Formation and properties of reactive aldehydes.

4-Hydroxyalkenals react easily with SH groups in enzymes and structural proteins to give stable adducts in which the aldehyde is bound through a thioether linkage to the protein. This reaction represents the mechanism by which these compounds block certain metabolic processes (DNA, RNA and protein synthesis, respiration, glycolysis) and exert their antitumour activity. A highly significant inverse correlation exists between the number of hydroxypentenal-sensitive SH groups in the soluble proteins and the doubling time of 12 transplantable animal tumours. Hydroxyalkenals applied peritumourally completely prevent or significantly delay growth of the solid forms of four animal tumours. The almost non-toxic adducts of 4-hydroxypentenal-cysteine 1:1 and crotonal-cysteine 1:2 applied intraperitoneally prevent or inhibit growth of Ehrlich ascites tumour in mice. The possible formation of unsaturated aldehydes in vivo from lipids, carbohydrates and diamines is discussed.