PubMed Health⌕ Search

Biomedical subjects

Sanjiv Sam Gambhir

Publications and source records attributed to Sanjiv Sam Gambhir.

18 recordsLinked to original sources
PubMed2006

Quantitative micro positron emission tomography (PET) imaging for the in vivo determination of pancreatic islet graft survival.

Islet transplantation is an attractive approach for treating type-1 diabetes, but there is a massive loss of transplanted islets. It is currently only possible to estimate islet mass indirectly, through measurement of circulating C-peptide and insulin levels. This type of estimation, however, is not sufficiently sensitive or reproducible for follow-up of individuals who have undergone islet transplantation. Here we show that islet graft survival could be assessed for 1 month in diabetic NOD mice using 9-(4-[(18)F]-fluoro-3-hydroxymethylbutyl)guanine ([(18)F]FHBG)-positron emission tomography (PET) technology, the PET signal reflecting insulin secretory capacity of transplanted islets. Expression of the gene encoding viral interleukin-10 (vIL-10), was measurable in real time with PET scanning. Additionally, we addressed the clinical potential of this approach by visualizing transplanted islets in the liver, the preferred clinical transplantation site. We conclude that quantitative in vivo PET imaging is a valid method for facilitating the development of protocols for prolonging islet survival, with the potential for tracking human transplants.

Animals↗
PubMed2006

Long-term monitoring of transplanted islets using positron emission tomography.

Islet transplantation can restore glucose homeostasis in those with type 1 diabetes; however, most recipients eventually lose graft function. A noninvasive method to monitor islets following transplantation would enable assessment of their survival and aid the development of therapeutics to prolong graft survival. Here, we show that recombinant lentivirus can be used to engineer human islets to express a positron emission tomography (PET) reporter gene. Following transplantation into mice, transduced islets could be imaged in vivo using microPET and a radiolabeled probe approved by the FDA for clinical use in humans. The magnitude of signal from engineered islets implanted into the axillary cavity reflected the implanted islet mass. Signals from implanted islets decreased by approximately one-half during the first few weeks following transplantation, which may reflect islet cell death shortly after transplantation. Thereafter, the magnitude of signals from the implanted islets remained fairly constant when the recipients were repetitively reimaged over 90 days. Histological analysis of the implants showed healthy islets with PET reporter-expressing cells distributed throughout the islet architecture. These studies suggest that PET imaging of lentivirus-transduced islets could provide a safe and feasible method for long-term monitoring of islet graft survival.

Animals↗
PubMed2006

Noninvasive imaging of islet grafts using positron-emission tomography.

Islet transplantation offers a potential therapy to restore glucose homeostasis in type 1 diabetes patients. However, islet transplantation is not routinely successful because most islet recipients gradually lose graft function. Furthermore, serological markers of islet function are insensitive to islet loss until the latter stages of islet graft rejection. A noninvasive method of monitoring islet grafts would aid in the assessment of islet graft survival and the evaluation of interventions designed to prolong graft survival. Here, we show that recombinant adenovirus can engineer isolated islets to express a positron-emission tomography (PET) reporter gene and that these islets can be repeatedly imaged by using microPET after transplantation into mice. The magnitude of signal from engineered islets implanted into the axillary cavity was directly related to the implanted islet mass. PET signals attenuated over the following weeks because of the transient nature of adenovirus-mediated gene expression. Because the liver is the preferred site for islet implantation in humans, we also tested whether islets could be imaged after transfusion into the mouse liver. Control studies revealed that both intrahepatic islet transplantation and hyperglycemia altered the biodistribution kinetics of the PET probe systemically. Although transplanted islets were dispersed throughout the liver, clear signals from the liver region of mice receiving PET reporter-expressing islets were detectable for several weeks. Viral transduction, PET reporter expression, and repeated microPET imaging had no apparent deleterious effects on islet function after implantation. These studies lay a foundation for noninvasive quantitative assessments of islet graft survival using PET.

Animals↗
PubMed2006

Consensus guided mutagenesis of Renilla luciferase yields enhanced stability and light output.

Luciferases, which have seen expansive employment as reporter genes in biological research, could also be used in applications where the protein itself is conjugated to ligands to create probes that are appropriate for use in small animal imaging. As the bioluminescence activity of commonly used luciferases is too labile in serum to permit this application, specific mutations of Renilla luciferase, selected using a consensus sequence driven strategy, were screened for their ability to confer stability of activity in serum as well as their light output. Using this information, a total of eight favorable mutations were combined to generate a mutant Renilla luciferase (RLuc8) that, compared with the parental enzyme, is 200-fold more resistant to inactivation in murine serum and exhibits a 4-fold improvement in light output. Results of the mutational analysis were also used to generate a double mutant optimized for use as a reporter gene. The double mutant had half the resistance to inactivation in serum of the native enzyme while yielding a 5-fold improvement in light output. These variants of Renilla luciferase, which exhibit significantly improved properties compared with the native enzyme, will allow enhanced sensitivity in existing luciferase-based assays as well as enable the development of novel probes labeled with the luciferase protein.

Amino Acid Sequence↗
PubMed2005

Noninvasive imaging of protein-protein interactions from live cells and living subjects using bioluminescence resonance energy transfer.

This study demonstrates a significant advancement of imaging of a distance-dependent physical process, known as the bioluminescent resonance energy transfer (BRET2) signal in living subjects, by using a cooled charge-coupled device (CCD) camera. A CCD camera-based spectral imaging strategy enables simultaneous visualization and quantitation of BRET signal from live cells and cells implanted in living mice. We used the BRET2 system, which utilizes Renilla luciferase (hRluc) protein and its substrate DeepBlueC (DBC) as an energy donor and a mutant green fluorescent protein (GFP2) as the acceptor. To accomplish this objective in this proof-of-principle study, the donor and acceptor proteins were fused to FKBP12 and FRB, respectively, which are known to interact only in the presence of the small molecule mediator rapamycin. Mammalian cells expressing these fusion constructs were imaged using a cooled-CCD camera either directly from culture dishes or by implanting them into mice. By comparing the emission photon yields in the presence and absence of rapamycin, the specific BRET signal was determined. The CCD imaging approach of BRET signal is particularly appealing due to its capacity to seamlessly bridge the gap between in vitro and in vivo studies. This work validates BRET as a powerful tool for interrogating and observing protein-protein interactions directly at limited depths in living mice.

Animals↗
PubMed2005

Image-guided cardiac cell delivery using high-resolution small-animal ultrasound.

Open-chest cardiac injection is the preferred delivery method for cardiac gene and stem cell therapy in small animals, but it is invasive and the operator is unable to see the actual delivery site. High-resolution ultrasound has recently been developed for small-animal imaging. We tested the hypothesis that image-guided cardiac cell delivery using high-resolution ultrasound guidance is feasible and reproducible. Sprague-Dawley rats (n = 11) were imaged using high-resolution ultrasound, and stably transfected cardiomyoblasts (plasmid-CMV-firefly luciferase) were injected into the anterior cardiac wall under ultrasound guidance (parasternal long-axis view), using a 28-gauge needle. After injection, bioluminescence imaging was performed using a cooled charged-coupled camera. Injection was successful in all animals and was associated with no mortality. The signal detected was positively correlated with the amount of cells transplanted (R(2) = 0.94, P = 0.03) and highly correlated with ex vivo assays (R(2) = 0.82). In addition, the optical signal could be followed longitudinally using bioluminescence imaging. Ultrasound image-guided cardiac cell delivery is an effective, safe, and reproducible way to perform cell delivery to a specific myocardial region and can be combined with assessment of cardiac function. We are confident that the use of these technologies will play a significant role in the future of gene and cell therapy.

Animals↗
PubMed2004

Molecular imaging applications for immunology.

The use of multimodality molecular imaging has recently facilitated the study of molecular and cellular events in living subjects in a noninvasive and repetitive manner to improve the diagnostic capability of traditional assays. The noninvasive imaging modalities utilized for both small animal and human imaging include positron emission tomography (PET), single photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), ultrasound, and computed tomography (CT). Techniques specific to small-animal imaging include bioluminescent imaging (BIm) and fluorescent imaging (FIm). Molecular imaging permits the study of events within cells, the examination of cell trafficking patterns that relate to inflammatory diseases and metastases, and the ability to rapidly screen new drug treatments for distribution and effectiveness. In this paper, we will review the current field of molecular imaging assays (especially those utilizing PET and BIm modalities) and examine how they might impact animal models and human disease in the field of clinical immunology.

Animals↗
PubMed2004

Bioluminescent monitoring of islet graft survival after transplantation.

Islet transplantation offers a potential therapy to restore glucose homeostasis in type 1 diabetes patients. A method to image transplanted islets noninvasively and repeatedly would greatly assist studies of islet transplantation. Using recombinant adenovirus, we show that isolated rodent and human islets can be genetically engineered to express luciferase and then imaged after implantation into NOD-scid mice using a cooled charge-coupled device. The magnitude of the signal was dependent on the islet dose. Adenovirus-directed luciferase expression, however, rapidly attenuated. We next tested lentivirus vectors that should direct the long-term expression of reporter genes in transduced islets. Transplanted lentivirus-transduced islets restored euglycemia long term in streptozotocin-treated NOD-scid mice. The signal from implanted lentivirus-transduced islets was related directly to the implanted islet mass, and the signal did not attenuate over the observation period. Viral transduction, luciferase expression, and repeated imaging had no apparent long-term deleterious effects on islet function after implantation. These data demonstrate that the introduction of reporter genes into an isolated tissue allows the long-term monitoring of its survival following implantation. Such imaging technologies may allow earlier detection of graft rejection and the adjustment of therapies to prolong graft survival posttransplantation.

Adenoviridae↗
PubMed2003

Noninvasive imaging of lentiviral-mediated reporter gene expression in living mice.

Lentiviral-mediated gene delivery holds significant promise for sustained gene expression within living systems. Vesicular stomatitis virus glycoprotein-pseudotyped human immunodeficiency virus type 1-based lentiviral vectors can be used to introduce transgenes in a broad spectrum of dividing as well as nondividing cells. In the current study, we construct a lentiviral vector carrying two reporter genes separated by an internal ribosomal entry site and utilize that virus in delivering both genes into neuroblastoma cells in cell culture and into cells implanted in living mice. We utilize two reporter genes, a mutant herpes simplex virus type 1 (HSV1) sr39tk as a reporter gene compatible with positron emission tomography (PET) and a bioluminescent optical reporter gene, firefly luciferase (Fluc), to image expression in living mice by an optical charge-coupled device (CCD) camera. By using this lentivirus, neuroblastoma (N2a) cells are stably transfected and a high correlation (R(2) = 0.91) between expressions of the two reporter genes in cell culture is established. Imaging of both reporter genes using microPET and optical CCD camera in living mice is feasible, with the optical approach being more sensitive, and a high correlation (R(2) = 0.86) between gene expressions is again observed in lentiviral-infected N2a tumor xenografts. Indirect imaging of HSV1-sr39tk suicide gene therapy utilizing Fluc is also feasible and can be detected with increased sensitivity by using the optical CCD. These preliminary results validate the use of lentiviral vectors carrying reporter genes for multimodality imaging of gene expression and should have many applications, including imaging of xenografts, metastasis, and cell trafficking as well as noninvasive monitoring of lentiviral-mediated gene delivery and expression.

Animals↗
PubMed2003

AMIDE: a free software tool for multimodality medical image analysis.

Amide's a Medical Image Data Examiner (AMIDE) has been developed as a user-friendly, open-source software tool for displaying and analyzing multimodality volumetric medical images. Central to the package's abilities to simultaneously display multiple data sets (e.g., PET, CT, MRI) and regions of interest is the on-demand data reslicing implemented within the program. Data sets can be freely shifted, rotated, viewed, and analyzed with the program automatically handling interpolation as needed from the original data. Validation has been performed by comparing the output of AMIDE with that of several existing software packages. AMIDE runs on UNIX, Macintosh OS X, and Microsoft Windows platforms, and it is freely available with source code under the terms of the GNU General Public License.

Costs and Cost Analysis↗
PubMed2003

Positron emission tomography in diagnosis and management of invasive breast cancer: current status and future perspectives.

[18F]fluorodeoxyglucose positron emission tomography (FDG-PET) is a metabolic imaging modality that has increasing applications in oncology, neurology, and cardiology. Among the oncology applications, breast cancer is one of the most extensively studied diseases. FDG-PET has been performed for diagnosis, staging, and restaging of invasive breast cancer and for monitoring responsiveness to therapies. At the present time, the results of FDG-PET in detection of primary breast cancer and axillary staging are mixed and inconclusive. However, results demonstrating the superiority of FDG-PET over anatomic imaging modalities in detection of distant metastasis, recurrence, and monitoring therapies are relatively well documented. These applications have been accepted by medical professionals and the public, as evidenced by a recent decision by the Centers for Medicare and Medicaid Services (formerly Health Care Financing Agency) to provide coverage for the procedure. Future trends in this exciting area include development of novel breast cancer-specific PET radiopharmaceuticals and use of dedicated breast PET technologies for scans of breast/axillary lesions. PET/computed tomography technology, which combines anatomic and molecular/biochemical information, is also rapidly proliferating and should help to further improve the management of patients with breast cancer. The role of FDG-PET in breast cancer is increasing and evolving, and this metabolic imaging modality, in conjunction with newer tracers and other anatomic imaging methods, should improve diagnosis and management of patients with breast cancer

Breast Neoplasms↗
PubMed2002

Ex vivo cell labeling with 64Cu-pyruvaldehyde-bis(N4-methylthiosemicarbazone) for imaging cell trafficking in mice with positron-emission tomography.

We have used copper-64-pyruvaldehyde-bis(N4-methylthiosemicarbazone) (64Cu-PTSM) to radiolabel cells ex vivo for in vivo positron-emission tomography (PET) imaging studies of cell trafficking in mice and for eventual application in patients. 2-[18F]-Fluoro-2-deoxy-d-glucose (FDG) cell labeling also was evaluated for comparison. 64Cu-PTSM uptake by C6 rat glioma (C6) cells increased for 180 min and then stabilized. The labeling efficiency was directly proportional to 64Cu-PTSM concentration and influenced negatively by serum. Label uptake per cell was greater with 64Cu-PTSM than with FDG. However, both 64Cu-PTSM- and FDG-labeled cells showed efflux of cell activity into supernatant. The 64Cu-PTSM labeling procedure did not interfere significantly with C6 cell viability and proliferation rate. MicroPET images of living mice indicate that tail-vein-injected labeled C6 cells traffic to the lungs and liver. In addition, transient splenic accumulation of radioactivity was clearly detectable in a mouse scanned at 3.33 h postinfusion of 64Cu-PTSM-labeled lymphocytes. In contrast, the liver was the principal organ of tracer localization after tail-vein administration of 64Cu-PTSM alone. These results indicate that in vivo imaging of cell trafficking is possible with 64Cu-PTSM-labeled cells. Given the longer t(1/2) of 64Cu (12.7 h) relative to 18F (110 min), longer cell-tracking periods (up to 24-36 h) should be possible now with PET.

Animals↗
PubMed2002

Molecular imaging of cancer with positron emission tomography.

The imaging of specific molecular targets that are associated with cancer should allow earlier diagnosis and better management of oncology patients. Positron emission tomography (PET) is a highly sensitive non-invasive technology that is ideally suited for pre-clinical and clinical imaging of cancer biology, in contrast to anatomical approaches. By using radiolabelled tracers, which are injected in non-pharmacological doses, three-dimensional images can be reconstructed by a computer to show the concentration and location(s) of the tracer of interest. PET should become increasingly important in cancer imaging in the next decade.

Animals↗
PubMedDate not supplied

Standardized uptake value atlas: characterization of physiological 2-deoxy-2-[18F]fluoro-D-glucose uptake in normal tissues.

PURPOSE: The purpose of this study was to map the distribution of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) uptake in organs of patients with no known abnormalities in those tissues. PROCEDURES: We measured maximum and mean standardized uptake values (SUV) from FDG-positron emission tomography (PET)/computed tomography (CT) obtained from 98 patients (48 males and 50 females). RESULTS: Significant uptake (mean SUVmean>2.5) was visualized in the cerebellum (8.0+/-2.2), soft palate (2.92+/-0.86), palatine tonsils (3.45+/-1.4), lingual tonsils (3.08+/-1.05), sublingual glands (3.3+/-1.5), and testes (2.57+/-0.56). Negative correlation for FDG uptake versus age was observed for the palatine tonsils, sublingual glands, and lungs (P<0.001). CONCLUSION: Better understanding of physiological uptake throughout the body is valuable for improved interpretive accuracy and should be useful for future semi-automated comparisons to a normal SUV database.

Adult↗
PubMedDate not supplied

Near-infrared fluorescent RGD peptides for optical imaging of integrin alphavbeta3 expression in living mice.

Near-infrared fluorescence optical imaging is a powerful technique for studying diseases at the molecular level in preclinical models. We recently reported that monomeric RGD peptide c(RGDyK) conjugated to the NIR fluorescent dye specifically targets integrin receptor both in cell culture and in living subjects. In this report, Cy5.5-conjugated mono-, di-, and tetrameric RGD peptides were evaluated in a subcutaneous U87MG glioblastoma xenograft model in order to investigate the effect of multimerization of RGD peptide on integrin avidity and tumor targeting efficacy. The binding affinities of Cy5.5-conjugated RGD monomer, dimer, and tetramer for alpha(v)beta(3) integrin expressed on U87MG cell surface were determined to be 42.9 +/- 1.2, 27.5 +/- 1.2, and 12.1 +/- 1.3 nmol/L, respectively. All three peptide-dye conjugates had integrin specific uptake both in vitro and in vivo. The subcutaneous U87MG tumor can be clearly visualized with each of these three fluorescent probes. Among them, tetramer displayed highest tumor uptake and tumor-to-normal tissue ratio from 0.5 to 4 h postinjection. Tumor-to-normal tissue ratio for Cy5.5-conjugated RGD monomer, dimer, and tetramer were found to be 3.18 +/- 0.16, 2.98 +/- 0.05, and 3.63 +/- 0.09, respectively, at 4 h postinjection. These results suggest that Cy5.5-conjugated monomeric, dimeric, and tetrameric RGD peptides are all suitable for integrin expression imaging. The multmerization of RGD peptide results in moderate improvement of imaging characteristics of the tetramer, compared to that of the monomer and dimeric counterparts.

Animals↗
PubMedDate not supplied

Near-infrared fluorescent deoxyglucose analogue for tumor optical imaging in cell culture and living mice.

2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) has extensively been used for clinical diagnosis, staging, and therapy monitoring of cancer and other diseases. Nonradioactive glucose analogues enabling the screening of the glucose metabolic rate of tumors are of particular interest for anticancer drug development. A nonradioactive fluorescent deoxyglucose analogue may have many applications for both imaging of tumors and monitoring therapeutic efficacy of drugs in living animals and may eventually translate to clinical applications. We found that a fluorescent 2-deoxyglucose analogue, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), can be delivered in several tumor cells via the glucose transporters (GLUTs). We therefore conjugated D-glucosamine with a near-infrared (NIR) fluorphor Cy5.5 and tested the feasibility of the Cy5.5-D-glucosamine (Cy5.5-2DG) conjugate for NIR fluorescence imaging of tumors in a preclinical xenograft animal model. Cy5.5-2DG was prepared by conjugating Cy5.5 monofunctional N-hydroxysuccinimide ester (Cy5.5-NHS) and D-glucosamine followed by high-performance liquid chromatography purification. The accumulation of Cy5.5-2DG and Cy5.5-NHS in different tumor cell lines at 37 and 4 degrees C were imaged using a fluorescence microscope. Tumor targeting and retention of Cy5.5-2DG and Cy5.5-NHS in a subcutaneous U87MG glioma and A375M melanoma tumor model were evaluated and quantified by a Xenogen IVIS 200 optical cooled charged-coupled device system. Fluorescence microscopy imaging shows that Cy5.5-2DG and Cy5.5-NHS are taken up and trapped by a variety of tumor cell lines at 37 degrees C incubation, while they exhibit marginal uptake at 4 degrees C. The tumor cell uptake of Cy5.5-2DG cannot be blocked by the 50 mM D-glucose, suggesting that Cy5.5-2DG may not be delivered in tumor cells by GLUTs. U87MG and A375M tumor localization was clearly visualized in living mice with both NIR fluorescent probes. Tumor/muscle contrast was clearly visible as early as 30 min postinjection (pi), and the highest U87MG tumor/muscle ratios of 2.81 +/- 0.10 and 3.34 +/- 0.23 were achieved 24 h pi for Cy5.5-2DG and Cy5.5-NHS, respectively. While as a comparison, the micropositron emission tomography imaging study shows that [18F]FDG preferentially localizes to the U87MG tumor, with resulting tumor/muscle ratios ranging from 3.89 to 4.08 after 30 min to 2 h postadministration of the probe. In conclusion, the NIR fluorescent glucose analogues, Cy5.5-2DG and Cy5.5-NHS, both demonstrate tumor-targeting abilities in cell culture and living mice. More studies are warranted to further explore their application for optical tumor imaging. To develop NIR glucose analogues with the ability to target GLUTs/hexokinase, it is highly important to select NIR dyes with a reasonable molecular size.

Animals↗
PubMedDate not supplied

Bioluminescent monitoring of NIS-mediated (131)I ablative effects in MCF-7 xenografts.

Optical imaging has made it possible to monitor response to anticancer therapies in tumor xenografts. The concept of treating breast cancers with (131)I is predicated on the expression of the Na(+)/I- symporter (NIS) in many tumors and uptake of I- in some. The pattern of (131)I radioablative effects were investigated in an MCF-7 xenograft model dually transfected with firefly luciferase and NIS genes. On Day 16 after tumor cell implantation, 3 mCi of (131)I was injected. Bioluminescent imaging using d-luciferin and a cooled charge-coupled device camera was carried out on Days 1, 2, 3, 7, 10, 16, 22, 29, and 35. Tumor bioluminescence decreased in (131)I-treated tumors after Day 3 and reached a nadir on Day 22. Conversely, bioluminescence steadily increased in controls and was 3.85-fold higher than in treated tumors on Day 22. Bioluminescence in (131)I-treated tumors increased after Day 22, corresponding to tumor regrowth. By Day 35, treated tumors were smaller and accumulated 33% less (99m)TcO(4)(-) than untreated tumors. NIS immunoreactivity was present in <50% of (131)I-treated cells compared to 85-90% of controls. In summary, a pattern of tumor regression occurring over the first three weeks after (131)I administration was observed in NIS-expressing breast cancer xenografts.

Animals↗