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Pharmacology: Capecitabine is a non-cytotoxic Fluoropyrimidine Carbamate, which functions as an orally administered precursor of the cytotoxic moiety 5-Fluorouracil (5-FU). Capecitabine is activated via several enzymatic steps. The enzyme involved in the final conversion to 5-FU, Thymidine Phosphorylase (ThyPase), is found in tumour tissues, but also in normal tissues albeit usually at lower levels. Capecitabine demonstrated a synergistic effect in combination with Docetaxel, which may be related to the up-regulation of Thymidine Phosphorylase by Docetaxel.
The metabolism of 5-FU in the anabolic pathway blocks the methylation reaction of deoxyuridylic acid to thymidylic acid, thereby interfering with the synthesis of deoxyribonucleic acid (DNA). The incorporation of 5-FU also leads to inhibition of RNA and protein synthesis. Since DNA and RNA are essential for cell division and growth, the effect of 5-FU may be to create a Thymidine deficiency that provokes unbalanced growth and death of a cell. The effects of DNA and RNA deprivation are most marked on those cells which proliferate more rapidly and which metabolism 5-FU at a more rapid rate.
