Effects of Chloroquine, Quinine, and Cycloguanil upon the Maturation of Asexual Erythrocytic Forms of Two Strains of Plasmodium Falciparum in Vitro *

The studies reported here stemmed from a personal report by Geiman on the capacity of the 4-aminoquinoline amodiaquin to inhibit in vitro maturation of ring stages of the chloroquine-resistant Monterey strain ofPlasmodium falciparum. This observation, confirmed in owl monkeys infected with this strain, led to a comparison of the activities of chloroquine, amodiaquin, amopyroquin, and dichlorquinazine (12,278 RP) against infections with various chloroquine-susceptible and chloroquine-resistant strains. The results showed that: (i) these 4-aminoquinolines were essentially equally active against infections with chloroquine-susceptible strains and (ii) the activities of amodiaquin, amopyroquin, and dichlorquinazine were reduced significantly in the face of chloroquine resistance, but (iii) well-tolerated doses of these compounds would cure infections with strains that fully resisted treatment with maximally tolerated doses of chloroquine. Two other 4-aminoquinolines, SN-8137 and SN-9584, which also exhibited activity against chloroquine-resistant parasites in vitro, displayed curative activity in monkeys infected with a chloroquine-resistant strain. These observations show that there is cross-resistance among the 4-aminoquinolines, confirming earlier findings, but indicate that the dimensions of this phenomenon are sufficiently limited so that some derivatives are therapeutically effective against infections refractory to maximally tolerated doses of chloroquine.

Section: Discussionmentioning

confidence: 99%

Activities of Various 4-Aminoquinolines Against Infections with Chloroquine-Resistant Strains of Plasmodium falciparum

Schmidt

Vaughan

Mueller

et al. 1977

“…Simple in vitro susceptibility tests for P. falciparum have been available since 1968 (9). However, the development of similar in vitro susceptibility tests for P. vivax has been problematic because of the poor in vitro growth of P. vivax.…”

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confidence: 99%

Simple In Vitro Assay for Determining the Sensitivity of Plasmodium vivax Isolates from Fresh Human Blood to Antimalarials in Areas where P. vivax Is Endemic

Russell

Udomsangpetch

Rieckmann³

et al. 2003

Self Cite

The aim of this study was to develop a simple, field-practical, and effective in vitro method for determining the sensitivity of fresh erythrocytic Plasmodium vivax isolates to a range of antimalarials. The method used is a modification of the standard World Health Organization (WHO) microtest for determination of P. falciparum drug sensitivity. The WHO method was modified by removing leukocytes and using a growth medium supplemented with AB ؉ serum. We successfully carried out 34 in vitro drug assays on 39 P. vivax isolates collected from the Mae Sod malaria clinic, Tak Province, Thailand. The mean percentage of parasites maturing to schizonts (six or more merozoites) in control wells was 66.5% ؎ 5.9% (standard deviation). This level of growth in the control wells enabled rapid microscopic determination (5 min per isolate per drug) of the MICs of chloroquine, dihydroartemisinin, WR238605 (tafenoquine), and sulfadoxine. P. vivax was relatively sensitive to chloroquine (MIC ‫؍‬ 160 ng/ml, 50% inhibitory concentration [IC 50 ] ‫؍‬ 49.8 ng/ml) and dihydroartemisinin (MIC ‫؍‬ 0.5 ng/ml, IC 50 ‫؍‬ 0.47 ng/ml). The poor response of P. vivax to both tafenoquine (MIC ‫؍‬ 14,000 ng/ml, IC 50 ‫؍‬ 9,739 ng/ml) and sulfadoxine (MIC ‫؍‬ 500,000 ng/ml, IC 50 ‫؍‬ 249,000 ng/ml) was due to the slow action of these drugs and the innate resistance of P. vivax to sulfadoxine. The in vitro assay developed in our study should be useful both for assessing the antimalarial sensitivity of P. vivax populations and for screening new antimalarials in the absence of long-term P. vivax cultures.

“…One challenge facing the in vitro field is that culture-based assessment of parasite susceptibility has undergone a natural evolution since techniques for studying chloroquine (CQ) resistance were established more than 4 decades ago (3). The basic measurement of drug susceptibility is the growth of parasites in the presence of a range of concentrations of a given drug, expressed as the concentration of the drug needed to suppress growth to 50% of that observed in the absence of the drug (50% inhibitory concentration [IC 50 ]).…”

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confidence: 99%

High-Throughput Analysis of Antimalarial Susceptibility Data by the WorldWide Antimalarial Resistance Network (WWARN) In Vitro Analysis and Reporting Tool

Woodrow

Dahlström

Cooksey

et al. 2013

v Assessment of in vitro susceptibility is a fundamental component of antimalarial surveillance studies, but wide variations in the measurement of parasite growth and the calculation of inhibitory constants make comparisons of data from different laboratories difficult. Here we describe a Web-based, high-throughput in vitro analysis and reporting tool (IVART) generating inhibitory constants for large data sets. Fourteen primary data sets examining laboratory-determined susceptibility to artemisinin derivatives and artemisinin combination therapy partner drugs were collated from 11 laboratories. Drug concentrations associated with half-maximal inhibition of growth (IC 50 s) were determined by a modified sigmoid E max model-fitting algorithm, allowing standardized analysis of 7,350 concentration-inhibition assays involving 1,592 isolates. Examination of concentration-inhibition data revealed evidence of apparent paradoxical growth at high concentrations of nonartemisinin drugs, supporting amendment of the method for calculating the maximal drug effect in each assay. Criteria for defining more-reliable IC 50 s based on estimated confidence intervals and growth ratios improved correlation coefficients for the drug pairs mefloquine-quinine and chloroquine-desethylamodiaquine in 9 of 11 and 8 of 8 data sets, respectively. Further analysis showed that maximal drug inhibition was higher for artemisinins than for other drugs, particularly in ELISA (enzyme-linked immunosorbent assay)-based assays, a finding consistent with the earlier onset of action of these drugs in the parasite life cycle. This is the first high-throughput analytical approach to apply consistent constraints and reliability criteria to large, diverse antimalarial susceptibility data sets. The data also illustrate the distinct biological properties of artemisinins and underline the need to apply more sensitive approaches to assessing in vitro susceptibility to these drugs.