Experimental and epidemiological studies indicate that significant reductions in dietary methionine intake profoundly impact both health and life spans. Methionine levels also decrease in the blood of mammals as they age. Here, we report that methionine uptake by four of the major methionine-consuming organs, the liver, kidneys, heart, and brain, is increased in old rats as compared to young adult rats, as measured by [11C]methionine uptake by these organs using positron emission tomography. This increased uptake was sustained for at least 30 min and resulted in 1.6- to 1.9-fold increases in methionine uptake by the major methionine-consuming organs in old rats, suggesting an age-associated acceleration of methionine metabolism and its associated biochemical pathways. By contrast, the uptake of [18F]fluorodeoxyglucose by the liver, kidneys, heart, and brain of older rats was reduced relative to that by their younger adult counterparts, indicating a decline in glucose metabolic activity with age. Remarkably, the uptake of 2-[18F]fluoropropionic acid by these organs remained essentially unchanged between young and aged adult rats, suggesting the presence of a stable biochemical equilibrium in propionate metabolism across the aging spectrum. These findings underscore the utility of positron emission tomography in revealing significant age-related alterations in organ-specific biochemical processes.

FDG PET is widely used to assess tumor glucose uptake and serves as a non-invasive prognostic tool for predicting overall survival (OS) in cancer patients. However, FDG uptake may vary between lesions within individuals and even between patients with the same cancer. The underlying biological mechanisms of this heterogeneous FDG uptake and its association with poor prognosis remain unclear. For example, the interaction between hexokinase 2 (HK2) and mitochondrial voltage-dependent anion channel 1 (VDAC1) is recognized as a hallmark of cancer metabolism, but its role in FDG accumulation has not been fully elucidated. Here, we investigated whether adenine nucleotide translocase 2 (ANT2)—a mitochondrial ADP/ATP carrier overexpressed in glycolytic tumors—contributes to FDG uptake via the HK2-VDAC1 interaction and is associated with OS. Higher ANT2 expression was significantly associated with worse OS in several malignancies, and was correlated with tumor progression and increased FDG PET signal in aggressive thyroid cancers. Mechanistically, the ANT2 preferentially interacted with VDAC1 to form a ternary HK2-VDAC1-ANT2 complex, which enhanced FDG phosphorylation and accumulation. These findings provide important insights into the functional role of ANT2 in this metabolic axis and the molecular basis of tumor glucose metabolism, highlighting its potential as a prognostic biomarker and therapeutic target in cancer.

Changes in cardiac metabolism typically precede cardiac dysfunction and therefore represent an important target for diagnosis and treatment designed to prevent progression to heart failure, a leading cause of death. Profound changes in pyruvate metabolism, including reduced expression of the mitochondrial pyruvate carrier (MPC), are increasingly recognized as early maladaptive alterations in cardiomyopathies, but no methods currently exist to determine MPC expression in vivo. We exposed mice to doxorubicin (DOX), an anthracycline chemotherapeutic known to perturb pyruvate metabolism, and demonstrated that cardiac tissue levels of MPC decrease within 4 weeks of initial DOX exposure. Using a combination of stable isotope tracing metabolomics, hyperpolarized [1-13C]pyruvate magnetic resonance imaging (MRI), and [3-11C]pyruvate positron emission tomography (PET), we found that loss of MPC and monocarboxylate transporter 1 (MCT1) resulted in decreased utilization of pyruvate for mitochondrial oxidative metabolism and resulted in decreased cardiac carbon-11 clearance. Despite recovery of expression levels of pyruvate transporters, including MPC, 16 weeks after initial DOX exposure, cardiac carbon-11 clearance still trends towards differences between control mice and the mice exposed to this chemotherapeutic. [3-11C]Pyruvate PET is therefore a promising approach to imaging cardiac pyruvate transport with potential applications to the identification of early maladaptive changes in pyruvate metabolism and monitoring response to therapy.

Anthracycline chemotherapy, widely used in cancer treatment, poses a significant risk of cardiotoxicity that results in functional decline. Current diagnostic methods poorly predict cardiotoxicity because they do not detect early damage that precedes dysfunction. Positron emission tomography (PET) is well suited to address this need when coupled with suitable imaging biomarkers. We used PET to evaluate cardiac molecular changes in male C57BL/6J mice exposed to doxorubicin (DOX). These mice initially developed cardiac atrophy, experienced functional deficits within 10 weeks of treatment, and developed cardiac fibrosis by 16 weeks. Elevated cardiac uptake of [68Ga]Ga-FAPI-04, a PET tracer targeting fibroblast activation protein α (FAP), was evident by 2 weeks and preceded the onset of functional deficits. Cardiac PET signal correlated with FAP expression and activity as well as other canonical indicators of cardiac remodeling. By contrast, cardiac uptake of [18F]DPA-714 and [18F]MFBG, which target translocator protein 18 kDa and the norepinephrine transporter, respectively, did not differ between the DOX animals and their controls. These findings identify FAP as an early imaging biomarker for DOX-induced cardiac remodeling in males and support the use of FAP PET imaging to detect some cancer patients at risk for treatment-related myocardial damage before cardiac function declines.

Dansylcadaverine is often used at a final concentration of 1 mM to identify transglutaminase substrate glutaminyl residues. At this concentration, dansylcadaverine only labels a fraction of the possible substrates. Therefore, we developed a 500 mM stock dansylcadaverine solution in dimethyl sulfoxide:acetic acid (19:1) that allows the identification of all transglutaminase substrate glutaminyl residues. This solution was used to identify these substrate residues: Gln 283, Gln 325, and Gln 677 in a fragment of arginine-specific gingipain A.

(Radio)haloaromatic moieties are prevalent in drug molecules and radiopharmaceuticals, driving significant and sustained interest in the development of methods for synthesizing these compounds. There is a particular demand for rapid, efficient, and reproducible (radio)halogenation of electron-deficient or sterically hindered aromatic rings when the halide is in significant stoichiometric deficiency. We report a convenient method of regioselective bismuth-mediated radiohalogenation of arylboronates that tolerates a wide range of functional groups and is effective with electron-rich, electron-deficient, electron-neutral, and sterically crowded aryl and heteroaryl rings. As a proof of concept, we prepared 77Br-, 124I-, and 211At-labeled derivatives of radiopharmaceuticals, including the prostate-specific membrane antigen (PSMA) inhibitor MIP-1095, with excellent radiochemical conversion (80-99%), radiochemical yield (42-78%), and radiochemical purity (>99%) at molar activities exceeding 250 GBq/μmol. These experiments highlight the suitability of this method for the synthesis of (radio)haloaromatic drugs and radiopharmaceuticals for clinical applications.

Anthracycline chemotherapy, widely used in cancer treatment, poses a significant risk of cardiotoxicity that results in functional decline. Current diagnostic methods poorly predict cardiotoxicity because they do not detect early damage that precedes dysfunction. Positron emission tomography (PET) is well suited to address this need when coupled with suitable imaging biomarkers. We used PET to evaluate cardiac molecular changes in male C57BL/6J mice exposed to doxorubicin (DOX). These mice initially developed cardiac atrophy, experienced functional deficits within 10 weeks of treatment, and developed cardiac fibrosis by 16 weeks. Elevated cardiac uptake of [68Ga]Ga-FAPI-04, a PET tracer targeting fibroblast activation protein alpha (FAP), was evident by 2 weeks and preceded the onset of functional deficits. Cardiac PET signal correlated with FAP expression and activity as well as other canonical indicators of cardiac remodeling. By contrast, cardiac uptake of [18F]DPA-714 and [18F]MFBG, which target translocator protein 18 kDa and the norepinephrine transporter, respectively, did not differ between the DOX animals and their controls. These findings identify FAP as an early imaging biomarker for DOX-induced cardiac remodeling in males and support the use of FAP PET imaging to detect some cancer patients at risk for treatment-related myocardial damage before cardiac function declines.

Treatment of pediatric cancers with doxorubicin is a common and predictable cause of cardiomyopathy. Early diagnosis of treatment-induced cardiotoxicity and intervention are major determinants for the prevention of advanced disease. The onset of cardiomyopathies is often accompanied by profound changes in lipid metabolism, including an enhanced uptake of short-chain fatty acids (SCFA). Therefore, we explored the utility of 2-[18F]fluoropropionic acid ([18F]FPA), an SCFA analog, as an imaging biomarker of cardiac injury in mice exposed to doxorubicin. Cardiotoxicity and cardiac dysfunction were induced in mice by an 8-dose regimen of doxorubicin (cumulative dose 24 mg/kg) administered over 14 days. The effects of doxorubicin exposure were assessed by measurement of heart weights, left ventricular ejection fractions, and blood cardiac troponin levels. Whole body and cardiac [18F]FPA uptakes were determined by PET and tissue gamma counting in the presence or absence of AZD3965, a pharmacological inhibitor of monocarboxylate transporter 1 (MCT1). Radiation absorbed doses were estimated using tissue time-activity concentrations. Significantly higher cardiac [18F]FPA uptake was observed in doxorubicin-treated animals. This uptake remained constant from 30 to 120 min post-injection. Pharmacological inhibition of MCT1-mediated transport by AZD3965 selectively decreased the uptake of [18F]FPA in tissues other than the heart. Co-administration of [18F]FPA and AZD3965 enhanced the imaging contrast of the diseased heart while reducing overall exposure to radioactivity. [18F]FPA, especially when co-administered with AZD3965, is a new tool for imaging changes in fatty acid metabolism occurring in response to doxorubicin-induced cardiomyopathy by PET.

17β-estradiol, the most biologically active estrogen, exerts wide-ranging effects in brain through its action on estrogen receptors (ERs), influencing higher-order cognitive function and neurobiological aging. However, our knowledge of ER expression and regulation by neuroendocrine aging in the living human brain is limited. This in vivo brain 18F-fluoroestradiol (18F-FES) Positron Emission Tomography (PET) study of healthy midlife women reveals progressively higher ER density over the menopause transition in estrogen-regulated networks. Effects were independent of age, plasma estradiol and sex hormone binding globulin, and were highly consistent, correctly classifying all women as being postmenopausal or premenopausal. Higher ER density in target regions was associated with poorer memory performance for both postmenopausal and perimenopausal groups, and predicted presence of self-reported mood and cognitive symptoms after menopause. These findings provide novel insights on brain ER density modulation by female neuroendocrine aging, with clinical implications for women's health.

We demonstrate that regioselective aryl transfer to the nucleophile occurs rapidly under mild conditions via reductive elimination and show that regioselectivity is primarily governed by steric factors imparted by ortho substituents on the recipient ring. Computational modeling and x‐ray crystallography confirm that the recipient aryl ring is positioned in the equatorial coordination site and oriented orthogonally to the axial X−Bi−Ph bond (X=nucleophile) in a trigonal bipyramidal structure. The orientation of the ortho ‐substituted aryl ring allows the appropriate orbital to overlap between its ipso carbon and nucleophile, which enhances the rate of aryl transfer to the nucleophile and dictates the regioselective reductive elimination from Bi(V) compounds. This level of stereoelectronic control results in significantly enhanced reaction rate and selectivity and creates an opportunity to rationally design ligand systems for selective aryl transfer reactions.

Abstract Background Reduced clearance of cerebrospinal fluid (CSF) has been suggested as a pathological feature of Alzheimer’s disease (AD). With extensive documentation in non-human mammals and contradictory human neuroimaging data it remains unknown whether the nasal mucosa is a CSF drainage site in humans. Here, we used dynamic PET with [1-11C]-Butanol, a highly permeable radiotracer with no appreciable brain binding, to test the hypothesis that tracer drainage from the nasal pathway reflects CSF drainage from brain. As a test of the hypothesis, we examined whether brain and nasal fluid drainage times were correlated and affected by brain amyloid. Methods 24 cognitively normal subjects (≥ 65 years) were dynamically PET imaged for 60 min. using [1-11C]-Butanol. Imaging with either [11C]-PiB or [18F]-FBB identified 8 amyloid PET positive (Aβ+) and 16 Aβ- subjects. MRI-determined regions of interest (ROI) included: the carotid artery, the lateral orbitofrontal (LOF) brain, the cribriform plate, and an All-turbinate region comprised of the superior, middle, and inferior turbinates. The bilateral temporalis muscle and jugular veins served as control regions. Regional time-activity were used to model tracer influx, egress, and AUC. Results LOF and All-turbinate 60 min AUC were positively associated, thus suggesting a connection between the brain and the nose. Further, the Aβ+ subgroup demonstrated impaired tracer kinetics, marked by reduced tracer influx and slower egress. Conclusion The data show that tracer kinetics for brain and nasal turbinates are related to each other and both reflect the amyloid status of the brain. As such, these data add to evidence that the nasal pathway is a potential CSF drainage site in humans. These data warrant further investigation of brain and nasal contributions to protein clearance in neurodegenerative disease.

Cancer is one of the most complex and challenging human diseases, with rising incidences and cancer-related deaths despite improved diagnosis and personalized treatment options. Targeted alpha therapy (TαT) offers an exciting strategy emerging for cancer treatment which has proven effective even in patients with advanced metastatic disease that has become resistant to other treatments. Yet, in many cases, more sophisticated strategies are needed to stall disease progression and overcome resistance to TαT. The combination of two or more therapies which have historically been used as stand-alone treatments is an approach that has been pursued in recent years. This review aims to provide an overview on TαT and the four main pillars of therapeutic strategies in cancer management, namely external beam radiation therapy (EBRT), immunotherapy with checkpoint inhibitors (ICI), cytostatic chemotherapy (CCT), and brachytherapy (BT), and to discuss their potential use in combination with TαT. A brief description of each therapy is followed by a review of known biological aspects and state-of-the-art treatment practices. The emphasis, however, is given to the motivation for combination with TαT as well as the pre-clinical and clinical studies conducted to date.

Introduction: We aimed to validate a PET imaging biomarker for the detection of incipient anthracycline-induced cardiotoxicity. This condition affects >5% of all pediatric cancer patients, leading to long-term health deficits. We hypothesized that fibroblast activation protein (FAP) would be a suitable candidate due to its role in extracellular matrix remodeling and fibrosis during early cardiac injury and the availability of high-affinity PET probes. Methods: Cardiotoxicity was established in male C57BL/6J mice by administering a cumulative 24 mg/kg dose of doxorubicin (DOX) intraperitoneally over 2 weeks [1]. The DOX mice were imaged serially with echocardiography and [68Ga]Ga-FAPI-04 PET over 12 weeks and compared to age- and sex-matched controls. Fractional shortening (FS) was determined from the echocardiograms, and cardiac uptake of [68Ga]Ga-FAPI-04 was quantified and expressed as percent injected dose per cubic centimeter (%ID/cm3). Heart tissue samples were collected and used for the analysis of bulk RNA-seq, RT-qPCR, Western blot, in situ hybridization (ISH), and histological staining. Finally, we used the DAVID tools and STRING database to confirm the relationship between PET signal and gene expression. Results: DOX mice exhibited decreased body weight (33% by 9 weeks after end-of-treatment) and heart weight-to-tibia length ratio (HW/TL, 39%). Cardiac [ 68 Ga]Ga-FAPI-04 PET signal was significantly higher (1.7-fold) in DOX mice from 2 weeks through the study endpoint. By contrast, no cardiac dysfunction was evident by echocardiography until 10 weeks after end-of-treatment, at which point FS was significantly reduced relative to the control group (30%). Transcription and translation of FAP were elevated in the DOX hearts, in agreement with the PET data. In the heatmap generated from the RNA-seq data, genes related to cell adhesion and extracellular remodeling were significantly upregulated in the DOX mice relative to controls. The H-score of FAP ISH was linearly related to the cardiac signal of [ 68 Ga]Ga-FAPI-04 PET (p = 0.001). Conclusions: FAP is a suitable imaging biomarker for cardiotoxicity and FAPI-PET is a promising tool for identifying patients at risk of cardiotoxicity during or after anthracycline chemotherapy.

ABSTRACT Background Anthracycline chemotherapy is associated with a risk of cardiotoxicity leading to heart disease, particularly in pediatric cancer patients. Gold standard methods of detecting cardiotoxicity are insufficiently sensitive to early damage and specific pathophysiologies driving disease. Positron emission tomography (PET) couples anatomical resolution with biochemical mechanistic selectivity and potentially addresses the current diagnostic limitations in cardio-oncology. We aimed to validate PET imaging biomarkers targeting fibroblast activation protein alpha (FAP), Translocator protein (TSPO), and norepinephrine receptor (NET) for detection of incipient anthracycline-induced cardiotoxicity. Methods Cardiotoxicity was established in male C57BL/6J mice by a cumulative dose of 24 mg/kg doxorubicin (DOX) over 2 weeks. DOX mice and their age-matched controls were imaged with echocardiography and PET, using [ 68 Ga]Ga-FAPI-04, [ 18 F]DPA-714, and [ 18 F]MFBG, over 12 weeks. Fractional shortening (FS) was determined from the echocardiograms, and cardiac uptake of the radioligands was quantified from the PET images. Heart sections were collected and used for the analysis of bulk RNA-seq, RT-qPCR, Western blot, in situ hybridization (ISH), and histopathological analysis. Results DOX mice exhibited cardiotoxicity and cardiac atrophy. Cardiac [ 68 Ga]Ga-FAPI-04 PET signal was significantly higher in DOX mice from 2 weeks through the study endpoint. By contrast, no cardiac dysfunction was evident by echocardiography until 10 weeks, at which point FS was significantly reduced in DOX mice. There were no differences in [ 18 F]DPA-714 and [ 18 F]MFBG signals. Transcription and translation of FAP, but not TSPO or NET, was detected in cardiomyocytes and were elevated in the DOX hearts, in agreement with the PET data. Genes related to cell adhesion and extracellular remodeling were significantly upregulated in the DOX mice relative to controls. Conclusions FAP is a sensitive and selective imaging biomarker for incipient cardiotoxicity and FAPI PET is a promising non-invasive imaging tool for identifying patients at risk of cardiotoxicity during or after anthracycline chemotherapy. GRAPHICAL ABSTRACT NOVELTY AND SIGNIFICANCE What is Known? Anthracycline chemotherapy results in cardiotoxicity for a sizeable population of treated patients. Cardiotoxocity manifests as cardiac dysfunction, and may result in long-term cardiac disease and heart failure, particularly in survivors of pediatric cancer. Cardiotoxicity is typically defined in terms of left ventricular ejection fraction (LVEF) deficits, as measured by echocardiography. However, this metric is often poorly sensitive to early disease and agnostic to underlying pathophysiology. Early treatment of cardiotoxicity improves recovery and long-term survival, emphasizing the need for accurate diagnostics in incipient disease. What New Information Does This Article Contain? [ 68 Ga]Ga-FAPI-04 accumulates in the hearts of mice experiencing doxorubicin-induced cardiotoxicity as a function of fibroblast activation protein alpha (FAP) expression and activity. By contrast, cardiac uptake of radioligands targeting the translocator protein 18-kDa (TSPO) and the norepinephrine transporter (NET) do not differ between DOX animals and controls. Positron emission tomography (PET) imaging following administration of [ 68 Ga]Ga-FAPI-04 detects abnormal cardiac remodeling significantly earlier than LVEF decrease is observed, indicating that it may be more sensitive to incipient disease. Our study identifies fibroblast activation protein alpha (FAP) as a promising diagnostic imaging biomarker in anthracycline-induced cardiotoxicity. We show that cardiac PET signal increases immediately after doxorubicin treatment, and the signal increase is sustained for at least 10 weeks. In addition, we demonstrate that FAP inhibitor (FAPI) PET correlates with expression of FAP protein and gene. Thus, we provide mechanistic insight into potentially-treatable pathophysiologies driving cardiac atrophy and toxicity, and have identified a translational PET tracer that can image the activation of these processes at an early stage.

Dietary methionine restriction (MR) increases longevity by improving health. In experimental models, MR is accompanied by decreased cystathionine β-synthase activity and increased cystathionine γ-lyase activity. These enzymes are parts of the transsulfuration pathway which produces cysteine and 2-oxobutanoate. Thus, the decrease in cystathionine β-synthase activity is likely to account for the loss of tissue cysteine observed in MR animals. Despite this decrease in cysteine levels, these tissues exhibit increased H 2 S production which is thought to be generated by β-elimination of the thiol moiety of cysteine, as catalyzed by cystathionine β-synthase or cystathionine γ-lyase. Another possibility for this H 2 S production is the cystathionine γ-lyase-catalyzed β-elimination of cysteine persulfide from cystine, which upon reduction yields H 2 S and cysteine. Here, we demonstrate that MR increases cystathionine γ-lyase production and activities in the liver and kidneys, and that cystine is a superior substrate for cystathionine γ-lyase catalyzed β-elimination as compared to cysteine. Moreover, cystine and cystathionine exhibit comparable K cat / K m values (6000 M −1 s −1 ) as substrates for cystathionine γ-lyase-catalyzed β-elimination. By contrast, cysteine inhibits cystathionine γ-lyase in a non-competitive manner ( K i ~ 0.5 mM), which limits its ability to function as a substrate for β-elimination by this enzyme. Cysteine inhibits the enzyme by reacting with its pyridoxal 5′-phosphate cofactor to form a thiazolidine and in so doing prevents further catalysis. These enzymological observations are consistent with the notion that during MR cystathionine γ-lyase is repurposed to catabolize cystine and thereby form cysteine persulfide, which upon reduction produces cysteine.