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Phosphorothioate oligonucleotides reduce melanoma growth in a SCID-hu mouse model by a nonantisense mechanism
1Institute for Specific Prophylaxis and Tropical Medicine, Vienna, Austria.
Abstract:
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 oligonucleotides at a concentration of 10 microM all similarly and strongly inhibited growth of our human melanoma target cell line SK-2 in vitro but without 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 mouse model confirmed these findings. Both antisense and sense control oligonucleotides administered through osmotic pumps significantly (p < 0.006) reduced the mean tumor weight (1.5 g +/- 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 oligonucleotide-treated tumors was greatly reduced. Clinical signs of oligonucleotide-related toxicity were not observed, and there was no evidence of histopathologic alterations in a variety of mouse tissues. We could demonstrate that the antimelanoma effects can be abrogated in vitro by adding basic fibroblast growth factor (bFGF). In the context of the importance of bFGF in melanocyte biology and angiogenesis, we argue in favor of an interaction between polyanionic phosphorothioate oligonucleotides and bFGF in our melanoma system. These findings stress the notion that phosphorothioate oligonucleotides may be promising antineoplastic lead compounds capable of employing antitumor effects by mechanisms other than specific inhibition of gene expression.
Insights
Phosphorothioate oligonucleotides, including antisense and control sequences, effectively inhibited human melanoma growth in vitro and in vivo. These compounds show promise as antineoplastic agents, potentially acting through mechanisms beyond gene expression inhibition.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- The biologic role of Ha-ras oncogenes in human melanoma is under investigation.
- Phosphorothioate antisense oligonucleotides are being explored as a therapeutic strategy.
- Melanoma progression is linked to oncogene activity and angiogenesis.
Purpose of the Study:
- To investigate the anti-melanoma effects of Ha-ras phosphorothioate antisense oligonucleotides.
- To determine if these effects are specific to antisense activity or mediated by other mechanisms.
- To explore the potential of oligonucleotides as antineoplastic agents.
Main Methods:
- In vitro studies using human melanoma cell line SK-2 treated with antisense, sense, and scrambled oligonucleotides.
- In vivo studies using a SCID-hu mouse model with oligonucleotide administration via osmotic pumps.
- Assessment of cell number, tumor weight, vascularity, and histopathology.
- In vitro experiments to test abrogation of effects by basic fibroblast growth factor (bFGF).
Main Results:
- Antisense, sense, and scrambled oligonucleotides significantly inhibited melanoma cell growth in vitro (82-84% reduction).
- In vivo studies showed significant reduction in tumor weight (1.5-1.8 g) compared to controls (5.7-5.8 g).
- Oligonucleotide treatment led to reduced tumor vascularity without observable toxicity or histopathologic changes.
- Antimelanoma effects were abrogated by bFGF in vitro, suggesting an interaction.
Conclusions:
- Phosphorothioate oligonucleotides, irrespective of sequence specificity, exhibit potent anti-melanoma activity.
- The observed antitumor effects may involve mechanisms other than direct gene expression inhibition, possibly through interaction with factors like bFGF.
- These findings highlight phosphorothioate oligonucleotides as promising lead compounds for antineoplastic drug development.