Hybridization and cell uptake studies with radiolabelled antisense oligonucleotides

Background Radiolabelled antisense oligonucleotides have been proposed as r adiopharmaceuticals for imaging changes in the level of gene expression in vivo. This paper describes a study of the uptake of radiolabelled oligonucl eotides in cell lines expressing different levels of the target mRNA. Methods A 15-mer phosphorodiester deoxyoligonucleotide antisense to c-myc w as labelled with Tc-99m and P-32. Hybridization and stability studies were performed in vitro. Cell uptake studies were carried out in a c-myc express ing transformed rat embryonic fibroblast cell-line, TGR-1, and a knock-out cell line HO15.19 which does not express c-myc. Results The oligonucleotides were efficiently labelled with both radionucli des and retained their ability to hybridize with their complementary mRNA w hen extracted from cell lines. The radiolabelled oligonucleotides were stab le for a few hours in human serum. No statistically significant difference was found between the uptake of radioactivity by the two cell lines. Conclusions Although able to bind efficiently to their target in cell-free systems, radiolabelled oligonucleotides may be prevented from performing ef fectively as radiopharmaceutical vectors by the barriers imposed by cell me mbranes and/or intracellular metabolism. ((C) 2001 Lippincott Williams & Wi lkins).