Bridging the Translation of ICG-1-Maltotriose: A Multimodal Sensor for Monitoring and Detecting Bacterial Infections.

Bacterial infections lack reliable, specific, and quick detection methods, which incur substantial costs to patients and caretakers. Our team conjugated the FDA-approved fluorescent dye indocyanine green (ICG) with a maltotriose sugar, resulting in two highly specific imaging agents (ICG-DBCO-1-Maltotriose and ICG-Amide-1-Maltotriose) for detecting bacterial infections. We then evaluated the two derivatives using fluorescence imaging (FLI), bioluminescence imaging (BLI), and photoacoustic imaging (PAI) in bacterial infection murine models. Our findings indicate that both imaging agents can correlate with and reliably detect the infection site using FLI and PAI for both Gram-negative and Gram-positive strains, with various bacterial loads. Furthermore, the differences in pharmacokinetic (PK) properties between the two agents allow for one to be used for immediate imaging (2-4 h postinjection), while the other is more effective for longitudinal studies (18-40 h postinjection).

Alternative medicine: therapeutic effects on gastric original signet ring carcinoma via ascorbate and combination with sodium alpha lipoate.

BACKGROUND: Gastric signet ring cell carcinoma (SRCC) is an aggressive gastric adenocarcinoma with a poor prognosis when diagnosed at an advanced stage. As alternative medicine, two natural supplements (ascorbate (AA) and sodium alpha lipoate (LA)) have been shown to inhibit various cancers with mild side effects. METHODS: These two natural supplements and a series of combinations (AA&LA, AA+LA and LA + AA) were incubated with non-SRCC cells (GPM-1), patient-derived gastric origin SRCC (GPM-2), gastric-origin SRCCs (HSC-39 and KATO-3), human pancreatic (MIA PaCa-2) and ovarian (SKOV-3) cells for evaluating their therapeutic effects. Moreover, these treatments were applied in 3D-cultured organoids to reveal the feasibility of these approaches for in vivo study. RESULTS: Analyzing their antioxidant capabilities and dose-response curves, we observed that all four gastric cell lines, including three patient-derived cell lines were sensitive to ascorbate (~ 10 mM). The influence of ascorbate incubation time was studied, with a 16-h incubation found to be optimal for in vitro studies. Moreover, a simultaneous combination of AA and LA (AA&LA) did not significantly inhibit cell proliferation, while prior LA treatment increased the growth inhibition of AA therapy (LA + AA). Anti-cancer efficacy of AA was further confirmed in 3D-cultured SRCC (KATO-3) organoids. CONCLUSIONS: This study highlights the potential of AA and LA + AA in treating gastric origin SRCC, and demonstrates the influence of order in which the drugs are administered.

Minicircles for a two-step blood biomarker and PET imaging early cancer detection strategy.

Early cancer detection can dramatically increase treatment options and survival rates for patients, yet detection of early-stage tumors remains difficult. Here, we demonstrate a two-step strategy to detect and locate cancerous lesions by delivering tumor-activatable minicircle (MC) plasmids encoding a combination of blood-based and imaging reporter genes to tumor cells. We genetically engineered the MCs, under the control of the pan-tumor-specific Survivin promoter, to encode: 1) Gaussia Luciferase (GLuc), a secreted biomarker that can be easily assayed in blood samples; and 2) Herpes Simplex Virus Type 1 Thymidine Kinase mutant (HSV-1 sr39TK), a PET reporter gene that can be used for highly sensitive and quantitative imaging of the tumor location. We evaluated two methods of MC delivery, complexing the MCs with the chemical transfection reagent jetPEI or encapsulating the MCs in extracellular vesicles (EVs) derived from a human cervical cancer HeLa cell line. MCs delivered by EVs or jetPEI yielded significant expression of the reporter genes in cell culture versus MCs delivered without a transfection reagent. Secreted GLuc correlated with HSV-1 sr39TK expression with R2 = 0.9676. MC complexation with jetPEI delivered a larger mass of MC for enhanced transfection, which was crucial for in vivo animal studies, where delivery of MCs via jetPEI resulted in GLuc and HSV-1 sr39TK expression at significantly higher levels than controls. To the best of our knowledge, this is the first report of the PET reporter gene HSV-1 sr39TK delivered via a tumor-activatable MC to tumor cells for an early cancer detection strategy. This work explores solutions to endogenous blood-based biomarker and molecular imaging limitations of early cancer detection strategies and elucidates the delivery capabilities and limitations of EVs.

PET Reporter Gene Imaging and Ganciclovir-Mediated Ablation of Chimeric Antigen Receptor T Cells in Solid Tumors.

Imaging strategies to monitor chimeric antigen receptor (CAR) T-cell biodistribution and proliferation harbor the potential to facilitate clinical translation for the treatment of both liquid and solid tumors. In addition, the potential adverse effects of CAR T cells highlight the need for mechanisms to modulate CAR T-cell activity. The herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene has previously been translated as a PET reporter gene for imaging of T-cell trafficking in patients with brain tumor. The HSV1-TK enzyme can act as a suicide gene of transduced cells through treatment with the prodrug ganciclovir. Here we report the molecular engineering, imaging, and ganciclovir-mediated destruction of B7H3 CAR T cells incorporating a mutated version of the HSV1-tk gene (sr39tk) with improved enzymatic activity for ganciclovir. The sr39tk gene did not affect B7H3 CAR T-cell functionality and in vitro and in vivo studies in osteosarcoma models showed no significant effect on B7H3 CAR T-cell antitumor activity. PET/CT imaging with 9-(4-[18F]-fluoro-3-[hydroxymethyl]butyl)guanine ([18F]FHBG) of B7H3-sr39tk CAR T cells in an orthotopic model of osteosarcoma revealed tumor homing and systemic immune expansion. Bioluminescence and PET imaging of B7H3-sr39tk CAR T cells confirmed complete tumor ablation with intraperitoneal ganciclovir administration. This imaging and suicide ablation system can provide insight into CAR T-cell migration and proliferation during clinical trials while serving as a suicide switch to limit potential toxicities. SIGNIFICANCE: This study showcases the only genetically engineered system capable of serving the dual role both as an effective PET imaging reporter and as a suicide switch for CAR T cells.

Synthesis and Characterization of 9-(4-[18F]Fluoro-3-(hydroxymethyl)butyl)-2-(phenylthio)-6-oxopurine as a Novel PET Agent for Mutant Herpes Simplex Virus Type 1 Thymidine Kinase Reporter Gene Imaging.

PURPOSE: [18F]FHBG has been used as a positron emission tomography (PET) imaging tracer for the monitoring of herpes simplex virus type 1 thymidine kinase (HSV1-tk), a reporter gene for cell and gene therapy in humans. However, this tracer shows inadequate blood-brain barrier (BBB) penetration and, therefore, would be limited for accurate quantification of reporter gene expression in the brain. Here, we report the synthesis and evaluation of 9-(4-[18F]fluoro-3-(hydroxymethyl)butyl)-2(phenylthio)-6-oxopurine ([18F]FHBT) as a new PET tracer for imaging reporter gene expression of HSV1-tk and its mutant HSV1-sr39tk, with the aim of improved BBB penetration. PROCEDURES: [18F]FHBT was prepared by using a tosylate precursor and [18F]KF. The cellular uptake of [18F]FHBT was performed in HSV1-sr39tk-positive (+) or HSV1-sr39tk-negative (-) MDA-MB-231 breast cancer cells. The specificity of [18F]FHBT to assess HSV1-sr39tk expression was evaluated by in vitro blocking studies using 1 mM of ganciclovir (GCV). Penetration of [18F]FHBT and [18F]FHBG across the BBB was assessed by dynamic PET imaging studies in normal mice. RESULTS: The tosylate precursor reacted with [18F]KF using Kryptofix2.2.2 followed by deprotection to give [18F]FHBT in 10 % radiochemical yield (decay-corrected). The uptake of [18F]FHBT in HSV1-sr39tk (+) cells was significantly higher than that of HSV1-sr39tk (-) cells. In the presence of GCV (1 mM), the uptake of [18F]FHBT was significantly decreased, indicating that [18F]FHBT serves as a selective substrate of HSV1-sr39TK. PET images and time-activity curves of [18F]FHBT in the brain regions showed similar initial brain uptakes (~ 12.75 min) as [18F]FHBG (P > 0.855). Slower washout of [18F]FHBT was observed at the later time points (17.75 - 57.75 min, P > 0.207). CONCLUSIONS: Although [18F]FHBT showed no statistically significant improvement of BBB permeability compared with [18F]FHBG, we have demonstrated that the 2-(phenylthio)-6-oxopurine backbone can serve as a novel scaffold for developing HSV1-tk/HSV1-sr39tk reporter gene imaging agents for additional research in the future.

New synthesis of 6″-[18 F]fluoromaltotriose for positron emission tomography imaging of bacterial infection.

6″-[18 F]fluoromaltotriose is a positron emission tomography tracer that can differentiate between bacterial infection and inflammation in vivo. Bacteria-specific uptake of 6″-[18 F]fluoromaltotriose is attributed to the targeting of maltodextrin transporter in bacteria that is absent in mammalian cells. Herein, we report a new synthesis of 6″-[18 F]fluoromaltotriose as a key step for its clinical translation. In comparison with the previously reported synthesis, the new synthesis features unambiguous assignment of the fluorine-18 position on the maltotriose unit. The new method utilizes direct fluorination of 2″,3″,4″-tri-O-acetyl-6″-O-trifyl-α-D-glucopyranosyl-(1-4)-O-2',3',6'-tri-O-acetyl-α-D-glucopyranosyl-(1-4)-1,2,3,6-tetra-O-acetyl-D-glucopyranose followed by basic hydrolysis. Radiolabeling of the new maltotriose triflate precursor proceeds using a single HPLC purification step, which results in shorter reaction time in comparison with the previously reported synthesis. Successful synthesis of 6″-[18 F]fluoromaltotriose has been achieved in 3.5 ± 0.3% radiochemical yield (decay corrected, n = 7) and radiochemical purity above 95%. The efficient radiosynthesis of 6″-[18 F]fluoromaltotriose would be critical in advancing this positron emission tomography tracer into clinical trials for imaging bacterial infections.

Maltotriose-based probes for fluorescence and photoacoustic imaging of bacterial infections.

Currently, there are no non-invasive tools to accurately diagnose wound and surgical site infections before they become systemic or cause significant anatomical damage. Fluorescence and photoacoustic imaging are cost-effective imaging modalities that can be used to noninvasively diagnose bacterial infections when paired with a molecularly targeted infection imaging agent. Here, we develop a fluorescent derivative of maltotriose (Cy7-1-maltotriose), which is shown to be taken up in a variety of gram-positive and gram-negative bacterial strains in vitro. In vivo fluorescence and photoacoustic imaging studies highlight the ability of this probe to detect infection, assess infection burden, and visualize the effectiveness of antibiotic treatment in E. coli-induced myositis and a clinically relevant S. aureus wound infection murine model. In addition, we show that maltotriose is an ideal scaffold for infection imaging agents encompassing better pharmacokinetic properties and in vivo stability than other maltodextrins (e.g. maltohexose).

Molecular imaging of bacterial infections: Overcoming the barriers to clinical translation.

Clinical diagnostic tools requiring direct sample testing cannot be applied to infections deep within the body, and clinically available imaging tools lack specificity. New approaches are needed for early diagnosis and monitoring of bacterial infections and rapid detection of drug-resistant organisms. Molecular imaging allows for longitudinal, noninvasive assessments and can provide key information about infectious processes deep within the body.

The Characterization of 18F-hGTS13 for Molecular Imaging of xC- Transporter Activity with PET.

The aim of this study was development of an improved PET radiotracer for measuring xC- activity with increased tumor uptake and reduced uptake in inflammatory cells compared with (S)-4-(3-18F-fluoropropyl)-l-glutamate (18F-FSPG). Methods: A racemic glutamate derivative, 18F-hGTS13, was evaluated in cell culture and animal tumor models. 18F-hGTS13 was separated into C5 epimers, and the corresponding 18F-hGTS13-isomer1 and 18F-hGTS13-isomer2 were evaluated in H460 tumor-bearing rats. Preliminary studies investigated the cellular uptake of 18F-hGTS13-isomer2 in multiple immune cell populations and states. Results:18F-hGTS13 demonstrated excellent H460 tumor visualization with high tumor-to-background ratios, confirmed by ex vivo biodistribution studies. Tumor-associated radioactivity was significantly higher for 18F-hGTS13 (7.5 ± 0.9 percentage injected dose [%ID]/g, n = 3) than for 18F-FSPG (4.6 ± 0.7 %ID/g, n = 3, P = 0.01). 18F-hGTS13-isomer2 exhibited excellent H460 tumor visualization (6.3 ± 1.1 %ID/g, n = 3) and significantly reduced uptake in multiple immune cell populations relative to 18F-FSPG. 18F-hGTS13-isomer2 exhibited increased liver uptake relative to 18F-FSPG (4.6 ± 0.8 vs. 0.7 ± 0.01 %ID/g), limiting its application in hepatocellular carcinoma. Conclusion:18F-hGTS13-isomer2 is a new PET radiotracer for molecular imaging of xC- activity that may provide information on tumor oxidation states. 18F-hGTS13-isomer2 has potential for clinical translation for imaging cancers of the thorax because of the low background signal in healthy tissue.

Positron emission tomography reporter gene strategy for use in the central nervous system.

There is a growing need for monitoring or imaging gene therapy in the central nervous system (CNS). This can be achieved with a positron emission tomography (PET) reporter gene strategy. Here we report the development of a PET reporter gene system using the PKM2 gene with its associated radiotracer [18F]DASA-23. The PKM2 reporter gene was delivered to the brains of mice by adeno-associated virus (AAV9) via stereotactic injection. Serial PET imaging was carried out over 8 wk to assess PKM2 expression. After 8 wk, the brains were excised for further mRNA and protein analysis. PET imaging at 8 wk post-AAV delivery showed an increase in [18F]DASA-23 brain uptake in the transduced site of mice injected with the AAV mice over all controls. We believe PKM2 shows great promise as a PET reporter gene and to date is the only example that can be used in all areas of the CNS without breaking the blood-brain barrier, to monitor gene and cell therapy.

Engineered immune cells as highly sensitive cancer diagnostics.

Endogenous biomarkers remain at the forefront of early disease detection efforts, but many lack the sensitivities and specificities necessary to influence disease management. Here, we describe a cell-based in vivo sensor for highly sensitive early cancer detection. We engineer macrophages to produce a synthetic reporter on adopting an M2 tumor-associated metabolic profile by coupling luciferase expression to activation of the arginase-1 promoter. After adoptive transfer in colorectal and breast mouse tumor models, the engineered macrophages migrated to the tumors and activated arginase-1 so that they could be detected by bioluminescence imaging and luciferase measured in the blood. The macrophage sensor detected tumors as small as 25-50 mm3 by blood luciferase measurements, even in the presence of concomitant inflammation, and was more sensitive than clinically used protein and nucleic acid cancer biomarkers. Macrophage sensors also effectively tracked the immunological response in muscle and lung models of inflammation, suggesting the potential utility of this approach in disease states other than cancer.

Assessment of Tumor Redox Status through (S)-4-(3-[18F]fluoropropyl)-L-Glutamic Acid PET Imaging of System xc - Activity.

The cell's endogenous antioxidant system is vital to maintenance of redox homeostasis. Despite its central role in normal and pathophysiology, no noninvasive tools exist to measure this system in patients. The cystine/glutamate antiporter system xc - maintains the balance between intracellular reactive oxygen species and antioxidant production through the provision of cystine, a key precursor in glutathione biosynthesis. Here, we show that tumor cell retention of a system xc --specific PET radiotracer, (S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG), decreases in proportion to levels of oxidative stress following treatment with a range of redox-active compounds. The decrease in [18F]FSPG retention correlated with a depletion of intracellular cystine resulting from increased de novo glutathione biosynthesis, shown through [U-13C6, U-15N2]cystine isotopic tracing. In vivo, treatment with the chemotherapeutic doxorubicin decreased [18F]FSPG tumor uptake in a mouse model of ovarian cancer, coinciding with markers of oxidative stress but preceding tumor shrinkage and decreased glucose utilization. Having already been used in pilot clinical trials, [18F]FSPG PET could be rapidly translated to the clinic as an early redox indicator of tumor response to treatment. SIGNIFICANCE: [18F]FSPG PET imaging provides a sensitive noninvasive measure of tumor redox status and provides an early marker of tumor response to therapy.See related commentary by Lee et al., p. 701.

[18F]FSPG-PET reveals increased cystine/glutamate antiporter (xc-) activity in a mouse model of multiple sclerosis.

BACKGROUND: The cystine/glutamate antiporter (xc-) has been implicated in several neurological disorders and, specifically, in multiple sclerosis (MS) as a mediator of glutamate excitotoxicity and proinflammatory immune responses. We aimed to evaluate an xc-specific positron emission tomography (PET) radiotracer, (4S)-4-(3-[18F]fluoropropyl)-L-glutamate ([18F]FSPG), for its ability to allow non-invasive monitoring of xc- activity in a mouse model of MS. METHODS: Experimental autoimmune encephalomyelitis (EAE) was induced in C57BL/6 mice by subcutaneous injection of myelin oligodendrocyte glycoprotein (MOG35-55) peptide in complete Freund's adjuvant (CFA) followed by pertussis toxin. Control mice received CFA emulsion and pertussis toxin without MOG peptide, while a separate cohort of naïve mice received no treatment. PET studies were performed to investigate the kinetics and distribution of [18F]FSPG in naïve, control, pre-symptomatic, and symptomatic EAE mice, compared to 18F-fluorodeoxyglucose ([18F]FDG). After final PET scans, each mouse was perfused and radioactivity in dissected tissues was measured using a gamma counter. Central nervous system (CNS) tissues were further analyzed using ex vivo autoradiography or western blot. [18F]FSPG uptake in human monocytes, and T cells pre- and post-activation was investigated in vitro. RESULTS: [18F]FSPG was found to be more sensitive than [18F]FDG at detecting pathological changes in the spinal cord and brain of EAE mice. Even before clinical signs of disease, a small but significant increase in [18F]FSPG signal was observed in the spinal cord of EAE mice compared to controls. This increase in PET signal became more pronounced in symptomatic EAE mice and was confirmed by ex vivo biodistribution and autoradiography. Likewise, in the brain of symptomatic EAE mice, [18F]FSPG uptake was significantly higher than controls, with the largest changes observed in the cerebellum. Western blot analyses of CNS tissues revealed a significant correlation between light chain of xc- (xCT) protein levels, the subunit of xc- credited with its transporter activity, and [18F]FSPG-PET signal. In vitro [18F]FSPG uptake studies suggest that both activated monocytes and T cells contribute to the observed in vivo PET signal. CONCLUSION: These data highlight the promise of [18F]FSPG-PET as a technique to provide insights into neuroimmune interactions in MS and the in vivo role of xc- in the development and progression of this disease, thus warranting further investigation.

A novel synthesis of 6''-[18 F]-fluoromaltotriose as a PET tracer for imaging bacterial infection.

The aim of this study was to develop a positron emission tomography (PET) tracer to visualize and monitor therapeutic response to bacterial infections. In our continued efforts to find maltose based PET tracers that can image bacterial infections, we have designed and prepared 6''-[18 F]fluoromaltotriose as a second generation PET imaging tracer targeting the maltodextrin transporter of bacteria. We have developed methods to synthesize 6''-deoxy-6''-[18 F]fluoro-α-D-glucopyranosyl-(1-4)-O-α-D-glucopyranosyl-(1-4)-O-D-glucopyranose (6''-[18 F]-fluoromaltotriose) as a bacterial infection PET imaging agent. 6''-[18 F]fluoromaltotriose was prepared from precursor, 2'',3'',4''-tri-O-acetyl-6''-O-nosyl-α-D-glucopyranosyl-(1-4)-O-2',3',6'-tri-O-acetyl-α-D-glucopyranosyl-(1-4)-1,2,3,6-tetra-O-acetyl-D-glucopyranose (per-O-acetyl-6''-O-nosyl-maltotriose 4). This method utilizes the reaction between precursor 4 and anhydrous [18 F]KF/Kryptofix 2.2.2 in dimethylformamide (DMF) at 85°C for 10 minutes to yield per-O-acetyl-6''-deoxy-6-'' [18 F]-fluoromaltotriose (7). Successive acidic and basic hydrolysis of the acetyl protecting groups in 7 produced 6''-[18 F]fluoromaltotriose (8). Also, cold 6''- [19 F]fluoromaltotriose was prepared from per-O-acetyl-6''-hydroxymaltotriose via a diethylaminosulfur trifluoride reaction followed by a basic hydrolysis. A successful synthesis of 6''-[18 F]-fluoromaltotriose has been accomplished in 8 ± 1.2% radiochemical yield (decay corrected). Total synthesis time was 120 minutes. Serum stability of 6''-[18 F]fluoromaltotriose at 37°C indicated that 6''-[18 F]-fluoromaltotriose remained intact up to 2 hours. In conclusion, we have successfully synthesized 6''-[18 F]-fluoromaltotriose via direct fluorination of an appropriate precursor of a protected maltotriose.

The Exosome Total Isolation Chip.

Circulating tumor-derived extracellular vesicles (EVs) have emerged as a promising source for identifying cancer biomarkers for early cancer detection. However, the clinical utility of EVs has thus far been limited by the fact that most EV isolation methods are tedious, nonstandardized, and require bulky instrumentation such as ultracentrifugation (UC). Here, we report a size-based EV isolation tool called ExoTIC (exosome total isolation chip), which is simple, easy-to-use, modular, and facilitates high-yield and high-purity EV isolation from biofluids. ExoTIC achieves an EV yield ∼4-1000-fold higher than that with UC, and EV-derived protein and microRNA levels are well-correlated between the two methods. Moreover, we demonstrate that ExoTIC is a modular platform that can sort a heterogeneous population of cancer cell line EVs based on size. Further, we utilize ExoTIC to isolate EVs from cancer patient clinical samples, including plasma, urine, and lavage, demonstrating the device's broad applicability to cancers and other diseases. Finally, the ability of ExoTIC to efficiently isolate EVs from small sample volumes opens up avenues for preclinical studies in small animal tumor models and for point-of-care EV-based clinical testing from fingerprick quantities (10-100 µL) of blood.

Imaging B Cells in a Mouse Model of Multiple Sclerosis Using 64Cu-Rituximab PET.

B lymphocytes are a key pathologic feature of multiple sclerosis (MS) and are becoming an important therapeutic target for this condition. Currently, there is no approved technique to noninvasively visualize B cells in the central nervous system (CNS) to monitor MS disease progression and response to therapies. Here, we evaluated 64Cu-rituximab, a radiolabeled antibody specifically targeting the human B cell marker CD20, for its ability to image B cells in a mouse model of MS using PET. Methods: To model CNS infiltration by B cells, experimental autoimmune encephalomyelitis (EAE) was induced in transgenic mice that express human CD20 on B cells. EAE mice were given subcutaneous injections of myelin oligodendrocyte glycoprotein fragment1-125 emulsified in complete Freund adjuvant. Control mice received complete Freund adjuvant alone. PET imaging of EAE and control mice was performed 1, 4, and 19 h after 64Cu-rituximab administration. Mice were perfused and sacrificed after the final PET scan, and radioactivity in dissected tissues was measured with a γ-counter. CNS tissues from these mice were immunostained to quantify B cells or were further analyzed via digital autoradiography. Results: Lumbar spinal cord PET signal was significantly higher in EAE mice than in controls at all evaluated time points (e.g., 1 h after injection: 5.44 ± 0.37 vs. 3.33 ± 0.20 percentage injected dose [%ID]/g, P < 0.05). 64Cu-rituximab PET signal in brain regions ranged between 1.74 ± 0.11 and 2.93 ± 0.15 %ID/g for EAE mice, compared with 1.25 ± 0.08 and 2.24 ± 0.11 %ID/g for controls (P < 0.05 for all regions except striatum and thalamus at 1 h after injection). Similarly, ex vivo biodistribution results revealed notably higher 64Cu-rituximab uptake in the brain and spinal cord of huCD20tg EAE, and B220 immunostaining verified that increased 64Cu-rituximab uptake in CNS tissues corresponded with elevated B cells. Conclusion: B cells can be detected in the CNS of EAE mice using 64Cu-rituximab PET. Results from these studies warrant further investigation of 64Cu-rituximab in EAE models and consideration of use in MS patients to evaluate its potential for detecting and monitoring B cells in the progression and treatment of this disease. These results represent an initial step toward generating a platform to evaluate B cell-targeted therapeutics en route to the clinic.

A PET Imaging Strategy to Visualize Activated T Cells in Acute Graft-versus-Host Disease Elicited by Allogenic Hematopoietic Cell Transplant.

A major barrier to successful use of allogeneic hematopoietic cell transplantation is acute graft-versus-host disease (aGVHD), a devastating condition that arises when donor T cells attack host tissues. With current technologies, aGVHD diagnosis is typically made after end-organ injury and often requires invasive tests and tissue biopsies. This affects patient prognosis as treatments are dramatically less effective at late disease stages. Here, we show that a novel PET radiotracer, 2'-deoxy-2'-[18F]fluoro-9-ß-D-arabinofuranosylguanine ([18F]F-AraG), targeted toward two salvage kinase pathways preferentially accumulates in activated primary T cells. [18F]F-AraG PET imaging of a murine aGVHD model enabled visualization of secondary lymphoid organs harboring activated donor T cells prior to clinical symptoms. Tracer biodistribution in healthy humans showed favorable kinetics. This new PET strategy has great potential for early aGVHD diagnosis, enabling timely treatments and improved patient outcomes. [18F]F-AraG may be useful for imaging activated T cells in various biomedical applications. Cancer Res; 77(11); 2893-902. ©2017 AACR.

Specific Imaging of Bacterial Infection Using 6″-18F-Fluoromaltotriose: A Second-Generation PET Tracer Targeting the Maltodextrin Transporter in Bacteria.

6″-18F-fluoromaltotriose is a PET tracer that can potentially be used to image and localize most bacterial infections, much like 18F-FDG has been used to image and localize most cancers. However, unlike 18F-FDG, 6″-18F-fluoromaltotriose is not taken up by inflammatory lesions and appears to be specific to bacterial infections by targeting the maltodextrin transporter that is expressed in gram-positive and gram-negative strains of bacteria. Methods: 6″-18F-fluoromaltotriose was synthesized with high radiochemical purity and evaluated in several clinically relevant bacterial strains in cultures and in living mice. Results: 6″-18F-fluoromaltotriose was taken up in both gram-positive and gram-negative bacterial strains. 6″-18F-fluoromaltotriose was also able to detect Pseudomonas aeruginosa in a clinically relevant mouse model of wound infection. The utility of 6″-18F-fluoromaltotriose to help monitor antibiotic therapies was also evaluated in rats. Conclusion: 6″-18F-fluoromaltotriose is a promising new tracer that has significant diagnostic utility, with the potential to change the clinical management of patients with infectious diseases of bacterial origin.