Synaptic signaling modeled by functional connectivity predicts metabolic demands of the human brain.

PURPOSE: The human brain is characterized by interacting large-scale functional networks fueled by glucose metabolism. Since former studies could not sufficiently clarify how these functional connections shape glucose metabolism, we aimed to provide a neurophysiologically-based approach. METHODS: 51 healthy volunteers underwent simultaneous PET/MRI to obtain BOLD functional connectivity and [18F]FDG glucose metabolism. These multimodal imaging proxies of fMRI and PET were combined in a whole-brain extension of metabolic connectivity mapping. Specifically, functional connectivity of all brain regions were used as input to explain glucose metabolism of a given target region. This enabled the modeling of postsynaptic energy demands by incoming signals from distinct brain regions. RESULTS: Functional connectivity input explained a substantial part of metabolic demands but with pronounced regional variations (34 - 76%). During cognitive task performance this multimodal association revealed a shift to higher network integration compared to resting state. In healthy aging, a dedifferentiation (decreased segregated/modular structure of the brain) of brain networks during rest was observed. Furthermore, by including data from mRNA maps, [11C]UCB-J synaptic density and aerobic glycolysis (oxygen-to-glucose index from PET data), we show that whole-brain functional input reflects non-oxidative, on-demand metabolism of synaptic signaling. The metabolically-derived directionality of functional inputs further marked them as top-down predictions. In addition, the approach uncovered formerly hidden networks with superior efficiency through metabolically informed network partitioning. CONCLUSIONS: Applying multimodal imaging, we decipher a crucial part of the metabolic and neurophysiological basis of functional connections in the brain as interregional on-demand synaptic signaling fueled by anaerobic metabolism. The observed task- and age-related effects indicate promising future applications to characterize human brain function and clinical alterations.

CXCR4 PET/MRI for follow-up of gastric mucosa-associated lymphoid tissue lymphoma after first-line Helicobacter pylori eradication.

Posttreatment evaluation of gastric mucosa-associated lymphoid tissue (MALT) lymphoma currently relies on esophagogastroduodenoscopy with histological assessment of biopsies. Overexpression of the G protein-coupled C-X-C chemokine receptor type 4 (CXCR4) has been previously observed in MALT lymphoma. The aim of this prospective study was to evaluate positron emission tomography (PET) with the novel CXCR4 tracer [68Ga]Pentixafor as a potential alternative to follow up biopsies for assessment of residual disease (noncomplete remission [CR]) after first-line Helicobacter pylori eradication. Forty-six post-H pylori eradication [68Ga]Pentixafor-PET/magnetic resonance imaging (MRI) examinations of 26 gastric MALT lymphoma patients, and 20 [68Ga]Pentixafor-PET/MRI examinations of 20 control group patients without lymphoma, were analyzed. In the MALT lymphoma group, time-matched gastric biopsies were used as reference standard and showed CR in 6 cases. Pooled examination-based accuracy, sensitivity, specificity, and positive and negative predictive values of [68Ga]Pentixafor-PET for detection of residual gastric MALT lymphoma at follow-up were 97.0%, 95.0%, 100.0%, 100.0%, and 92.9%, respectively. Maximum and mean PET standardized uptake values showed moderate correlation with immunohistochemistry-based CXCR4+ cell counts, with correlation coefficients of r = 0.51 and r = 0.52 (P = .008 and P = .006). In summary, CXCR4 imaging with [68Ga]Pentixafor-PET may represent a promising test for assessment of residual gastric MALT lymphomas after H pylori eradication.

High-temporal resolution functional PET/MRI reveals coupling between human metabolic and hemodynamic brain response.

PURPOSE: Positron emission tomography (PET) provides precise molecular information on physiological processes, but its low temporal resolution is a major obstacle. Consequently, we characterized the metabolic response of the human brain to working memory performance using an optimized functional PET (fPET) framework at a temporal resolution of 3 s. METHODS: Thirty-five healthy volunteers underwent fPET with [18F]FDG bolus plus constant infusion, 19 of those at a hybrid PET/MRI scanner. During the scan, an n-back working memory paradigm was completed. fPET data were reconstructed to 3 s temporal resolution and processed with a novel sliding window filter to increase signal to noise ratio. BOLD fMRI signals were acquired at 2 s. RESULTS: Consistent with simulated kinetic modeling, we observed a constant increase in the [18F]FDG signal during task execution, followed by a rapid return to baseline after stimulation ceased. These task-specific changes were robustly observed in brain regions involved in working memory processing. The simultaneous acquisition of BOLD fMRI revealed that the temporal coupling between hemodynamic and metabolic signals in the primary motor cortex was related to individual behavioral performance during working memory. Furthermore, task-induced BOLD deactivations in the posteromedial default mode network were accompanied by distinct temporal patterns in glucose metabolism, which were dependent on the metabolic demands of the corresponding task-positive networks. CONCLUSIONS: In sum, the proposed approach enables the advancement from parallel to truly synchronized investigation of metabolic and hemodynamic responses during cognitive processing. This allows to capture unique information in the temporal domain, which is not accessible to conventional PET imaging.

Non-invasive assessment of stimulation-specific changes in cerebral glucose metabolism with functional PET.

PURPOSE: Functional positron emission tomography (fPET) with [18F]FDG allows quantification of stimulation-induced changes in glucose metabolism independent of neurovascular coupling. However, the gold standard for quantification requires invasive arterial blood sampling, limiting its widespread use. Here, we introduce a novel fPET method without the need for an input function. METHODS: We validated the approach using two datasets (DS). For DS1, 52 volunteers (23.2 ± 3.3 years, 24 females) performed Tetris® during a [18F]FDG fPET scan (bolus + constant infusion). For DS2, 18 participants (24.2 ± 4.3 years, 8 females) performed an eyes-open/finger tapping task (constant infusion). Task-specific changes in metabolism were assessed with the general linear model (GLM) and cerebral metabolic rate of glucose (CMRGlu) was quantified with the Patlak plot as reference. We then estimated simplified outcome parameters, including GLM beta values and percent signal change (%SC), and compared them, region and whole-brain-wise. RESULTS: We observed higher agreement with the reference for DS1 than DS2. Both DS resulted in strong correlations between regional task-specific beta estimates and CMRGlu (r = 0.763…0.912). %SC of beta values exhibited strong agreement with %SC of CMRGlu (r = 0.909…0.999). Average activation maps showed a high spatial similarity between CMRGlu and beta estimates (Dice = 0.870…0.979) as well as %SC (Dice = 0.932…0.997), respectively. CONCLUSION: The non-invasive method reliably estimates task-specific changes in glucose metabolism without blood sampling. This streamlines fPET, albeit with the trade-off of being unable to quantify baseline metabolism. The simplification enhances its applicability in research and clinical settings.

Comparison of discovery rates and prognostic utility of [68Ga]Ga-PSMA-11 PET/CT and circulating tumor DNA in prostate cancer-a cross-sectional study.

BACKGROUND: Circulating-tumor DNA (ctDNA) and prostate-specific membrane antigen (PSMA) ligand positron-emission tomography (PET) enable minimal-invasive prostate cancer (PCa) detection and survival prognostication. The present study aims to compare their tumor discovery abilities and prognostic values. METHODS: One hundred thirty men with confirmed PCa (70.5 ± 8.0 years) who underwent [68Ga]Ga-PSMA-11 PET/CT (184.8 ± 19.7 MBq) imaging and plasma sample collection (March 2019-August 2021) were included. Plasma-extracted cell-free DNA was subjected to whole-genome-based ctDNA analysis. PSMA-positive tumor lesions were delineated and their quantitative parameters extracted. ctDNA and PSMA PET/CT discovery rates were compared, and the prognostic value for overall survival (OS) was evaluated. RESULTS: PSMA PET discovery rates according to castration status and PSA ranges did differ significantly (P = 0.013, P < 0.001), while ctDNA discovery rates did not (P = 0.311, P = 0.123). ctDNA discovery rates differed between localized and metastatic disease (P = 0.013). Correlations between ctDNA concentrations and PSMA-positive tumor volume (PSMA-TV) were significant in all (r = 0.42, P < 0.001) and castration-resistant (r = 0.65, P < 0.001), however not in hormone-sensitive patients (r = 0.15, P = 0.249). PSMA-TV and ctDNA levels were associated with survival outcomes in the Logrank (P < 0.0001, P < 0.0001) and multivariate Cox regression analysis (P = 0.0023, P < 0.0001). CONCLUSION: These findings suggest that PSMA PET imaging outperforms ctDNA analysis in detecting prostate cancer across the whole spectrum of disease, while both modalities are independently highly prognostic for survival outcomes.

Validation of cardiac image-derived input functions for functional PET quantification.

PURPOSE: Functional PET (fPET) is a novel technique for studying dynamic changes in brain metabolism and neurotransmitter signaling. Accurate quantification of fPET relies on measuring the arterial input function (AIF), traditionally achieved through invasive arterial blood sampling. While non-invasive image-derived input functions (IDIF) offer an alternative, they suffer from limited spatial resolution and field of view. To overcome these issues, we developed and validated a scan protocol for brain fPET utilizing cardiac IDIF, aiming to mitigate known IDIF limitations. METHODS: Twenty healthy individuals underwent fPET/MR scans using [18F]FDG or 6-[18F]FDOPA, utilizing bed motion shuttling to capture cardiac IDIF and brain task-induced changes. Arterial and venous blood sampling was used to validate IDIFs. Participants performed a monetary incentive delay task. IDIFs from various blood pools and composites estimated from a linear fit over all IDIF blood pools (3VOI) and further supplemented with venous blood samples (3VOIVB) were compared to the AIF. Quantitative task-specific images from both tracers were compared to assess the performance of each input function to the gold standard. RESULTS: For both radiotracer cohorts, moderate to high agreement (r: 0.60-0.89) between IDIFs and AIF for both radiotracer cohorts was observed, with further improvement (r: 0.87-0.93) for composite IDIFs (3VOI and 3VOIVB). Both methods showed equivalent quantitative values and high agreement (r: 0.975-0.998) with AIF-derived measurements. CONCLUSION: Our proposed protocol enables accurate non-invasive estimation of the input function with full quantification of task-specific changes, addressing the limitations of IDIF for brain imaging by sampling larger blood pools over the thorax. These advancements increase applicability to any PET scanner and clinical research setting by reducing experimental complexity and increasing patient comfort.

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.

Performance and Sensitivity of [99mTc]Tc-sestamibi Compared with Positron Emission Tomography Radiotracers to Measure P-glycoprotein Function in the Kidneys and Liver.

P-glycoprotein (P-gp, encoded in humans by the ABCB1 gene and in rodents by the Abcb1a/b genes) is a membrane transporter that can restrict the intestinal absorption and tissue distribution of many drugs and may also contribute to renal and hepatobiliary drug excretion. The aim of this study was to compare the performance and sensitivity of currently available radiolabeled P-gp substrates for positron emission tomography (PET) with the single-photon emission computed tomography (SPECT) radiotracer [99mTc]Tc-sestamibi for measuring the P-gp function in the kidneys and liver. Wild-type, heterozygous (Abcb1a/b(+/-)), and homozygous (Abcb1a/b(-/-)) Abcb1a/b knockout mice were used as models of different P-gp abundance in excretory organs. Animals underwent either dynamic PET scans after intravenous injection of [11C]N-desmethyl-loperamide, (R)-[11C]verapamil, or [11C]metoclopramide or consecutive static SPECT scans after intravenous injection of [99mTc]Tc-sestamibi. P-gp in the kidneys and liver of the mouse models was analyzed with immunofluorescence labeling and Western blotting. In the kidneys, Abcb1a/b() mice had intermediate P-gp abundance compared with wild-type and Abcb1a/b(-/-) mice. Among the four tested radiotracers, renal clearance of radioactivity (CLurine,kidney) was significantly reduced (-83%) in Abcb1a/b(-/-) mice only for [99mTc]Tc-sestamibi. Biliary clearance of radioactivity (CLbile,liver) was significantly reduced in Abcb1a/b(-/-) mice for [11C]N-desmethyl-loperamide (-47%), [11C]metoclopramide (-25%), and [99mTc]Tc-sestamibi (-79%). However, in Abcb1a/b(+/-) mice, CLbile,liver was significantly reduced (-47%) only for [99mTc]Tc-sestamibi. Among the tested radiotracers, [99mTc]Tc-sestamibi performed best in measuring the P-gp function in the kidneys and liver. Owing to its widespread clinical availability, [99mTc]Tc-sestamibi represents a promising probe substrate to assess systemic P-gp-mediated drug-drug interactions and to measure renal and hepatic P-gp function under different (patho-)physiological conditions.

Whole-body metabolic connectivity framework with functional PET.

The nervous and circulatory system interconnects the various organs of the human body, building hierarchically organized subsystems, enabling fine-tuned, metabolically expensive brain-body and inter-organ crosstalk to appropriately adapt to internal and external demands. A deviation or failure in the function of a single organ or subsystem could trigger unforeseen biases or dysfunctions of the entire network, leading to maladaptive physiological or psychological responses. Therefore, quantifying these networks in healthy individuals and patients may help further our understanding of complex disorders involving body-brain crosstalk. Here we present a generalized framework to automatically estimate metabolic inter-organ connectivity utilizing whole-body functional positron emission tomography (fPET). The developed framework was applied to 16 healthy subjects (mean age ± SD, 25 ± 6 years; 13 female) that underwent one dynamic 18F-FDG PET/CT scan. Multiple procedures of organ segmentation (manual, automatic, circular volumes) and connectivity estimation (polynomial fitting, spatiotemporal filtering, covariance matrices) were compared to provide an optimized thorough overview of the workflow. The proposed approach was able to estimate the metabolic connectivity patterns within brain regions and organs as well as their interactions. Automated organ delineation, but not simplified circular volumes, showed high agreement with manual delineation. Polynomial fitting yielded similar connectivity as spatiotemporal filtering at the individual subject level. Furthermore, connectivity measures and group-level covariance matrices did not match. The strongest brain-body connectivity was observed for the liver and kidneys. The proposed framework offers novel opportunities towards analyzing metabolic function from a systemic, hierarchical perspective in a multitude of physiological pathological states.

Positron Emission Tomography-Based Pharmacokinetic Analysis To Assess Renal Transporter-Mediated Drug-Drug Interactions of Antimicrobial Drugs.

Transporter-mediated drug-drug interactions (DDIs) are of concern in antimicrobial drug development, as they can have serious safety consequences. We used positron emission tomography (PET) imaging-based pharmacokinetic (PK) analysis to assess the effect of different drugs, which may cause transporter-mediated DDIs, on the tissue distribution and excretion of [18F]ciprofloxacin as a radiolabeled model antimicrobial drug. Mice underwent PET scans after intravenous injection of [18F]ciprofloxacin, without and with pretreatment with either probenecid (150 mg/kg), cimetidine (50 mg/kg), or pyrimethamine (5 mg/kg). A 3-compartment kidney PK model was used to assess the involvement of renal transporters in the examined DDIs. Pretreatment with probenecid and cimetidine significantly decreased the renal clearance (CLrenal) of [18F]ciprofloxacin. The effect of cimetidine (-86%) was greater than that of probenecid (-63%), which contrasted with previously published clinical data. The kidney PK model revealed that the decrease in CLrenal was caused by inhibition of basal uptake transporters and apical efflux transporters in kidney proximal tubule cells. Changes in the urinary excretion of [18F]ciprofloxacin after pretreatment with probenecid and cimetidine resulted in increased blood and organ exposure to [18F]ciprofloxacin. Our results suggest that multiple membrane transporters mediate the tubular secretion of ciprofloxacin, with possible species differences between mice and humans. Concomitant medication inhibiting renal transporters may precipitate DDIs, leading to decreased urinary excretion and increased blood and organ exposure to ciprofloxacin, potentially exacerbating adverse effects. Our study highlights the strength of PET imaging-based PK analysis to assess transporter-mediated DDIs at a whole-body level.

Evaluation of Intestinal Fibrosis with 68Ga-FAPI PET/MR Enterography in Crohn Disease.

Background In Crohn disease, differentiation between active intestinal inflammation and fibrosis has implications for treatment, but current imaging modalities are not reliably accurate. Purpose To evaluate the predictive value of gallium 68 (68Ga)-labeled fibroblast activation protein inhibitor (FAPI) PET/MR enterography for the assessment of bowel wall fibrosis in Crohn disease. Materials and Methods In this prospective single-center study, consecutive participants with Crohn disease and obstructive symptoms underwent preoperative 68Ga-FAPI PET/MR enterography from May 2021 to January 2022. Histopathologic analysis of resected bowel segments was performed to grade active inflammation (A0-A2) and fibrosis (F0-F2), which served as the reference standard. The fibroblast activation protein (FAP) expression in bowel wall layers was analyzed immunohistochemically for each layer. 68Ga-FAPI-derived maximum standardized uptake value (SUVmax) was compared with histopathologic results by using mixed-model analysis of variance and Bonferroni-corrected post hoc tests. Results In 14 participants (mean age, 45 years ± 9 [SD]; 10 men), fibrosis was diagnosed histopathologically in 28 of 51 bowel segments (grade F1, n = 14; grade F2, n = 14). Mean SUVmax was higher in segments with fibrosis than without (7.6 vs 2.0; P < .001). In severe fibrosis, mean SUVmax was higher than in mild to moderate fibrosis (8.9 ± 0.9 vs 6.2 ± 0.9; P = .045). Bowel segments with isolated active inflammation had lower mean 68Ga-FAPI uptake than segments with combined active inflammation and fibrosis (SUVmax, 3.2 ± 0.4 vs 8.1 ± 0.1; P = .005). With an SUVmax cutoff value of 3.5, the area under the receiver operating characteristic curve for the prediction of fibrosis was 0.94 (95% CI: 0.9, 1.0), with sensitivity of 26 of 28 segments (93%) and specificity of five of six segments (83%). 68Ga-FAPI-derived SUVmax correlated with FAP expression across all bowel layers (R2 = 0.50, P < .001). Conclusion Higher gallium 68 fibroblast activation protein inhibitor uptake at PET/MR enterography was associated with histopathologically assessed bowel wall fibrosis in participants with Crohn disease, suggesting diagnostic potential for treatment decisions. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by O'Shea in this issue.

A Prognostic Risk Score for Prostate Cancer Based on PSMA PET-derived Organ-specific Tumor Volumes.

Background Prostate-specific membrane antigen (PSMA) PET has high specificity in localizing primary tumors and metastases in patients with prostate cancer, but the individual overall survival probability is still difficult to estimate. Purpose To develop a prognostic risk score using PSMA PET-derived organ-specific total tumor volumes for predicting overall survival in patients with prostate cancer. Materials and Methods Men with prostate cancer who underwent PSMA PET/CT from January 2014 to December 2018 were evaluated retrospectively. All patients from center A were split into training (80%) and internal validation (20%) cohorts. Randomly selected patients from center B were used for external validation. Organ-specific tumor volumes were automatically quantified from PSMA PET scans by a neural network. A prognostic score was selected using multivariable Cox regression guided by the Akaike information criterion (AIC). The final prognostic risk score fitted on the training set was applied to both validation cohorts. Results A total of 1348 men (mean age, 70 years ± 8 [SD]) were included, with 918 patients in the training cohort, 230 in the internal validation cohort, and 200 in the external validation cohort. The median follow-up time was 55.7 months (IQR, 46.7-65.1 months; >4 years; 429 deaths occurred). A body weight-adjusted prognostic risk score integrating total, bone, and visceral tumor volumes obtained high C index values in the internal (0.82) and external (0.74) validation cohorts, as well as in patients with castration-resistant (0.75) and hormone-sensitive (0.68) disease. The fit of the statistical model for the prognostic score was improved compared with a model containing total tumor volume only (AIC, 3324 vs 3351; likelihood ratio test, P < .001). Calibration plots ascertained good model fit. Conclusion The newly developed risk score that included prostate-specific membrane antigen PET-derived organ-specific tumor volumes had good model fit for predicting overall survival in both internal and external validation cohorts. Published under a CC BY 4.0 license. Supplemental material is available for this article. See also the editorial by Civelek in this issue.

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).

Comparing the clinical value of baseline [68 Ga]Ga-FAPI-04 PET/CT and [18F]F-FDG PET/CT in pancreatic ductal adenocarcinoma: additional prognostic value of the distal pancreatitis.

PURPOSE: Anatomical and molecular staging strategies are needed for the personalized treatment of localized pancreatic ductal adenocarcinoma (PDAC). This study evaluated the performance of [68 Ga]Ga-FAPI-04 and [18F]F-FDG PET/CT on the disease staging and prognostic value of patients with localized PDAC on contrast-enhanced (CE)-CT images. METHODS: Patients with suspected localized PDAC on CE-CT were recruited for static [68 Ga]Ga-FAPI-04 and 18[F]F-FDG and PET/CT, and select patients underwent simultaneous 60-min dynamic 68 Ga-FAPI-04 PET/CT. The diagnostic and staging performances of the static PET/CT results were evaluated by delineating regions of interest in the primary tumor, whole pancreas, and distal pancreas in both types of scans and then evaluating correlations between the PET/CT findings and clinicopathological characteristics. Furthermore, Kaplan-Meier and hazard ratio (log-rank) methods were used to evaluate the prognostic value of the combined dynamic [68 Ga]Ga-FAPI-04 and static [18F]F-FDG PET/CT method. RESULTS: We included 49 patients with histologically confirmed PDAC adenocarcinomas; 32 underwent 60-min dynamic [68 Ga]Ga-FAPI-04 PET/CT imaging simultaneously. The static [68 Ga]Ga-FAPI-04 method had significantly higher accuracy and uptake values than the static [18F]F-FDG method for primary PDAC lesions, metastatic lymph nodes, and distal metastases. Furthermore, 18.4% and 10.2% of the patients' stages changed after using the [68 Ga]Ga-FAPI-04 and [18F]F-FDG PET/CT methodologies, respectively, compared to the CE-CT-designated stage. The Ki values obtained from dynamic [68 Ga]Ga-FAPI-04 PET/CT did not differ between PDAC and distal obstructive pancreatitis lesions. Pathologically enlarged tumor size, poor differentiation, and perineural invasion were associated with increased [68 Ga]Ga-FAPI-04 uptake but not with [18F]F-FDG uptake. The preoperative prognostic performance of [68 Ga]Ga-FAPI-04 was better than that of [18F]F-FDG. Interestingly, combined [68 Ga]Ga-FAPI-04 and [18F]F-FDG uptake results in the whole pancreas could further stratify patients based on their postoperative prognosis. CONCLUSION: 6[68 Ga]Ga-FAPI-04 PET/CT was more sensitive and accurate than [18F]F-FDG PET/CT for tumor, node, and metastasis staging of PDAC identified on CE-CT. Additionally, [68 Ga]Ga-FAPI-04 uptake was significantly associated with pathologically aggressive tumor features. Combined [68 Ga]Ga-FAPI-04 and [18F]F-FDG PET/CT findings improved the prognostic value, potentially providing a non-invasive guide for clinical management. Finally, increased fibroblast activity in PDAC-induced obstructive pancreatitis may be associated with poor patient survival rates.

Metformin confers longitudinal cardiac protection by preserving mitochondrial homeostasis following myocardial ischemia/reperfusion injury.

PURPOSE: Myocardial ischemia-reperfusion (I/R) injury is associated with systemic oxidative stress, cardiac mitochondrial homeostasis, and cardiomyocyte apoptosis. Metformin has been recognized to attenuate cardiomyocyte apoptosis. However, the longitudinal effects and pathomechanism of metformin on the regulation of myocardial mitohormesis following I/R treatment remain unclear. This study aimed to investigate the longitudinal effects and mechanism of metformin in regulating cardiac mitochondrial homeostasis by serial imaging with the 18-kDa translocator protein (TSPO)-targeted positron emission tomography (PET) tracer 18F-FDPA. METHODS: Myocardial I/R injury was established in Sprague-Dawley rats, which were treated with or without metformin (150 mg/kg per day). Serial gated 18F-FDG and 18F-FDPA PET imaging were performed at 1, 4, and 8 weeks after surgery, followed by analysis of ventricular remodelling and cardiac mitochondrial homeostasis. The correlation between Hsp60 and 18F-FDPA uptake was analyzed. After PET imaging, the activity of antioxidant enzymes, immunostaining, and western blot analysis were performed to analyze the spatio-temporal effects and pathomechanism of metformin for cardiac protection after myocardial I/R injury. RESULTS: Oxidative stress and apoptosis increased 1 week after myocardial I/R injury (before significant progression of ventricular remodelling). TSPO expression was correlated with Hsp60 expression and was co-localized with inflammatory CD68+ macrophages in the infarct area, and TSPO uptake was associated with an upregulation of AMPK-p/AMPK and a downregulation of Bcl-2/Bax. However, these effects were reversed with metformin treatment. Eight weeks after myocardial I/R injury (representing the advanced stage of heart failure), 18F-FDPA uptake in myocardial cells in the distal non-infarct area increased without CD68+ expression, whereas the activity decreased with metformin treatment. CONCLUSION: Taken together, these results show that a prolonged metformin treatment has pleiotropic protective effects against myocardial I/R injury associated with a regional and temporal dynamic balance between mitochondrial homeostasis and cardiac outcome, which were assessed by TSPO-targeted imaging during cardiac remodelling.

Excretion of glucose analogue with SGLT2 affinity predicts response effectiveness to sodium glucose transporter 2 inhibitors in patients with type 2 diabetes mellitus.

PURPOSE: Sodium-glucose cotransporter 2 inhibitor (SGLT2i) regulation, developed as treatment for patients with type 2 diabetes, can be imaged with the glucose analogue alpha-methyl-4-deoxy-4-[18F]fluoro-D-glucopyranoside (Me4FDG), a positron emission tomography (PET) tracer with a high affinity for SGLT1 and SGLT2 proteins. With regard to therapy effectiveness, we aimed to investigate whether clinical parameters or Me4FDG excretion could predict response to SGLT2i in patients with type 2 diabetes. METHODS: In a longitudinal, prospective study, 19 patients with type 2 diabetes underwent Me4FDG combined PET and magnetic resonance imaging (PET/MRI) scans at baseline and 2 weeks after initiation of therapy with SGLT2i, accompanied by the collection of blood and urine samples. Me4FDG-excretion was determined from the Me4FDG uptake in the bladder. Long-term response was determined by HbA1c level after 3 months; a strong response to the therapy was defined as a reduction of HbA1c by at least 10% from baseline. RESULTS: SGLT2i resulted in significantly increased Me4FDG excretion (4.8 vs. 45.0, P < 0.001) and urine glucose (56 vs. 2806 mg/dl, P < 0.001). Baseline urine glucose and baseline Me4FDG excretion correlated both with long-term decline in HbA1c with r = 0.55 (P < 0.05). However, only Me4FDG excretion was a predictor of a strong response to SGLT2i (P = 0.005, OR 1.9). CONCLUSIONS: Using Me4FDG-PET, we demonstrated for the first time renal SGLT2-related excretion before and after short-term SGLT2i treatment. In contrary to other clinical parameters, SGLT2-related excretion before treatment was a robust predictor of long-term HbA1c response in patients with type 2 diabetes, suggesting that therapy effectiveness is only dependent of endogenous SGLT2 processes.

Prognostic value of preoperative [68 Ga]Ga-FAPI-04 PET/CT in patients with resectable pancreatic ductal adenocarcinoma in correlation with immunohistological characteristics.

PURPOSE: Our aim was to assess the prognostic value of [68 Ga]Ga-FAPI-04 positron emission tomography (PET) uptake in PDAC and to evaluate the correlation between in vivo lesional radioactivity with pathological characteristics of pancreatic ductal adenocarcinoma (PDAC). METHODS: We retrospectively analyzed treatment-naïve PDAC patients who underwent preoperative [68 Ga]Ga-FAPI-04 PET/CT followed by pancreatectomy. The tracer uptake was determined as maximum tumor standardized uptake value (SUVmax), FAPI-avid tumor volume (FTV), total lesion FAP expression (TLF) as well total pancreatic uptake (TSUVmax), total FAPI-avid pancreatic volume (FPV), and total pancreatic FAP expression (TPF). Spearman's correlation analysis was performed to evaluate the association between [68 Ga]Ga-FAPI-04 PET/CT imaging and ex vivo immunohistological FAP expression and pathological characteristics of surgical specimens (differentiation, size, vascularity, perineural invasion, and lymph node metastases). Kaplan-Meier and hazard ratio (HR, log-rank) methods were used to evaluate the prognostic value of [68 Ga]Ga-FAPI-04 PET/CT and clinicopathological factors. RESULTS: Thirty-seven surgical PDAC patients were included. The ex vivo expression of FAP was significantly associated with the tumor SUVmax and TLF. FAP expression was more abundant in poorly differentiated PDAC than in well- to moderately differentiated neoplasms. Tumor SUVmax or TLF and pancreatic TSUVmax or TPF were significantly correlated with tumor size, differentiation, and perineural invasion, respectively. SUVmax had a significant independent prognostic value for recurrence-free survival (HR = 2.46, P < 0.05), while [68 Ga]Ga-FAPI-04 TPF predicted overall survival (HR = 12.82, P < 0.05). CONCLUSION: The in vivo [68 Ga]Ga-FAPI-04 uptake in localized PDAC showed a significant correlation with ex vivo FAP expression and aggressive pathological characteristics. [68 Ga]Ga-FAPI-04 PET/CT also presented a potential for postoperative prognostication of PDAC. Elevated fibroblast activity induced by obstructive pancreatitis might be associated with the patient's survival.

Radiogenomic markers enable risk stratification and inference of mutational pathway states in head and neck cancer.

PURPOSE: Head and neck squamous cell carcinomas (HNSCCs) are a molecularly, histologically, and clinically heterogeneous set of tumors originating from the mucosal epithelium of the oral cavity, pharynx, and larynx. This heterogeneous nature of HNSCC is one of the main contributing factors to the lack of prognostic markers for personalized treatment. The aim of this study was to develop and identify multi-omics markers capable of improved risk stratification in this highly heterogeneous patient population. METHODS: In this retrospective study, we approached this issue by establishing radiogenomics markers to identify high-risk individuals in a cohort of 127 HNSCC patients. Hybrid in vivo imaging and whole-exome sequencing were employed to identify quantitative imaging markers as well as genetic markers on pathway-level prognostic in HNSCC. We investigated the deductibility of the prognostic genetic markers using anatomical and metabolic imaging using positron emission tomography combined with computed tomography. Moreover, we used statistical and machine learning modeling to investigate whether a multi-omics approach can be used to derive prognostic markers for HNSCC. RESULTS: Radiogenomic analysis revealed a significant influence of genetic pathway alterations on imaging markers. A highly prognostic radiogenomic marker based on cellular senescence was identified. Furthermore, the radiogenomic biomarkers designed in this study vastly outperformed the prognostic value of markers derived from genetics and imaging alone. CONCLUSION: Using the identified markers, a clinically meaningful stratification of patients is possible, guiding the identification of high-risk patients and potentially aiding in the development of effective targeted therapies.

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.

Dissimilar Effect of P-Glycoprotein and Breast Cancer Resistance Protein Inhibition on the Distribution of Erlotinib to the Retina and Brain in Humans and Mice.

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two ATP-binding cassette efflux transporters that are coexpressed at the human blood-brain barrier (BBB) and blood-retina barrier (BRB). While pharmacological inhibition of P-gp and/or BCRP results in increased brain distribution of dual P-gp/BCRP substrate drugs, such as the tyrosine kinase inhibitor erlotinib, the effect of P-gp and/or BCRP inhibition on the retinal distribution of such drugs has hardly been investigated. In this study, we used positron emission tomography (PET) imaging to assess the effect of transporter inhibition on the distribution of [11C]erlotinib to the human retina and brain. Twenty two healthy volunteers underwent two PET scans after intravenous (i.v.) injection of a microdose (<5 µg) of [11C]erlotinib, a baseline scan, and a second scan either with concurrent i.v. infusion of tariquidar to inhibit P-gp (n = 5) or after oral intake of single ascending doses of erlotinib (300 mg, 650 mg, or 1000 mg, n = 17) to saturate erlotinib transport. In addition, transport of [3H]erlotinib to the retina and brain was assessed in mice by in situ carotid perfusion under various drug transporter inhibition settings. In comparison to the baseline PET scan, coadministration of tariquidar or erlotinib led to a significant decrease of [11C]erlotinib total volume of distribution (VT) in the human retina by -25 ± 8% (p ≤ 0.05) and -41 ± 16% (p ≤ 0.001), respectively. In contrast, erlotinib intake led to a significant increase in [11C]erlotinib VT in the human brain (+20 ± 16%, p ≤ 0.001), while administration of tariquidar did not result in any significant changes. In situ carotid perfusion experiments showed that both P-gp and BCRP significantly limit the distribution of erlotinib to the mouse retina and brain but revealed a similar discordant effect at the mouse BRB and BBB following co-perfusion with tariquidar and erlotinib as in humans. Co-perfusion with prototypical inhibitors of solute carrier transporters did not reveal a significant contribution of organic cation transporters (e.g., OCTs and OCTNs) and organic anion-transporting polypeptides (e.g., OATP2B1) to the retinal and cerebral distribution of erlotinib. In conclusion, we observed a dissimilar effect after P-gp and/or BCRP inhibition on the retinal and cerebral distribution of [11C]erlotinib. The exact mechanism for this discrepancy remains unclear but may be related to the function of an unidentified erlotinib uptake carrier sensitive to tariquidar inhibition at the BRB. Our study highlights the great potential of PET to study drug distribution to the human retina and to assess the functional impact of membrane transporters on ocular drug distribution.