The antitumor and radiosensitizing properties of
5-bromo-2'-deoxyuridine (
BUdR) appear to be due, in part, to its incorporation into cellular
DNA. To optimize conditions for incorporation of 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdUMP) into
DNA, we investigated the metabolism of
BUdR to its
DNA precursor form, the 5'-triphosphate
BrdUTP, in the U251 human
glioblastoma cell line. The results demonstrated that
BrdUTP accumulated rapidly in this cell line, achieving steady-state values within 2 hr of
drug addition. The level of
BrdUTP accumulation was proportional to the amount of exogenous
BUdR up to a concentration of 100 microM, without apparent saturation. Exposure of
glioblastoma cells to
BUdR was associated with substantial selective decreases in both the cellular
dCTP and
TTP pools, the extent of which was dependent on the exogenous
BUdR concentration. In the absence of exogenous
BUdR,
BrdUTP was eliminated rapidly from cells with an initial half-life of approximately 15 min. As the cellular
BrdUTP level declined, the
dCTP and
TTP levels increased to control values. Incorporation of BrdUMP into
DNA appeared linear with time as long as the cellular
BrdUTP level remained constant. This incorporation was not enhanced by the addition of
5-fluoro-2'-deoxyuridine (
FUdR), a potent inhibitor of
thymidylate synthetase, which at a concentration of 10 nM had no effect on
TTP pools in this cell line. Thus, the decrease in cellular
TTP pools mediated by
BrdUTP allows the halogenated
pyrimidine to enhance its own incorporation into
DNA.