Interaction between 5-fluorouracil and DNA of human colon adenocarcinoma.

The effect of 5-fluorouracil on the stability of DNA and the synthesis of DNA replication intermediates was analyzed in human colon adenocarcinoma cells. Density gradient analysis showed that some of the drug is incorporated into DNA. Moreover, DNA fragments are released when cells with drug-containing DNA are lysed in dilute alkali. The DNA fragments can be separated from the bulk DNA by agarose gel electrophoresis. The fragmentation of the DNA can be prevented by pretreatment with aphidicolin which inhibits DNA polymerase alpha. In 5-fluorouracil-treated cells, a heterogeneous population of DNA replication intermediates is formed, instead of discrete DNA replication intermediates which are formed in untreated cells. Aphidicolin prevents the formation of the heterogeneous population of DNA fragments. However, replication intermediates formed before the blockade with aphidicolin are ligated to high-molecular-weight DNA. In cells released from aphidicolin inhibition, there is preferential labeling of the heterogeneous population of DNA fragments. This population, therefore, shows the same characteristics as the discrete DNA populations formed in untreated cells.