Alan A. Divo

An In vitro Assay System for the Identification of Potential Antimalarial Drugs

Current models for antimalarial drug screening generally measure the survival of drug-treated rodents infected with Plasmodium berghei. Modifications of existing continuous culture methods for P. falciparum allow the rapid, accurate and economical determination of drug effects directly against the human pathogen. Parasite cultures can be maintained in RPMI 1640 medium supplemented with human or rabbit serum or with hypoxanthine-supplemented bovine serum. The antiparasite effects of four drugs, chloroquine, chloramphenicol, clindamycin, and halofuginone, are identical in these sera; drugs can be screened routinely against P. falciparum grown in bovine serum supplemented with hypoxanthine. Drug effects may be rapidly and accurately determined by monitoring the incorporation of 3H-hypoxanthine into parasite nucleic acids. Results obtained with this technique are highly correlated with those derived from visual counting of parasites in thin blood films. Compounds with antimalarial activity in culture may be further screened by measuring the effects of serum obtained from drug-treated rabbits on parasites in culture. The advantages of this system over models currently used for antimalarial screening are discussed.

Activity of quinoline-containing antimalarials against chloroquine-sensitive and -resistant strains of Plasmodium falciparum in vitro

9 quinoline-containing antimalarials and the phenanthrene methanol halofantrine were tested in vitro against 6 strains of Plasmodium falciparum with known sensitivity to chloroquine. Sensitivity to chloroquine was not uniformly associated with sensitivity to mepacrine (quinacrine), halofantrine, SN-12108 or SN-6911 (3-methylchloroquine, sontochin). Amodiaquine was slightly less potent with chloroquine-resistant strains, whereas SN-12309 closely resembled chloroquine in the pattern of sensitivity. (Bis)desethylchloroquine was nearly as potent as chloroquine against chloroquine-sensitive strains but was about 10-fold less potent than the parent drug against chloroquine-resistant strains. 2 8-aminoquinolines, primaquine and pamaquine, were more potent against chloroquine-resistant than chloroquine-sensitive strains. The mutation(s) responsible for chloroquine resistance in P. falciparum greatly reduce(s) the sensitivity to a major metabolite of the drug but also generate(s) parasites which are more susceptible to a different class of drugs, the 8-aminoquinolines.

Evaluation of rhodamine 123 as a probe for monitoring mitochondrial function in Trypanosoma brucei spp.

ABSTRACT. Rhodamine 123, a membrane potential‐specific dye, has been evaluated as a probe to monitor the function of the mitochondrion in long slender bloodstream and procyclic trypomastigotes of several Trypanosoma brucei spp. By epifluorescence microscopy, mitochondrial development has been followed in long slender bloodstream and procyclic organisms stained with rhodamine 123. to photograph stained long slender bloodstream forms, it was necessary to develop a method to completely immobilize viable organisms. In both parasite forms, as the cell cycle progressed, the mitochondrion developed from a thread‐like structure to a highly branched organelle. A dramatic reorganization occurred preceding cytokinesis to produce two progeny thread‐like structures which were partitioned into newly formed daughter cells. the organelle within the long slender trypomastigote was found to stain optimally at 0.3 μ/ml of rhodamine 123, while the procyclic form required 3.0 μ/ml. the results suggest that the plasma membrane potential is higher in the long slender parasite than in the procyclic form. the effects of inhibitors that disrupt mitochondrial function were examined in long slender and procyclic parasites, and some of these agents were shown to affect rhodamine 123 accumulation and retention. In long slender trypomastigotes the trypanosome alternative oxidase does not appear to be coupled to proton pumping, whereas in procyclic organisms the effects of inhibitors indicate that this oxidase may be coupled to a pathway that is branched preceding an antimycin A1‐sensitive site.

ISOLATION AND CULTIVATION OF PLASMODIUM FALCIPARUM USING ADULT BOVINE SERUM

RPMI 1640 medium supplemented with adult bovine serum and hypoxanthine was superior to human serum-supplemented medium for the isolation of new strains of Plasmodium falciparum in Sudan. Similar observations in Indonesia have since confirmed our results. The chloroquine sensitivity of new isolates was identical in either human or bovine serum. Once acclimated to culture conditions P. falciparum strains grew better when using human serum. Erythrocyte-specific antibody present in adult bovine serum slightly inhibited merozoite invasion of uninfected cells. Removal of this cross-reactive antibody from bovine serum increased parasite multiplication to the level obtained in human serum.