Nitrosoureas belong to the group of alkylants. Like the nitrogen-lost derivatives, they contain chloroethyl radicals as well as a highly reactive nitroso group. The substances decompose spontaneously and release the alkylating ethyl carbonium ion, which causes cross-linking of the DNA by alkylation of guanine and cytosine. In addition, isocyanates are formed, which also inhibit DNA repair by combining with the DNA polymerase. Nitrosourea derivatives have a non-phase-specific effect, i.e. they also act on resting cells.
Many nitrosoureas are able to cross the blood-brain barrier due to their small molecule size and lipophilicity. They are therefore suitable for the treatment of CNS metastases and brain tumours.