A Comparison of the in Vitro Activities of Amodiaquine and Desethylamodiaquine against Isolates of Plasmodium falciparum

Intermittent exposure to halofantrine (HF) of both chloroquine-susceptible (T9.96) and chloroquine-resistant (K1) isolates of Plasmodium falciparum in vitro resulted in a rapid reduction in susceptibility to HF. After 6 months, the 50%o inhibitory concentration (IC..) (14,19,22,23) or the exposure of cultures to mutagenic agents followed by drug pressure to select for resistant mutants (1,16,17). However, the relevance of resistance mechanisms developed as a result of mutagenesis to resistance mechanisms developed in the field (presumably as a result of drug pressure) is very unclear. In general, it has proven difficult to induce resistance to the aminoquinolines and related schizontocides in vitro. Brockelman et al. (4) produced a mefloquine-tolerant line of P. falciparum by exposing cultures to the drug for 48-h periods separated by several cycles of culturing in non-drug-treated medium, but the stability of resistance was not assessed in that study. * Corresponding author.In the present study, we compared the ability of two different methods used to select resistance to the 9-phenanthrenemethanol halofantrine (HF) {1,3-dichloro-a-[2-(dibutylamino)ethyl] -6 -(trifluoromethyl) -9 -phenanthrenemethanol} in chloroquine-susceptible and chloroquine-resistant isolates of P. falciparum (i.e., intermittent versus continuous drug pressure). The cross-resistance patterns of the resulting resistant isolates were also evaluated. MATERIALS AND METHODSParasites and cultures. Chloroquine-resistant isolate K, (29)

Section: Resultsmentioning

confidence: 99%

Development of halofantrine resistance and determination of cross-resistance patterns in Plasmodium falciparum

Nateghpour

Ward

Howells

1993

“…Earlier in vitro studies indicated that DAQ and AQ have equal activity against P. falciparum (8). Other observations suggest that the two compounds possess independent modes of action (7,27). However, recent comparative in vitro studies with fresh isolates of P. falciparum showed a significant correlation between the activities of the two compounds that indicates similarities in the way they act against the parasite (12).…”

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confidence: 99%

“…Several in vitro studies have shown a positive activity correlation between AQ and chloroquine. Cross-resistance between DAQ and chloroquine has also been observed in vitro in P. falciparum isolates from various regions of Africa (1a, 26), Southeast Asia (7,31), and South America (28). However, in the presence of low-grade resistance to chloroquine, the activity correlation with AQ may be considered a phenomenon that might anticipate overt cross-resistance in the future but is not necessarily a sign of manifest clinical-parasitological AQ resistance (11).…”

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confidence: 99%

Synergism between Amodiaquine and Its Major Metabolite, Desethylamodiaquine, against Plasmodium falciparum In Vitro

Mariga

Gil

Sisowath

et al. 2004

The in vitro activity of the prodrug amodiaquine and its metabolite monodesethyl-amodiaquine has been studied for three strains of Plasmodium falciparum: LS-2, LS-3, and LS-1. Both compounds showed significant activity against all three strains; the activity of amodiaquine was slightly higher than that of the metabolite. By use of a checkerboard design, interaction studies with both compounds yielded evidence of significant synergism; means of the sums of the fractional inhibitory concentrations were 0.0392 to 0.0746 for strain LS-2, 0.1567 to 0.3102 for strain LS-3, and 0.025 to 0.3369 for strain LS-1. In further investigations, the interaction of amodiaquine with monodesethyl-amodiaquine was tested at clinically relevant concentrations of both compounds. In these studies, involving amodiaquine at picomolar and femtomolar concentrations, the compound was found to exert high potentiating activity on monodesethyl-amodiaquine. This interaction produced mean ratios of observed to expected activity of 0.0505 to 0.0642 for strain LS-2, 0.0882 to 0.3820 for strain LS-3, and 0.0752 to 0.2924 for strain LS-1. The synergistic activity was most marked at monodesethyl-amodiaquine/ amodiaquine ratios up to 100,000:1 but was still evident at higher ratios.The widespread increase of resistance to chloroquine in Plasmodium falciparum has resulted in renewed interest in amodiaquine (AQ) as a replacement for chloroquine in the treatment of malaria, especially in sub-Saharan Africa. Although AQ belongs to the same chemical class of compounds as chloroquine, the 4-aminoquinolines, this drug often shows adequate clinical-parasitological efficacy in chloroquine-resistant infections. Furthermore, adverse reactions reported previously, such as agranulocytosis (14) and hepatitis (20), were mainly associated with the prophylactic use of AQ, and more recent reports show that therapeutic regimens are well tolerated (22). Therefore, the World Health Organization has again listed AQ as a drug for treatment of chloroquine-resistant falciparum malaria (40).During and after absorption, orally administered AQ is rapidly metabolized to desethylamodiaquine (DAQ) and other derivatives of lesser antimalarial significance (9). Clinically, the antimalarial activity of AQ is exerted mainly through DAQ (37). Earlier in vitro studies indicated that DAQ and AQ have equal activity against P. falciparum (8). Other observations suggest that the two compounds possess independent modes of action (7,27). However, recent comparative in vitro studies with fresh isolates of P. falciparum showed a significant correlation between the activities of the two compounds that indicates similarities in the way they act against the parasite (12).Chloroquine-resistant falciparum malaria on the African continent was first detected in Kenya and Tanzania. During the past 2 decades it has extended to practically all parts of tropical Africa (32,39). AQ has been shown to maintain high efficacy in the areas of malaria endemicity in the continent where chloroquine resistance is st...

“…AQ and its slowly eliminated active metabolite desethylamodiaquine (DEAQ) are 4-aminoquinolines structurally related to chloroquine (CQ). AQ has been used previously in monotherapy for uncomplicated P. falciparum malaria in parts of Africa, where it has remained relatively efficacious despite the similarities and putative cross-resistance with CQ (3,4).…”

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confidence: 99%

Assessing the Cost-Benefit Effect of a Plasmodium falciparum Drug Resistance Mutation on Parasite Growth In Vitro

Fröberg

Ferreira

Mårtensson

et al. 2013

f Plasmodium falciparum mutations associated with antimalarial resistance may be beneficial for parasites under drug pressure, although they may also cause a fitness cost. We herein present an in vitro model showing how this combined effect on parasite growth varies with the drug concentration and suggest a calculated drug-specific cost-benefit index, indicating the possible advantage for mutated parasites. We specifically studied the D-to-Y change at position 1246 encoded by the pfmdr1 gene (pfmdr1 D1246Y) in relation to amodiaquine resistance. Susceptibilities to amodiaquine, desethylamodiaquine, and chloroquine, as well as relative fitness, were determined for two modified isogenic P. falciparum clones differing only in the pfmdr1 1246 position. Data were used to create a new comparative graph of relative growth in relation to the drug concentration and to calculate the ratio between the benefit of resistance and the fitness cost. Results were related to an in vivo allele selection analysis after amodiaquine or artesunate-amodiaquine treatment. pfmdr1 1246Y was associated with decreased susceptibility to amodiaquine and desethylamodiaquine but at a growth fitness cost of 11%. Mutated parasites grew less in low drug concentrations due to a predominating fitness cost, but beyond a breakpoint concentration they grew more due to a predominating benefit of increased resistance. The cost-benefit indexes indicated that pfmdr1 1246Y was most advantageous for amodiaquine-exposed parasites. In vivo, a first drug selection of mutant parasites followed by a fitness selection of wild-type parasites supported the in vitro data. This cost-benefit model may predict the risk for selection of drug resistance mutations in different malaria transmission settings.