5­Fluorouracil and capecitabine therapies for the treatment of colorectal cancer (Review).

Although 5­fluorouracil (5­FU)­based chemotherapy is the major treatment for colorectal cancer, it has disadvantages such as systemic toxicity, lack of effectiveness and selectivity, and development of resistance. Capecitabine, a prodrug form of 5­FU, was designed to overcome these drawbacks, to fulfill the need for more convenient therapy, and to improve safety, tolerability and intratumor drug concentration levels through a tumor­specific conversion to the active 5­FU drug. The purpose of the present review is to provide a comprehensive comparison between 5­FU therapy and capecitabine. In the current review, anticancer drug classification was discussed and the development of capecitabine from the original fluorinated analogue (5­FU) to overcome its drawbacks was explained. Specifically, 5­FU is compared with capecitabine therapy regarding various properties, including drug metabolism, cellular mechanism, effect on the apoptosis pathway and cell cycle phases, safety and tolerability. Moreover, three metabolizing enzymes required for the activation of capecitabine to 5­FU were discussed. Capecitabine, as monotherapy or in combination with other chemotherapies, exhibited improved drug efficacy and survival. However, the changes that mediate the chemoresistance of capecitabine treatment were classified as intracellular, extracellular or cell surface factors, or cell­phenotype state. Future studies should examine the efficacy of capecitabine combined with novel and safe drugs other than chemotherapeutic agents that play a role in the inhibition of tumor initiation, progression and metastasis.