Abstract

The exposure of sarcoma 180 ascites cells to the cupric chelate [Cu(II)KTS] of kethoxal bis(thiosemicarbazone) (KTS) resulted in the death of a large proportion of the cell population; both the ligand portion of the molecule, KTS, and cupric chloride were less toxic. Cells isolated from mice treated with Cu(II)KTS contained considerably greater amounts of copper than did those cells exposed to the same number of gram-atoms of copper presented as either copper chloride or copper stearate. The results suggested that the relatively lipidsoluble chelate-form of copper was more readily assimilated. Dissociation of Cu(II)KTS occurred within neoplastic cells, and this resulted in a relatively rapid loss from the cells of the ligand portion, KTS. In contrast, the copper derived from Cu(II)KTS persisted for a much longer period of time. The relationship of nucleic acid and protein synthesis to the phenomenon of cell death induced by these agents was assessed by measuring the effects of the compounds on these metabolic processes. The formation of DNA was more sensitive to the inhibitory action of Cu(II)KTS, CuCl₂, and KTS, than were either the syntheses of RNA or protein. In agreement with the cellular toxicity, Cu(II)KTS caused more pronounced depression of the incorporation of isotopic precursors into DNA than did either CuCl₂ or KTS. The copper present in cells treated with Cu(II)KTS induced at least three metabolic blocks on the pathways of DNA biosynthesis. The most sensitive site was measured by the incorporation of thymidine-³H into DNA and presumably was the result of the loss of activity of thymidine kinase. The findings obtained using a variety of isotopic precursors of DNA as biochemical probes suggested that the intracellular localization of copper derived from Cu(II)KTS differed from that of CuCl₂.