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.
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