Studies on Uptake of 6-Cyclohexyl-1-hydroxy-4-methyl-2(1H)-pyridone Ethanolamine Salt (Hoe 296) by Candida albicans

Abstract

Hoe 296, a synthetic antimycotic, was not degraded by the sensitive Candida albicans cells; no metabolic product of the drug was detected in the culture fluid of the organism or in the cellular extract. Growing cells of C. albicans rapidly took up large amounts of ¹⁴C-labeled Hoe 296 from the medium. The rate and extent of drug uptake were dependent on the exogenous concentration of the ¹⁴C-drug. Although Hoe 296 was accumulated intracellularly to levels up to 200 times that present in the medium, 2,4-dinitrophenol had no effect on drug uptake. In cultures exposed to a given concentration of Hoe 296, an increase in inoculum size caused a significant decrease in the extent of growth inhibition as well as the amount of drug taken up which was expressed as molecules drug per cell. Irrespective of the inoculum size and the amount of drug added to the medium, fungistasis was attained when approximately 1.7 × 10⁷ or more molecules of the drug were taken up by each Candida cell. Kinetic studies of ¹⁴C-loss from the cells preloaded with labeled drug revealed that the binding was largely irreversible and unexchangeable between inside and outside of the cell. More than 97% of the total amount of Hoe 296 taken up was bound to some cellular structures and organelles including cell walls, cell membranes, mitochondria and ribosomes (or microsomes), whereas only a minor portion was present in the cytosol fraction.