E. Chu et al., ENHANCEMENT OF 5-FLUORO-2'-DEOXYURIDINE ANTINEOPLASTIC ACTIVITY BY 5-BENZYLOXYBENZYLOXYBENZYLACYCLOURIDINE IN A HUMAN COLON-CARCINOMA CELL-LINE, Cancer research, 52(7), 1992, pp. 1729-1736
The pyrimidine acyclonucleoside benzyloxybenzyloxybenzylacyclouridine
(BBBAU) showed growth inhibitory activity against the human colon canc
er HCT-8 cell line with a 50% inhibitory concentration of 55-mu-M. Unl
ike its parent compounds, BBBAU was an extremely weak inhibitor of uri
dine phosphorylase. This acyclonucleoside analogue is an inhibitor of
thymidylate synthase (TS) as determined by inhibition of [6-H-3]-2'-de
oxyuridine incorporation into DNA, inhibition of H-3 release from [5-H
-3]-2'-deoxyuridine, and decrease in both the free and total TS 5'-flu
oro-2'-deoxyuridine 5'-monophosphate binding sites. Kinetic analysis r
evealed that BBBAUMP, the monophosphate analogue of BBBAU, is a compet
itive inhibitor of purified human recombinant TS with a K(i) of 8.0-mu
-M. Nucleoside transport and uptake studies revealed that BBBAU (30-mu
-M) inhibited the initial rate of transport and the total uptake of th
ymidine (25-mu-M). In contrast, while BBBAU (30-mu-M) inhibited the in
itial rate of transport of 5-fluoro-2'-deoxyuridine (FdUrd, 25-mu-M),
its intracellular accumulation was increased. BBBAU (10 and 50-mu-M, r
espectively) potentiated FdUrd growth inhibition of HCT-8 cells and si
gnificantly enhanced the cytotoxic effects of FdUrd (0.3 and 1-mu-M, r
espectively) against HCT-8 cells using a clonogenic assay system. This
combination resulted in additive inhibitory effects on TS activity re
sulting in greater depletion of dTTP pools. Moreover, the incorporatio
n of radiolabeled FdUrd into the DNA fraction of HCT-8 cells was enhan
ced. The potential importance of this novel combination for human colo
n cancer chemotherapy is discussed.