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Selective inhibition with sodium cyanate of protein synthesis in colon cancer cells
Abstract:
Sodium cyanate, which in its tautomeric acidic form, isocyanic acid, acts as a protein carbamylating reagent, has been previously shown to inhibit selectively both DNA and protein synthesis in a variety of solid tumors. We have now compared its effects on protein synthesis in normal colonic epithelium and in colon tumors induced by the administration of 1,2-dimethylhydrazine to rats. The incorporation of 3H-amino acids into cytoplasmic and nuclear protein fractions was suppressed to a much greater extent in the tumor tissue than in colonic epithelial tissue surrounding the tumors of cyanate-treated rats. Despite its effect on tumor protein synthesis in whole animals, cyanate had little or no effect on cultured cells (HT-29) derived from a human adenocarcinoma of the colon, nor on other malignant cell lines such as HeLa S3 cells, chick fibroblasts transformed by the Rous sarcoma virus, mouse Ehrlich ascites tumor cells, or rat Novikoff hepatoma cells. However, the administration of cyanate i.p. does suppress amino acid incorporation by Novikoff hepatoma cells in the peritoneal cavity of rats. The implication that the mechanism of cyanate inhibition of protein synthesis in tumors may require its in vivo metabolism or utilization to produce a postsynthetic modification of circulatory factors is discussed.
Insights
Sodium cyanate significantly inhibits protein synthesis in colon tumors more than normal tissue. This suggests in vivo metabolism is crucial for its anti-tumor effects, not direct action on cancer cells.
Area of Science:
- Biochemistry
- Oncology
- Pharmacology
Background:
- Sodium cyanate, as isocyanic acid, is a protein carbamylating agent.
- Previous studies demonstrated its selective inhibition of DNA and protein synthesis in solid tumors.
Purpose of the Study:
- To compare the effects of sodium cyanate on protein synthesis in normal colonic epithelium versus chemically induced colon tumors.
- To investigate the mechanism of cyanate's anti-tumor activity, particularly its dependence on in vivo conditions.
Main Methods:
- Administered 1,2-dimethylhydrazine to rats to induce colon tumors.
- Compared 3H-amino acid incorporation into proteins in tumor and normal colonic tissues after cyanate treatment.
- Evaluated cyanate's effect on various cultured cell lines and in vivo on Novikoff hepatoma cells.
Main Results:
- Sodium cyanate suppressed protein synthesis significantly more in colon tumors than in surrounding normal epithelium.
- Cyanate showed minimal inhibitory effects on cultured colon adenocarcinoma (HT-29) and other malignant cell lines.
- Intraperitoneal administration of cyanate inhibited protein synthesis in Novikoff hepatoma cells within the peritoneal cavity.
Conclusions:
- The selective inhibition of protein synthesis in colon tumors by sodium cyanate suggests a complex mechanism.
- In vivo metabolism or utilization of cyanate may be essential for its anti-tumor effects.
- Further research is needed to elucidate the role of postsynthetic modification of circulatory factors in cyanate's action.