Which of the following is NOT an antimetabolite?

Chlorambucil is not classified as an antimetabolite. It is an alkylating agent, which means it works by adding alkyl groups to the DNA, leading to disruption of DNA function and ultimately cell death. Alkylating agents like Chlorambucil directly modify the DNA molecule, thereby interfering with DNA replication and transcription processes.

On the other hand, antimetabolites are drugs that mimic the natural substances within cells, disrupting the normal metabolism of nucleotides or DNA synthesis. Fludarabine and mercaptopurine are examples of antimetabolites, as they interfere with the synthesis of DNA and RNA by incorporating themselves into the metabolic pathways. Cyclophosphamide, while primarily an alkylating agent, is often discussed in relation to antimetabolites due to its effects on rapidly dividing cells, but it does not fall into the traditional definition of antimetabolites.

Thus, understanding these classifications helps in grasping how different chemotherapy agents affect cellular processes and contribute to cancer treatment.