Potential Imaging Probe Research Articles

Incorporation of quantum dots on virus in polycationic solution

Developing methods to label viruses with fluorescent moieties has its merits in elucidating viral infection mechanisms and exploring novel antiviral therapeutics. Fluorescent quantum dots (QDs), an emerging probe for biological imaging and medical diagnostics, were employed in this study to tag retrovirus encoding enhanced green fluorescent protein (EGFP) genes. Electrostatic repulsion forces generated from both negatively charged retrovirus and QDs were neutralized by cationic Polybrene, forming colloidal complexes of QDs-virus. By examining the level of EGFP expression in 3T3 fibroblast cells treated with QDs-tagged retroviruses for 24 hours, the infectivity of retrovirus incorporated with QDs was shown to be only slightly decreased. Moreover, the imaging of QDs can be detected in the cellular milieu. In summary, the mild method developed here makes QDs-tagged virus a potential imaging probe for direct tracking the infection process and monitoring distribution of viral particles in infected cells.

Synthesis and in vitro evaluation of new benzovesamicol analogues as potential imaging probes for the vesicular acetylcholine transporter

Our goal was to synthesize new stereospecific benzovesamicol analogues, which could potentially be used as SPECT or PET radioligands for the vesicular acetylcholine transporter (VAChT). This paper describes the chemical synthesis, resolution and determination of binding affinity for four enantiomeric pairs of derivatives. Their intrinsic affinities were determined by competition against binding of [ 3H]vesamicol to human VAChT. Of the eight enantiomers, ( E)-( R, R)-5-AOIBV [( R, R)- 3], and ( R, R)-5-FPOBV [( R, R)- 4] displayed the highest binding affinities for VAChT ( K d = 0.45 and 0.77 nM, respectively), which indicated that an elongation of the chain from 5-idodo as in the case of 5-iodobenzovesamicol (5-IBVM), to a 5-( E)-3-iodoallyloxy or 5-fluoropropoxy substituent, as in 5-AOIBV and 5-FPOBV, respectively, was very well tolerated at the vesamicol binding site. The enantiomer ( R, R)-4-MAIBV [( R, R)- 16], which retains the basic structure of (−)-5-IBVM but possess an additional aminomethyl substituent in the 4-position of the piperidine ring, displayed lower binding affinity ( K d = 8.8 nM). Nevertheless, the result suggests that substitution at this position may be an interesting alternative to investigate for development of new benzovesamicol analogues. As expected, the corresponding ( S, S) enantiomers displayed lower K d values, they were approximately 10-fold lower in the case of ( S, S)-5-FPOBV ( K d = 8.4 nM) and ( E)-( S, S)-5-AOIBV ( K d = 4.3 nM). ( R, R)- 3, and ( R, R)- 4 showed the same high affinity for VAChT as (−)-5-IBVM and may be suitable as imaging agents of cholinergic nerve terminals.

Luminescent nonacoordinate cationic lanthanide complexes as potential cellular imaging and reactive probes.

Nonacoordinate delta- and lambda-Eu and Tb complexes have been tested as imaging and reactive probes in mouse fibroblast (NIH 3T3) cells. The uptake of these complexes by the cells was assessed by fluorescence microscopy. Complex-induced DNA damage was studied by gel electrophoresis and shown to be a function of complex chirality.

Synthesis, in vitro receptor binding, and in vivo evaluation of fluorescein and carbocyanine peptide-based optical contrast agents.

Site-specific delivery of drugs and contrast agents to tumors protects normal tissues from the cytotoxic effects of drugs and enhances the contrast between normal and pathologic tissues. One approach to achieve selectivity is to target overexpressed receptors on the membranes of tumor cells and to visualize the tumors by a noninvasive optical imaging method. Accordingly, we conjugated fluorescein and carbocyanine dyes to somatostatin and bombesin receptor-avid peptides and examined their receptor binding affinities. We also prepared potential dual imaging probes consisting of a bioactive peptide for tumor targeting, a biocompatible dye for optical imaging, and a radioactive or paramagnetic metal chelator for scintigraphic or magnetic resonance imaging of tumors. Using these approaches, the resulting carbocyanine derivatives of somatostatin and bombesin analogues retained high binding for their respective receptors. Further evaluation of representative molecules in rats bearing somatostatin- and bombesin-positive tumors showed selective uptake of the agents by the tumor cells. Unlike carbocyanine derivatives, the receptor binding of fluorescein-somatostatin peptide conjugates was highly sensitive to the type of linker and the site of fluorescein attachment on the nonreceptor binding region of the peptide. In general, the presence of flexible linkers disrupted binding affinity, possibly due to the interaction of the linker's thiourea group with the peptide's cyclic disulfide bond. While the receptor binding affinity of the dual probes was not dependent on the type of chelating group examined, it was affected by the relative positions of fluorescein and chelator on the lysine linker. For somatostatin compounds, best results were obtained when the chelator was on the alpha-amino lysine linker and fluorescein was on the epsilon-amino group. In contrast, conjugation of the chelator to epsilon- and fluorescein to the alpha-amino lysine linker of bombesin peptides resulted in high receptor binding. These findings indicate that despite their small size, conjugation of dyes to truncated somatostatin and bombesin peptide analogues results in promising diagnostic agents that retain high receptor binding activity in vitro. The results further show that these contrast agents can selectively and specifically localize in receptor-positive tumors in rat models.

Synthesis of 2,6‐dideoxy‐2‐fluoro‐6‐[18F]‐fluoro‐β‐D‐glucopyranosyl fluoride (2,6FGF) as a potential imaging probe for glucocerebrosidase

We have previously synthesized 2-deoxy-2-[18F]-fluoro-β-mannosyl [18F]-fluoride and shown that it behaves as a mechanism-based inhibitor of Agrobacterium sp. β-glucosidase. In-vivo experiments indicate that this compound undergoes partial hydrolysis to produce 2-deoxy-2-fluoro-mannose, which can become phosphorylated and trapped within the cell. We now report the synthesis of another 2-fluoro glycoside which is 18F-labelled at the 6 position so that the label cannot be lost during such glycoside hydrolysis and which, further, cannot be phosphorylated. The mechanism-based glycosidase inhibitor 2,6-dideoxy-2-fluoro-6-[18F]-fluoro-β-D-glucopyranosyl fluoride (2,6FGF) was synthesized in 69% overall chemical yield and in 9% radiochemical yield (decay corrected) as a potential imaging probe for glycosidase. Copyright © 2001 John Wiley & Sons, Ltd.

Synthesis of 2,6‐dideoxy‐2‐fluoro‐6‐[18F]‐fluoro‐β‐D‐glucopyranosyl fluoride (2,6FGF) as a potential imaging probe for glucocerebrosidase

AbstractWe have previously synthesized 2‐deoxy‐2‐[18F]‐fluoro‐β‐mannosyl [18F]‐fluoride and shown that it behaves as a mechanism‐based inhibitor of Agrobacterium sp. β‐glucosidase. In‐vivo experiments indicate that this compound undergoes partial hydrolysis to produce 2‐deoxy‐2‐fluoro‐mannose, which can become phosphorylated and trapped within the cell. We now report the synthesis of another 2‐fluoro glycoside which is 18F‐labelled at the 6 position so that the label cannot be lost during such glycoside hydrolysis and which, further, cannot be phosphorylated. The mechanism‐based glycosidase inhibitor 2,6‐dideoxy‐2‐fluoro‐6‐[18F]‐fluoro‐β‐D‐glucopyranosyl fluoride (2,6FGF) was synthesized in 69% overall chemical yield and in 9% radiochemical yield (decay corrected) as a potential imaging probe for glycosidase. Copyright © 2001 John Wiley & Sons, Ltd.

Synthesis of 2‐deoxy‐2‐[18F]‐fluoro‐β‐mannosyl [18F]‐fluoride as a potential imaging probe for Glycosidases

AbstractThe mechanisms‐based glycosidase inhibitor 2‐deoxy‐2‐[18F]‐fluoro‐β‐mannosyl [18F]‐fluoride was synthesized and its covalent binding to Agrobacterium β‐glucosidase was demonstrated in vitro.