Cl. Vanderwilt et al., BIOCHEMICAL-MECHANISMS OF INTERFERON MODULATION OF 5-FLUOROURACIL ACTIVITY IN COLON-CANCER CELLS, European journal of cancer, 33(3), 1997, pp. 471-478
The antiproliferative effect of 5-fluorouracil (5-FU) in colon cancer
can be enhanced by interferons (IFN-alpha and IFN-gamma). The mechanis
ms by which IFNs modulate 5-FU activity are not completely elucidated.
IFN-alpha may elevate the levels of the active 5-FU metabolite 5-fluo
ro-2'-deoxyuridine-5'-monophosphate (FdUMP) in the cell, possibly lead
ing to increased inhibition of the target enzyme thymidylate synthase
(TS), which might enhance DNA damage. It has been shown that IFN-gamma
can prevent 5-FU induced overexpression of TS. We studied IFN modulat
ion in three colon cancer cell lines (SW948, WiDr, human; C26-10, muri
ne) and the sublines WiDr/F and C26-10/F, which were adapted to low fo
late levels. A 1.5-fold increase in 5-FU sensitivity was observed in C
26-10 and C26-10/F (by murine IFN-alpha,beta); in SW948, WiDr and WiDr
/F (by human IFN-gamma) and in SW948 and WiDr/F (by human IFN-alpha).
In none of the cell lines did human IFN-alpha, IFN-gamma or murine IFN
-alpha,beta increase FdUMP levels after exposure to 5-FU. TS activity,
indirectly measured by incorporation of [6-H-3]-deoxyuridine into DNA
, was inhibited by 5-FU, but the IFNs did not enhance inhibition. DNA
damage was measured as a drug-induced decrease of double-stranded (dss
) DNA compared to control cells. After 5-FU exposure, dss DNA decrease
d to 60-75% in WiDr, WiDr/F and SW948 cells. Human IFN-alpha alone cau
sed minimal DNA damage (95% dss DNA), but increased 5-FU-induced effec
ts to 35-50% dss DNA. IFN-gamma did not cause DNA damage and did not e
nhance 5-FU-mediated DNA damage. Expression of TS protein, analysed by
ELISA, was increased after 5-FU exposure of SW948 cells, but this inc
rease was not affected by addition of either IFN-alpha or IFN-gamma. I
t is concluded that one of the mechanisms involved in modulation of 5-
FU activity is the effect of IFN-alpha on 5-FU-mediated DNA damage, bu
t for IFN-gamma no mechanism of action was found. (C) 1997 Elsevier Sc
ience Ltd.