Videos

Library of recent studies

Cancer Biology

Anti-PD-1/L1 lead-in before MAPK inhibitor combination maximizes antitumor immunity and efficacy.
In vivo imaging of mitochondrial membrane potential in non-small-cell lung cancer.
PKM2 rewires glucose metabolism during radiation therapy to promote an antioxidant response and glioblastoma radioresistance.
Spatial mapping of mitochondrial networks and bioenergetics in lung cancer.
Sodium-glucose transporter 2 is a diagnostic and therapeutic target for early-stage lung adenocarcinoma.
Hexokinase 2 is targetable for HK1 negative, HK2 positive tumors from a wide variety of tissues of origin.
The GSK3 Signaling Axis Regulates Adaptive Glutamine Metabolism in Lung Squamous Cell Carcinoma.
Cytoplasmic p53 couples oncogene-driven metabolism to apoptosis and is a therapeutic target in glioblastoma.
The distinct metabolic phenotype of lung squamous cell carcinoma defines selective vulnerability to glycolytic inhibition.
Targeted Inhibition of EGFR and Glutaminase Induces Metabolic Crisis in EGFR Mutant Lung Cancer.
N-Myc Drives Neuroendocrine Prostate Cancer Initiated from Human Prostate Epithelial Cells.
Fluorescent Image-Guided Surgery with an Anti-Prostate Stem Cell Antigen (PSCA) Diabody Enables Targeted Resection of Mouse Prostate Cancer Xenografts in Real Time.
MCT1 Modulates Cancer Cell Pyruvate Export and Growth of Tumors that Co-express MCT1 and MCT4.
Functional screen identifies kinases driving prostate cancer visceral and bone metastasis.
Macrophage Blockade Using CSF1R Inhibitors Reverses the Vascular Leakage Underlying Malignant Ascites in Late-Stage Epithelial Ovarian Cancer.
Heightening Energetic Stress Selectively Targets LKB1-Deficient Non-Small Cell Lung Cancers.
Use of a lipid-coated mesoporous silica nanoparticle platform for synergistic gemcitabine and paclitaxel delivery to human pancreatic cancer in mice.
Functional expression of sodium-glucose transporters in cancer.
α2-Adrenergic blockade mimics the enhancing effect of chronic stress on breast cancer progression.
Applications of immunoPET: using ¹²⁴I-anti-PSCA A11 minibody for imaging disease progression and response to therapy in mouse xenograft models of prostate cancer.
Co-targeting of convergent nucleotide biosynthetic pathways for leukemia eradication.
LKB1 inactivation dictates therapeutic response of non-small cell lung cancer to the metabolism drug phenformin.
Metabolomics strategy reveals subpopulation of liposarcomas sensitive to gemcitabine treatment.
Conditional bicistronic Cre reporter line expressing both firefly luciferase and β-galactosidase.

Meng H, Wang M, Liu H, Liu X, Situ A, Wu B, Ji Z, Chang CH, Nel AE. Use of a lipid-coated mesoporous silica nanoparticle platform for synergistic gemcitabine and paclitaxel delivery to human pancreatic cancer in mice. ACS Nano. 2015;9:3540-57. PMC4415452.

Abstract

Recently, a commercial albumin-bound paclitaxel (PTX) nanocarrier (Abraxane) was approved as the first new drug for pancreatic ductal adenocarcinoma in almost a decade. PTX improves the pharmaceutical efficacy of the first-line pancreatic cancer drug, gemcitabine (GEM), through suppression of the tumor stroma and inhibiting the expression of the GEM-inactivating enzyme, cytidine deaminase (CDA). We asked, therefore, whether it was possible to develop a mesoporous silica nanoparticle (MSNP) carrier for pancreatic cancer to co-deliver a synergistic GEM/PTX combination. High drug loading was achieved by a custom-designed coated lipid film technique to encapsulate a calculated dose of GEM (40 wt %) by using a supported lipid bilayer (LB). The uniform coating of the 65 nm nanoparticles by a lipid membrane allowed incorporation of a sublethal amount of hydrophobic PTX, which could be co-delivered with GEM in pancreatic cells and tumors. We demonstrate that ratiometric PTX incorporation and delivery by our B-MSNP could suppress CDA expression, contemporaneous with induction of oxidative stress as the operating principle for PTX synergy. To demonstrate the 𝘪𝘯 𝘷𝘪𝘷𝘰 efficacy, mice carrying subcutaneous PANC-1 xenografts received intravenous (IV) injection of PTX/GEM-loaded LB-MSNP. Drug co-delivery provided more effective tumor shrinkage than GEM-loaded LB-MSNP, free GEM, or free GEM plus Abraxane. Comparable tumor shrinkage required coadministration of 12 times the amount of free Abraxane. High-performance liquid chromatography analysis of tumor-associated GEM metabolites confirmed that, compared to free GEM, MSNP co-delivery increased the phosphorylated DNA-interactive GEM metabolite 13-fold and decreased the inactivated and deaminated metabolite 4-fold. IV injection of MSNP-delivered PTX/GEM in a PANC-1 orthotopic model effectively inhibited primary tumor growth and eliminated metastatic foci. The enhanced 𝘪𝘯 𝘷𝘪𝘷𝘰 efficacy of the dual delivery carrier could be achieved with no evidence of local or systemic toxicity. In summary, we demonstrate the development of an effective LB-MSNP nanocarrier for synergistic PTX/GEM delivery in pancreatic cancer.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4415452/ ×

Immunology / Immunotherapy

Freise AC, Zettlitz KA, Salazar FB, Tavaré R, Tsai WK, Hadjioannou A, Rozengurt N, Braun J, Wu AM, Freise AC, Salazar FB, Chatziioannou AF. Immuno-PET in Inflammatory Bowel Disease: Imaging CD4-Positive T Cells in a Murine Model of Colitis. J Nucl Med. 2018 Jun 1;59:980-985. PMC6004558

Abstract

Inflammatory bowel diseases (IBDs) in humans are characterized in part by aberrant CD4-positive (CD4+) T-cell responses. Currently, identification of foci of inflammation within the gut requires invasive procedures such as colonoscopy and biopsy. Molecular imaging with antibody fragment probes could be used to noninvasively monitor cell subsets causing intestinal inflammation. Here, GK1.5 cys-diabody (cDb), an antimouse CD4 antibody fragment derived from the GK1.5 hybridoma, was used as a PET probe for CD4+ T cells in the dextran sulfate sodium (DSS) mouse model of IBD. 𝐌𝐞𝐭𝐡𝐨𝐝𝐬: The DSS mouse model of IBD was validated by assessing changes in CD4+ T cells in the spleen and mesenteric lymph nodes (MLNs) using flow cytometry. Furthermore, CD4+ T cell infiltration in the colons of colitic mice was evaluated using immunohistochemistry. ⁸⁹Zr-labeled GK1.5 cDb was used to image distribution of CD4+ T cells in the abdominal region and lymphoid organs of mice with DSS-induced colitis. Region-of-interest analysis was performed on specific regions of the gut to quantify probe uptake. Colons, ceca, and MLNs were removed and imaged ex vivo by PET. Imaging results were confirmed by ex vivo biodistribution analysis. 𝐑𝐞𝐬𝐮𝐥𝐭𝐬: An increased number of CD4+ T cells in the colons of colitic mice was confirmed by anti-CD4 immunohistochemistry. Increased uptake of ⁸⁹Zr-maleimide-deferoxamine (malDFO)-GK1.5 cDb in the distal colon of colitic mice was visible in vivo in PET scans, and region-of-interest analysis of the distal colon confirmed increased activity in DSS mice. MLNs from colitic mice were enlarged and visible in PET images. Ex vivo scans and biodistribution confirmed higher uptake in DSS-treated colons (DSS, 1.8 ± 0.40; control, 0.45 ± 0.12 percentage injected dose [%ID] per organ, respectively), ceca (DSS, 1.1 ± 0.38; control, 0.35 ± 0.09 %ID per organ), and MLNs (DSS, 1.1 ± 0.58; control, 0.37 ± 0.25 %ID per organ). 𝐂𝐨𝐧𝐜𝐥𝐮𝐬𝐢𝐨𝐧: ⁸⁹Zr-malDFO-GK1.5 cDb detected CD4+ T cells in the colons, ceca, and MLNs of colitic mice and may prove useful for further investigations of CD4+ T cells in preclinical models of IBD, with potential to guide development of antibody-based imaging in human IBD.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6004558

Freise AC, Zettlitz KA, Salazar FB, Lu X, Tavaré R, Wu AM. ImmunoPET Imaging of Murine CD4+T Cells Using Anti-CD4 Cys-Diabody: Effects of Protein Dose on T Cell Function and Imaging. Mol Imaging Biol. 2017 Aug 1;19:599-609. PMC5524218

Abstract

PURPOSE: Molecular imaging of CD4⁺ T cells throughout the body has implications for monitoring autoimmune disease and immunotherapy of cancer. Given the key role of these cells in regulating immunity, it is important to develop a biologically inert probe. GK1.5 cys-diabody (cDb), a previously developed anti-mouse CD4 antibody fragment, was tested at different doses to assess its effects on positron emission tomography (PET) imaging and CD4⁺ T cell viability, proliferation, CD4 expression, and function.

PROCEDURES: The effect of protein dose on image contrast (lymphoid tissue-to-muscle ratio) was assessed by administering different amounts of ⁸⁹Zr-labeled GK1.5 cDb to mice followed by PET imaging and 𝘦𝘹 𝘷𝘪𝘷𝘰 biodistribution analysis. To assess impact of GK1.5 cDb on T cell biology, GK1.5 cDb was incubated with T cells 𝘪𝘯 𝘷𝘪𝘵𝘳𝘰 or administered intravenously to C57BL/6 mice at multiple protein doses. CD4 expression and T cell proliferation were analyzed with flow cytometry and cytokines were assayed.

RESULTS: For immunoPET imaging, the lowest protein dose of 2 µg ⁸⁹Zr-labeled GK1.5 cDb resulted in significantly higher % injected dose/gram in inguinal lymph nodes (ILN) and spleen compared to the 12 µg protein dose. 𝘐𝘯 𝘷𝘪𝘷𝘰 administration of GK1.5 cDb at the high dose of 40 µg caused a transient decrease in CD4 expression in spleen, blood, lymph nodes, and thymus, which recovered within 3 days post-injection; this effect was reduced, although not abrogated, when 2 µg was administered. Proliferation was inhibited 𝘪𝘯 𝘷𝘪𝘷𝘰 in ILN but not the spleen by injection of 40 µg GK1.5 cDb. Concentrations of GK1.5 cDb in excess of 25 nM significantly inhibited CD4⁺ T cell proliferation and interferon-γ production 𝘪𝘯 𝘷𝘪𝘵𝘳𝘰. Overall, using low dose GK1.5 cDb minimized biological effects on CD4⁺ T cells.

CONCLUSIONS: Low dose GK1.5 cDb yields high-contrast immunoPET images with minimal effects on T cell biology 𝘪𝘯 𝘷𝘪𝘵𝘳𝘰 and 𝘪𝘯 𝘷𝘪𝘷𝘰, and may be a useful tool for investigating CD4⁺ T cells in the context of preclinical disease models. Future approaches to minimizing biological effects may include the creation of monovalent fragments or selecting anti-CD4 antibodies which target alternative epitopes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5524218

Neuroscience

Cardiology

Hsu JJ, Lu J, Umar S, Lee JT, Kulkarni RP, Ding Y, Chang CC, Hsiai TK, Hokugo A, Gkouveris I, Tetradis S, Nishimura I, Demer LL, Tintut Y. Effects of teriparatide on morphology of aortic calcification in aged hyperlipidemic mice. Am J Physiol Heart Circ Physiol. 2018 Jun 1;314(6):H1203-H1213. doi: 10.1152/ajpheart.00718.2017. Epub 2018 Feb 16. PMID: 29451816; PMCID: PMC6032086.

Abstract

Calcific aortic vasculopathy correlates with bone loss in osteoporosis in an age-independent manner. Prior work suggests that teriparatide, the bone anabolic treatment for postmenopausal osteoporosis, may inhibit the onset of aortic calcification. Whether teriparatide affects the progression of preexisting aortic calcification, widespread among this patient population, is unknown. Female apolipoprotein E-deficient mice were aged for over 1 yr to induce aortic calcification, treated for 4.5 wk with daily injections of control vehicle (PBS), 40 µg/kg teriparatide (PTH40), or 400 µg/kg teriparatide (PTH400), and assayed for aortic calcification by microcomputed tomography (microCT) before and after treatment. In a followup cohort, aged female apolipoprotein E-deficient mice were treated with PBS or PTH400 and assayed for aortic calcification by serial microCT and micropositron emission tomography. In both cohorts, aortic calcification detected by microCT progressed similarly in all groups. Mean aortic ¹⁸F-NaF incorporation, detected by serial micropositron emission tomography, increased in the PBS-treated group (+14 ± 5%). In contrast, ¹⁸F-NaF incorporation decreased in the PTH400-treated group (-33 ± 20%, P = 0.03). Quantitative histochemical analysis by Alizarin red staining revealed a lower mineral surface area index in the PTH400-treated group compared with the PBS-treated group ( P = 0.04). Furthermore, Masson trichrome staining showed a significant increase in collagen deposition in the left ventricular myocardium of mice that received PTH400 [2.1 ± 0.6% vs. control mice (0.5 ± 0.1%), P = 0.02]. In summary, although teriparatide may not affect the calcium mineral content of aortic calcification, it reduces ¹⁸F-NaF uptake in calcified lesions, suggesting the possibility that it may reduce mineral surface area with potential impact on plaque stability. NEW & NOTEWORTHY Parathyroid hormone regulates bone mineralization and may also affect vascular calcification, which is an important issue, given that its active fragment, teriparatide, is widely used for the treatment of osteoporosis. To determine whether teriparatide alters vascular calcification, we imaged aortic calcification in mice treated with teriparatide and control mice. Although teriparatide did not affect the calcium content of cardiovascular deposits, it reduced their fluoride tracer uptake.

https://pubmed.ncbi.nlm.nih.gov/29451816/

Drug Development

Xu S, Catapang A, Braas D, Stiles L, Doh HM, Lee JT, Graeber TG, Damoiseaux R, Shirihai O, Herschman HR. A precision therapeutic strategy for hexokinase 1-null, hexokinase 2-positive cancers. Cancer Metab. 2018 Jun 28;6:7. doi: 10.1186/s40170-018-0181-8. eCollection 2018. PMC6022704

Abstract

Background: Precision medicine therapies require identification of unique molecular cancer characteristics. Hexokinase (HK) activity has been proposed as a therapeutic target; however, different hexokinase isoforms have not been well characterized as alternative targets. While HK2 is highly expressed in the majority of cancers, cancer subtypes with differential HK1 and HK2 expression have not been characterized for their sensitivities to HK2 silencing.

Methods: HK1 and HK2 expression in the Cancer Cell Line Encyclopedia dataset was analyzed. A doxycycline-inducible shRNA silencing system was used to examine the effect of HK2 knockdown in cultured cells and in xenograft models of HK1⁻HK2⁺ and HK1⁺HK2⁺ cancers. Glucose consumption and lactate production rates were measured to monitor HK activity in cell culture, and ¹⁸F-FDG PET/CT was used to monitor HK activity in xenograft tumors. A high-throughput screen was performed to search for synthetically lethal compounds in combination with HK2 inhibition in HK1⁻HK2⁺ liver cancer cells, and a combination therapy for liver cancers with this phenotype was developed. A metabolomic analysis was performed to examine changes in cellular energy levels and key metabolites in HK1⁻HK2⁺ cells treated with this combination therapy. The CRISPR Cas9 method was used to establish isogenic HK1⁺HK2⁺ and HK1⁻HK2⁺ cell lines to evaluate HK1⁻HK2⁺ cancer cell sensitivity to the combination therapy.

Results: Most tumors express both HK1 and HK2, and subsets of cancers from a wide variety of tissues of origin express only HK2. Unlike HK1⁺HK2⁺ cancers, HK1⁻HK2⁺ cancers are sensitive to HK2 silencing-induced cytostasis. Synthetic lethality was achieved in HK1⁻HK2⁺ liver cancer cells, by the combination of DPI, a mitochondrial complex I inhibitor, and HK2 inhibition, in HK1⁻HK2⁺ liver cancer cells. Perhexiline, a fatty acid oxidation inhibitor, further sensitizes HK1⁻HK2⁺ liver cancer cells to the complex I/HK2-targeted therapeutic combination. Although HK1⁺HK2⁺ lung cancer H460 cells are resistant to this therapeutic combination, isogenic HK1ᴷᴼHK2⁺ cells are sensitive to this therapy.

Conclusions: The HK1⁻HK2⁺ cancer subsets exist among a wide variety of cancer types. Selective inhibition of the HK1⁻HK2⁺ cancer cell-specific energy production pathways (HK2-driven glycolysis, oxidative phosphorylation and fatty acid oxidation), due to the unique presence of only the HK2 isoform, appears promising to treat HK1⁻HK2⁺ cancers. This therapeutic strategy will likely be tolerated by most normal tissues, where only HK1 is expressed.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6022704

Accurate Measure by High Resolution CT

Imaging Technology Development

Wang J, Rios A, Lisova K, Slavik R, Chatziioannou AF, van Dam RM. High-throughput radio-TLC analysis. Nuclear Medicine and Biology. 2020; 82-83:41-48. doi: 10.1016/j.nucmedbio.2019.12.003.

Abstract

𝐈𝐧𝐭𝐫𝐨𝐝𝐮𝐜𝐭𝐢𝐨𝐧: Radio thin layer chromatography (radio-TLC) is commonly used to analyze purity of radiopharmaceuticals or to determine the reaction conversion when optimizing radiosynthesis processes. In applications where there are few radioactive species, radio-TLC is preferred over radio-high-performance liquid chromatography due to its simplicity and relatively quick analysis time. However, with current radio-TLC methods, it remains cumbersome to analyze a large number of samples during reaction optimization. In a couple of studies, Cerenkov luminescence imaging (CLI) has been used for reading radio-TLC plates spotted with a variety of isotopes. We show that this approach can be extended to develop a high-throughput approach for radio-TLC analysis of many samples.

𝐌𝐞𝐭𝐡𝐨𝐝𝐬: The high-throughput radio-TLC analysis was carried out by performing parallel development of multiple radioactive samples spotted on a single TLC plate, followed by simultaneous readout of the separated samples using Cerenkov imaging. Using custom-written MATLAB software, images were processed and regions of interest (ROIs) were drawn to enclose the radioactive regions/spots. For each sample, the proportion of integrated signal in each ROI was computed. Various crude samples of [¹⁸F]fallypride, [¹⁸F]FET and [¹⁷⁷Lu]Lu-PSMA-617 were prepared for demonstration of this new method.

𝐑𝐞𝐬𝐮𝐥𝐭𝐬: Benefiting from a parallel developing process and high resolution of CLI-based readout, total analysis time for eight [¹⁸F]fallypride samples was 7.5 min (2.5 min for parallel developing, 5 min for parallel readout), which was significantly shorter than the 48 min needed using conventional approaches (24 min for sequential developing, 24 min for sequential readout on a radio-TLC scanner). The greater separation resolution of CLI enabled the discovery of a low-abundance side product from a crude [¹⁸F]FET sample that was not discernable using the radio-TLC scanner. Using the CLI-based readout method, we also observed that high labeling efficiency (99%) of [¹⁷⁷Lu]Lu-PSMA-617 can be achieved in just 10 min, rather than the typical 30 min timeframe used.

𝐂𝐨𝐧𝐜𝐥𝐮𝐬𝐢𝐨𝐧𝐬: Cerenkov imaging in combination with parallel developing of multiple samples on a single TLC plate proved to be a practical method for rapid, high-throughput radio-TLC analysis.

https://pubmed.ncbi.nlm.nih.gov/31891883/

Gu Z, Taschereau R, Vu NT, Prout DL, Lee J, Chatziioannou AF. Performance evaluation of HiPET, a high sensitivity and high resolution preclinical PET tomograph. Phys Med Biol. 2020 Feb 12; 65(4):045009. doi: 10.1088/1361-6560/ab6b44

Abstract

HiPET is a recently developed prototype preclinical PET scanner dedicated to high sensitivity and high resolution molecular imaging. The HiPET system employs a phoswich depth of interaction (DOI) detector design, which also allows identification of the large majority of the cross layer crystal scatter (CLCS) events. This work evaluates its performance characteristics following the National Electrical Manufacturers Association (NEMA) NU4-2008 protocol. The HiPET consists of twenty flat panel type detectors arranged in two rings. The inner diameter is 160 mm and the axial field of view (FOV) is 104 mm. Each detector is comprised of two layers of phoswich scintillator crystal arrays, a tapered, pixelated glass lightguide and a multi anode photomultiplier tube (MAPMT). The front (gamma ray entrance) layer is a 48 × 48 pixelated cerium doped lutetium yttrium orthosilicate (LYSO) scintillator array with individual crystals measuring 1.01 × 1.01 × 6.1 mm. The back (towards the PMT) layer is a 32 × 32 pixelated bismuth germanate (BGO) scintillator array with individual crystals measuring 1.55 × 1.55 × 8.9 mm. For energy windows of 250-650 keV and 350-650 keV, the peak absolute sensitivity at the center of the FOV was 13.5% and 10.4% including CLCS events, and 11.8% and 8.9% excluding CLCS events, respectively. The average detector energy resolution derived by averaging the individual crystal spectra was 11.7% ± 1.4% for LYSO and 17.0% ± 1.4% for BGO. The 3D ordered-subsets expectation maximization (OSEM) reconstructed image of a point source in air, ranged from 0.73 mm to 1.19 mm, with an average value of 0.93 ± 0.09 mm at all measured locations. The peak noise equivalent count rate (NECR) and scatter fraction were 179 kcps at 12.4 MBq and 6.9% for the mouse-sized phantom, and 63 kcps at 11.3 MBq and 18.3% for the rat-sized phantom. For the NEMA image quality phantom, the uniformity was 5.8%, and the spillover ratios measured in the water- and air-filled cold region chambers were 0.047 and 0.044, respectively. The recovery coefficients (RC) ranged from 0.31 to 0.92. These results and in vivo evaluation demonstrate that the HiPET can achieve high quality molecular imaging for biomedical applications.

https://pubmed.ncbi.nlm.nih.gov/31935693/

Gu Z, Taschereau R, Vu NT, Wang H, Prout DL, Silverman RW, Bai B, Stout DB, Phelps ME, Chatziioannou AF. NEMA NU-4 performance evaluation of PETbox4, a high sensitivity dedicated PET preclinical tomograph. Phys Med Biol. 2013 Jun 7;58(11):3791-814. doi: 10.1088/0031-9155/58/11/3791. Epub 2013 May 10.

Abstract

PETbox4 is a new, fully tomographic bench top PET scanner dedicated to high sensitivity and high resolution imaging of mice. This manuscript characterizes the performance of the prototype system using the National Electrical Manufacturers Association NU 4-2008 standards, including studies of sensitivity, spatial resolution, energy resolution, scatter fraction, count-rate performance and image quality. The PETbox4 performance is also compared with the performance of PETbox, a previous generation limited angle tomography system. PETbox4 consists of four opposing flat-panel type detectors arranged in a box-like geometry. Each panel is made by a 24 × 50 pixelated array of 1.82 × 1.82 × 7 mm bismuth germanate scintillation crystals with a crystal pitch of 1.90 mm. Each of these scintillation arrays is coupled to two Hamamatsu H8500 photomultiplier tubes via a glass light guide. Volumetric images for a 45 × 45 × 95 mm field of view (FOV) are reconstructed with a maximum likelihood expectation maximization algorithm incorporating a system model based on a parameterized detector response. With an energy window of 150-650 keV, the peak absolute sensitivity is approximately 18% at the center of FOV. The measured crystal energy resolution ranges from 13.5% to 48.3% full width at half maximum (FWHM), with a mean of 18.0%. The intrinsic detector spatial resolution is 1.5 mm FWHM in both transverse and axial directions. The reconstructed image spatial resolution for different locations in the FOV ranges from 1.32 to 1.93 mm, with an average of 1.46 mm. The peak noise equivalent count rate for the mouse-sized phantom is 35 kcps for a total activity of 1.5 MBq (40 µCi) and the scatter fraction is 28%. The standard deviation in the uniform region of the image quality phantom is 5.7%. The recovery coefficients range from 0.10 to 0.93. In comparison to the first generation two panel PETbox system, PETbox4 achieves substantial improvements on sensitivity and spatial resolution. The overall performance demonstrates that the PETbox4 scanner is suitable for producing high quality images for molecular imaging based biomedical research.

http://www.ncbi.nlm.nih.gov/pubmed/23666034

Radiochemistry Technology Development

Claggett SB, Quinn KM, Lazari M, Moore MD,van Dam RM. Simplified programming and control of automated radiosynthesizers through unit operations. EJNMMI Research, vol. 3, no. 1, p. 53, Jul. 2013.

Abstract

Background: Many automated radiosynthesizers for producing positron emission tomography (PET) probes provide a means for the operator to create custom synthesis programs. The programming interfaces are typically designed with the engineer rather than the radiochemist in mind, requiring lengthy programs to be created from sequences of low-level, non-intuitive hardware operations. In some cases, the user is even responsible for adding steps to update the graphical representation of the system. In light of these unnecessarily complex approaches, we have created software to perform radiochemistry on the ELIXYS radiosynthesizer with the goal of being intuitive and easy to use.

Methods: Radiochemists were consulted, and a wide range of radiosyntheses were analyzed to determine a comprehensive set of basic chemistry unit operations. Based around these operations, we created a software control system with a client–server architecture. In an attempt to maximize flexibility, the client software was designed to run on a variety of portable multi-touch devices. The software was used to create programs for the synthesis of several ¹⁸F-labeled probes on the ELIXYS radiosynthesizer, with [¹⁸F]FDG detailed here. To gauge the user-friendliness of the software, program lengths were compared to those from other systems. A small sample group with no prior radiosynthesizer experience was tasked with creating and running a simple protocol.

Results: The software was successfully used to synthesize several ¹⁸F-labeled PET probes, including [¹⁸F]FDG, with synthesis times and yields comparable to literature reports. The resulting programs were significantly shorter and easier to debug than programs from other systems. The sample group of naive users created and ran a simple protocol within a couple of hours, revealing a very short learning curve. The client–server architecture provided reliability, enabling continuity of the synthesis run even if the computer running the client software failed. The architecture enabled a single user to control the hardware while others observed the run in progress or created programs for other probes.

Conclusions: We developed a novel unit operation-based software interface to control automated radiosynthesizers that reduced the program length and complexity and also exhibited a short learning curve. The client–server architecture provided robustness and flexibility.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3717018/

Dooraghi AA, Keng PY, Chen S, Javed MR, Kim CJ, Chatziioannou AF, van Dam RM. Optimization of microfluidic PET tracer synthesis with Cerenkov imaging. Analyst, vol. 138, no. 19, pp. 5654–5664, Aug. 2013.

Abstract

Microfluidic technologies provide an attractive platform for the synthesis of radiolabeled compounds. Visualization of radioisotopes on chip is critical for synthesis optimization and technological development. With Cerenkov imaging, beta particle emitting isotopes can be localized with a sensitive CCD camera. In order for Cerenkov imaging to also serve as a quantitative tool, it is necessary to understand how material properties relevant to Cerenkov emission, namely, index of refraction and beta particle stopping power, affect Cerenkov light output. In this report, we investigate the fundamental physical characteristics of Cerenkov photon yield at different stages of [(18)F]FDG synthesis on the electrowetting on dielectric (EWOD) microfluidic platform. We also demonstrate how Cerenkov imaging has enabled synthesis optimization. Geant4, a Monte Carlo program applied extensively in high energy physics, is used to simulate Cerenkov photon yield from (18)F beta particles traversing materials of interest during [(18)F]FDG synthesis on chip. Our simulations show that the majority (approximately two-thirds) of the (18)F beta particle energy available to produce Cerenkov photons is deposited on the glass plates of the EWOD chip. This result suggests the possibility of using a single calibration factor to convert Cerenkov signal to radioactivity, independent of droplet composition. We validate our simulations with a controlled measurement examining varying ratios of [(18)O]H2O, dimethyl sulfoxide (DMSO), and acetonitrile (MeCN), and find a consistent calibration independent of solvent composition. However, the calibration factor may underestimate the radioactivity in actual synthesis due to discoloration of the droplet during certain steps of probe synthesis. In addition to the attractive quantitative potential of Cerenkov imaging, this imaging strategy provides indispensable qualitative data to guide synthesis optimization. We are able to use this imaging technique to optimize the mixing protocol as well as identify and correct for loss of radioactivity due to the migration of radioactive vapor outside of the EWOD heater, enabling an overall increase in the crude radiochemical yield from 50 ± 3% (n = 3) to 72 ± 13% (n = 5).

https://pubmed.ncbi.nlm.nih.gov/23928799/

Ha NS, Ly J, Jones J, Cheung S, van Dam RM. Novel volumetric method for highly repeatable injection in microchip electrophoresis. Analytica Chimica Acta 985: 129-140, 2017.

Abstract

A novel injector for microchip electrophoresis (MCE) has been designed and evaluated that achieves very high repeatability of injection volume suitable for quantitative analysis. It eliminates the injection biases in electrokinetic injection and the dependence on pressure and sample properties in hydrodynamic injection. The microfluidic injector, made of poly(dimethylsiloxane) (PDMS), operates similarly to an HPLC injection valve. It contains a channel segment (chamber) with a well-defined volume that serves as an “injection loop”. Using on-chip microvalves, the chamber can be connected to the sample source during the “loading” step, and to the CE separation channel during the “injection” step. Once the valves are opened in the second state, electrophoretic potential is applied to separate the sample. For evaluation and demonstration purposes, the microinjector was connected to a 75 µm ID capillary and UV absorbance detector. For single compounds, a relative standard deviation (RSD) of peak area as low as 1.04% (n=11) was obtained, and for compound mixtures, RSD as low as 0.40% (n=4) was observed. Using the same microchip, the performance of this new injection technique was compared to hydrodynamic injection and found to have improved repeatability and less dependence on sample viscosity. Furthermore, a non-radioactive version of the positron-emission tomography (PET) imaging probe, FLT, was successfully separated from its known 3 structurally-similar byproducts with baseline resolution, demonstrating the potential for rapid, quantitative analysis of impurities to ensure the safety of batches of short-lived radiotracers. Both the separation efficiency and injection repeatability were found to be substantially higher when using the novel volumetric injection approach compared to electrokinetic injection (performed in the same chip). This novel microinjector provides a straightforward way to improve the performance of hydrodynamic injection and enables extremely repeatable sample volume injection in MCE. It could be used in any MCE application where volume repeatability is needed, including the quantitation of impurities in pharmaceutical or radiopharmaceutical samples.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5657552/

Ly J, Ha NS, Cheung S, van Dam Rm. Toward miniaturized analysis of chemical identity and purity of radiopharmaceuticals via microchip electrophoresis. Analytical and Bioanalytical Chemistry 410(9): 2423-2436, 2018.

Abstract

Miniaturized synthesis of positron emission tomography (PET) tracers is poised to offer numerous advantages including reduced tracer production costs and increased availability of diverse tracers. While many steps of the tracer production process have been miniaturized, there has been relatively little development of microscale systems for the quality control (QC) testing process that is required by regulatory agencies to ensure purity, identity, and biological safety of the radiotracer before use in human subjects. Every batch must be tested, and in contrast with ordinary pharmaceuticals, the whole set of tests of radiopharmaceuticals must be completed within a short-period of time to minimize losses due to radioactive decay. By replacing conventional techniques with microscale analytical ones, it may be possible to significantly reduce instrument cost, conserve lab space, shorten analysis times, and streamline this aspect of PET tracer production. We focus in this work on miniaturizing the subset of QC tests for chemical identity and purity. These tests generally require high-resolution chromatographic separation prior to detection to enable the approach to be applied to many different tracers (and their impurities), and have not yet, to the best of our knowledge, been tackled in microfluidic systems. Toward this end, we previously explored the feasibility of using the technique of capillary electrophoresis (CE) as a replacement for the ‘gold standard’ approach of using high-performance liquid chromatography (HPLC) since CE offers similar separating power, flexibility and sensitivity, but can readily be implemented in a microchip format. Using a conventional CE system, we previously demonstrated the successful separation of non-radioactive version of a clinical PET tracer, 3’-deoxy-3’-fluorothymidine (FLT), from its known byproducts, and the separation of the PET tracer 1-(2’-deoxy-2’-fluoro-β-D-arabinofuranosyl)-cytosine (D-FAC) from its α-isomer, with sensitivity nearly as good as HPLC. Building on this feasibility study, in this paper, we describe the first effort to miniaturize the chemical identity and purity tests by using microchip electrophoresis (MCE). The fully-automated proof-of-concept system comprises a chip for sample injection, a separation capillary, and an optical detection chip. Using the same model compound (FLT and its known byproducts), we demonstrate that samples can be injected, separated, and detected, and show the potential to match the performance of HPLC. Addition of a radiation detector in the future would enable analysis of radiochemical identity and purity in the same device. We envision that eventually this MCE method could be combined with other miniaturized QC tests into a compact integrated system for automated routine QC testing of radiopharmaceuticals in the future.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6482050/

Lisova K, Chen BY, Wang J, Fong KMM, Clark PM,van Dam RM. Rapid, efficient, and economical synthesis of PET tracers in a droplet microreactor: application to O-(2-([¹⁸F]fluoroethyl)-L-tyrosine ([¹⁸F]FET). EJNMMI Radiopharmacy and Chemistry 5: 1, 2020.

Abstract

Background: Conventional scale production of small batches of PET tracers (e.g. for preclinical imaging) is an inefficient use of resources. Using O-(2-[¹⁸F]fluoroethyl)-L-tyrosine ([¹⁸F]FET), we demonstrate that simple microvolume radiosynthesis techniques can improve the efficiency of production by consuming tiny amounts of precursor, and maintaining high molar activity of the tracers even with low starting activity.

Procedures: The synthesis was carried out in microvolume droplets manipulated on a disposable patterned silicon “chip” affixed to a heater. A droplet of [¹⁸F]fluoride containing TBAHCO3 was first deposited onto a chip and dried at 100 °C. Subsequently, a droplet containing 60 nmol of precursor was added to the chip and the fluorination reaction was performed at 90 °C for 5 min. Removal of protecting groups was accomplished with a droplet of HCl heated at 90 °C for 3 min. Finally, the crude product was collected in a methanol-water mixture, purified via analytical-scale radio-HPLC and formulated in saline. As a demonstration, using [¹⁸F]FET produced on the chip, we prepared aliquots with different molar activities to explore the impact on preclinical PET imaging of tumor-bearing mice.

Results: The microdroplet synthesis exhibited an overall decay-corrected radiochemical yield of 55 ± 7% (𝘯 = 4) after purification and formulation. When automated, the synthesis could be completed in 35 min. Starting with < 370 MBq of activity, ~ 150 MBq of [¹⁸F]FET could be produced, sufficient for multiple in vivo experiments, with high molar activities (48–119 GBq/μmol). The demonstration imaging study revealed the uptake of [¹⁸F]FET in subcutaneous tumors, but no significant differences in tumor uptake as a result of molar activity differences (ranging 0.37–48 GBq/μmol) were observed.

Conclusions: A microdroplet synthesis of [¹⁸F]FET was developed demonstrating low reagent consumption, high yield, and high molar activity. The approach can be expanded to tracers other than [¹⁸F]FET, and adapted to produce higher quantities of the tracer sufficient for clinical PET imaging.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6938530/

Wang J, Rios A, Lisova K, Slavik R, Chatziioannou AF, van Dam RM. High-throughput radio-TLC analysis. Nuclear Medicine and Biology. 2020; 82-83:41-48. doi: 10.1016/j.nucmedbio.2019.12.003.

Abstract

https://pubmed.ncbi.nlm.nih.gov/31891883/

Lazari M, Quinn KM, Claggett SB, Collins J, Shah GJ, Herman HE, Maraglia B, Phelps ME, Moore MD, van Dam RM. ELIXYS - a fully automated, three-reactor high-pressure radiosynthesizer for development and routine production of diverse PET tracers. EJNMMI Res. 2013 Jul 12;3(1):52. doi: 10.1186/2191-219X-3-52.

Abstract

BACKGROUND: Automated radiosynthesizers are vital for routine production of positron-emission tomography tracers to minimize radiation exposure to operators and to ensure reproducible synthesis yields. The recent trend in the synthesizer industry towards the use of disposable kits aims to simplify setup and operation for the user, but often introduces several limitations related to temperature and chemical compatibility, thus requiring reoptimization of protocols developed on non-cassette-based systems. Radiochemists would benefit from a single hybrid system that provides tremendous flexibility for development and optimization of reaction conditions while also providing a pathway to simple, cassette-based production of diverse tracers.

METHODS: We have designed, built, and tested an automated three-reactor radiosynthesizer (ELIXYS) to provide a flexible radiosynthesis platform suitable for both tracer development and routine production. The synthesizer is capable of performing high-pressure and high-temperature reactions by eliminating permanent tubing and valve connections to the reaction vessel. Each of the three movable reactors can seal against different locations on disposable cassettes to carry out different functions such as sealed reactions, evaporations, and reagent addition. A reagent and gas handling robot moves sealed reagent vials from storage locations in the cassette to addition positions and also dynamically provides vacuum and inert gas to ports on the cassette. The software integrates these automated features into chemistry unit operations (e.g., React, Evaporate, Add) to intuitively create synthesis protocols. 2-Deoxy-2-[¹⁸F]fluoro-5-methyl-β-l-arabinofuranosyluracil (l-[¹⁸F]FMAU) and 2-deoxy-2-[¹⁸F]fluoro-β-d-arabinofuranosylcytosine (d-[¹⁸F]FAC) were synthesized to validate the system.

RESULTS: l-[¹⁸F]FMAU and d-[¹⁸F]FAC were successfully synthesized in 165 and 170 min, respectively, with decay-corrected radiochemical yields of 46% ± 1% (n = 6) and 31% ± 5% (n = 6), respectively. The yield, repeatability, and synthesis time are comparable to, or better than, other reports. d-[¹⁸F]FAC produced by ELIXYS and another manually operated apparatus exhibited similar biodistribution in wild-type mice.

CONCLUSION: The ELIXYS automated radiosynthesizer is capable of performing radiosyntheses requiring demanding conditions: up to three reaction vessels, high temperatures, high pressures, and sensitive reagents. Such flexibility facilitates tracer development and the ability to synthesize multiple tracers on the same system without customization or replumbing. The disposable cassette approach simplifies the transition from development to production.

http://www.ncbi.nlm.nih.gov/pubmed/23849185

Probe and Assay Development

Yong J, Rasooly J, Dang H, Lu Y, Middleton B, Zhang Z, Hon L, Namavari M, Stout DB, Atkinson MA, Tian J, Gambhir SS, Kaufman DL. Multimodality imaging of β-cells in mouse models of type 1 and 2 diabetes. Diabetes. 2011 May;60(5):1383-92. doi: 10.2337/db10-0907. Epub 2011 Mar 25.

Abstract

OBJECTIVE: β-Cells that express an imaging reporter have provided powerful tools for studying β-cell development, islet transplantation, and β-cell autoimmunity. To further expedite diabetes research, we generated transgenic C57BL/6 "MIP-TF" mice that have a mouse insulin promoter (MIP) driving the expression of a trifusion (TF) protein of three imaging reporters (luciferase/enhanced green fluorescent protein/HSV1-sr39 thymidine kinase) in their β-cells. This should enable the noninvasive imaging of β-cells by charge-coupled device (CCD) and micro-positron emission tomography (PET), as well as the identification of β-cells at the cellular level by fluorescent microscopy.

RESEARCH DESIGN AND METHODS: MIP-TF mouse β-cells were multimodality imaged in models of type 1 and type 2 diabetes.

RESULTS: MIP-TF mouse β-cells were readily identified in pancreatic tissue sections using fluorescent microscopy. We show that MIP-TF β-cells can be noninvasively imaged using microPET. There was a correlation between CCD and microPET signals from the pancreas region of individual mice. After low-dose streptozotocin administration to induce type 1 diabetes, we observed a progressive reduction in bioluminescence from the pancreas region before the appearance of hyperglycemia. Although there have been reports of hyperglycemia inducing proinsulin expression in extrapancreatic tissues, we did not observe bioluminescent signals from extrapancreatic tissues of diabetic MIP-TF mice. Because MIP-TF mouse β-cells express a viral thymidine kinase, ganciclovir treatment induced hyperglycemia, providing a new experimental model of type 1 diabetes. Mice fed a high-fat diet to model early type 2 diabetes displayed a progressive increase in their pancreatic bioluminescent signals, which were positively correlated with area under the curve-intraperitoneal glucose tolerance test (AUC-IPGTT).

CONCLUSIONS: MIP-TF mice provide a new tool for monitoring β-cells from the single cell level to noninvasive assessments of β-cells in models of type 1 diabetes and type 2 diabetes.
http://www.ncbi.nlm.nih.gov/pubmed/21441442

Tracer Kinetic Modeling

Wilks MQ, Knowles SM, Wu AM, Huang SC. Improved modeling of in vivo kinetics of slowly diffusing radiotracers for tumor imaging. J Nucl Med. 2014 Sep;55(9):1539-44. doi: 10.2967/jnumed.114.140038. Epub 2014 Jul 3.

Abstract

Large-molecule tracers, such as labeled antibodies, have shown success in immuno-PET for imaging of specific cell surface biomarkers. However, previous work has shown that localization of such tracers shows high levels of heterogeneity in target tissues, due to both the slow diffusion and the high affinity of these compounds. In this work, we investigate the effects of subvoxel spatial heterogeneity on measured time-activity curves in PET imaging and the effects of ignoring diffusion limitation on parameter estimates from kinetic modeling.

METHODS: Partial differential equations (PDE) were built to model a radially symmetric reaction-diffusion equation describing the activity of immuno-PET tracers. The effects of slower diffusion on measured time-activity curves and parameter estimates were measured in silico, and a modified Levenberg-Marquardt algorithm with Bayesian priors was developed to accurately estimate parameters from diffusion-limited data. This algorithm was applied to immuno-PET data of mice implanted with prostate stem cell antigen-overexpressing tumors and injected with (124)I-labeled A11 anti-prostate stem cell antigen minibody.

RESULTS: Slow diffusion of tracers in linear binding models resulted in heterogeneous localization in silico but no measurable differences in time-activity curves. For more realistic saturable binding models, measured time-activity curves were strongly dependent on diffusion rates of the tracers. Fitting diffusion-limited data with regular compartmental models led to parameter estimate bias in an excess of 1,000% of true values, while the new model and fitting protocol could accurately measure kinetics in silico. In vivo imaging data were also fit well by the new PDE model, with estimates of the dissociation constant (Kd) and receptor density close to in vitro measurements and with order of magnitude differences from a regular compartmental model ignoring tracer diffusion limitation.

CONCLUSION: Heterogeneous localization of large, high-affinity compounds can lead to large differences in measured time-activity curves in immuno-PET imaging, and ignoring diffusion limitations can lead to large errors in kinetic parameter estimates. Modeling of these systems with PDE models with Bayesian priors is necessary for quantitative in vivo measurements of kinetics of slow-diffusion tracers.

http://www.ncbi.nlm.nih.gov/pubmed/24994929

Wong KP, Zhang X, Huang SC. Improved derivation of input function in dynamic mouse [¹⁸F]FDG PET using bladder radioactivity kinetics. Mol Imaging Biol. 2013 Aug;15(4):486-96. doi: 10.1007/s11307-013-0610-6.

Abstract

PURPOSE: Accurate determination of the plasma input function (IF) is essential for absolute quantification of physiological parameters in positron emission tomography (PET). However, it requires an invasive and tedious procedure of arterial blood sampling that is challenging in mice because of the limited blood volume. In this study, a hybrid modeling approach is proposed to estimate the plasma IF of 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) in mice using accumulated radioactivity in urinary bladder together with a single late-time blood sample measurement.

METHODS: Dynamic PET scans were performed on nine isoflurane-anesthetized male C57BL/6 mice after a bolus injection of [¹⁸F]FDG at the lateral caudal vein. During a 60- or 90-min scan, serial blood samples were taken from the femoral artery. Image data were reconstructed using filtered backprojection with computed tomography-based attenuation correction. Total accumulated radioactivity in the urinary bladder at late times was fitted to a renal compartmental model with the last blood sample and a one-exponential function that described the [¹⁸F]FDG clearance in blood. Multiple late-time blood sample estimates were calculated by the blood [¹⁸F]FDG clearance equation. A sum of four-exponentials was assumed for the plasma IF that served as a forcing function to all tissues. The estimated plasma IF was obtained by simultaneously fitting the [¹⁸F]FDG model to the time-activity curves (TACs) of liver and muscle and the forcing function to early (0-1 min) left-ventricle data (corrected for delay, dispersion, partial-volume effects, and erythrocyte uptake) and the late-time blood estimates. Using only the blood sample collected at the end of the study to estimate the IF and the use of liver TAC as an alternative IF were also investigated.

RESULTS: The area under the plasma IFs calculated for all studies using the hybrid approach was not significantly different from that using all blood samples. [¹⁸F]FDG uptake constants in brain, myocardium, skeletal muscle, and liver computed by the Patlak analysis using estimated and measured plasma IFs were in excellent agreement (slope∼1; R2>0.983). The IF estimated using only the last blood sample drawn at the end of the study and the use of liver TAC as the plasma IF provided less reliable results.

CONCLUSIONS: The estimated plasma IFs obtained with the hybrid method agreed well with those derived from arterial blood sampling. Importantly, the proposed method obviates the need of arterial catheterization, making it possible to perform repeated dynamic [¹⁸F]FDG PET studies on the same animal. Liver TAC is unsuitable as an input function for absolute quantification of [¹⁸F]FDG PET data.

http://www.ncbi.nlm.nih.gov/pubmed/23322346

Sha W, Ye H, Iwamoto KS, Wong KP, Wilks MQ, Stout D, McBride W, Huang SC. Factors affecting tumor (18) F-FDG uptake in longitudinal mouse PET studies. EJNMMI Res. 2013 Jul 10;3:51. doi: 10.1186/2191-219X-3-51. eCollection 2013.

Abstract

BACKGROUND: Many biological factors of 2-[(18) F]fluoro-2-deoxy-d-glucose ((18) F-FDG) in blood can affect (18) F-FDG uptake in tumors. In this study, longitudinal (18) F-FDG positron emission tomography (PET) studies were performed on tumor-bearing mice to investigate the effect of blood glucose level and tumor size on (18) F-FDG uptake in tumors.

METHODS: Six- to eight-week-old severe combined immunodeficiency mice were implanted with glioblastoma U87 (n = 8) or adenocarcinoma MDA-MB-231 (MDA) (n = 11) in the shoulder. When the tumor diameter was approximately 2.5 mm, a 60-min dynamic (18) F-FDG PET scan was performed weekly until the tumor diameter reached 10 mm. Regions of interests were defined in major organs and tumor. A plasma curve was derived based on a modeling method that utilizes the early heart time-activity curve and a late-time blood sample. The (18) F-FDG uptake constant K i was calculated using Patlak analysis on the tumors without an apparent necrotic center shown in the PET images. For each tumor type, the measured K i was corrected for partial volume (PV), and multivariate regression analysis was performed to examine the effects of blood glucose level ([Glc]) and tumor growth. Corrected Akaike's information criterion was used to determine the best model.

RESULTS: The regression model that best fit the PV-corrected K i for U87 data was K i /RC = (1/[Glc]) × (0.27 ± 0.027) mL/min/mL (where [Glc] is in mmol/L), and for MDA, it was K i /RC = (0.04 ± 0.005) mL/min/mL, where K i /RC denotes the PV-corrected K i using an individual recovery coefficient (RC). The results indicated that (18) F-FDG K i /RC for U87 was inversely related to [Glc], while [Glc] had no effect on (18) F-FDG K i /RC of MDA. After the effects of PV and [Glc] were accounted for, the data did not support any increase of (18) F-FDG K i as the tumor (of either type) grew larger in size.

CONCLUSIONS: The effect of [Glc] on the tumor (18) F-FDG K i was tumor-dependent. PV- and [Glc]-corrected (18) F-FDG K i did not show significant increase as the tumor of either type grew in size.

http://www.ncbi.nlm.nih.gov/pubmed/23841937

Kreissl MC, Stout DB, Wong KP, Wu HM, Caglayan E, Ladno W, Zhang X, Prior JO, Reiners C, Huang SC, Schelbert HR. Influence of dietary state and insulin on myocardial, skeletal muscle and brain [F]-fluorodeoxyglucose kinetics in mice. EJNMMI Res. 2011 Jul 6;1:8. doi: 10.1186/2191-219X-1-8.

Abstract

BACKGROUND: We evaluated the effect of insulin stimulation and dietary changes on myocardial, skeletal muscle and brain [(18)F]-fluorodeoxyglucose (FDG) kinetics and uptake in vivo in intact mice.

METHODS: Mice were anesthetized with isoflurane and imaged under different conditions: non-fasted (n = 7; "controls"), non-fasted with insulin (2 IU/kg body weight) injected subcutaneously immediately prior to FDG (n = 6), fasted (n = 5), and fasted with insulin injection (n = 5). A 60-min small-animal PET with serial blood sampling and kinetic modeling was performed.

RESULTS: We found comparable FDG standardized uptake values (SUVs) in myocardium in the non-fasted controls and non-fasted-insulin injected group (SUV 45-60 min, 9.58 ± 1.62 vs. 9.98 ± 2.44; p = 0.74), a lower myocardial SUV was noted in the fasted group (3.48 ± 1.73; p < 0.001). In contrast, the FDG uptake rate constant (K(i)) for myocardium increased significantly by 47% in non-fasted mice by insulin (13.4 ± 3.9 ml/min/100 g vs. 19.8 ± 3.3 ml/min/100 g; p = 0.030); in fasted mice, a lower myocardial K(i) as compared to controls was observed (3.3 ± 1.9 ml/min/100 g; p < 0.001). Skeletal muscle SUVs and K(i) values were increased by insulin independent of dietary state, whereas in the brain, those parameters were not influenced by fasting or administration of insulin. Fasting led to a reduction in glucose metabolic rate in the myocardium (19.41 ± 5.39 vs. 3.26 ± 1.97 mg/min/100 g; p < 0.001), the skeletal muscle (1.06 ± 0.34 vs. 0.34 ± 0.08 mg/min/100 g; p = 0.001) but not the brain (3.21 ± 0.53 vs. 2.85 ±0.25 mg/min/100 g; p = 0.19).

CONCLUSIONS: Changes in organ SUVs, uptake rate constants and metabolic rates induced by fasting and insulin administration as observed in intact mice by small-animal PET imaging are consistent with those observed in isolated heart/muscle preparations and, more importantly, in vivo studies in larger animals and in humans. When assessing the effect of insulin on the myocardial glucose metabolism of non-fasted mice, it is not sufficient to just calculate the SUV - dynamic imaging with kinetic modeling is necessary.

http://www.ncbi.nlm.nih.gov/pubmed/21841971

Wong KP, Sha W, Zhang X, Huang SC. Effects of administration route, dietary condition, and blood glucose level on kinetics and uptake of ¹⁸F-FDG in mice. J Nucl Med. 2011 May;52(5):800-7. doi: 10.2967/jnumed.110.085092. Epub 2011 Apr 15.

Abstract

The effects of dietary condition and blood glucose level on the kinetics and uptake of (18)F-FDG in mice were systematically investigated using intraperitoneal and tail-vein injection.

METHODS: Dynamic PET was performed for 60 min on 23 isoflurane-anesthetized male C57BL/6 mice after intravenous (n = 11) or intraperitoneal (n = 12) injection of (18)F-FDG. Five and 6 mice in the intravenous and intraperitoneal groups, respectively, were kept fasting overnight (18 ± 2 h), and the others were fed ad libitum. Serial blood samples were collected from the femoral artery to measure (18)F-FDG and glucose concentrations. Image data were reconstructed using filtered backprojection with CT-based attenuation correction. The standardized uptake value (SUV) was estimated from the 45- to 60-min image. The metabolic rate of glucose (MRGlu) and (18)F-FDG uptake constant (K(i)) were derived by Patlak graphical analysis.

RESULTS: In the brain, SUV and K(i) were significantly higher in fasting mice with intraperitoneal injection, but MRGlu did not differ significantly under different dietary states and administration routes. Cerebral K(i) was inversely related to elevated blood glucose levels, irrespective of administration route or dietary state. In myocardium, SUV, K(i), and MRGlu were significantly lower in fasting than in nonfasting mice for both routes of injection. Myocardial SUV and K(i) were strongly dependent on the dietary state, and K(i) did not correlate with the blood glucose level. Similar results were obtained for skeletal muscle, although the differences were not as pronounced.

CONCLUSION: Intraperitoneal injection is a valid alternative route, providing pharmacokinetic data equivalent to data from tail-vein injection for small-animal (18)F-FDG PET. Cerebral K(i) varies inversely with blood glucose level, but the measured cerebral MRGlu does not correlate with blood glucose level or dietary condition. Conversely, the K(i) values of the myocardium and skeletal muscle are strongly dependent on dietary condition but not on blood glucose level. In tissue in which (18)F-FDG uptake declines with increasing blood glucose, correction for blood glucose level will make SUV a more robust outcome measure of MRGlu.

http://www.ncbi.nlm.nih.gov/pubmed/21498533

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