Department of Biological Chemistry, Molecular Biology Institute, Crump Institute for Molecular Imaging, David Geffen School of Medicine at UCLA, 341 Boyer Hall, 611 Charles E. Young Drive East, Los Angeles, CA 90095, USA.
Positron-emission tomography (PET) has been used extensively in the clinic for cancer diagnosis, for staging and for monitoring of therapeutic efficacy. PET has not, however, been used extensively in contemporary animal cancer models. Until recently, appropriate instrumentation was not available and the expertise and knowledge necessary to perform PET analyses in murine models has not been widespread. The fabrication of microPET instruments with appropriate resolution for murine experiments has lead to the establishment of non-invasive techniques for functional imaging. The development of "PET reporter genes" whose activity can be monitored in living animals, based on the reporter gene-dependent sequestration of positron-emitting "PET reporter probes," has lead to innovative analyses of gene expression in transgenic animals, to methods to monitor the location, magnitude and duration of expression for gene therapy vectors and to the ability to non-invasively track the targeting, viability and expansion of cellular therapeutics.
"SPECT gathers imaging information based on the amount of gamma-emitting radionucleotides that emit a single photon, but it is generally not as sensitive and less quantifiable than PET. PET detects biochemical processes in cells by measuring the positrons emitted by the probe as it decays and collides with electrons in vivo (Doubrovin et al. 2004, Herschman 2004). The PET emissions are two photons released 180° from one another and detected in an array, which measure the volume and concentration of the probe (Blasberg 2002). "
[Show abstract][Hide abstract] ABSTRACT: Imaging is one of the fastest growing fields of study. New technologies and multimodal approaches are increasing the application of imaging to determine molecular targets and functional processes in vivo. The identification of a specific target, transporter, or biological process using imaging has introduced major breakthroughs to the field of endocrinology primarily utilizing computed tomography, magnetic resonance imaging, ultrasonography, positron emission tomography, single-photon emission computed tomography, and optical imaging. This review provides a general background to the specific developments in imaging that pertains to in vivo function and target identification in endocrine-based diseases.
"Now, reporter genes are used to visually identify transformed cells, calculate the efficiency of gene delivery systems, follow the intracellular fate of a gene product, monitor recombination events , measure signal transduction , detect the interaction of two proteins in the two-hybrid system , or for noninvasive in vivo imaging of gene expression. Examples of the latter are positron emission tomography , magnetic resonance  and optical imaging systems . "
[Show abstract][Hide abstract] ABSTRACT: Establishing a suitable level of exogenous gene expression in mammalian cells in general, and embryonic stem (ES) cells in particular, is an important aspect of understanding pathways of cell differentiation, signal transduction and cell physiology. Despite its importance, this process remains challenging because of the poor correlation between the presence of introduced exogenous DNA and its transcription. Consequently, many transfected cells must be screened to identify those with an appropriate level of expression. To improve the screening process, we investigated the utility of the human interleukin 12 (IL-12) p40 cDNA as a reporter gene for studies of mammalian gene expression and for high-throughput screening of engineered mouse embryonic stem cells.
A series of expression plasmids were used to study the utility of IL-12 p40 as an accurate reporter of gene activity. These studies included a characterization of the IL-12 p40 expression system in terms of: (i) a time course of IL-12 p40 accumulation in the medium of transfected cells; (ii) the dose-response relationship between the input DNA and IL-12 p40 mRNA levels and IL-12 p40 protein secretion; (iii) the utility of IL-12 p40 as a reporter gene for analyzing the activity of cis-acting genetic elements; (iv) expression of the IL-12 p40 reporter protein driven by an IRES element in a bicistronic mRNA; (v) utility of IL-12 p40 as a reporter gene in a high-throughput screening strategy to identify successful transformed mouse embryonic stem cells; (vi) demonstration of pluripotency of IL-12 p40 expressing ES cells in vitro and in vivo; and (vii) germline transmission of the IL-12 p40 reporter gene.
IL-12 p40 showed several advantages as a reporter gene in terms of sensitivity and ease of the detection procedure. The IL-12 p40 assay was rapid and simple, in as much as the reporter protein secreted from the transfected cells was accurately measured by ELISA using a small aliquot of the culture medium. Remarkably, expression of Il-12 p40 does not affect the pluripotency of mouse ES cells. To our knowledge, human IL-12 p40 is the first secreted reporter protein suitable for high-throughput screening of mouse ES cells. In comparison to other secreted reporters, such as the widely used alkaline phosphatase (SEAP) reporter, the IL-12 p40 reporter system offers other real advantages.
[Show abstract][Hide abstract] ABSTRACT: Tumor cells transduced with herpes simplex virus thymidine kinase gene has been intensively applied to the field of positron emission tomography via imaging of its substrate. As a pilot synthesis approach, a facial preparation of 5-[125I]iodoarabinosyl uridine starting from commercial available uridine is reported herein. Interestingly, the tin group in 5-trimethylstannyl arabinosyluridine was easily removed during purification. The destannylation through the formation of a six-ligand coordination involving 2'-hydroxyl and tin was thereby proposed.
Nuclear Medicine and Biology 05/2006; 33(3):367-70. DOI:10.1016/j.nucmedbio.2005.12.005 · 2.41 Impact Factor
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