Methyl methanesulfonate

Methyl methanesulfonate (MMS) is an alkylating agent and a carcinogen. It is also a suspected reproductive toxicant, and may also be a skin/sense organ toxicant. It is used in cancer treatment.

Chemical reactions with DNA
MMS methylates DNA on N7-deoxyguanine and N3-deoxyadenine. Originally, this action was believed to directly cause double-stranded DNA breaks, because homologous recombination-deficient cells are particularly vulnerable to the effects of MMS. However, it is now believed that MMS stalls replication forks, and cells that are homologous recombination-deficient have difficulty repairing the damaged replication forks.