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 GNG (N being a nucleotide residue), the 1,3-trans-{Pt-(NH3)2[GNG]} cross-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 paired with their complementary RNA strands. The rate of the interstrand cross-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 (T1/2 >/= 3 h at 37 degrees C). The rearrangement of the intrastrand cross-links into interstrand cross-links can be achieved in a few minutes when the triplets facing the intrastrand cross-links are replaced by doublet 5'-UA or 5'-CA. In vitro, the specificity of the cross-linking reaction between a platinated oligo(2'-O-methyl ribonucleotide) and its target sequence (containing the 5'-CA doublet) located within the coding 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 to the cognate Ha-ras mRNA. It also inhibits the proliferation of the HBL100ras1 cells in a dose-dependent manner. The fast and specific interstrand cross-linking reaction triggered by the formation of a double helix between platinated oligo(2'-O-methyl ribonucleotide)s and RNA enhances 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.