Research Focus and interests: Molecular Imaging, PET, Immuno-Oncology, Graft versus Host Disease, Cell therapies
Dr. Israt Alam is a Research Scientist at the Radiology Department at Stanford University, under the supervision of Prof. Sanjiv Sam Gambhir. Her research focuses on studying lymphocyte activation with the motivation of developing non-invasive imaging tools, to monitor immune dynamics in response to immunotherapy and for diagnosis of immune driven diseases. Her work has supported the clinical translation of several nuclear imaging agents for early disease diagnosis and prediction of treatment response for improved patient management.
Post-Doctoral Scholar and Research Scientist, Department of Radiology, Stanford (2015-present)
Visiting Researcher under supervision of Prof. Spencer Shorte, Plateforme d'imagerie dynamique, Pasteur Institute, Paris (2014)
Science Education Intern and Consultant: United Nations Educational, Science and Cultural Organization (UNESCO), Paris (2012-2013)
Education & Certifications
MSCi, Imperial College London, Biochemistry
PhD, University of Cambridge, Emmanuel College, Molecular Imaging-Supervisor Prof. Kevin Brindle
Israt Alam. "United States Patent US-2018-0043040-A1 Imaging tumor glycolysis by non-invasive measurement of pyruvate kinase M2.", Feb 15, 2018
Israt Alam, Maaike de Backer, Andre Neves, Kevin Brindle. "United Kingdom Patent Europe EP2280735 Agents for detecting and imaging cell death", University of Cambridge, Apr 29, 2009
Professional Affiliations and Activities
Course Co-Director and Lecturer, Stanford BioEngineering (BioE 224)-Probes for Multi-modality Molecular Imaging (2016 - Present)
Member, Society of Nuclear Medicine and Molecular Imaging (2018 - 2019)
Member, World Molecular Imaging Society (WMIS) (2015 - Present)
Member, European Society of Molecular Imaging (ESMI) (2015 - Present)
Evaluation of [18F]DASA-23 for non-invasive measurement of aberrantly expressed pyruvate kinase M2 in glioblastoma: preclinical and first in human studies
SOC NUCLEAR MEDICINE INC. 2019
View details for Web of Science ID 000473116800052
The characterization of 18F-hGTS13 for molecular imaging of xC- transporter activity with positron emission tomography.
Journal of nuclear medicine : official publication, Society of Nuclear Medicine
Purpose: The aim of this study was development of an improved positron emission tomography (PET) radiotracer for measuring xC- activity with increased tumor uptake and reduced uptake in inflammatory cells compared to (S)-4-(3-18F-Fluoropropyl)-L-glutamic acid (18F-FSPG). Experimental design: 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 evaluated in H460 tumor bearing rats. Preliminary studies investigate 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 of 18F-hGTS13 (7.5±0.9%ID/g, n = 3) was significantly higher than with 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%ID/g 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 which may provide information regarding tumor oxidation states. 18F-hGTS13-isomer2 has potential for clinical translation for imaging cancers of the thorax due to the low background signal in healthy tissue.
View details for DOI 10.2967/jnumed.119.225870
View details for PubMedID 31171595
Development and Evaluation of an 18F-Radiolabeled Monocyclam Derivative for Imaging CXCR4 Expression.
C-X-C chemokine receptor type 4 (CXCR4) is a protein that in humans is encoded by the CXCR4 gene and binds the ligand CXCL12 (also known as SDF-1). The CXCR4-CXCL12 interaction in cancer elicits biological activities that result in tumor progression and has accordingly been the subject of significant investigation for detection and treatment of disease. Peptidic antagonists have been labeled with a variety of radioisotopes for detection of CXCR4, but methodology utilizing small molecules have predominantly used radiometals. We report here the development of a 18F-radiolabeled cyclam-based small molecule radioprobe, [18F]MCFB, for imaging CXCR4 expression. The IC50 of [19F]MCFB for CXCR4 was similar to that of AMD3465 (111.3 and 89.9 nM, respectively). In vitro binding assays show that the tracer depicted differential CXCR4 expression, which was blocked in the presence of AMD3465, demonstrating specificity of [18F]MCFB. Positron emission tomography (PET) imaging studies showed distinct uptake of radioprobe in lymphoma and breast cancer xenografts. High liver and kidney uptake were seen with [18F]MCFB leading us to further examine the basis of its pharmacokinetics in relation to the tracer's cationic nature, thus, the role of organic cation transporters (OCTs). Substrate competition following the intravenous injection of metformin led to a marked decrease in urinary excretion of [18F]MCFB, with moderate changes observed in other organs, including the liver. Our results suggest involvement of OCTs in renal elimination of the tracer. In conclusion, the 18F radiolabeled monocyclam, [18F]MCFB, has potential to detect tumor CXCR4 in non-hepatic tissue.
View details for DOI 10.1021/acs.molpharmaceut.9b00069
View details for PubMedID 30883140
Imaging of Red-Shifted Light From Bioluminescent Tumors Using Fluorescence by Unbound Excitation From Luminescence
Front. Bioeng. Biotechnol
View details for DOI 10.3389/fbioe.2019.00073
Positron emission tomography reporter gene strategy for use in the central nervous system
View details for DOI 10.1073/pnas.1901645116
- An intravascular magnetic wire for the high-throughput retrieval of circulating tumour cells in vivo NATURE BIOMEDICAL ENGINEERING 2018; 2 (9): 696–705
Emerging Intraoperative Imaging Modalities to Improve Surgical Precision.
Molecular imaging and biology : MIB : the official publication of the Academy of Molecular Imaging
Intraoperative imaging (IOI) is performed to guide delineation and localization of regions of surgical interest. While oncological surgical planning predominantly utilizes x-ray computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US), intraoperative guidance mainly remains on surgeon interpretation and pathology for confirmation. Over the past decades however, intraoperative guidance has evolved significantly with the emergence of several novel imaging technologies, including fluorescence-, Raman, photoacoustic-, and radio-guided approaches. These modalities have demonstrated the potential to further optimize precision in surgical resection and improve clinical outcomes for patients. Not only can these technologies enhance our understanding of the disease, they can also yield large imaging datasets intraoperatively that can be analyzed by deep learning approaches for more rapid and accurate pathological diagnosis. Unfortunately, many of these novel technologies are still under preclinical or early clinical evaluation. Organizations like the Intra-Operative Imaging Study Group of the European Society for Molecular Imaging (ESMI) support interdisciplinary interactions with the aim to improve technical capabilities in the field, an approach that can succeed only if scientists, engineers, and physicians work closely together with industry and regulatory bodies to resolve roadblocks to clinical translation. In this review, we provide an overview of a variety of novel IOI technologies, discuss their challenges, and present future perspectives on the enormous potential of IOI for oncological surgical navigation.
View details for PubMedID 29916118
- [F-18] FSPG-PET reveals increased cystine/glutamate antiporter (xc-) activity in a mouse model of multiple sclerosis JOURNAL OF NEUROINFLAMMATION 2018; 15
Imaging activated T cells predicts response to cancer vaccines.
The Journal of clinical investigation
In situ cancer vaccines are under active clinical investigation, given their reported ability to eradicate both local and disseminated malignancies. Intratumoral vaccine administration is thought to activate a T cell-mediated immune response, which begins in the treated tumor and cascades systemically. In this study, we describe a PET tracer (64Cu-DOTA-AbOX40) that enabled noninvasive and longitudinal imaging of OX40, a cell-surface marker of T cell activation. We report the spatiotemporal dynamics of T cell activation following in situ vaccination with CpG oligodeoxynucleotide in a dual tumor-bearing mouse model. We demonstrate that OX40 imaging was able to predict tumor responses on day 9 after treatment on the basis of tumor tracer uptake on day 2, with greater accuracy than both anatomical and blood-based measurements. These studies provide key insights into global T cell activation following local CpG treatment and indicate that 64Cu-DOTA-AbOX40 is a promising candidate for monitoring clinical cancer immunotherapy strategies.
View details for PubMedID 29596062
Eradication of spontaneous malignancy by local immunotherapy.
Science translational medicine
2018; 10 (426)
It has recently become apparent that the immune system can cure cancer. In some of these strategies, the antigen targets are preidentified and therapies are custom-made against these targets. In others, antibodies are used to remove the brakes of the immune system, allowing preexisting T cells to attack cancer cells. We have used another noncustomized approach called in situ vaccination. Immunoenhancing agents are injected locally into one site of tumor, thereby triggering a T cell immune response locally that then attacks cancer throughout the body. We have used a screening strategy in which the same syngeneic tumor is implanted at two separate sites in the body. One tumor is then injected with the test agents, and the resulting immune response is detected by the regression of the distant, untreated tumor. Using this assay, the combination of unmethylated CG-enriched oligodeoxynucleotide (CpG)-a Toll-like receptor 9 (TLR9) ligand-and anti-OX40 antibody provided the most impressive results. TLRs are components of the innate immune system that recognize molecular patterns on pathogens. Low doses of CpG injected into a tumor induce the expression of OX40 on CD4+ T cells in the microenvironment in mouse or human tumors. An agonistic anti-OX40 antibody can then trigger a T cell immune response, which is specific to the antigens of the injected tumor. Remarkably, this combination of a TLR ligand and an anti-OX40 antibody can cure multiple types of cancer and prevent spontaneous genetically driven cancers.
View details for PubMedID 29386357
Intraoperative Molecular Imaging in Lung Cancer: The State of the Art and the Future.
Molecular therapy : the journal of the American Society of Gene Therapy
2018; 26 (2): 338–41
View details for PubMedID 29398484
The Utility of [18F]DASA-23 for Molecular Imaging of Prostate Cancer with Positron Emission Tomography.
Molecular imaging and biology : MIB : the official publication of the Academy of Molecular Imaging
There is a strong, unmet need for superior positron emission tomography (PET) imaging agents that are able to measure biochemical processes specific to prostate cancer. Pyruvate kinase M2 (PKM2) catalyzes the concluding step in glycolysis and is a key regulator of tumor growth and metabolism. Elevation of PKM2 expression was detected in Gleason 8-10 tumors compared to Gleason 6-7 carcinomas, indicating that PKM2 may potentially be a marker of aggressive prostate cancer. We have recently reported the development of a PKM2-specific radiopharmaceutical [18F]DASA-23 and herein describe its evaluation in cell culture and preclinical models of prostate cancer.The cellular uptake of [18F]DASA-23 was evaluated in a panel of prostate cancer cell lines and compared to that of [18F]FDG. The specificity of [18F]DASA-23 to measure PKM2 levels in cell culture was additionally confirmed through the use of PKM2-specific siRNA. PET imaging studies were then completed utilizing subcutaneous prostate cancer xenografts using either PC3 or DU145 cells in mice.[18F]DASA-23 uptake values over 60-min incubation period in PC3, LnCAP, and DU145 respectively were 23.4 ± 4.5, 18.0 ± 2.1, and 53.1 ± 4.6 % tracer/mg protein. Transient reduction in PKM2 protein expression with siRNA resulted in a 50.1 % reduction in radiotracer uptake in DU145 cells. Small animal PET imaging revealed 0.86 ± 0.13 and 1.6 ± 0.2 % ID/g at 30 min post injection of radioactivity in DU145 and PC3 subcutaneous tumor bearing mice respectively.Herein, we evaluated a F-18-labeled PKM2-specific radiotracer, [18F]DASA-23, for the molecular imaging of prostate cancer with PET. [18F]DASA-23 revealed rapid and extensive uptake levels in cellular uptake studies of prostate cancer cells; however, there was only modest tumor uptake when evaluated in mouse subcutaneous tumor models.
View details for PubMedID 29736561
A PET Imaging Strategy to Visualize Activated T Cells in Acute Graft-versus-Host Disease Elicited by Allogenic Hematopoietic Cell Transplant.
2017; 77 (11): 2893-2902
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-β-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.
View details for DOI 10.1158/0008-5472.CAN-16-2953
View details for PubMedID 28572504
Rapid Imaging of Tumor Cell Death In Vivo Using the C2A Domain of Synaptotagmin-I
JOURNAL OF NUCLEAR MEDICINE
2017; 58 (6): 881–87
Cell death is an important target for imaging the early response of tumors to treatment. We describe here the validation of a phosphatidylserine-binding agent for detecting tumor cell death in vivo based on the C2A domain of synaptotagmin-I. Methods: The capability of near-infrared fluorophore-labeled and 99mTc- and 111In-labeled derivatives of C2Am for imaging tumor cell death, using planar near-infrared fluorescence imaging and SPECT, respectively, was evaluated in implanted and genetically engineered mouse models of lymphoma and in a human colorectal xenograft. Results: The fluorophore-labeled C2Am derivative showed predominantly renal clearance and high specificity and sensitivity for detecting low levels of tumor cell death (2%-5%). There was a significant correlation (R > 0.9, P < 0.05) between fluorescently labeled C2Am binding and histologic markers of cell death, including cleaved caspase-3, whereas there was no such correlation with a site-directed mutant of C2Am (iC2Am) that does not bind phosphatidylserine. 99mTc-C2Am and 111In-C2Am also showed favorable biodistribution profiles, with predominantly renal clearance and low nonspecific retention in the liver and spleen at 24 h after probe administration. 99mTc-C2Am and 111In-C2Am generated tumor-to-muscle ratios in drug-treated tumors of 4.3× and 2.2×, respectively, at 2 h and 7.3× and 4.1×, respectively, at 24 h after administration. Conclusion: Given the favorable biodistribution profile of 99mTc- and 111In-labeled C2Am, and their ability to produce rapid and cell death-specific image contrast, these agents have potential for clinical translation.
View details for DOI 10.2967/jnumed.116.183004
View details for Web of Science ID 000402572500010
View details for PubMedID 28209913
F]DASA-23 for Imaging Tumor Glycolysis Through Noninvasive Measurement of Pyruvate Kinase M2.
Molecular imaging and biology
A hallmark of cancer is metabolic reprogramming, which is exploited by cancer cells to ensure rapid growth and survival. Pyruvate kinase M2 (PKM2) catalyzes the final step in glycolysis, a key step in tumor metabolism and growth. Recently, we reported the radiosynthesis of the first positron emission tomography tracer for visualizing PKM2 in vivo-i.e., [(11)C]DASA-23. Due to the highly promising imaging results obtained with [(11)C]DASA-23 in rodent model glioblastoma, we set out to generate an F-18-labeled version of this tracer, with the end goal of clinical translation in mind. Herein, we report the radiosynthesis of 1-((2-fluoro-6-[(18)F]fluorophenyl)sulfonyl)-4-((4-methoxyphenyl)sulfonyl)piperazine ([(18)F]DASA-23) and our initial investigation of its binding properties in cancer cells.We synthesized [(18)F]DASA-23 via fluorination of 1-((2-fluoro-6-nitrophenyl)sulfonyl)-4-((4-methoxyphenyl)sulfonyl)piperazine (10) with K[(18)F]F/K2.2.2 in N,N-dimethylformamide at 110 °C for 20 min. Subsequently, we evaluated uptake of [(18)F]DASA-23 in HeLa cervical adenocarcinoma cells and in vitro stability in human and mouse serum.We successfully prepared [(18)F]DASA-23 in 2.61 ± 1.54 % radiochemical yield (n = 10, non-decay corrected at end of synthesis) with a specific activity of 2.59 ± 0.44 Ci/μmol. Preliminary cell uptake experiments revealed high uptake in HeLa cells, which was effectively blocked by pretreating cells with the structurally distinct PKM2 activator, TEPP-46. [(18)F]DASA-23 remained intact in human and mouse serum up to 120 min.Herein, we have identified a F-18-labeled PKM2 specific radiotracer which shows potential for in vivo imaging. The promising cell uptake results reported herein warrant the further evaluation of [(18)F]DASA-23 for its ability to detect and monitor cancer noninvasively.
View details for DOI 10.1007/s11307-017-1068-8
View details for PubMedID 28236227
- Microwave gallium-68 radiochemistry for kinetically stable bis(thiosemicarbazone) complexes: structural investigations and cellular uptake under hypoxia DALTON TRANSACTIONS 2016; 45 (1): 144-155
- Radiopharmaceuticals as probes to characterize tumour tissue EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING 2015; 42 (4): 537-561
Acetyl-CoA Synthetase 2 Promotes Acetate Utilization and Maintains Cancer Cell Growth under Metabolic Stress
2015; 27 (1): 57-71
A functional genomics study revealed that the activity of acetyl-CoA synthetase 2 (ACSS2) contributes to cancer cell growth under low-oxygen and lipid-depleted conditions. Comparative metabolomics and lipidomics demonstrated that acetate is used as a nutritional source by cancer cells in an ACSS2-dependent manner, and supplied a significant fraction of the carbon within the fatty acid and phospholipid pools. ACSS2 expression is upregulated under metabolically stressed conditions and ACSS2 silencing reduced the growth of tumor xenografts. ACSS2 exhibits copy-number gain in human breast tumors, and ACSS2 expression correlates with disease progression. These results signify a critical role for acetate consumption in the production of lipid biomass within the harsh tumor microenvironment.
View details for DOI 10.1016/j.ccell.2014.12.002
View details for Web of Science ID 000347906900010
View details for PubMedID 25584894
View details for PubMedCentralID PMC4297291
Preclinical Evaluation of 3-F-18-Fluoro-2,2-Dimethylpropionic Acid as an Imaging Agent for Tumor Detection
JOURNAL OF NUCLEAR MEDICINE
2014; 55 (9): 1506-1512
Deregulated cellular metabolism is a hallmark of many cancers. In addition to increased glycolytic flux, exploited for cancer imaging with (18)F-FDG, tumor cells display aberrant lipid metabolism. Pivalic acid is a short-chain, branched carboxylic acid used to increase oral bioavailability of prodrugs. After prodrug hydrolysis, pivalic acid undergoes intracellular metabolism via the fatty acid oxidation pathway. We have designed a new probe, 3-(18)F-fluoro-2,2-dimethylpropionic acid ((18)F-FPIA), for the imaging of aberrant lipid metabolism and cancer detection.Cell intrinsic uptake of (18)F-FPIA was measured in murine EMT6 breast adenocarcinoma cells. In vivo dynamic imaging, time course biodistribution, and radiotracer stability testing were performed. (18)F-FPIA tumor retention was further compared in vivo to (18)F-FDG uptake in several xenograft models and inflammatory tissue.(18)F-FPIA rapidly accumulated in EMT6 breast cancer cells, with retention of intracellular radioactivity predicted to occur via a putative (18)F-FPIA carnitine-ester. The radiotracer was metabolically stable to degradation in mice. In vivo imaging of implanted EMT6 murine and BT474 human breast adenocarcinoma cells by (18)F-FPIA PET showed rapid and extensive tumor localization, reaching 9.1% ± 0.5% and 7.6% ± 1.2% injected dose/g, respectively, at 60 min after injection. Substantial uptake in the cortex of the kidney was seen, with clearance primarily via urinary excretion. Regarding diagnostic utility, uptake of (18)F-FPIA was comparable to that of (18)F-FDG in EMT6 tumors but superior in the DU145 human prostate cancer model (54% higher uptake; P = 0.002). Furthermore, compared with (18)F-FDG, (18)F-FPIA had lower normal-brain uptake resulting in a superior tumor-to-brain ratio (2.5 vs. 1.3 in subcutaneously implanted U87 human glioma tumors; P = 0.001), predicting higher contrast for brain cancer imaging. Both radiotracers showed increased localization in inflammatory tissue.(18)F-FPIA shows promise as an imaging agent for cancer detection and warrants further investigation.
View details for DOI 10.2967/jnumed.114.140343
View details for Web of Science ID 000341286900019
View details for PubMedID 25012458
- Radiolabeled RGD Tracer Kinetics Annotates Differential alpha(v)beta(3) Integrin Expression Linked to Cell Intrinsic and Vessel Expression MOLECULAR IMAGING AND BIOLOGY 2014; 16 (4): 558-566
A Novel Radiotracer to Image Glycogen Metabolism in Tumors by Positron Emission Tomography
2014; 74 (5): 1319-1328
The high rate of glucose uptake to fuel the bioenergetic and anabolic demands of proliferating cancer cells is well recognized and is exploited with (18)F-2-fluoro-2-deoxy-d-glucose positron emission tomography ((18)F-FDG-PET) to image tumors clinically. In contrast, enhanced glucose storage as glycogen (glycogenesis) in cancer is less well understood and the availability of a noninvasive method to image glycogen in vivo could provide important biologic insights. Here, we demonstrate that (18)F-N-(methyl-(2-fluoroethyl)-1H-[1,2,3]triazole-4-yl)glucosamine ((18)F-NFTG) annotates glycogenesis in cancer cells and tumors in vivo, measured by PET. Specificity of glycogen labeling was demonstrated by isolating (18)F-NFTG-associated glycogen and with stable knockdown of glycogen synthase 1, which inhibited (18)F-NFTG uptake, whereas oncogene (Rab25) activation-associated glycogen synthesis led to increased uptake. We further show that the rate of glycogenesis is cell-cycle regulated, enhanced during the nonproliferative state of cancer cells. We demonstrate that glycogen levels, (18)F-NFTG, but not (18)F-FDG uptake, increase proportionally with cell density and G1-G0 arrest, with potential application in the assessment of activation of oncogenic pathways related to glycogenesis and the detection of posttreatment tumor quiescence. Cancer Res; 74(5); 1319-28. ©2014 AACR.
View details for DOI 10.1158/0008-5472.CAN-13-2768
View details for Web of Science ID 000332475900006
View details for PubMedID 24590807
- RGD-targeted MnO nanoparticles as T-1 contrast agents for cancer imaging - the effect of PEG length in vivo JOURNAL OF MATERIALS CHEMISTRY B 2014; 2 (7): 868-876
PET imaging with multimodal upconversion nanoparticles
2014; 43 (14): 5535-5545
A series of new upconversion nanoparticles have been functionalised with tumour-targeting molecules and metal chelates, prepared following standard peptidic and thiol chemistry. The targeting strategy has been delivered via the αvβ3 integrin, which is a heterodimeric cell surface receptor that is up-regulated in a variety of cancers, such as melanoma and breast cancer. The well-known DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) motif allows coordination to the radionuclide (68)Ga. Radiolabelling experiments were optimised under relatively mild conditions, and are rare amongst nanoparticulate materials. In vivo application of these probes in mouse tumour models revealed their potential as specific cancer contrast agents for PET imaging.
View details for DOI 10.1039/c3dt53095g
View details for Web of Science ID 000332929200033
View details for PubMedID 24535647
Evaluation of Deuterated F-18- and C-11-Labeled Choline Analogs for Cancer Detection by Positron Emission Tomography
CLINICAL CANCER RESEARCH
2012; 18 (4): 1063-1072
(11)C-Choline-positron emission tomography (PET) has been exploited to detect the aberrant choline metabolism in tumors. Radiolabeled choline uptake within the imaging time is primarily a function of transport, phosphorylation, and oxidation. Rapid choline oxidation, however, complicates interpretation of PET data. In this study, we investigated the biologic basis of the oxidation of deuterated choline analogs and assessed their specificity in human tumor xenografts.(11)C-Choline, (11)C-methyl-[1,2-(2)H(4)]-choline ((11)C-D4-choline), and (18)F-D4-choline were synthesized to permit comparison. Biodistribution, metabolism, small-animal PET studies, and kinetic analysis of tracer uptake were carried out in human colon HCT116 xenograft-bearing mice.Oxidation of choline analogs to betaine was highest with (11)C-choline, with reduced oxidation observed with (11)C-D4-choline and substantially reduced with (18)F-D4-choline, suggesting that both fluorination and deuteration were important for tracer metabolism. Although all tracers were converted intracellularly to labeled phosphocholine (specific signal), the higher rate constants for intracellular retention (K(i) and k(3)) of (11)C-choline and (11)C-D4-choline, compared with (18)F-D4-choline, were explained by the rapid conversion of the nonfluorinated tracers to betaine within HCT116 tumors. Imaging studies showed that the uptake of (18)F-D4-choline in three tumors with similar radiotracer delivery (K(1)) and choline kinase α expression-HCT116, A375, and PC3-M-were the same, suggesting that (18)F-D4-choline has utility for cancer detection irrespective of histologic type.We have shown here that both deuteration and fluorination combine to provide protection against choline oxidation in vivo. (18)F-D4-choline showed the highest selectivity for phosphorylation and warrants clinical evaluation.
View details for DOI 10.1158/1078-0432.CCR-11-2462
View details for Web of Science ID 000300628100016
View details for PubMedID 22235095
Imaging sialylated tumor cell glycans in vivo
2011; 25 (8): 2528-2537
Cell surface glycans are involved in numerous physiological processes that involve cell-cell interactions and migration, including lymphocyte trafficking and cancer metastasis. We have used a bioorthogonal metabolic labeling strategy to detect cell surface glycans and demonstrate, for the first time, fluorescence and radionuclide imaging of sialylated glycans in a murine tumor model in vivo. Peracetylated azido-labeled N-acetyl-mannosamine, injected intraperitoneally, was used as the metabolic precursor for the biosynthesis of 5-azidoneuraminic, or azidosialic acid. Azidosialic acid-labeled cell surface glycans were then reacted, by Staudinger ligation, with a biotinylated phosphine injected intraperitoneally, and the biotin was detected by subsequent intravenous injection of a fluorescent or radiolabeled avidin derivative. At 24 h after administration of NeutrAvidin, labeled with either a far-red fluorophore or (111)In, there was a significant azido-labeled N-acetyl-mannosamine-dependent increase in tumor-to-tissue contrast, which was detected using optical imaging or single-photon-emission computed tomography (SPECT), respectively. The technique has the potential to translate to the clinic, where, given the prognostic relevance of altered sialic acid expression in cancer, it could be used to monitor disease progression.
View details for DOI 10.1096/fj.10-178590
View details for Web of Science ID 000293337800004
View details for PubMedID 21493886
Comparison of the C2A Domain of Synaptotagmin-I and Annexin-V As Probes for Detecting Cell Death
2010; 21 (5): 884-891
The induction of apoptosis is frequently accompanied by the exposure of phosphatidylserine (PS) on the cell surface, which has been detected using radionuclide and fluorescently labeled derivatives of the PS-binding protein, Annexin V. The fluorescently labeled protein has been used extensively in vitro as a diagnostic reagent for detecting cell death, and radionuclide-labeled derivatives have undergone clinical trials for detecting tumor cell death in vivo following treatment. We show here that the C2A domain of Synaptotagmin-I, which had been fluorescently labeled at a single cysteine residue introduced by site-directed mutagenesis, detected the same levels of cell death as a similarly labeled Annexin-V derivative, in drug-treated murine lymphoma and human breast cancer cell lines in vitro. However, the C2A derivative showed significantly less binding to viable cells and, as a consequence, up to 4-fold more specific binding to apoptotic and necrotic cells when compared with Annexin-V. C2A offers a potential route for the development of a new generation of more specific imaging probes for the detection of tumor cell death in the clinic.
View details for DOI 10.1021/bc9004415
View details for Web of Science ID 000277683300013
View details for PubMedID 20402461