Pyrimidine Antagonists
The pyrimidine antagonists act to block the synthesis of pyrimidine containing nucleotides (C and T in DNA; C and U in RNA). The drugs used to block the construction of these nucleotide have structures that are similar to the natural compound. By acting as 'decoys', these drugs can prevent the production of the finished nucleotides. They may exert their effects at different steps in that pathway and may directly inhibit crucial enzymes. The pyrimidine antagonist may also be incorporated into a growing DNA chain and lead to termination of the process.
For a cell to reproduce, it must first faithfully replicate all of the DNA in its genome. During DNA synthesis, pyrimidine and purine molecules must be made available to allow for the synthesis of the nucleotide building blocks and ultimately the new DNA molecules. A reduction in the availability of the raw materials needed to build DNA, such as is caused by the pyrimidine antagonists, leads to stoppage of DNA synthesis and inhibition of cell division.
Cancer cells are often quite rapidly dividing and therefore engaged in DNA synthesis. RNA synthesis is necessary for protein production. The pyrimidine antagonists inhibit the normal processes of DNA and/or RNA synthesis.
Some pyrimidine antagonists used in cancer therapy are:
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