Selection and characterization of 5-fluoroorotate-resistant Plasmodium falciparum

Antimicrob Agents Chemother. 1994 Dec;38(12):2871-6. doi: 10.1128/AAC.38.12.2871.


Previous studies have shown that 100 nM 5-fluoroorotate (5-FO) is sufficient to block the in vitro proliferation of Plasmodium falciparum without causing toxicity to mammalian cells. In anticipation of potential drug resistance, a study was undertaken to identify P. falciparum cells that would proliferate in the presence of 5-FO. About 3 x 10(6) UV-irradiated as well as nonirradiated parasites were subjected to a one-step selection with 100 nM 5-FO both in the absence and in the presence of preformed pyrimidines (uracil, uridine, thymine, and thymidine). The P. falciparum cells that emerged after 3 weeks were cloned, and the 90% inhibitory concentration of 5-FO for the cloned cells was found to be 100- to 400-fold greater than that for the parent cell line. Two clones that were further characterized retained resistance to 5-FO even after prolonged propagation in culture without drug pressure. Since the mutants were not cross-resistant to 5-fluorouracil or to dihydrofolate reductase inhibitors, it was unlikely that alteration of thymidylate synthase or overproduction of the bifunctional dihydrofolate reductase-thymidylate synthase was responsible for 5-FO resistance. Similarly, resistance was not due to the expression of a pyrimidine salvage pathway since the cells were not pyrimidine auxotrophs, they did not show increased utilization of pyrimidine nucleosides, and they did not show increased susceptibility to 5-fluoropyrimidine nucleosides. When the selection experiments were repeated, without mutagenesis, in the presence of 10(-7) M 5-FO with fewer than 10(6) parasites or in the presence of more than 10(-7) M 5-FO with more than 10(8) parasites, viable mutants could not be recovered from the cultures. The implications of these findings for the in vivo use of 5-FO for malaria chemotherapy are discussed.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Drug Resistance
  • Fluorouracil / pharmacology
  • Orotic Acid / analogs & derivatives*
  • Orotic Acid / pharmacology
  • Plasmodium falciparum / drug effects*
  • Plasmodium falciparum / radiation effects
  • Pyrimidines / metabolism
  • Ultraviolet Rays


  • Pyrimidines
  • Orotic Acid
  • 5-fluoroorotic acid
  • Fluorouracil