Fungistatic Activity, Uptake and Incorporation of 5-FIuorocytosine in <i>Candida albicans, </i>as influenced by Pyrimidines and Purines

Abstract

Uptake of the radiolabelled antimycotic 5-fluorocytosine (5-FC) by Candida albicans and distribution of radioactivity in the cell fractions, expandable pool, internal pool, and RNA, as influenced by the three strong antagonists against the fungistatic activity of the drug, adenine, uridine and cytosine were studied. In the stationary growth phase of the yeast, a reciprocal correlation was found between the concentrations of the antagonists and the presence of radioactive compound(s) in the cells, particularly in RNA. The correlation was similar with radio-labelled cytosine which was studied comparatively, but, considering the proportions, the normal pyrimidine was preferred to its fluorinated analogue. In the logarithmic phase of yeast growth, two phases of transport were distinguished: a first phase of 5-FC uptake, when there was a transient accumulation of radioactivity in the internal pool, and a second one of incorporation into RNA. The addition of cytosine resulted in a marked impairment of 5-FC uptake in the expandable pool, preventing any significant passage to the internal pool and RNA, whereas with uridine only the incorporation into RNA was inhibited. With adenine, the picture was similar to that observed with cytosine, suggesting a hitherto unknown interference of purines with pyrimidine uptake in yeasts. Confirming the findings of Giégé and Weil [4] in Saccharomyces cerevisiae, it was proved that in C. albicans, cultured in the presence of 5-FC, 5-fluorouracil becomes incorporated in place of uracil in both rRNA and tRNA, without any 5-FC being detectable.

Studies on the Mode of Action of 5-Fluorocytosine in <i>Aspergillus</i> Species

“…First, the presence of 5-FC meta bolites in the TCA-insoluble fraction (RNA fraction) of the cells would support the mode of action of the drug as proposed by previous investigations in yeasts [19]. Whether or not the small differences in the amount of radiolabeled material incorporat ed into RNA are sufficient to produce such a large disparity in MIC values is unclear.…”

“…The amount of radioactivity ap pearing in the TCA-insoluble fraction of these cells is highest in the more susceptible cells. We accounted for a maximum of only 16% of the total label taken up in the TCA fraction, however, while as much as 50% of the radiolabeled material taken up by yeast cells has been found in the TCA-insoluble fraction [19].…”

Anticandidal activity of 5-fluorocytosine-peptide conjugates

“…Boc groups were removed with 1 N HCI in acetic acid, producing hydrochlorides that were reacted with succinic anhydride and triethylamine in chloroform to form /3-carboxypropionyl-substituted peptide benzyl esters. IV4-Ac-(15), N4-(Cbz-Gly)- (16), and N4-(Boc-Ala-Gly)-5-FC (17) were prepared by reacting the appropriate p-nitrophenyl esters with 5-FC in dimethylformamide using 1-hydroxybenzotriazole as a catalyst. Details of this procedure will be published elsewhere.…”