On interactions of cytostatic benzylidine hydrazines with SH-groups

The cytostatic and mutagenic compound N'-methyl-N'-cyano-(p-chloro)-benzaldehyde hydrazone (CyB4) has been found to be a strong SH-blocking agent since it reacts with the thiol groups of glutathione and of the cell membrane of Ehrlich ascites carcinoma cells (EAC). Furthermore, it decreases the intracellular, non-proteinogenic SH(NPSH)-level of tumor cells. CyB4 is not able to alkylate 4-(p-nitrobenzyl)-pyridine (NBP) by a nucleophilic substitution reaction, but it could be shown that the reactivity of CyB4 with thiol groups is due to a Michael-addition-type reaction of SH-groups with the cyano-group of CyB4. On the other hand, cytostatic beta-chloroethyl hydrazones showed a negligible reactivity against glutathione and led even to an increase of thiol groups, detectable by the 5,5'-dithiobis-2-nitrobenzoic acid (DTNB)-method, at the cell membrane of EAC when incubated in the presence of beta-chloroethyl hydrazones N-benzylidene-N'-methyl-N'-(2-chloroethyl) hydrazine (B1) and N-(4-dimethylaminobenzylidene)-N'-methyl-N'-(2-chloroethyl) hydrazine (B2). Therefore, it is concluded that the cytostatic efficiency of CyB4 is due to its SH-blocking while that of the beta-chloroethyl hydrazones is due to a rearrangement of the tumor cell membrane, as indicated by the increased level of reactive SH-groups.