Inhibition of pyrimidine biosynthesis de novo in Plasmodium falciparum by 2-(4-t-butylcyclohexyl)-3-hydroxy-1,4-naphthoquinone in vitro.

The effects of the hydroxynaphthoquinone BW58C on some metabolite levels and the flux of H14CO3 through the de novo pyrimidine biosynthetic pathway of intact Plasmodium falciparum have been studied in vitro using HPLC techniques. 800 nM BW58C appeared to have no significant effect on the energy status of isolated P. falciparum, but at 0.1 nM it caused a dramatic decrease in the concentrations of pyrimidine nucleotides, specifically UTP, during 256 min of incubation. Although about one hour was required to achieve a significant decrease in pyrimidine nucleotide concentrations, a much more rapid inhibition of the flux of H14CO3 through the de novo pathway was found upon addition of 0.1 nM BW58C. This inhibition caused about a 10 fold increase in the radioactivity of carbamoyl-aspartate over a 64 min period, and an overall increase in the concentration of this metabolite of about 3 fold during 256 min of incubation. These effects of BW58C against P. falciparum in vitro are discussed in terms of inhibition of de novo pyrimidine biosynthesis at the site of dihydroorotate dehydrogenase.