Nuclease stability

To avoid the problem of chirality and to improve the potency and limit the non-specific actions of AS-ODN, new compounds are required. Synthesis of new AS-ODNs has further improved their nuclease stability, enhanced of cellular uptake and affinity through modification of the base, sugar and phosphate moieties of the oligonucleotides [105-108],... 

Peyman A, Helsberg M, Kretzschmar G, Mag M, Ryte A, Uhlmann E. Nuclease stability as dominant factor in the antiviral activity of oligonucleotides directed against HSV-I IE I 10. Antiviral Res 1997 33 135-139. 

Lupoid SE, Hicke BJ, Lin Y, Coffey DS, Identification and characterization of nuclease-stabilized RNA molecules that bind human prostate cancer cells via the prostate-specific membrane antigen, Cancer Res., 60 5237-5243, 2000. 

Fig. 1 Modified nucleic acids with enhanced nuclease stability, a DNA, b phosphorothioate, c Z -OjT-C-methylene-bridged (locked) nucleic acid (LNA), d 2f-0,A -C-ethylene-bridged nucleic acid (ENA), e Z -O-methyl nucleic acid, f methylphosphonate-linked nucleic acid, g morpholino-linked nucleic acid, h peptide nucleic acid (PNA)...

Stereoenriched Rp and Sp phosphorothioate ODNs have been synthesised using oxazaphospholidine monomers (12, Rp isomer shown). A comparison of duplexes containing stereoenriched Rp, Sp and stereo-random ODNs has been made by hybridisation studies. The binding affinities were found to be in the order Rp > stereo-random > Sp, whilst the in vitro nuclease stability was the reverse order. All ODNs activated RNase H activity, though Rp phos-phorothioates were the most efficient. 

Modifications in the base, sugar, and phosphate moieties of oligonucleotides and oligonucleotide conjugates have been reported. The subjects of medicinal chemical programs include approaches to create enhanced affinity and more selective affinity for RNA or duplex structures the ability to cleave nucleic acid targets enhanced nuclease stability cellular uptake and distribution and in vivo tissue distribution, metabolism, and clearance. 

The demonstration that modificationsmay induce nuclease stability sufficient to enhance activity in cells in tissue culture and in animals has proved to be much more complicated because of the presence of 5 -exonucleases and -endonucleases. In our laboratory, 3 -modifi-cations and internal point modifications have not provided sufficient nuclease stability to demonstrate pharmacological activity in cells (183). In fact, even a 5-nucleotide-long phos-phodiester gap in the middle of a phosphoro-thioate oligonucleotide resulted in sufficient loss of nuclease resistance to cause complete loss of pharmacological activity (164). In mice, neither a 5 -cholesterol nor 5 -C18 amine conjugate altered the metabolic rate of a phospho-rothioate oligodeoxynucleotide in liver, kid-... 

Modifications involving linkage of cholesterol have been the most prominent approach [135,381,384-388]. ODNs, which are linked to cholesterol at their 5 -end, exhibit increased nuclease stability. Their uptake into human cancer cells is increased by a factor of 30-100 when compared with natural ODNs [389]. In addition, they have been found to reduce... 

Wong C-Y, Eftink M R (1998). Incorporation of tryptophan analogues into staphylococcal nuclease Stability toward thermal and guanidine-HCl induced unfolding. Biochem. 37 8947-8953. 

Modifioations in the base, sugar, and phosphate moieties as well as in the length of the polymer have been reported in attempts to create molecules with enhanced or more seleotive affinity for speoific sites on the RNA, to enhance nuclease stability, to improve... 

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