Alkylating agents form covalent bonds with nucleic acids. These agents alter the integrity of DNA by transferring an alkyl group to the nucleic acids. Agents in this class are both cytotoxic and carcinogenic. Cyclophosphamide is the most commonly used alkylating agent.
Antimetabolites are structurally similar to normal metabolic substrates.
They impair cellular functions by substituting for normal precursors in vital physiologic reactions or by blocking these reactions. The most commonly used antimetabolites are methotrexate and fluorouracil, both of which interfere with nucleic acid synthesis. Antibiotics, biologic products of bacteria and fungi, are of increasing importance in cancer chemotherapy. They do not share a single mechanism of action. Bleomycin and the anthracyclines daunorubicin and doxorubicin are some of the more commonly used antibiotics.