Glucose-6-phosphatase Expression-Mediated [18F]FDG Efflux in Murine Inflammation and Cancer Models

68Ga Fibroblast Activation Protein Inhibitor PET/CT in the Detection of Metastatic Thyroid Cancer: Comparison with 18F-FDG PET/CT

Background Gallium 68 (⁶⁸Ga)-labeled fibroblast activation protein inhibitor (FAPI) has been proposed as a potential radiotracer for visualizing cancerous lesions, but its utility for identifying metastatic differentiated thyroid cancer (DTC) is not well established in the literature. Purpose To evaluate the clinical utility of ⁶⁸Ga-FAPI PET/CT for detecting metastatic DTC and to compare the results with those of fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) PET/CT. Materials and Methods Participants with clinically suspected or confirmed metastatic DTC were prospectively enrolled and underwent paired ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT from May to August 2020. Histopathologic results and clinical follow-up (mean, 12 months ± 0.7 [SD]; range, 11-13 months) were used as reference standards for the final diagnosis. ¹⁸F-FDG and ⁶⁸Ga-FAPI uptake was compared by using the Wilcoxon signed-rank test. The McNemar test was used to compare the diagnostic accuracy of the two techniques, and the influence of various clinicopathologic characteristics on ¹⁸F-FDG and ⁶⁸Ga-FAPI uptake was evaluated with Mann-Whitney and Kruskal-Wallis tests. Results In total, 35 participants (median age, 44 years; IQR, 28-58 years; 18 [51%] men) were evaluated. In all 35 participants, the ⁶⁸Ga-FAPI-derived maximum standardized uptake value (SUV_max) was higher than the ¹⁸F-FDG-derived SUV_max in the metastatic lateral compartment (6.0 vs 3.5; P = .001), axillary (8.5 vs 4.3; P = .01), mediastinal lymph nodes (9.1 vs 5.0; P = .001), and pulmonary metastases (1.7 vs 1.1; P = .004). ⁶⁸Ga-FAPI PET/CT had a higher sensitivity than ¹⁸F-FDG PET/CT for depicting neck lesions (83% [65 of 78; 95% CI: 73, 90] vs 65% [51 of 78; 95% CI: 54, 75], P = .01) and distant metastases (79% [87 of 110; 95% CI: 71, 86] vs 59% [65 of 110; 95% CI: 50, 68], P < .001). Conclusion Gallium 68-labeled fibroblast activation protein inhibitor PET/CT was superior to fluorine 18 fluorodeoxyglucose PET/CT for depicting metastatic differentiated thyroid cancer, especially in lymph nodes and pulmonary metastases. Published under a CC BY 4.0 license. Online supplemental material is available for this article.

Cardio-Oncology: Understanding the Intersections Between Cardiac Metabolism and Cancer Biology

An important priority in the cardiovascular care of oncology patients is to reduce morbidity and mortality, and improve the quality of life in cancer survivors through cross-disciplinary efforts. The rate of survival in cancer patients has improved dramatically over the past decades. Nonetheless, survivors may be more likely to die from cardiovascular disease in the long term, secondary, not only to the potential toxicity of cancer therapeutics, but also to the biology of cancer. In this context, efforts from basic and translational studies are crucial to understanding the molecular mechanisms causal to cardiovascular disease in cancer patients and survivors, and identifying new therapeutic targets that may prevent and treat both diseases. This review aims to highlight our current understanding of the metabolic interaction between cancer and the heart, including potential therapeutic targets. An overview of imaging techniques that can support both research studies and clinical management is also provided. Finally, this review highlights opportunities and challenges that are necessary to advance our understanding of metabolism in the context of cardio-oncology.

Hyperpolarized 13 C magnetic resonance imaging for noninvasive assessment of tissue inflammation

Inflammation is a central mechanism underlying numerous diseases and incorporates multiple known and potential future therapeutic targets. However, progress in developing novel immunomodulatory therapies has been slowed by a need for improvement in noninvasive biomarkers to accurately monitor the initiation, development and resolution of immune responses as well as their response to therapies. Hyperpolarized magnetic resonance imaging (MRI) is an emerging molecular imaging technique with the potential to assess immune cell responses by exploiting characteristic metabolic reprogramming in activated immune cells to support their function. Using specific metabolic tracers, hyperpolarized MRI can be used to produce detailed images of tissues producing lactate, a key metabolic signature in activated immune cells. This method has the potential to further our understanding of inflammatory processes across different diseases in human subjects as well as in preclinical models. This review discusses the application of hyperpolarized MRI to the imaging of inflammation, as well as the progress made towards the clinical translation of this emerging technique.

Robust nonlinear parameter estimation in tracer kinetic analysis using infinity norm regularization and particle swarm optimization

In positron emission tomography (PET) studies, the voxel-wise calculation of individual rate constants describing the tracer kinetics is quite challenging because of the nonlinear relationship between the rate constants and PET data and the high noise level in voxel data. Based on preliminary simulations using a standard two-tissue compartment model, we can hypothesize that it is possible to reduce errors in the rate constant estimates when constraining the overestimation of the larger of two exponents in the model equation. We thus propose a novel approach based on infinity-norm regularization for limiting this exponent. Owing to the non-smooth cost function of this regularization scheme, which prevents the use of conventional Jacobian-based optimization methods, we examined a proximal gradient algorithm and the particle swarm optimization (PSO) through a simulation study. Because it exploits multiple initial values, the PSO method shows much better convergence than the proximal gradient algorithm, which is susceptible to the initial values. In the implementation of PSO, the use of a Gamma distribution to govern random movements was shown to improve the convergence rate and stability compared to a uniform distribution. Consequently, Gamma-based PSO with regularization was shown to outperform all other methods tested, including the conventional basis function method and Levenberg-Marquardt algorithm, in terms of its statistical properties.

Radiolabeled Cationic Peptides for Targeted Imaging of Infection

Molecular probes targeting bacteria provide opportunities to target bacterial infections in vivo for both imaging and therapy. In the current study, we report the development of positron emission tomography (PET) probes for imaging of live bacterial infection based on the small molecules HLys-DOTA, a polycationic peptide synthesized as the D-isomer (RYWVAWRNRG) conjugated to 1, 4, 7, 10-tetraazacyclododecane-N',N″,N‴,N-tetraacetic acid (DOTA) and AB1-HLys-DOTA, which includes an unnatural amino acid AB1 that preferentially binds to bacteria membrane lipids with amine groups via formation of iminoboronates. HLys-DOTA and AB1-HLys-DOTA peptides were radiolabeled with ⁶⁴Cu and investigated as PET imaging agents to track bacterial infection in vitro and in intramuscularly infected (IM) mice models. Cell uptake studies at 37°C in Staphylococcus aureus (SA) show higher uptake of ⁶⁴Cu-AB1-HLys-DOTA; 98.47 ± 3.54% vs ⁶⁴Cu-HLys-DOTA; 39.12 ± 3.27% at 24 h. Standard uptake values (SUV) analysis of the PET images resulted in mean SUV of 0.70 ± 0.08, 0.49 ± 0.04, and 0.31 ± 0.01 for ⁶⁴Cu-AB1-HLys-DOTA and 0.17 ± 0.06, 0.16 ± 0.02, and 0.13 ± 0.01 for ⁶⁴Cu-HLys-DOTA at 1, 4, and 24 h post injection, respectively, in the infected muscles. Similarly, in the biodistribution studies, dose uptake in the infected muscles was 4 times higher in the targeted ⁶⁴Cu-AB1-HLys-DOTA group than in the ⁶⁴Cu-HLys-DOTA group and 2-3 times higher than in the PBS control group at 1, 4, and 24 h post injection. ⁶⁴Cu-AB1-HLys-DOTA was able to distinguish between SA-infected muscle and Pseudomonas aeruginosa (PA) infected muscle with lower mean SUV of 0.28 ± 0.10 at 1 h post injection. This illustrates the utility of the AB1 covalently targeting group in synergy with the HLys peptide, which noncovalently binds to bacterial membranes. These results suggest that ⁶⁴Cu-labeled AB1-HLys-DOTA peptide could be used as an imaging probe for detection of bacterial infection in vivo with specificity for Gram-positive bacteria.