The antitumor activity of Cu(II)KTS, the copper (II) chelate of 3-ethoxy-2-oxobutyraldehyde bis(thiosemicarbazone).

The antitumor activity of the copper(H) chelate of 3-ethoxy-2oxobutyraldehyde bis(thiosemicarbazone), Cu(II)KTS, against the Walker 256 carcinosarcoma in rats is shown, and the im portance of considering this chelate as the active intermediate in the mechanism of action of the free ligand, KTS, is indicated. The potentiation of the antitumor activity and toxicity of Cu(II)KTS by KTS and Vu(II) was demonstrated. Results of experiments with combinations of these agents are consistent with the hypoth esis that the dynamics of the chemical equilibria governing the interaction of KTS and Cu(II) to form Cu(II)KTS also govern their biologic activity. The protonated chelate, Cu(II)KTS-2HCl, appears to be less active as an antitumor agent than is the un charged chelate but also somewhat more toxic for rats.