Biomedical subjects
Publications and source records attributed to C Boiziau.
Synthetic oligodeoxynucleotides, either unmodified or linked to an intercalating agent, have been used to prevent cDNA elongation by the AMV reverse transcriptase. Oligonucleotide/RNA hybrids specifically arrest primer extension. The blockage involves the degradation of the RNA part bound to the antisense oligonucleotide by the RNase-H activity associated with the retroviral polymerase.
The binding of an oligodeoxynucleotide, so-called anti-sense, to the complementary sequence of a messenger RNA can prevent the synthesis of the encoded protein. This approach constitutes a very efficient and specific means to artificially regulate gene expression. Numerous chemical modifications have been introduced into synthetic oligos in order to provide them with properties that unmodified molecules do not display. For instance, oligos built up with methylphosphonate, phosphorothioate and alpha-anomer units lead to molecules that are resistant to DNases. Acridine-linked oligos exhibit an increased affinity for the target sequence due to the intercalation of the dye into the oligo/RNA duplex. Two different mechanisms account for translation inhibition by antisense oligos. Inhibition of the elongation step results only from the induced cleavage of the target RNA by RNase-H. In contrast, oligos targeted upstream of the AUG initiation codon can block the initiation step through an RNase-H independent mechanism. As a consequence, methylphosphonate- and alpha-oligos, which do not elicit RNase-H activity, targeted to the 5' region, are efficient antisense; but they are inactive if targeted to the coding sequence. Experiments performed with antisense oligos in cell-free extracts supported the notion that the mini-exon sequence, acquired by trans-splicing, was present on every message in trypanosomatids and on some of them in nematodes. Furthermore, an acridine-linked oligo complementary to the mini-exon sequence of Trypanosoma brucei induced a lethal effect on cultured procyclics. Therefore these compounds constitute promising tools in molecular genetics and could open new routes to rationally tailor therapeutic agents.
Oligodeoxynucleotides with a phosphorus atom in which one of the non-bridging oxygen atoms is substituted by selenium were prepared and investigated with respect to their antisense properties. A general synthesis of phosphoroselenoate analogs of oligonucleotides is described using potassium selenocyanate as the selenium donor. The compounds, characterized by 31P NMR, were shown to decompose to phosphate with a half-life of ca. 30 days. Melting temperatures of duplexes between poly(rA) or poly(rI) with oligo(dT) and oligo(dC), respectively, indicate diminished hybridization capability of phosphoroselenoate oligomers relative to both the unmodified phosphodiester oligomers and the phosphorothioate congeners. A phosphoroselenoate 17-mer is a sequence specific inhibitor of rabbit beta-globin synthesis in wheat germ extract and in injected Xenopus oocytes. In contrast phosphoroselenoate analogs are potent non-sequence specific inhibitors in rabbit reticulocyte lysate. In vitro HIV assays were carried out on a phosphoroselenoate sequence and compared with a phosphorothioate analogue that has previously been shown to exhibit anti-HIV activity (Matsukura et al., Proc. Natl. Acad. Sci. (1987) 84, 7706-7710). The phosphoroselenoate was somewhat less active, and was much more toxic to the cells.