PHOSPHOROTHIOATE OLIGONUCLEOTIDES REDUCE MELANOMA GROWTH IN A SCID-HUMOUSE MODEL BY A NONANTISENSE MECHANISM

In our efforts to investigate the biologic role of Ha-ras oncogenes in human melanoma by Ha-ras phosphorothioate antisense oligonucleotides, we observed that antisense, sense, and scrambled control oligonucleot ides at a concentration of 10 mu M all similarly and strongly inhibite d growth of our human melanoma target cell line SK-2 in vitro but with out specific decrease of the target protein. Cell numbers with respect to the untreated control were reduced by 84% +/- 4.2% (ISD), 82.9% +/ - 3.6%, and 84% +/- 3%, respectively. In vivo studies in a SCID-hu mou se model confirmed these findings. Both antisense and sense control ol igonucleotides administered through osmotic pumps significantly (p < 0 .006) reduced the mean tumor weight (1.5 +/- 0.4 g and 1.8 g +/- 0.8 g , respectively) in comparison with saline-treated (5.7 g +/- 0.7 g) or untreated control animals (5.8 g +/- 1.0 g). The vascularity of oligo nucleotide-treated tumors was greatly reduced, Clinical signs of oligo nucleotide-related toxicity were not observed, and there was no eviden ce of histopathologic alterations in a variety of mouse tissues. We co uld demonstrate that the antimelanoma effects can be abrogated in vitr o by adding basic fibroblast growth factor (bFGF). In the context of t he importance of bFGF in melanocyte biology and angiogenesis, we argue in favor of an interaction between polyanionic phosphorothioate oligo nucleotides and bFGF in our melanoma system. These findings stress the notion that phosphorothioate oligonucleotides may be promising antine oplastic lead compounds capable of employing antitumor effects by mech anisms other than specific inhibition of gene expression.