Oxygen- and time-dependent effects of antibiotics and selected mitochondrial inhibitors on Plasmodium falciparum in culture.

Several antibiotics which inhibit protein synthesis on 70S ribosomes, including clindamycin, pirlimycin, 4'-pentyl-N-demethyl clindamycin, four tetracyclines, chloramphenicol, thiamphenicol, and erythromycin, had antimalarial effects against Plasmodium falciparum in culture which were greatly influenced by the duration of drug exposure and by oxygen tension. In 96-h incubations, potency was increased by a factor of up to 10(6) over the first 48-h period and by a factor of up to 10(4) in 15% O2 versus 1% O2. Two aminoglycosides, kanamycin and tobramycin, had no antimalarial activity. Rifampin and nalidixic acid, which inhibit nucleic acid synthesis, were not similar to the 70S inhibitors. The mitochondrial inhibitors Janus Green, rhodamine 123, antimycin A1, and 8-methylamino-8-desmethyl riboflavin had activities which were influenced by the duration of exposure and oxygen tension. Quinoline-containing antimalarial agents, ionophores, and other antimalarial drugs were influenced to a minor extent by the duration of exposure but were not affected by oxygen tension. These data can best be explained by the hypothesis that antimalarial 70S ribosome-specific protein synthesis inhibitors are toxic to the parasites by acting on the mitochondrion.