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Norharman and ellipticine: a comparison of their albilities to interact with DNA in vitro
Abstract:
The anti-tumor agent ellipticine has been compared in vitro with the bacterial co-mutagen norharman, a compound which it resembles superfically in chemical structure. Ellipticine was shown to stabilize the structure of double stranded calf-thymus DNA, to induce mutations in strain TA153 of Salmonella tryhimurium and to cause BHK cells to transform. Further, the major absorbance in its visible spectrum underwent a red shift of approximately 40 nm in the presence of native DNA. It is concluded that ellipticine intercalates with dna, and from this, that its action as an anti-tumor agent may, as has been previously suggested, be dependent upon this property. In contrast, norharman, a chemical suspected initially of being an intercalating agent, failed to stabilize the structure of DNA, was non-mutagenic to the same strain of S. typhimurium and was inactive as cell-transforming agent. In addition, its visible spectrum was not affected by the presence of DNA. The last observation is contrary to the conclusion of other workers, and an explanation of this difference is given. It is concluded that norharman is not capable of intercalating with DNA, and consequently, its mode of action as a co-mutagen is probably dependent upon its ability to inhibit certain mixed-function oxidase enzymes present in the liver activation system employed with in vitro mutagenicity assays.
Insights
The anti-tumor agent ellipticine intercalates with DNA, stabilizing its structure and causing mutations, unlike norharman, which does not interact with DNA and acts as a co-mutagen by inhibiting enzymes.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Ellipticine is an anti-tumor agent, while norharman is a bacterial co-mutagen.
- Both compounds share superficial structural similarities.
- Their differing biological activities warrant a comparative investigation of their interaction with DNA.
Purpose of the Study:
- To compare the in vitro effects of ellipticine and norharman on DNA structure and cellular processes.
- To determine if ellipticine and norharman interact with DNA via intercalation.
- To elucidate the mechanism of action for both compounds.
Main Methods:
- In vitro DNA stabilization assays using calf-thymus DNA.
- Mutagenicity testing in Salmonella typhimurium strain TA153.
- Cell transformation assays using BHK cells.
- Spectroscopic analysis (visible spectrum shifts in the presence of DNA).
Main Results:
- Ellipticine stabilized double-stranded DNA, induced mutations, and caused cell transformation.
- Ellipticine's visible spectrum showed a significant red shift with native DNA, indicating intercalation.
- Norharman did not stabilize DNA, was non-mutagenic, and did not cause cell transformation.
- Norharman's visible spectrum was unaffected by DNA, contradicting previous findings.
Conclusions:
- Ellipticine intercalates with DNA, supporting its proposed anti-tumor mechanism.
- Norharman does not intercalate with DNA.
- Norharman's co-mutagenic activity likely stems from its inhibition of mixed-function oxidase enzymes.
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