Cancer is associated with rapidly growing and proliferating cells . Because cells cannot multiply if they cannot synthesize DNA, several cancer chemotherapeutic agents have been developed to inhibit thymidylate synthase. If a cell cannot make thymidine( T ), it cannot synthesize DNA.
A common anticancer drug that inhibits thymidylate synthase is 5-fluorouracil. The enzyme reacts with 5-fluorouracil the same way it reacts with uracil. However, the fluorine substituent causes 5-fluorouracil to become permanently attached to the enzyme (because the base cannot remove a F+ in an elimination reaction) , blocking the active site of the enzyme so it can no longer bind uracil. Therefore, thymidine can on longer be synthesized , and without thymidine, DNA cannot be synthesized.
Unfortunately, most anticancer drugs cannot discriminate between diseased and normal cells. As a result, cancer chemotherapy is accompanied by terrible side affects. However, cancer cells undergo uncontrolled cell division; thus, because they are dividing more rapidly than normal cells, they are harder hit by cancer-fighting chemotheraputic agents.
Ref; Essentia Organic Chemistry, Paula Y. Bruice
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