2',2'-DIFLUORO-DEOXYCYTIDINE (GEMCITABINE) INCORPORATION INTO RNA ANDDNA OF TUMOR-CELL LINES

Gemcitabine (dFdC) is a new cytidine analogue which is active mainly b y the incorporation of its triphosphate (dFdCTP) into DNA, leading to cell death. We determined incorporation of dFdC into nucleic acids of two solid tumour cell lines: the murine colon carcinoma cell line Colo n 26-10, the human ovarian carcinoma cell line A2780, and the human le ukemic cell line CCRF-CEM. dFdC was not only incorporated into DNA, bu t also into RNA. The extent of incorporation into DNA was highest in A 2780 cells and lowest in CCRF-CEM cells (2-4-fold difference). The sam e pattern was observed for incorporation into RNA, but with a 10-20-fo ld difference. In A2780, incorporation into DNA was about twice that o f the incorporation into RNA, in CEM cells 10-20-fold that of RNA. Inc orporation into RNA was verified using two methods for separation of R NA and DNA, acid precipitation and CsCl-gradient centrifugation. Incor poration into DNA was time and concentration dependent, but incorporat ion into RNA seemed to be only concentration dependent. We also determ ined the effect of dFdC on DNA and RNA synthesis by measurement of thy midine and uridine incorporation, respectively, using similar conditio ns as for the incorporation studies. In all three cell lines DNA synth esis was inhibited almost completely, even at 0. 1 muM dFdC and at 4-h r exposure. RNA synthesis inhibition did not exceed 50% in both solid tumour cell lines, even at 1 muM dFdC exposure for 24 hr. A clear conc entration effect was only observed in the CCRF-CEM cell line and only after 24 hr exposure. At a 1 muM dFdC exposure for 24 hr, RNA synthesi s was completely inhibited in these cells. Incorporation of dFdC into RNA and inhibition of RNA synthesis represent an unrecognized but poss ibly important mechanism of action of this drug.