Development of the novel drug releasing system triggered by hybridization with target sequence

We have already established the strategy of synchronous activation by hybridization, in which the highly reactive cross-linking agent, 2-amino-6-vinylpurine nucleoside analog, can be generated from its stable precursors, the phenylsulfide derivatives, by a hybridization-promoted activation process with selectivity to cytosine. In this study, this in situ activation system was applied to the method for the drug releasing system triggered by hybridization with the target sequence.

Efficient cross-linking to cytidine using substituted phenylsulfide derivatives of 2-amino-6-vinylpurine nucleoside via synchronous activation within duplex

We have previously described that oligonucleotides containing phenylsulfoxide derivative of 2-amino-6-vinyulpurine nucleoside analog (1) are activated within duplex to form cross-link toward cytidine selectively at the target site. The new cross-linking motif with phenylsulfoxide structure (2) is characteristic in that the stable precursor may be transformed automatically within duplex to a reactive species. To search for more stable precursor susceptible for activation, we designed a series of substituted phenylsulfide analogs of 1. It has been demonstrated that introduction of an electron-donating group on the phenyl ring improved the cross-linking reaction. Particularly, 2-carboxyphenyl sulfide derivative exhibited cross-linking as effectively as phenylsulfoxide derivative without chemical oxidation prior to cross-linking.

Design and synthesis of the novel cross-linking reagents triggered by the triple helix formation

In our attempt to new nucleobase analogs capable of interstrand cross-linking, we developed 2-amino-6-vinyl purine analog (1). The oligonucleotides incorporating 1 showed efficient interstrand cross-linking with selectivity toward cytidine at a target site. In this paper, we describe the design of the new cross-linking reagents (2) bearing 2-amino-6-vinyl purine motif, and triplex-directed alkylation with 2 to double-stranded DNA.

Efficient cross-linking to cytidine under neutral conditions using the 2-amino-6-vinylpurine derivative having an additional activating group

We have previously reported that the oligonucleotides incorporating 2-amino-6-vinyl purine analog (1) showed efficient interstrand cross-linking with selectivity toward cytidine at a target site. In this paper, we describe the design of more efficient cross-linking reagent (2) bearing 2-amino-6-vinyl purine motif to react to cytidine selectively under neutral condition.

A new reactive nucleoside analogue for highly reactive and selective cross-linking reaction to cytidine under neutral conditions

We have already demonstrated that the oligonucleotides DNA (ODNs) bearing a 2-amino-6-vinylpurine derivative (1) exhibited efficient interstrand cross-linking to cytidine selectively. In this study, a new reactive nucleoside analogue, 2-amino-6-(1-ethylsulfoxy)vinylpurine derivative (7), was designed based on a computational method to achieve high and selective alkylation with cytidine under neutral conditions. It has been demonstrated that the ODN (13) bearing 2-amino-6-(1-ethylsulfoxy)vinylpurine achieved highly selective and efficient cross-linking to cytidine under neutral conditions.

Site-directed alkylation to cytidine within duplex by the oligonucleotides containing functional nucleobases

We have previously described that oligonucleotides (ODN) containing phenylsulfoxide derivative of 2-amino-6-vinylpurine nucleoside analog (1) are activated within duplex to form cross-link toward cytidine selectively at the target site. In this paper, we wish to report the search for more stable precursor susceptible for activation within duplex.

Selective reaction to a flipping cytidine of the duplex DNA mediated by triple helix formation

A new nucleoside derivative (2) with a butyl spacer between the sugar part and the 2-amino-6-vinylpurine motif has been synthesized. The triplex-forming oligodeoxynucleotide incorporating 2 has achieved strand- and cytidine-selective cross-linking reaction to the G-C target site mediated by triple helix formation. It has been suggested that 2 reacts with a flipping cytidine at the target site.

Efficient cross-linking to cytidine by functional nucleobases capable of in situ activation

We have previously demonstrated that the ODNs with 2-amino-6-(2-phenylsulfoxyethyl)purine nucleoside derivative were capable of efficient interstrand cross-linking with cytidine selectively. In this new strategy, less reactive precursor was auto-activated within a duplex to generate 2-amino-6-vinylpurine derivative. However, it turned out that 2-amino-6-(2-phenylsulfinyl)-ethylpurine nucleoside was not applicable as the precursor for the synthesis of DNA oligomers with G-rich sequences. In this report, 2-amino-6-(2-methylsulfinylethyl)purine nucleoside has been proven to be more suitable as a precursor for DNA synthesis. In addition, the ODNs incorporating either 2-amino-6-(2-phenylsulfoxy ethyl)purine or 2-amino-6-vinylpurine showed high reactivity toward the cytidine at the target site but quite less reactivity was observed for it at non-target site, demonstrating high site-selectivity.

Synthesis and evaluation of oligonucleotides incorporating novel artificial nucleobases for the selective formation of non-natural type triplexes

Regulation of specific gene expression by the sequence specific triplex formation has been expected as a new biological tool or a new therapeutic method in the so-called antigene strategy. As native nucleobases form triplexes only within homopurine-homopyrimidine duplexes, expansion of the target sequences to general ones has been desired. We have previously reported the selective formation of base triplets by the non-native nucleobases (1, 2) with a CG or a TA base pair, respectively, in the organic solvent. In this paper, we wish to report the synthesis of the new non-native bases (3, 4, 9-11) and their incorporation into the triplex-forming oligonucleotides (TFOs), as well as their ability of triplex formation.

Novel cross-linking reaction of oligonucleotides incorporating new base analogs with selective reactivity toward cytidine

2-Amino-6-vinylpurine analog (1) has been proven to react with cytidine and guanosine in a model reaction of cross-linking. However, its incorporation into the ODNs was unsuccessful because of the high reactivity of its vinyl group. A new precursor for 1, 2-amino-6-[2-(phenylthio)ethyl]purine (2), was designed so as to generate the reactive vinyl group after introduction into the oligomers. In this paper, synthesis of ODN containing 2, easy generation of the vinyl group within the oligomer, and interstrand cross-linking between the ODN incorporating 1 and the target DNA, are described.

20-[18F]fluoroarachidonic acid: tissue biodistribution and incorporation into phospholipids

The in vivo behavior of 20-[18F]fluoroarachidonic acid (18F-FAA) was investigated to evaluate its potential use as a radiotracer for studying the regional brain and heart lipid metabolism by positron emission tomography (PET). Tissue biodistribution studies in rats have revealed that 18F-FAA has a high uptake in the liver and lung, thus probably reflecting the metabolism, and is accompanied by both low in vivo defluorination and low blood levels. At 30 min postinjection, the uptake in the brain and heart reached values of 0.26 +/- 0.02 and 1.22 +/- 0.58% dose/g, respectively, with ratios to the blood radioactivity of 1.04 and 4.88, respectively. Lipid extraction at 30 min postinjection showed that 39% of the brain radioactivity was in the organic phase whereas the organic phase from heart tissue contained 73% of the total radioactivity. A TLC analysis demonstrated that 18F-FAA was mainly bound to phospholipids in the brain and heart tissue as expected. Based on the findings of this study, the utility of 18F-FAA as an in vivo tracer for cerebral phospholipid studies appears to be limited because of its relatively high radioactivity in the aqueous brain fraction. However, our findings do suggest that this agent might be useful as a tool for studies of cardiac phospholipid turnover, even though it demonstrated a poor heart-to-lung and heart-to-liver contrast.

18F-labeled octanoates as potential agents for cerebral fatty acid studies. The influence of 4-substitution and the fluorine position on biodistribution

In order to understand the structural features that might lead to an in vivo radiotracer for studying cerebral fatty acid metabolism, 8-[18F]fluorooctanoate derivatives with methyl or gem-dimethyl branching at the C4 position have been prepared. 3-[18F]Fluoro- and 4-[18F]fluorooctanoic acid have also been synthesized for studying the influence of the fluorine position on the in vivo behavior of 18F-labeled octanoic acid analogs. Radiochemical synthesis was achieved by the nucleophilic displacement of a tosylate or mesylate precursor with [18F]fluoride ion. Tissue distribution studies in rats showed low cerebral uptakes of these 18F-labeled fatty acid analogs with poor brain-to-blood ratios. 3-[18F]Fluorooctanoic acid showed considerable defluorination, evident as a high bone activity level. The initial uptake of activity in the brain after injection of ethyl 8-[18F]fluoro-4-methyloctanoate and 4-[18F]-fluorooctanoic acid remained virtually unchanged over an extended time period, similar to that previously observed for the unbranched analogs, ethyl 8-[18F]fluorooctanoate and its free acid. In contrast, the 4-gem-dimethyl branched analog was rapidly and preferentially taken up by the liver. It was shown in the metabolite analysis that labeled metabolites produced from 8-[18F]fluoro-4-methyloctanoic acid were found in blood, and that they could enter the brain to a significant degree. Thus, the present studies showed that radioactivity retention in the brain in the case of the 4-methyl branched analog was mainly attributable to its radioactive metabolites.

8-[18F]fluorooctanoic acid and its beta-substituted derivatives as potential agents for cerebral fatty acid studies: synthesis and biodistribution

Fluorine-18 labeled analogs of 8-fluorooctanoic acid and its structurally modified derivatives with methyl or gem-dimethyl branching or with oxygen substitution at the C3 position were prepared using nucleophilic substitution of the tosylate precursors by [18F]fluoride ion, for evaluation as tracers for cerebral fatty acid metabolism. Tissue distribution studies in rats showed low brain uptakes of these 18F-labeled fatty acid analogs with poor brain-to-blood ratios of activity. The oxygen-substituted analog did not show any significant accumulation of radioactivity in most tissues. The initial brain uptake of activity after injection of ethyl 8-[18F]fluorooctanoate and its free acid remained virtually unchanged over an extended time period, beta-Monomethyl and beta-gem-dimethyl branched analogs had similar brain uptake at the early time period, but they showed rapid clearance of activity from the brain. TLC analysis showed no incorporation of 8-[18F]fluorooctanoic acid and its beta-dimethyl analogs into brain lipids. It was also shown in the metabolite analysis that the labeled metabolites produced from 8-[18F]fluorooctanoic acid are found in blood, and that they could enter the brain to a significant degree. On the contrary, such radioactive metabolites could not be found in the brain in the experiment with the beta-gem-dimethyl branched analog. Thus, the present studies showed that retention of radioactivity in the brain with 8-[18F]fluorooctanoic acid derivatives is mainly attributable to their radioactive metabolites, and that the rapid clearance of beta-branched analogs from the brain is due to the lack of availability as substrates in the cerebral fatty acid metabolism.