TRANSPLATIN-MODIFIED OLIGO(2'-O-METHYL RIBONUCLEOTIDE)S - A NEW TOOL FOR SELECTIVE MODULATION OF GENE-EXPRESSION

In the reaction between trans-diamminedichloroplatinum(II) and single- stranded oligo(2'-O-methyl ribonucleotide)s containing the sequence GN G (N being a nucleotide residue), the 1,3-trans-(Pt (NH3)(2)[GNG]} cro ss-links are formed. The 1,3-intrastrand cross-links are inert within the single-stranded oligonucleotides. By contrast, they rearrange into interstrand cross-links when the platinated oligonucleotides are pair ed with their complementary RNA strands. The rate of the interstrand c ross-linking reaction depends upon the sequence facing the intrastrand cross-links. When the complementary sequences are 5'-CN'C (N' being a nucleotide), the rates are rather slow (tau(1/2) greater than or equa l to 3 h at 37 degrees C). The rearrangement of the intrastrand cross- links into interstrand cross-links can be achieved in a few minutes wh en the triplets facing the intrastrand cross-links are replaced by dou blet 5'-UA or 5'-CA. In vitro, the specificity of the cross-linking re action between a platinated oligo(2'-O-methyl ribonucleotide) and its target sequence (containing the 5'-CA doublet) located within the codi ng region of Ha-ras mRNA is demonstrated by steric blocking of reverse transcriptase and translation machinery. Within the HBL100ras1 cells, this platinated oligonucleotide binds specifically and irreversibly t o the cognate Ha-ras mRNA. It also inhibits the proliferation of the H BL100ras1 cells in a dose-dependent manner. The fast and specific inte rstrand cross-linking reaction triggered by the formation of a double helix between platinated oligo(2'-O-methyl ribonucleotide)s and RNA en hances the potential of the oligonucleotides which do not induce mRNA cleavage by RNase H, to modulate gene expression by steric blocking of the translation machinery.