DNA strand scission in vivo and in vitro by auromomycin

The mechanism of action of auromomycin, a new tumor-inhibitory antibiotic, was studied in a growing culture of mouse lymphoblastoma L5178Y cells and with isolated viral DNA. Auromomycin prevented growth of L5178Y cells completely and irreversibly at antibiotic concentrations higher than 0.03 microgram/ml. DNA synthesis was preferentially inhibited by the antibiotic, whereas RNA and protein syntheses were not significantly affected. In synchronous cultures of L5178Y cells, results indicated that limited auromomycin-induced inhibition of DNA synthesis may occur independently of a much stronger inhibition of mitosis. In a short incubation period, a marked strand scission in cellular DNA of auromomycin-treated L5178Y cells was observed by an analysis of alkaline sucrose gradient centrifugation. In vitro, the antibiotic also induced strand breaks in linear duplex T-7 phage DNA and in the supercoiled circular duplex of SV40 DNA. 2-Mercaptoethanol neither enhanced nor was required for strand scission of isolated DNA by auromomycin. These data indicate that the mechanism of the antitumor activity of auromomycin is different from that of bleomycin, neocarzinostatin, or macromomycin.