Antisense phosphorothioate oligodeoxynucleotide down‐regulation of the insulin‐like growth factor I receptor in ovarian cancer cells

The insulin‐like growth factors (IGF‐I and IGF‐II) play a key role in cellular proliferation and are involved in cellular transformation. The expression of the IGF‐I receptor has been demonstrated in a variety of human tumor cell lines including ovarian cancer cells. Phosphorothioate antisense oligodeoxynucleotides (S‐ODNs) were analyzed for their potential to suppress the IGF‐I receptor in the NIH:OVCAR‐3 ovarian cancer cell line. The application of the antisense S‐ODN reduced potently the cell growth of unstimulated NIH:OVCAR‐3 cells, whereas sense and mismatch S‐ODNs were without any effect. This effect resembled that of the monoclonal antibody (MAb) αIR‐3. In contrast to the antisense compound, this MAb only partially inhibited the IGF‐I‐induced proliferation of ovarian cancer cells. The concentration of the antisense S‐ODN to exhibit an identical inhibition of cell proliferation was reduced to 50 nM when the oligonucleotides were delivered by the cationic lipid formulation lipofectin. The specificity of the antisense S‐ODN action was confirmed by reduction of the receptor protein and of the receptor mRNA, as assayed by flow cytometry and by Northern blot hybridizations. Our data demonstrate the potency of antisense S‐ODNs to target the IGF‐I receptor message and show that antisense strategies against the IGF‐I receptor may provide new strategies for the therapy of ovarian cancer. Int. J. Cancer 77:567–571, 1998. © 1998 Wiley‐Liss, Inc.