Strand scission of superhelical and linear duplex DNAs by the antitumor protein macromomycin. Relationship of in vitro DNA damage to cell growth inhibition.

Macromomycin, a protein antitumor drug, was found to cause strand scissions in vitro in superhelical PM2 and SV40 DNA as well as linear duplex lambda DNA. DNA damage appeared to be single rather than double-strand scissions, and there is an indication that DNA breaks occur at some preferential base sites. The DNA breaks were predominantly true single-strand scissions as opposed to alkali-labile bonds. The cutting reaction was inhibited by low temperature (0 degrees C) and reached a maximum at 45 degrees C. The reaction was not affected by 2-mercaptoethanol, although EDTA did cause a slight decrease in the reaction rate. MgCl2 was found to be an effective inhibitor of the strand scission activity of the drug. The rate of DNA cutting was linear over a wide range of DNA substrate levels. There appeared to be a correlation between the drug's ability to damage DNA and to inhibit cell growth in that similar losses of these two activities occurred as the drug was thermally denatured.