5-FLUOROURACIL INCORPORATION INTO DNA OF CF-1 MOUSE BONE-MARROW CELLS AS A POSSIBLE MECHANISM OF TOXICITY

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  • 1 January 1984
    • journal article
    • research article
    • Vol. 44  (4) , 1358-1363
Abstract
Isolated CF-1 mouse bone marrow cells were exposed for 1 h to 5-fluorouracil (FUra) [an antitumor agent with bone marrow toxicity] at concentrations from 1.8-50 .mu.M and then washed and suspended in a soft agar growth medium to assess the effect on toxicity (measured as reduction in colony growth compared to control). Specific toxic concentrations ranging from 25-90% lethal doses were determined. Subsequent studies examined in parallel the effect of these toxic concentrations of FUra on the possible sites of toxicity including: inhibtion of thymidylate synthetase activity using a modified 3H release assay; incorporation of FUra into RNA (FUra-RNA); and incorporatin of FUra into DNA (FUra-DNA). Thymidylate synthetase activity was slightly decreased (75% of control) after 1-h exposure to a 50% lethal dose and was not significantly further reduced as the FUra concentration was increased to an 85% lethal dose. Furthermore, subsequent exposure of FUra-treated cells to a nontoxic thymidine dose (5 .mu.M) failed to reverse toxicity. FUra-RNA increased during 1-h exposure to increasing concentrations of FUra (25-90% lethal doses). Although initially suggesting a relationship between the level of FUra-RNA and toxicity, subsequent studies in cells exposed to FUra in the presence of uridine demonstrated a significantly decreased toxicity while, at the same time, a minimal decrease of FUra in RNA. In contrast, FUra-DNA was significantly decreased in the presence of uridine and correlated with decreased toxicity. In additional subsequent studies, an apparent decrease in subsequent DNA synthesis was observed (measured by 32P or [3H]thymidine incorporation into DNA) as the level of FUra-DNA increased. FUra is incorporated into DNA of isolated CF-1 mouse bone marrow cells, and the level of FUra-DNA appears to be closely associated with toxicity and inhibition of further DNA synthesis. The parallel studies of thymidylate synthetase activity and FUra-RNA suggest that FUra-DNA may be an unrecognized mechanism of FUra toxicity in these cells.