5-Fluorouracil incorporation in DNA of human breast carcinoma cells.

We have demonstrated previously the presence of 5-fluorouracil (FUra) residues in L1210 DNA. These findings have been extended to the MCF-7 human breast carcinoma cell line. Cesium sulfate gradient centrifugation has been used to separate the MCF-7 RNA and DNA fractions. Alkali and RNase digests have also been used to remove any possible RNA contaminating the DNA fraction. The purified DNA has been analyzed by high-pressure liquid chromatography following digestion to nucleotides and nucleosides. The results demonstrate that FUra residues are detectable in the DNA of these human breast carcinoma cells following exposure to either FUra of 5-fluorodeoxyuridine. Further, the extend of FUra incorporation in both MCF-7 RNA and DNA is similar with either fluorinated pyrimidine. We also demonstrate that the FUra incorporation in DNA from this human cell line can be enhanced by concurrent incubation with thymidine.