The role of formaldehyde in methylene dimethanesulphonate-induced DNA cross-links and its relevance to cytotoxicity.

The interaction of the antitumour dialkanesulphonate ester, methylene dimethanesulphonate (MDMS) with the DNA of Yoshida sarcoma cells has been studied using the technique of alkaline elution. A marked retention which was reversed by proteolytic treatment indicated the presence of DNA-protein cross-links. A small proteinase-resistant retention was also observed which indicated that a low level of DNA-DNA interstrand cross-links also occurred. Treatment of cells with the amounts of formaldehyde expected by hydrolysis of the drug showed proteinase-reversible DNA-protein cross-linking which on proteolytic removal revealed a small number of single-strand breaks. Thus, MDMS causes both DNA-protein and DNA-DNA interstrand cross-links, the former component being attributed totally to the formaldehyde produced on the drug's hydrolysis. Cell survival data showed formaldehyde to be comparatively non-cytotoxic, providing evidence that DNA-DNA cross-links observable by this technique may be associated with the cytotoxicity of MDMS.