Antisense

Antirachitic vitamin Antiredeposition agents Antirust additives Antiscaling additives Antiscorbutic vitamin Antiseize material Antisense agents Antisense DNA... 

Many human diseases are caused when certain proteins are either over- or underexpressed. Eor example, breast cancer can be induced by overexpressing certain cellular oncogenes within mammary tissue. To study the disease, researchers produce a line of transgenic mice that synthesize an abnormal amount of the same protein. This leads to symptoms of the disease in mice that are similar to what is found in humans. A protein can be overexpressed by inserting a DNA constmct with a strong promotor. Conversely, underexpression of a protein can be achieved by inserting a DNA constmct that makes antisense RNA. This latter blocks protein synthesis because the antisense RNA binds and inactivates the sense mRNA that codes for the protein. Once a line of mice is developed, treatments are studied in mice before these therapies are appHed to humans. 

A newer, highly experimental approach to anxiety therapy is the use of antisense oligonucleotides to the anxiogenic peptide, NPY (44). 

An effective therapeutic agent must also have the abiUty to reach its target sequence m vivo. BioavailabiUty requires that the antisense oligonucleotide be able to pass through the cell membrane, and that it have a low affinity for nontarget cellular compartments and, in animal systems, nontarget organs. 

Cell membranes are lipophilic and designed to be barriers against large anionic molecules, although there is a natural mechanism for intercellular transport of anionic oligonucleotides. In order to enhance membrane transport, antisense oligonucleotides are frequentiy modified by covalent attachment of carrier molecules or lipophilic groups. 

Modification of the Phosphodiester Backbone. Oligonucleotides having modified phosphate backbones have been extensively studied (46). Because altering the backbone makes derivatives generally more resistant to degradation by cellular nucleases, these materials have the potential to be more resilient antisense dmgs. 

Both phosphoramidate and phosphate triester derivatives have been used as linkers to attach reporter groups to oligonucleotides. These derivatives are not entirely resistant to nucleases and they possess a chiral center. They have not been widely iavestigated as antisense dmgs. 

UACGGUCUAAGCUGA. What is the corresponding nucleotide sequence (5 —> 3 ) of the template strand in a DNA duplex that might be introduced into these cells so that an antisense RNA could be transcribed from it ... 

VEGF inhibitors Humanized neutralizing antibodies, antisense oligonucleotides, siRNA, aptamers... 

Oblimersen sodium is a DNA antisense oligonucleotide designed to specifically bind to human bcl-2 mRNA, resulting in catalytic degradation of bcl-2. This results in decreased translation of the protein Bcl-2, which is a cellular antiapoptotic protein. Thus, oblimersen enhances sensitivity to chemotherapy by shifting the intracellular balance to a state in which the cells are more likely to be killed by apoptosis. Currently, it is used in combination chemotherapy for treating advanced melanoma. 

Antisense therapy means the selective, sequence-specific inhibition of gene expression by single-stranded DNA oligonucleotides. By hybridizing to the target mRNA, which results in a subsequent double-helix formation, gene expression is blocked. This process can occur at any point between the conclusion of transcription and initiation of translation or even possibly during translation. 

ASON are sequences of usually 17-30 bases of single-stranded DNA that hybridize to specific genes or their mRNA products by Watson-Crick base pairing and disrupt their function. In the case of AS-ODN (antisense oligodeoxyribonucleotides) cellular RNAseH is able to bind to the DNA-RNA duplex and hydrolyze the RNA, resulting in increased transcript turnover. Modifications to the deoxy moiety at the 2 -sugar position prohibits RNAse H action. 

The therapeutic utility of systemically administered ASON had been limited by their short plasma half life (sometimes even less than 3 min). This is due to their sensitivity to nuclease digestion. When the first-generation ASON were chemically modified, e.g., by replacing the oxygen in the phosphodiester bond with sulfur (phosphorothiorate) they obtained an increased stability in biological fluids while their antisense effect has been maintained. First-generation agents can be delivered via intravitreal injection, parenterally, by topical cream, enema, and inhaled aerosol. These antisense... 

Antisense Oligonucleotides. Figure 1 Schematic representation of the action of antisense oligonucleotides. They bind to their respective target mRNA preventing protein translation. 

---