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Mutagenicity of topoisomerase-active agents in bacteriophage T4
1Genetic Toxicology Division, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.
Abstract:
Recently, the antitumor agent 4'-(9-acridinylamino)-methanesulfon-m-anisidide (m-AMSA) was shown to revert a frameshift mutant of T4 (rFC11), and its mutagenicity was shown to be mediated by T4 DNA topoisomerase II [Ripley et al.: J Mol Biol 200: 665-680, 1988]. Here we report dose-response data on the mutagenicity and toxicity of m-AMSA in T4 rFC11. We find that m-AMSA is among the most potent frameshift mutagens observed in T4, inducing a 10-fold increase in mutant frequency in the absence of toxicity and a 500-fold increase in mutant frequency at 31% survival. In addition to m-AMSA, the topoisomerase-active agents ellipticine, oxolinic acid, and nalidixic acid also reverted rFC11; however, they required concentrations 10-100 times greater than those required by m-AMSA in order to be mutagenic, and they did not produce mutant frequencies as high as those produced by m-AMSA. Unlike m-AMSA, all three agents were mutagenic only at toxic doses. The other agents evaluated--actinomycin D, adriamycin, 9-aminoellipticine, 9-methoxyellipticine, teniposide (VM-26), and novobiocin--were toxic but not mutagenic to T4 rFC11. Thus, m-AMSA appears to be distinctly different from the other topoisomerase-active agents in exhibiting such potent mutagenic activity in T4 rFC11. Because E. coli DNA gyrase may substitute for T4 topoisomerase II, we examined the ability of two inhibitors of E. coli DNA gyrase, novobiocin and nalidixic acid, to inhibit m-AMSA's mutagenicity. Both agents substantially reduced the mutagenicity of m-AMSA in T4 rFC11, further suggesting that topoisomerase mediates the mutagenicity of m-AMSA.
Insights
The antitumor agent m-AMSA is a highly potent frameshift mutagen in T4 phage, distinct from other topoisomerase-active compounds. Its mutagenicity is mediated by T4 DNA topoisomerase II and can be inhibited by E. coli DNA gyrase inhibitors.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The antitumor agent 4'-(9-acridinylamino)-methanesulfon-m-anisidide (m-AMSA) has been previously shown to revert frameshift mutations in T4 phage.
- The mutagenicity of m-AMSA is linked to its interaction with T4 DNA topoisomerase II.
Purpose of the Study:
- To investigate the dose-response relationship of m-AMSA's mutagenicity and toxicity in T4 phage.
- To compare the mutagenic potency of m-AMSA with other topoisomerase-active agents.
- To explore the role of DNA topoisomerase in mediating m-AMSA's mutagenicity.
Main Methods:
- Dose-response experiments were conducted using T4 rFC11 frameshift mutant.
- Mutant frequency and survival rates were measured after exposure to various agents.
- Inhibition assays were performed using inhibitors of E. coli DNA gyrase.
Main Results:
- m-AMSA demonstrated potent frameshift mutagenicity in T4, inducing significant increases in mutant frequency even at non-toxic doses.
- Other topoisomerase-active agents (ellipticine, oxolinic acid, nalidixic acid) were less potent and mutagenic only at toxic concentrations.
- Inhibitors of E. coli DNA gyrase (novobiocin, nalidixic acid) substantially reduced m-AMSA's mutagenicity, supporting topoisomerase mediation.
Conclusions:
- m-AMSA is a uniquely potent frameshift mutagen in T4, distinct from other topoisomerase-targeting drugs.
- T4 DNA topoisomerase II is the primary mediator of m-AMSA's mutagenic activity.
- The findings suggest a conserved mechanism of topoisomerase-mediated mutagenesis across different organisms.