antimetabolites


2.       ANTIMETABOLITES

These drugs are usually structural analogues of the natural (cell made) metabolites. They interfere with the normal synthesis of nucleic acids by falsely substituting purines with and pyrimidines in the metabolic pathways. The end result is a deformed nucleic structure that leads to initiation of apoptosis in the deformed cells.

Methotrexate is structurally similar to folic acid and it therefore acts as folic acid antagonist. It binds preferentially to the enzyme dihydrofolate reductase, which is responsible for the conversion of folic acid to folinic acid, the form of it that’s needed for the synthesis, repair, and methylation of DNA. This ends up impeding the reproduction of more tumor cells.

5-fluorouracil and cytosin arabinoside (cytarabine) are pyrimidine antagonists. 5-fluorouracil binds and blocks the activity of enzyme thymidylate synthase that is essential for pyrimidine synthesis. It is a major drug in treatment of solid tumors especially those of the gastrointestinal tract.

Cytosine arabinoside  is exclusively the drug of choice and the backbone therapy in the treatment of acute myeloid leukemia
6-mercaptopurine and 6- thioguanine are purine antagonists both exclusively used in the treatment of acute leukemia.


3. PLANT ALKALOIDS



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