Comparative evaluation of different modalities for measuring in vivo carnosine levels.

Carnosine is an endogenous di-peptide (ß-alanine -L- histidine) involved in maintaining tissue homeostasis. It is most abundant in skeletal muscle where its concentration has been determined in biopsy samples using tandem mass spectrometry (MS-MS). Carnosine levels can also be assessed in intact leg muscles by proton magnetic resonance spectroscopy (1H-MRS) or in blood and urine samples using mass spectrometry. Nevertheless, it remains uncertain how carnosine levels from these distinct compartments are correlated with each other when measured in the same individual. Furthermore, it is unclear which measurement modality might be most suitable for large-scale clinical studies. Hence, in 31 healthy volunteers, we assessed carnosine levels in skeletal muscle, via 1H-MRS, and in erythrocytes and urine by MS-MS. While muscle carnosine levels were higher in males (C2 peak, p = 0.010; C4 peak, p = 0.018), there was no sex-associated difference in urinary (p = 0.433) or erythrocyte (p = 0.858) levels. In a linear regression model adjusted for age, sex, race, and diet, there was a positive association between erythrocyte and urinary carnosine. However, no association was observed between 1H-MRS and erythrocytes or urinary measures. In the relationship between muscle versus urinary and erythrocyte measures, females had a positive association, while males did not show any association. We also found that 1H-MRS measures were highly sensitive to location of measurement. Thus, it is uncertain whether 1H-MRS can accurately and reliably predict endogenous carnosine levels. In contrast, urinary and erythrocyte carnosine measures may be stable and in greater synchrony, and given financial and logistical concerns, may be a feasible alternative for large-scale clinical studies.

Evaluation of 2-deoxy-2-[18F]fluoro glucaric acid (FGA) as a potential PET tracer for tumor necrosis.

In this study, [18F]FGA was obtained by a one-step oxidation of [18F]FDG using sodium hypochlorite. The conversion from [18F]FDG to [18F]FGA was confirmed by HPLC to be over 95% using the optimal condition. A549-luciferase NSCLC xenografted mice was used for in vivo PET imaging. Prior to either saline or cisplatin treatment, there was no significant difference on tumor uptake of [18F]FGA in all mice, with an average uptake of (0.21 ± 0.16) %ID/g. After treatment, tumor uptake of [18F]FGA was not changed significantly for saline-treated mice, whereas the tumor uptake of [18F]FGA drastically increased for cisplatin-treated mice, with an average uptake of (1.63 ± 0.16) %ID/g. The ratio of tumor uptake between cisplatin-treated vs. saline-treated mice was 7.8 ± 0.2 within one week of treatment. PET imaging results were consistent with ex vivo biodistribution data. BLI showed significant light intensity suppression after treatment, indicating necrosis. Our data indicate that [18F]FGA uptake was related to tumor necrosis. [18F]FGA PET/CT imaging might be a useful tool to monitor treatment response to chemotherapy by imaging tumor necrosis.

Consumption of fish oil high-fat diet induces murine hair loss via epidermal fatty acid binding protein in skin macrophages.

Fats are essential in healthy diets, but how dietary fats affect immune cell function and overall health is not well understood. Mimicking human high-fat diets (HFDs), which are rich in different fatty acid (FA) components, we fed mice various HFDs from different fat sources, including fish oil and cocoa butter. Mice consuming the fish oil HFD exhibit a hair-loss phenotype. Further studies show that omega-3 (n-3) FAs in fish oil promote atypical infiltration of CD207- (langerin-) myeloid macrophages in skin dermis, which induce hair loss through elevated TNF-α signaling. Mechanistically, epidermal fatty acid binding protein (E-FABP) is demonstrated to play an essential role in inducing TNF-α-mediated hair loss by activating the n-3 FA/ROS/IL-36 signaling pathway in dermal resident macrophages. Absence of E-FABP abrogates fish oil HFD-induced murine hair loss. Altogether, these findings support a role for E-FABP as a lipid sensor mediating n-3 FA-regulated macrophage function and skin health.

Synthesis of Radiolabeled Technetium- and Rhenium-Luteinizing Hormone-Releasing Hormone (99mTc/Re-Acdien-LHRH) Conjugates for Targeted Detection of Breast Cancer Cells Overexpressing the LHRH Receptor.

Currently, 186/188Re and 99mTc are widely used radionuclides for cancer detection and diagnosis. New advancements in modalities and targeting strategies of radiopharmaceuticals will provide an opportunity to enhance imagery and detection of smaller colonies of cancer cells while lowering false-positive diagnoses. To understand the chemistry of agents derived from fac-[99mTc(CO)3(H2O)3]+ species, the nonradioactive [Re(CO)3(H2O)3]+ analogue was used. We have designed and synthesized Re-Acdien-LHRH, Re-Acdien-peg-LHRH, and a radiolabeled 99mTc-Acdien-LHRH (rhenium- and technetium-luteinizing hormone-releasing hormone) conjugates using a tridentate linker to detect cancers overexpressing the LHRH receptor. Re-Acdien-LHRH and Re-Acdien-peg-LHRH were synthesized from non-PEGylated and PEGylated LHRH-Acdien, respectively. Cellular uptake of the compounds 99mTc-Acdien-LHRH, Re-Acdien-LHRH, and Re-Acdien-peg-LHRH was found to be significantly enhanced compared to that of untargeted 99mTc alone and unlabeled [Re(CO)3(H2O)3]+. In addition, the conjugate compounds showed no difference in cellular toxicity compared to untargeted 99mTc alone or unlabeled [Re(CO)3(H2O)3]+. Further, a competition assay using LHRH indicated selective targeting of Re-Acdien-peg-LHRH toward the LHRH receptor (p < 0.05) compared to that of [Re(CO)3(H2O)3]+ alone. Together, our data show the design paradigm and synthesis of targeting radionuclides using the LHRH peptide. Our data suggests that utilizing the LHRH peptide can lead to selective targeting and diagnosis of breast cancers expressing the LHRH receptor.

Consumption of the Fish Oil High-Fat Diet Uncouples Obesity and Mammary Tumor Growth through Induction of Reactive Oxygen Species in Protumor Macrophages.

Obesity is associated with increased risk of many types of cancer and can be induced by various high-fat diets (HFD) from different fat sources. It remains unknown whether fatty acid composition in different HFD influences obesity-associated tumor development. Here we report that consumption of either a cocoa butter or fish oil HFD induced similar obesity in mouse models. While obesity induced by the cocoa butter HFD was associated with accelerated mammary tumor growth, consumption of the fish oil HFD uncoupled obesity from increased mammary tumor growth and exhibited a decrease in protumor macrophages. Compared with fatty acid (FA) components in both HFDs, n-3 FA rich in the fish oil HFD induced significant production of reactive oxygen species (ROS) and macrophage death. Moreover, A-FABP expression in the protumor macrophages facilitated intracellular transportation of n-3 FA and oxidation of mitochondrial FA. A-FABP deficiency diminished n-3 FA-mediated ROS production and macrophage death in vitro and in vivo. Together, our results demonstrate a novel mechanism by which n-3 FA induce ROS-mediated protumor macrophage death in an A-FABP-dependent manner. SIGNIFICANCE: This study provides mechanistic insight into dietary supplementation with fish oil for breast cancer prevention and advances a new concept that not all HFDs leading to obesity are tumorigenic. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/12/2564/F1.large.jpg.

Targeting phosphatidylethanolamine and phosphatidylserine for imaging apoptosis in cancer.

INTRODUCTION: Both phosphatidylethanolamine (PE) and phosphatidylserine (PS) can be externalized to the outer cell membrane in apoptosis. Thus the objective was to determine whether PE-targeting 18F-duramycin and PS-targeting 18F-Zn-DPA could be used for imaging apoptosis. METHODS: Duramycin and Zn-DPA were labeled with either 18F-Al or 18F-SFB. U937 cells were incubated with four different concentrations of camptothecin (CPT). For assessing the effect of incubation time on uptake, 37 MBq of radiotracer was added to cells incubated for 15, 30, 60, and 120 min at 37 °C. For blocking experiments, 150 µg duramycin and 40 µg Zn-DPA were added to cells for 15 min prior to the addition of either duramycin or Zn-DPA labeled with 18F. Apoptosis was measured by flow cytometry using an annexin-V/PI kit. Cells were co-stained with Hoechst, Cy5-duramycin, and PSVue480 (FITC-Zn-DPA) to localize fluorescent dye uptake in cells. RESULTS: Apoptosis in cells increased proportionally with CTP as confirmed by both flow cytometry and fluorescent staining. Both FITC-Zn-DPA and FITC-duramycin localized mainly on the cell membrane during early apoptosis and then translocated to the inside during late apoptosis. Uptake of FITC-duramycin, however, was higher than that of FITC-Zn-DPA. Cellular uptake of four different radiotracers was also proportional to the degree of apoptosis, increasing slightly over time and reaching a plateau at about 1 h. The blocking experiments demonstrated that uptake in all the control groups was predominantly non-specific, whereas the specific uptake in all the treated groups was at least 50% for both 18F labeled duramycin and Zn-DPA. CONCLUSION: Both PE-targeting 18F-duramycin and PS-targeting 18F-Zn-DPA could be considered as potential radiotracers for imaging cellular apoptosis. Advances in knowledge and implications for patient care: Cellular data support the further development of radiotracers targeting either PE or PS for imaging apoptosis, which can associate with clinical outcome for cancer patients.

Carnosine Supplementation Enhances Post Ischemic Hind Limb Revascularization.

High (millimolar) concentrations of the histidine containing dipeptide - carnosine (ß-alanine-L-histidine) are present in the skeletal muscle. The dipeptide has been shown to buffer intracellular pH, chelate transition metals, and scavenge lipid peroxidation products; however, its role in protecting against tissue injury remains unclear. In this study, we tested the hypothesis that carnosine protects against post ischemia by augmenting HIF-1α angiogenic signaling by Fe2+ chelation. We found that wild type (WT) C57BL/6 mice, subjected to hind limb ischemia (HLI) and supplemented with carnosine (1g/L) in drinking water, had improved blood flow recovery and limb function, enhanced revascularization and regeneration of myocytes compared with HLI mice placed on water alone. Carnosine supplementation enhanced the bioavailability of carnosine in the ischemic limb, which was accompanied by increased expression of proton-coupled oligopeptide transporters. Consistent with our hypothesis, carnosine supplementation augmented HIF-1α and VEGF expression in the ischemic limb and the mobilization of proangiogenic Flk-1+/Sca-1+ cells into circulation. Pretreatment of murine myoblast (C2C12) cells with octyl-D-carnosine or carnosine enhanced HIF-1α protein expression, VEGF mRNA levels and VEGF release under hypoxic conditions. Similarly pretreatment of WT C57/Bl6 mice with carnosine showed enhanced blood flow in the ischemic limb following HLI surgery. In contrast, pretreatment of hypoxic C2C12 cells with methylcarcinine, a carnosine analog, lacking Fe2+ chelating capacity, had no effect on HIF-1α levels and VEGF release. Collectively, these data suggest that carnosine promotes post ischemic revascularization via augmentation of pro-angiogenic HIF-1α/VEGF signaling, possibly by Fe2+ chelation.

Targeted Gold Nanoparticle⁻Oligonucleotide Contrast Agents in Combination with a New Local Voxel-Wise MRI Analysis Algorithm for In Vitro Imaging of Triple-Negative Breast Cancer.

Gold nanoparticles (GNPs) have tremendous potential as cancer-targeted contrast agents for diagnostic imaging. The ability to modify the particle surface with both disease-targeting molecules (such as the cancer-specific aptamer AS1411) and contrast agents (such as the gadolinium chelate Gd(III)-DO3A-SH) enables tailoring the particles for specific cancer-imaging and diagnosis. While the amount of image contrast generated by nanoparticle contrast agents is often low, it can be augmented with the assistance of computer image analysis algorithms. In this work, the ability of cancer-targeted gold nanoparticle-oligonucleotide conjugates to distinguish between malignant (MDA-MB-231) and healthy cells (MCF-10A) is tested using a T1-weighted image analysis algorithm based on three-dimensional, deformable model-based segmentation to extract the Volume of Interest (VOI). The gold nanoparticle/algorithm tandem was tested using contrast agent GNP-Gd(III)-DO3A-SH-AS1411) and nontargeted c-rich oligonucleotide (CRO) analogs and control (CTR) counterparts (GNP-Gd(III)-DO3A-SH-CRO/CTR) via in vitro studies. Remarkably, the cancer cells were notably distinguished from the nonmalignant cells, especially at nanomolar contrast agent concentrations. The T1-weighted image analysis algorithm provided similar results to the industry standard Varian software interface (VNMRJ) analysis of T1 maps at micromolar contrast agent concentrations, in which the VNMRJ produced a 19.5% better MRI contrast enhancement. However, our algorithm provided more sensitive and consistent results at nanomolar contrast agent concentrations, where our algorithm produced ~500% better MRI contrast enhancement.

1H-MRS Quantitation of Age-Dependent Taurine Changes in Mouse Brain.

PURPOSE: A mouse model of Alzheimer's disease demonstrates reduced beta-amyloid levels in the whole brain, associated with a gain of hippocampal memory, after drinking taurine-enriched water; this suggests that a taurine supplement could be a promising treatment for cognitive deficit. The objective of this study is to establish a methodology for quantifying taurine in the whole brain, taking advantage of the rapid development of non-invasive imaging techniques such as magnetic resonance imaging and magnetic resonance spectroscopy (MRS). PROCEDURES: Single-voxel proton MRS was used to obtain quantifiable taurine peaks at 3.25 and 3.43 ppm. Quantitative MRS results were obtained in C57BL/6 mice of various age groups: 4, 11, 18, and 27 months old. RESULTS: Compared with the 4-month-old group, taurine levels dropped significantly only at 27 months of age (p = 0.03). However, a significant decrease of N-acetyl-aspartate (NAA) in the brain was observed at both 18 and 27 months (p = 0.03 and p = 0.02). In addition, MRS-measured taurine level is highly correlated with hippocampal volume (r = 0.95). CONCLUSIONS: These results suggest that decreased taurine levels in the brain could be used as biomarkers for hippocampal changes and are fully translatable into putative cognitive loss in both animal models and human studies without the ex vivo approach.

Validation of 2-18F-Fluorodeoxysorbitol as a Potential Radiopharmaceutical for Imaging Bacterial Infection in the Lung.

2-18F-fluorodeoxysorbitol (18F-FDS) has been shown to be a promising agent with high selectivity and sensitivity in imaging bacterial infection. The objective of our study was to validate 18F-FDS as a potential radiopharmaceutical for imaging bacterial infection longitudinally in the lung. Methods: Albino C57 female mice were intratracheally inoculated with either live or dead Klebsiella pneumoniae to induce either lung infection or lung inflammation. One group of mice was imaged to monitor disease progression. PET/CT was performed on days 0, 1, 2, and 3 after inoculation using either 18F-FDS or 18F-FDG (n = 12 for each tracer). The other group was first screened by bioluminescent imaging (BLI) to select only mice with visible infection (region of interest > 108 ph/s) for PET/CT imaging with 18F-FDS (n = 12). For the inflammation group, 5 mice each were imaged with PET/CT using either 18F-FDS or 18F-FDG from days 1 to 4 after inoculation. Results: For studies of disease progression, BLI showed noticeable lung infection on day 2 after inoculation and significantly greater infection on day 3. Baseline imaging before inoculation showed no focal areas of lung consolidation on CT and low uptake in the lung for both PET radiotracers. On day 2, an area of lung consolidation was identified on CT, with a corresponding 2.5-fold increase over baseline for both PET radiotracers. On day 3, widespread areas of patchy lung consolidation were found on CT, with a drastic increase in uptake for both 18F-FDS and 18F-FDG (9.2 and 3.9). PET and BLI studies showed a marginal correlation between 18F-FDG uptake and colony-forming units (r = 0.63) but a much better correlation for 18F-FDS (r = 0.85). The uptake ratio of infected lung over inflamed lung was 8.5 and 1.7 for 18F-FDS and 18F-FDG on day 3. Conclusion: Uptake of both 18F-FDS and 18F-FDG in infected lung could be used to track the degree of bacterial infection measured by BLI, with a minimum detection limit of 107 bacteria. 18F-FDS, however, is more specific than 18F-FDG in differentiating K. pneumoniae lung infection from lung inflammation.

Promoting Collaborations Between Radiologists and Scientists.

Radiology as a discipline thrives on the dynamic interplay between technological and clinical advances. Progress in almost all facets of the imaging sciences is highly dependent on complex tools sourced from physics, engineering, biology, and the clinical sciences to obtain, process, and view imaging studies. The application of these tools, however, requires broad and deep medical knowledge about disease pathophysiology and its relationship with medical imaging. This relationship between clinical medicine and imaging technology, nurtured and fostered over the past 75 years, has cultivated extraordinarily rich collaborative opportunities between basic scientists, engineers, and physicians. In this review, we attempt to provide a framework to identify both currently successful collaborative ventures and future opportunities for scientific partnership. This invited review is a product of a special working group within the Association of University Radiologists-Radiology Research Alliance.

(Radio)fluoroclick Reaction Enabled by a Hydrogen-Bonding Cluster.

We have developed a widely applicable nucleophilic (radio)fluoroclick reaction of ynamides with readily available and easy-to-handle KF(18 F). The reactions exhibited high functional-group tolerance and needed only an ambient atmosphere. This 18 F addition to C-C unsaturated bonds proceeded with extraordinarily high radiochemical yields.

Assessment of radiopharmaceutical retention for vascular access ports using positron emission tomography imaging.

PURPOSE: The purpose of this study was to resolve the issue of whether various generations of CR Bard peripheral vascular access ports and catheters are prone to retain PET radiopharmaceuticals. The study evaluates the residual radioactivity remaining following injection for two PET radiopharmaceuticals currently used extensively in the clinic, FDG and Na18 F. METHODS: FDG was purchased from a local cyclotron facility and Na18 F was prepared in-house. Three generations of currently marketed vascular access ports were tested. A total of five (n = 5) of each model was tested. Radiopharmaceutical of 2-3 mCi of each was injected into each port and flushed with 10, 30, 60, and 120 ml of saline. MicroPET scans were performed after each flush to detect the residual radioactivity on each port. A dose calibrator was used to detect the retention of radioactivity after each flush. RESULTS: Radioactivity retention for all vascular port models measured by microPET imaging was similar for both FDG and Na18 F, with less than 1% residual activity following a 10 ml saline flush. Based on the microPET images, all the subsequent flushes of 30, 60, and 120 ml were also considered. Dose calibrator activity measurements validated microPET measurements as negligible for all the ports, even with the first 10 ml flush. CONCLUSIONS: MicroPET imaging was more sensitive than the dose calibrator in determining the radioactivity retention of the vascular access ports from CR Bard. These ports may be used for the injection of FDG and Na18 F to track glucose metabolism and bone uptake with PET imaging. It is recommended to apply at least a 10 ml flush after radiopharmaceutical administration, to reduce residual activity to baseline levels.

Image-guided thermal ablation with MR-based thermometry.

Thermal ablation techniques such as radiofrequency, microwave, high intensity focused ultrasound (HIFU) and laser have been used as minimally invasive strategies for the treatment of variety of cancers. MR thermometry methods are readily available for monitoring thermal distribution and deposition in real time, leading to decrease of incidents of normal tissue damage around targeted lesion. HIFU and laser-induced thermal therapy (LITT) are the two widely accepted tumor ablation techniques because of their compatibility with MR systems. MRI provides multiple temperature dependent parameters for thermal imaging, such as signal intensity, T1, T2, diffusion coefficient, magnetization transfer, proton resonance frequency shift (PRFS, including phase imaging and spectroscopy) as well as frequency shift of temperature sensitive contrast agents. Absolute temperature mapping techniques, including both spectroscopic imaging using metabolites as a reference and phase imaging using fat as a reference, are immune to susceptibility effects and are not dependent on phase differences. These techniques are intrinsically more reliable than relative temperature measurement by phase mapping methods. If the limitation of low temporal and spatial resolution could be overcome, these methods may be preferred for MR-guided thermal ablation systems. As of today, the most popular MR thermal imaging method applied in tumor thermal ablation surgery is, however, still PRFS based phase mapping technique, which only provides relative temperature change and is prone to motion artifacts.

In Vitro PET Imaging of a Miniature Ventricular Assist Device.

UNLABELLED: Interactions between the life-sustaining ventricular assist devices and diagnostic therapies must be carefully considered to decrease the risk of inaccurate diagnostic imaging or pump failure. METHODS: The MVAD(®) pump, currently under investigational use, was tested for interaction with radiotracers in an in vitro flow-loop study. The radiotracers (18)F-sodium fluoride and (18)F-FDG were injected into a closed loop to determine the feasibility of direct imaging of the MVAD(®) pump in a PET scanner. RESULTS: No real-time changes were observed in pump operation, and there were no statistical differences in pump parameters (power consumption, speed, and estimated flow rate) between the baseline and circulation conditions. In addition, no effect was observed on any external components, including the permissive-action-link controller and the batteries powering the device. Imaging of the internal pump components was possible, with obscuration observed only in the portion of the pump where the spinning impeller is located. Retention of radiotracer in the pump components after circulation was minimal (<1%). CONCLUSION: PET imaging is an attractive diagnostic tool for patients with a ventricular assist device and may have additional utility outside its current use, detection of infection.

AS1411-conjugated gold nanospheres and their potential for breast cancer therapy.

AS1411 is a quadruplex-forming DNA oligonucleotide that functions as an aptamer to target nucleolin, a protein present on the surface of cancer cells. Clinical trials of AS1411 have indicated it is well tolerated with evidence of therapeutic activity, but improved pharmacology and potency may be required for optimal efficacy. In this report, we describe how conjugating AS1411 to 5 nm gold nanospheres influences its activities in vitro and in vivo. We find that the AS1411-linked gold nanospheres (AS1411-GNS) are stable in aqueous and serum-containing solutions. Compared to unconjugated AS1411 or GNS linked to control oligonucleotides, AS1411-GNS have superior cellular uptake and markedly increased antiproliferative/cytotoxic effects. Similar to AS1411, AS1411-GNS show selectivity for cancer cells compared to non-malignant cells. In a mouse model of breast cancer, systemic administration of AS1411-GNS could completely inhibit tumor growth with no signs of toxicity. These results suggest AS1411-GNS are promising candidates for clinical translation.

Systemically delivered adipose stromal vascular fraction cells disseminate to peripheral artery walls and reduce vasomotor tone through a CD11b+ cell-dependent mechanism.

Vasoactivity, an important aspect of tissue healing, is often compromised in disease and tissue injury. Dysfunction in the smaller vasoactive arteries is most impactful, given the role of these vessels in controlling downstream tissue perfusion. The adipose stromal vascular fraction (SVF) is a mix of homeostatic cells shown to promote tissue healing. Our objective was to test the hypothesis that autologous SVF cells therapeutically modulate peripheral artery vasoactivity in syngeneic mouse models of small artery function. Analysis of vasoactivity of saphenous arteries isolated from normal mice 1 week after intravenous injection of freshly isolated SVF cells revealed that pressure-dependent artery vasomotor tone was decreased by the SVF cell isolate, but not one depleted of CD11b(+) cells. Scavenging hydrogen peroxide in the vessel wall abrogated the artery relaxation promoted by the SVF cell isolate. Consistent with a CD11b(+) cell being the relevant cell type, SVF-derived F4/80-positive macrophages were present within the adventitia of the artery wall coincident with vasorelaxation. In a model of artery inflammation mimicking a common disease condition inducing vasoactive dysfunction, the SVF cells potentiated relaxation of saphenous arteries without structurally remodeling the artery via a CD11b(+) cell-dependent manner. Our findings demonstrate that freshly isolated, adipose SVF cells promote vasomotor relaxation in vasoactive arteries via a hydrogen peroxide-dependent mechanism that required CD11b(+) cells (most likely macrophages). Given the significant impact of small artery dysfunction in disease, we predict that the intravenous delivery of this therapeutic cell preparation would significantly improve tissue perfusion, particularly in diseases with diffuse vascular involvement.

Characterization of (18)F-dipicolylamine (DPA) derivatives in cells infected with influenza virus.

OBJECTIVE: Bis(Zn-dipicolylamine (Zn-DPA)) coordination complexes represent a new class of synthetic small molecules that can target anionic phosphatidylserine (PS) in the apoptotic cells with high affinity and specificity. In this study, we labeled Zn-DPA and Cy7-Zn-DPA with different (18)F-prosthetic groups and characterized their uptake in A549 cells infected with influenza A virus from the 2009 pandemic (H1N1pdm). METHODS: DPA was labeled with N-succinimidyl 4-(18)F-fluorobenzoate ((18)F-SFB), 4-nitrophenyl 2-(18)F-fluoropropionate ((18)F-NFP), 2-(18)F-Fluoroethyl toslyate ((18)F-FET), and (18)F-aluminum (Al(18)F), respectively. Cy7-DPA was labeled with (18)F-SFB and (18)F-NFP only. The tracers were reconstituted with zinc nitrate before use. Apoptosis in A549 cells was induced by infection with the H1N1pdm virus for 48 h. Three µCi of each tracer was added to each well and incubated at 37 °C. The effect of different prosthetic groups, different MOI, and incubation time on percent cellular uptake was studied. Cell internalization and efflux was evaluated within 2h of incubation. The competitive binding assay was performed with increasing concentration (10(-12)-10(-5)M) of Zn-DPA or Cy7-Zn-DPA prior to the addition of either (18)F-FB-Zn-DPA or (18)F-FB-Cy7-Zn-DPA into each well. IC50 values for the two Zn-DPA analogues were estimated by GraphPad Prism 6.0. RESULTS: Among all the four prosthetic groups, the (18)F-SFB method provided the highest conjugation yield for DPA and the highest uptake ratio between the infection cells and the control when both Zn-DPA and Cy7-Zn-DPA were present in the complex. The uptake ratio was similar for (18)F-FB-Zn-DPA and (18)F-FB-Cy7-Zn-DPA. Uptake of (18)F-FB-Zn-DPA and (18)F-FB-Cy7-Zn-DPA was proportional to the degree of apoptosis with a plateau at MOI 3. Uptake of (18)F-FB-Cy7-Zn-DPA also increased over incubation time and reached a plateau at 1h, whereas uptake of (18)F-FB-Zn-DPA did not show any significant change over time. Cell internalization studies showed that more than 70% of (18)F-FB-Zn-DPA remained on the cell surface over a time course of 2 hr in the cell media, but over 90% of (18)F-FB-Cy7-Zn-DPA was internalized within 15 min of incubation. IC50 values were estimated to be 1.5±0.3 nM and 26.2±5.1 nM for Zn-DPA and Cy7-Zn-DPA, respectively. CONCLUSIONS: (18)F-SFB was the optimal labeling method for Zn-DPA and Cy7-Zn-DPA with respect to radiochemistry and provided complexes with high target-to-background ratios. (18)F-FB-Zn-DPA and (18)F-FB-Cy7-Zn-DPA appeared to have a completely different internalization mechanism, while Zn-DPA showed higher binding affinity than Cy7-Zn-DPA. Based on these favorable characteristics, (18)F-FB-Zn-DPA and (18)F-FB-Cy7-Zn-DPA should be further evaluated as potential imaging agents for viral infection.

Focus on China: should clinicians engage in research? and lessons from other countries.

Following tremendous economic progress, society in China is also undergoing fundamental changes, as is the healthcare system. Currently the training of Chinese young doctors and their future work placement are all undergoing re-structuring. We compiled some thoughts and opinions on the topic of 'should clinicians in China engage in research?', and publish them as a special report in this issue of Quantitative Imaging in Medicine and Surgery (QIMS). The contributors included some editorial members of this journal, and a few personal friends. Besides a few minor linguistic corrections, opinions from the contributors have not been edited, as we want authors' to write their own independent views. However, it is possible there is a selection bias of the contributors of this paper; more likely those who are interested in the medical research are selected and therefore the views of the contributors may not be generalizable. To compare the structure and funding of China with other countries, authors from UK, The Netherlands, France, and USA are also invited.