Nature of toxicity for chick embryo fibroblast cells of coumermycin A1 and its physico-chemical interactions with protein and nucleic acid

The results reported in this paper describe the effects produced by the antibiotic Coumermycin A1 (CA1) on survival and metabolism of chick embryo fibroblast cells (CEF), and give a clue to the understanding of its toxicity. The drug acts primarily at the level of DNA and RNA synthetic enzymes; no effect on DNA superstructure is detectable at doses at which cytotoxicity is pronounced. A spectroscopic approach produced evidence that CA1 binds to DNA, RNA, chromatin components such as histones and to a structurally unrelated protein such as bovine serum albumin. Furthermore, CA1 behaves like a pure non-competitive inhibitor of lactic dehydrogenase, a ubiquitous enzyme not involved in nucleic acid metabolism. The interaction of CA1 with a wide range of macromolecules playing different biological roles is certainly relevant to its activity and adds a new insight into the mechanism of action of this antibiotic. These observations are also discussed in the light of the alleged role of CA1 as a specific inhibitor of DNA topoisomerase in eukaryotic cells.