Mustargen chemotherapy drug molecule. Computer model of a molecule of the chemotherapy drug mechlorethamine (marketed as Mustargen). Atoms are represented as spheres and are colour-coded: carbon (yellow), hydrogen (white), nitrogen (blue) and chlorine (green). Mechlorethamine is used to treat Hodgkin's disease, lymphomas and leukaemias. It is an alkylating agent, a substance that adds alkyl groups to DNA (deoxyribonucleic acid) molecules and so prevents them from replicating. This interferes with the cancer cell's growth and eventually destroys them.