Recently, we attended a meeting in Rockville, MD cosponsored by the National Cancer Institute and the National Institute for Allergy and Infectious Diseases. Entitled, Oligodeoxynucleotides as Antisense Inhibitors of Gene Expression: Therapeutic Implications, the conference provided chemists and biologists from academia, research institutes and industry with a forum to discuss research into the synthesis and biological activity of antisense oligonucleotides.
Frequent examples of the use of oligonucleotides to inhibit viral replication and translation of mRNA have been described in the literature. One of the main problems in this approach is that oligodeoxynucleotides are hydrolyzed by nuclease enzymes when they enter infected cells. A variety of modified oligonucleotides with nuclease resistant linkages and with enhanced antiviral activity were discussed. These modified oligonucleotides included phosphorothioates, phosphorodithioates, phosphotriesters, methyl phosphonates, and oligo-[o:)deoxynucleotides. Although the variety of linkages is wide, the majority 1f biological data presented used phosphorothioates.
Modification of oligonucleotides at the 5'- and/or 3'-terminus allows the attachment of molecules which may act as intercalating agents or as agents to cleave the complementary strand. Examples were presented demonstrating enhanced antiviral activity of acridine and anthroquinone conjugates. Similarly, intercalating agents which can be used to induce photocrosslinking, e.g., psoralen and proflavine, were also examined. Other intercalating agents, e.g., copperphenanthroline, can be added to oligonucleotides to induce cleavage of the complementary strand. The ability to modify phosphate linkages to induce nuclease resistance and increase cell permeability, along with techniques to stabilize, crosslink or cleave duplexes, clearly opens the way for the development of highly specific therapeutic agents.
The intricacies of triple helix formation, including a third strand binding code, were reviewed by several groups. The formation of triplex DNA has been shown to inhibit several biological processes including replication and transcription. Such sequence specific intervention offers the potential for the manipulation of protein binding.
The role of RNaseH in the action of antisense oligonucleotides was detailed. After hybridization of the antisense oligonucleotide to mRNA, the RNA strand of the duplex is cleaved by RNaseH. The oligonucleotide is then recycled for further mRNA cleavage.
The state of the art of RNA synthesis, along with the potential of modified oligoribonucleotides as therapeutic agents was detailed.
Because of our belief that therapeutic agents will eventually be developed from these lines of research, we will continue to support the role of
H-phosphonate chemistry in the synthesis of modified oligonucleotides. To help promote this methodology, we have reduced our H-phosphonate monomer prices as detailed below.
