyloid quantification of this atypical cohort allows the quantification of all the subjects, producing SUVr values and two novel biomarkers: AßL, showing important increased in their association with various cognitive tests, and ns, a parameter sensitive to non-specific retention variations caused by age and cerebrovascular diseases.

Identifying nonsmall-cell lung tumours bearing the T790M EGFR TKI resistance mutation using PET imaging.

Specific mutations significantly affect response to epidermal growth factor tyrosine kinase inhibitor (EGFR-TKI) treatment in lung cancer patients. Identifying patients with these mutations remains a major clinical challenge. EGFR T790M mutation, which conveys resistance to in the present study, [18 F]FEWZ was assessed in vitro to determine efficacy relative to the starting compound and in vivo to measure the biodistribution and specificity of binding to EGFR wild-type, L858R and T790M bearing tumours. [18 F]FEWZ is the first evidence of a radiolabeled third generation anilinopyrimidine-derived tyrosine kinase inhibitor targeting T790M mutation bearing tumours in vivo.

Octreotide Functionalized Nano-Contrast Agent for Targeted Magnetic Resonance Imaging.

Reversible addition-fragmentation chain transfer (RAFT) polymerization has been employed to synthesize branched block copolymer nanoparticles possessing 1,4,7,10-tetraazacyclododecane-N,N,'N,″N,‴-tetraacetic acid (DO3A) macrocycles within their cores and octreotide (somatostatin mimic) cyclic peptides at their periphery. These polymeric nanoparticles have been chelated with Gd3+ and applied as magnetic resonance imaging (MRI) nanocontrast agents. This nanoparticle system has an r1 relaxivity of 8.3 mM-1 s-1, which is 3 times the r1 of commercial gadolinium-based contrast agents (GBCAs). The in vitro targeted binding efficiency of these nanoparticles shows 5 times greater affinity to somatostatin receptor type 2 (SSTR2) with Ki = 77 pM (compared to somatostatin with Ki = 0.385 nM). We have also evaluated the tumor targeting molecular imaging ability of these branched copolymer nanoparticle in vivo using nude/NCr mice bearing AR42J rat pancreatic tumor (SSTR2 positive) and A549 human lung carcinoma tumor (SSTR2 negative) xenografts.

Directed Evolution of a Fluorinase for Improved Fluorination Efficiency with a Non-native Substrate.

Fluorinases offer an environmentally friendly alternative for selective fluorination under mild conditions. However, their diversity is limited in nature and they have yet to be engineered through directed evolution. Herein, we report the directed evolution of the fluorinase FlA1 for improved conversion of the non-native substrate 5'-chloro-5'-deoxyadenosine (5'-ClDA) into 5'-fluoro-5'-deoxyadenosine (5'-FDA). The evolved variants, fah2081 (A279Y) and fah2114 (F213Y, A279L), were successfully applied in the radiosynthesis of 5'-[18 F]FDA, with overall radiochemical conversion (RCC) more than 3-fold higher than wild-type FlA1. Kinetic studies of the two-step reaction revealed that the variants show a significantly improved kcat value in the conversion of 5'-ClDA into S-adenosyl-l-methionine (SAM) but a reduced kcat value in the conversion of SAM into 5'-FDA.

Palladium-meta-terarylphosphine catalyst for the Mizoroki-Heck reaction of (hetero)aryl bromides and functional olefins.

The evolutionary meta-terarylphosphine ligand architecture of Cy*Phine was recently shown to be a key feature that imposed outstanding performance in palladium-catalyzed copper-free Sonogashira applications. Herein, the Pd-Cy*Phine combination has similarly proven to be a powerful catalyst system for the Mizoroki-Heck reaction. Using high-throughput screening (HTS) methodology, DMF and NaHCO3 were rapidly identified as the most effective solvent and base pair for the cross-coupling catalysis of challenging and industrially valuable substrates including highly electron-rich heteroaryl bromides and unactivated olefins. Unprotected functional groups were well tolerated using low catalyst loadings, and the simple protocol produced excellent yields (up to 99%) with unprecedented substrate diversity. The Pd-Cy*Phine system broadly outperformed many state-of-the-art commercial alternatives, which demonstrated its potential as a next-generation cross-coupling catalyst.

2-Bromo-6-[(18) F]fluoropyridine: two-step fluorine-18 radiolabelling via transition metal-mediated chemistry.

Novel radiolabelling methods are important for the development of new tracers for positron emission tomography. Direct nucleophilic fluorination of aromatic rings with [(18) F]fluoride is limited to activated substrates, restricting the application of this approach. Inspired by transition metal-mediated transformations, a fluorine-18 synthon was prepared to supplement the radiolabelling methods available for molecules unsuitable for direct labelling. 2-Bromo-6-[(18) F]fluoropyridine (denoted [(18) F]1) was prepared in high yield, and palladium-mediated cross-coupling reactions were exemplified. High incorporation of fluoride and efficient cross-coupling reactions demonstrate that compound [(18) F]1 holds promise as a new synthon for construction of fluorine-18-labelled molecules via transition metal-mediated reactions.

Arginine-Selective Bioconjugation Reagent for Effective 18F-labeling of Native Proteins.

Protein-based 18F-PET tracers offer new possibilities in early disease detection and personalized medicine. Their development relies heavily on the availability and effectiveness of 18F-prosthetic groups. We prepared and evaluated a novel arginine-selective prosthetic group, 4-[18F]fluorophenylglyoxal ([18F]FPG). [18F]FPG was radiosynthesized by a one-pot, two-step procedure with a non-decay-corrected (n.d.c.) isolated radiochemical yield (RCY) of 41 ± 8% (n = 10). [18F]FPG constitutes a generic tool for 18F-labeling of various proteins, including human serum albumin (HSA), ubiquitin, interleukin-2, and interleukin-4 in ∼30-60% n.d.c. isolated RCYs. [18F]FPG conjugation with arginine residues is highly selective, even in the presence of a large excess of lysine, cysteine, and histidine. [18F]FPG protein conjugates are able to preserve the binding affinity of the native proteins while also demonstrating excellent in vivo stability. The [18F]FPG-HSA conjugate has prolonged blood retention, which can be applied as a potential blood pool PET imaging agent. Thus, [18F]FPG is an arginine-selective bioconjugation reagent that can be effectively used for the development of 18F-labeled protein radiopharmaceuticals.

Exploration of the structure-activity relationship of a novel tetracyclic class of TSPO ligands-potential novel positron emitting tomography imaging agents.

A series of novel TSPO ligands based on the tetracyclic class of translocator protein (TSPO) ligands first described by Okubo et al. was synthesised and evaluated as potential positron emitting tomography (PET) ligands for imaging TPSO in vivo. Fluorine-18 labelling of the molecules was achieved using direct radiolabelling or synthon based labelling approaches. Several of the ligands prepared have promising profiles as potential TSPO PET imaging ligands.

A practical synthesis of [(18) F]FtRGD: an angiogenesis biomarker for PET.

Integrins have become increasingly attractive targets for molecular imaging of angiogenesis with positron emission tomography or single-photon emission computed tomography, but the reliable production of radiopharmaceuticals remains challenging. A strategy for chemoselective labeling of the integrin ligand-c(RGDyK) peptide-has been developed on the basis of the Cu(I)-catalyzed conjugation reaction. Recently, we reported a nucleophilic detagging and fluorous solid-phase extraction method providing an easy way to implement an approach for obtaining 2-[(18) F]fluoroethyl azide. In this work, we report the practical use of this method for the preparation of the 2-[(18) F]fluoroethyl-triazolyl conjugated c(RGDyK) peptide: [(18) F]FtRGD. The two-step, two-pot synthesis, HPLC purification, and reformulation could be readily performed with a standard nucleophilic radiofluorination synthesizer (GE TRACERlab FXFN ), with minimal modifications. [(18) F]FtRGD was obtained in a solution for injection (>500 MBq/mL) in 10-30% nondecay-corrected radiochemical yield, excellent radiochemical purity (>98%), and 28 ± 13 GBq/µmol specific activity. [(18) F]FtRGD (Ki = 54 ± 14 nM for αV ß3 and 1.7 ± 0.2 nM for αV ß5 ) was evaluated in mice and showed good stability in vivo, good tumor-to-background ratio (1.6 ± 0.3 %ID/g at 1.5 h post-injection in U87-MG tumors), and rapid urinary excretion. Therefore, [(18) F]FtRGD proved valuable for preclinical positron emission tomography imaging of integrin expression.

Comparison of quantitative parameters and radiomic features as inputs into machine learning models to predict the Gleason score of prostate cancer lesions.

INTRODUCTION: The classification of prostate cancer (PCa) lesions using Prostate Imaging Reporting and Data System (PI-RADS) suffers from poor inter-reader agreement. This study compared quantitative parameters or radiomic features from multiparametric magnetic resonance imaging (mpMRI) or positron emission tomography (PET), as inputs into machine learning (ML) to predict the Gleason scores (GS) of detected lesions for improved PCa lesion classification. METHODS: 20 biopsy-confirmed PCa subjects underwent imaging before radical prostatectomy. A pathologist assigned GS from tumour tissue. Two radiologists and one nuclear medicine physician delineated the lesions on the mpMR and PET images, yielding 45 lesion inputs. Seven quantitative parameters were extracted from the lesions, namely T2-weighted (T2w) image intensity, apparent diffusion coefficient (ADC), transfer constant (KTRANS), efflux rate constant (Kep), and extracellular volume ratio (Ve) from mpMR images, and SUVmean and SUVmax from PET images. Eight radiomic features were selected out of 109 radiomic features from T2w, ADC and PET images. Quantitative parameters or radiomic features, with risk factors of age, prostate-specific antigen (PSA), PSA density and volume, of 45 different lesion inputs were input in different combinations into four ML models - Decision Tree (DT), Support Vector Machine (SVM), k-Nearest-Neighbour (kNN), Ensembles model (EM). RESULTS: SUVmax yielded the highest accuracy in discriminating detected lesions. Among the 4 ML models, kNN yielded the highest accuracies of 0.929 using either quantitative parameters or radiomic features with risk factors as input. CONCLUSIONS: ML models' performance is dependent on the input combinations and risk factors further improve ML classification accuracy.

Comparison of Three Automated Approaches for Classification of Amyloid-PET Images.

Automated amyloid-PET image classification can support clinical assessment and increase diagnostic confidence. Three automated approaches using global cut-points derived from Receiver Operating Characteristic (ROC) analysis, machine learning (ML) algorithms with regional SUVr values, and deep learning (DL) network with 3D image input were compared under various conditions: number of training data, radiotracers, and cohorts. 276 [11C]PiB and 209 [18F]AV45 PET images from ADNI database and our local cohort were used. Global mean and maximum SUVr cut-points were derived using ROC analysis. 68 ML models were built using regional SUVr values and one DL network was trained with classifications of two visual assessments - manufacturer's recommendations (gray-scale) and with visually guided reference region scaling (rainbow-scale). ML-based classification achieved similarly high accuracy as ROC classification, but had better convergence between training and unseen data, with a smaller number of training data. Naïve Bayes performed the best overall among the 68 ML algorithms. Classification with maximum SUVr cut-points yielded higher accuracy than with mean SUVr cut-points, particularly for cohorts showing more focal uptake. DL networks can support the classification of definite cases accurately but performed poorly for equivocal cases. Rainbow-scale standardized image intensity scaling and improved inter-rater agreement. Gray-scale detects focal accumulation better, thus classifying more amyloid-positive scans. All three approaches generally achieved higher accuracy when trained with rainbow-scale classification. ML yielded similarly high accuracy as ROC, but with better convergence between training and unseen data, and further work may lead to even more accurate ML methods.

Imaging Adipose Tissue Browning using Mitochondrial Complex-I Tracer [18F]BCPP-EF.

Browning of white adipose tissue (WAT) into beige adipocytes has been proposed as a strategy to tackle the ongoing obesity epidemic. Thermogenic stimuli have been investigated with the aim of converting existing white adipose tissue, primarily used for energy storage, into beige adipocytes capable of dissipating energy; however, evaluation is complicated by the dearth of noninvasive methodologies to quantify de novo beige adipocytes in WAT. Imaging with [18F]FDG is commonly used to measure brown adipose tissue (BAT) and beige adipocytes but the relationship between beige adipocytes, thermogenesis and [18F]FDG uptake is unclear. [18F]BCPP-EF, a tracer for mitochondrial complex-I (MC-I), acts as a marker of oxidative metabolism and may be useful for the detection of newly formed beige adipocytes. Mice received doses of the ß3-adrenergic agonist CL-316,243 subchronically for 7 days to induce formation of beige adipocytes in inguinal white fat. PET imaging was performed longitudinally with both [18F]FDG (a marker of glycolysis) and [18F]BCPP-EF (an MC-I marker) to assess the effect of thermogenic stimulation on uptake in browning inguinal WAT and interscapular BAT. Treatment with CL-316,243 led to significant increases in both [18F]FDG and [18F]BCPP-EF in inguinal WAT. The uptake of [18F]BCPP-EF in inguinal WAT was significantly increased above control levels after 3 days of stimulation, whereas [18F]FDG only showed a significant increase after 7 days. The uptake of [18F]BCPP-EF in newly formed beige adipocytes was blocked by pretreatment with an adrenoceptor antagonist suggesting that beige adipocyte formation may be associated with the activation of MC-I. However, in BAT, uptake of [18F]BCPP-EF was unaffected by ß3-adrenergic stimulation, potentially due to the high expression of MC-I. [18F]BCPP-EF can detect newly formed beige adipocytes in WAT generated after subchronic treatment with the ß3-adrenergic agonist CL-316,243 and displays both higher inguinal WAT uptake and earlier detection than [18F]FDG. The MC-I tracer may be a useful tool in the evaluation of new therapeutic strategies targeting metabolic adipose tissues to tackle obesity and metabolic diseases.

Granzyme B PET Imaging in Response to In Situ Vaccine Therapy Combined with αPD1 in a Murine Colon Cancer Model.

Immune checkpoint inhibitors (ICIs) block checkpoint receptors that tumours use for immune evasion, allowing immune cells to target and destroy cancer cells. Despite rapid advancements in immunotherapy, durable response rates to ICIs remains low. To address this, combination clinical trials are underway assessing whether adjuvants can enhance responsiveness by increasing tumour immunogenicity. CpG-oligodeoxynucleotides (CpG-ODN) are synthetic DNA fragments containing an unmethylated cysteine-guanosine motif that stimulate the innate and adaptive immune systems by engaging Toll-like receptor 9 (TLR9) present on the plasmacytoid dendritic cells (pDCs) and B cells. Here, we have assessed the ability of AlF-mNOTA-GZP, a peptide tracer targeting granzyme B, to serve as a PET imaging biomarker in response to CpG-ODN 1585 in situ vaccine therapy delivered intratumourally (IT) or intraperitoneally (IP) either as monotherapy or in combination with αPD1. [18F]AlF-mNOTA-GZP was able to differentiate treatment responders from non-responders based on tumour uptake. Furthermore, [18F]AlF-mNOTA-GZP showed positive associations with changes in tumour-associated lymphocytes expressing GZB, namely GZB+ CD8+ T cells, and decreases in suppressive F4/80+ cells. [18F]AlF-mNOTA-GZP tumour uptake was mediated by GZB expressing CD8+ cells and successfully stratifies therapy responders from non-responders, potentially acting as a non-invasive biomarker for ICIs and combination therapy evaluation in a clinical setting.