Although
docetaxel (
Taxotere; TXT), a taxoid anticancer drug, is clinically and experimentally very effective against
breast cancer, its antitumor effect is of very short duration. We addressed whether
5-fluorouracil (5-FU) and its derivatives can act synergistically with TXT against mammary
tumors, with placing particular stress on their use by oral route. Mouse mammary tumor cell line, MM2, was propagated in culture and as
ascites in mice.
Carmofur (
HCFU) and
doxifluridine (5'-DFUR) were used as
5-FU derivatives. In vitro, the cytotoxic effects of
antitumor drugs on MM2 cells were examined by MTS assay. In vivo, mice inoculated i.p. with MM2 cells were treated with i.p. injection of TXT and/or
oral administration of
5-FU or its derivatives, and observed for curing
tumor. In vitro, the synergistic effects were observed in the combination of TXT and
5-FU or
HCFU, but not in that of TXT and
5'-DFUR. In vivo, all of these combinations cured
tumors far more effectively than TXT alone. The discrepant result of the combination of TXT and
5'-DFUR between in vitro and in vivo was ascribed to up-regulation of
pyrimidine phosphorylase in
tumor cells in vivo by TXT. Thus,
5-FU, its masked compounds like
HCFU and its
prodrugs like
5'-DFUR can act synergistically with TXT in the therapy of
cancer even when administered by the oral route.