Hong-Gang Liu

Imaging and tissue biodistribution of 99mTc-labeled adenovirus knob (serotype 5)

Hepatic sequestration of systemically administered adenoviral vectors reduces the number of viral particles available for delivery to other tissues. The biological basis of this phenomenon was investigated using a new in vivo technique which permitted imaging in real time. Recombinant adenovirus serotype 5 knob (Ad5K) was radiolabeled with the gamma-emitter 99mTc (half-life = 6 h). Scatchard analysis of the 99mTc-Ad5K showed specific, high-affinity binding to U293 cells (Kd = 1.4u2009±u20090.5 nM), demonstrating that the radiolabeling process had no effect on receptor binding. In vivo dynamic imaging with an Anger gamma camera revealed that the liver binding followed an exponential rise to maximum, with a measured 100% extraction efficiency. Initially, the liver binding capacity was 3.1u2009±u20090.4 μg Ad5K, equivalent to approximately 17000 Ad5K molecules per liver cell. Liver binding was blocked by preincubation of Ad5K with neutralizing anti-Ad5K antibody; a 50% reduction in liver uptake was demonstrated by imaging. Unlabeled Ad5K was more effective in blocking liver uptake of 99mTc-Ad5K, whereas irrelevant unlabeled Ad3K had no effect. Imaging data for the liver uptake studies were in agreement with biodistribution determined by removing and measuring tissues. These data demonstrated that in vivo imaging is a sensitive tool for measuring changes to liver tropism. Similar imaging techniques can be applied to adenovirus vectors to measure specific targeting for gene therapy.

Specific targeting of activated endothelium in rat adjuvant arthritis with a 99mTc-radiolabeled E-selectin-binding peptide.

OBJECTIVEnTo determine the potential of an E-selectin-binding peptide (ESbp) to specifically bind activated endothelium in rheumatoid arthritis (RA) animal models.nnnMETHODSnESbp (KYDGDITWDQLWDLMK; 2,027 daltons) was labeled with biotin and 99mTc. The affinity of ESbp derivatives for E-selectin was measured by enzyme-linked immunosorbent assay. The binding of biotin-ESbp was compared with that of an anti-E-selectin antibody, by immunohistochemical analyses of human synovial sections and sections from the Mycoplasma pulmonis MRL-lpr/lpr mouse arthritis model. 99mTc-ESbp was sequentially imaged in vivo with a gamma camera in the rat adjuvant-induced arthritis model.nnnRESULTSnE-selectin expression was detected in human RA synovium and mouse arthritic synovium using biotin-ESbp. Both biotin-ESbp and 99mTc-labeled ESbp had high affinity for E-selectin (dissociation constant 2-5 nM). In vivo imaging showed specific binding of 99mTc-ESbp to the rat ankle joint prior to clinical manifestations of inflammation.nnnCONCLUSIONnThese results demonstrate that activated endothelium can be targeted with 99mTc-ESbp. The specificity of targeting can be used to evaluate up-regulation of E-selectin in RA models, and to follow changes in this up-regulation during treatment trials.

Anterior Cingulate Gyrus Epilepsy: The Role of Ictal rCBF SPECT in Seizure Localization

Summary: Purpose: The goal of this report is to demonstrate the utility of ictal brain single photon emission tomography (SPECT) in a 39‐year‐old man with complex partial seizures arising from the anterior cingulate gyrus. Seizures originating from the anterior cingulate gyrus are difficult to localize because they have variable ictal semiology, are usually brief, and have rapid cortical propagation.

Molecular imaging: New applications for biochemistry

Molecular imaging can reveal in vivo analysis and quantification of biochemical reactions. To enable cell‐surface imaging of receptors, novel ligands have been developed which can be radiolabeled or imaged by bioluminescence. Specific examples include somatostatin receptors, estrogen and progesterone receptors, receptors involved in adhesion and externalization of phosphatidyl serine as an indicator of apoptosis. Central nervous system imaging can be carried out using ligands for receptors including dopamine, serotonin and Gamma amino butyric acid (GABA). In addition, tumor and metabolic imaging can be carried out with the Na‐K ATPase pump using the tracer thallium‐201 for SPECT or F‐18 FDG for PET imaging. Finally, novel receptors or endogenous metabolic pathways can be analyzed combining cell‐gene therapy to create specific tracer targets in cells that can be studied by molecular imaging. The challenge of molecular imaging is to first identify key pathways that are unique for a specific disease processes, such as atherosclerosis, cancer, CNS disorders, immunologic and arthritis disorders and next to devise a high‐affinity specific small molecular ligand that can be adapted to be a radiolabeled tracer to study this pathway. Advances in genomics and proteomics combine with new peptide‐chemistry approaches should provide a large number of targets and tracers in the near future to achieve these imaging objectives. J. Cell. Biochem. Suppl. 39: 162–171, 2002.