Mechanisms of collateral sensitivity to fluorouracil of a cis-diamminedichloroplatinum(II)-resistant human non-small lung cancer cell line.

Y Sugimoto,Y Fujiwara,N Saijo,K Nishio,T Ohmori,Y Ohe,T Morikage

doi:10.1038/bjc.1992.181

Abstract

A cisplatin(CDDP)-resistant subline of a human lung cancer cell line, PC-7/CDDP, was 4.7-fold more resistant to CDDP than the parent line in a colony-forming assay. The sensitivity of this cell line to anthracyclines, vinca-alkaloid, etoposide, mitomycin C, and bleomycin was similar to that of the parental line, PC-7. However, PC-7/CDDP exhibited 4-fold higher sensitivity to fluorouracil (FUra). Possible mechanisms associated with the collateral sensitivity to FUra were studied in PC-7/CDDP cells. The sensitivity of both cell lines to FUra did not correlate with the effect of FUra on RNA. On the other hand, FUra induced a greater reduction in dTTP pools and more single strand breaks in PC-7/CDDP than in PC-7 cells. These results suggest that the pathway for de novo deoxyribonucleotide synthesis may be a target for FUra in PC-7/CDDP cells. However, inhibition of thymidylate synthase after FUra treatment did not correlate with the DNA-directed activity of FUra. Based on the above findings, the decreased salvage synthesis of dTTP was considered a possible mechanism of the greater reduction of dTTP pools in PC-7/CDDP cells. However, the activity of dThd kinase was the same in both cell lines. In the presence of physiological concentrations of exogenous dThd in the serum, uptake of dThd was less in PC-7/CDDP cells than that in PC-7 cells. Our data suggest that FUra-induced cytotoxicity in PC-7/CDDP cells is associated with the inhibition of dTTP synthesis and that the decreased uptake of dThd is a possible mechanism of the collateral sensitivity to FUra in PC-7/CDDP cells.

Highlights

MethodsRPMI 1640 medium and PBS were purchased from Nissui Pharmaceutical Co., Tokyo, Japan
Possible mechanisms associated with the collateral sensitivity to FUra were studied in PC-7/CDDP cells
These results suggest that the pathway for de novo deoxyribonucleotide synthesis may be a target for FUra in PC-7/CDDP cells

Summary

Methods

RPMI 1640 medium and PBS were purchased from Nissui Pharmaceutical Co., Tokyo, Japan. Other agents were obtained from the following sources: CDDP from Bristol Myers Squibb Co., Tokyo, Japan; FUra from Kyowa Hakko Kogyo Co., Ltd, Tokyo; FUrd from Mitsui Pharmaceutical Inc., Tokyo; [6-3H]-FUra (specific activity, 19.3 Ci mmol 1) and [methyl-'4C]-dThd (specific activity, 60 mCi mmol '). Prior to use for experiments, the cell lines were propagated by culturing them in RPMI 1640 medium supplemented with 10% heat-inactivated FBS (Immuno-Biochemical Laboratories, Fujioka, Japan), penicillin (100unitsml-') and streptomycin (100 gmlm'). Genous 3H-dThd (50 nM) into DNA than PC-7 cells (Ohe et al, 1990). Based on these data, we speculated that salvage synthesis of dTMP might be different in these cells, which could explain the greater reduction in dTTP levels in the PC-7/CDDP cells We speculated that salvage synthesis of dTMP might be different in these cells, which could explain the greater reduction in dTTP levels in the PC-7/CDDP cells.

Results

Discussion

Conclusion