Effects of Piperaquine, Chloroquine, and Amodiaquine on Drug Uptake and of These in Combination with Dihydroartemisinin against Drug-Sensitive and -Resistant Plasmodium falciparum Strains

Abstract

Piperaquine is being developed as a long-acting component in artemisinin combination therapies. It was highly active in vitro and drug interaction studies showed that dihydroartemisinin combinations with piperaquine, chloroquine, and amodiaquine were indifferent tending toward antagonism. Competitive uptake of radiolabeled chloroquine and dihydroartemisinin in combination with other antimalarials was observed.Bis-4-aminoquinoline piperaquine (PPQ) and its analogues have been shown to be potent against chloroquine (CQ)-sensitive (CQS) and CQ-resistant (CQR) parasites in vitro (1,5) and in the field (18). Artemisinin derivatives are being evaluated as combination regimens (ACTs) to treat malaria and in particular to combat multidrug-resistant Plasmodium falciparum. It is hoped that combination chemotherapy will delay or at best prevent the onset of resistance to new agents and avoid cross-resistance to existing ones (20). PPQ has been used successfully for mass prophylaxis and treatment in China (18) and is increasingly being developed as a long-acting component in ACTs (7). One recent study assessed the in vitro interaction between PPQ and dihydroartemisinin (DHA), finding antagonism for K1 (CQR) and no interaction for 3D7 (CQS) strains of P. falciparum (7). An antagonistic drug combination may compromise efficacy and possibly increase the chances of resistance developing and spreading (10), and there may be situations, such as when treatment is incomplete, in which an antagonistic interaction could become significant (7). Our aim was to assess the in vitro effects of DHA in combination with PPQ against a range of P. falciparum strains with various degrees of drug resistance and to compare these results with DHA combined with the common 4-aminoquinolines CQ and amodiaquine (AQ). In addition, we examined the effect of a range of antimalarial drugs on the in vitro uptake of radiolabeled DHA and CQ. Dose-response assays to obtain 50% inhibitory concentration (IC 50 ) values of individual drugs and fixed ratio combination assays were carried out as previously published (10) at 1% parasitemia and 1% hematocrit. Uptake of [ 3 H]DHA (Moravek Biochemicals) at 1.4 Ci/mmol and [ 3 H]CQ (DuPont NEN) at 50.4 Ci/mmol was done at 37°C for 90 min. The experiment was initiated with addition of trophozoite parasites (5% parasitemia, 1.5% hematocrit) to microtubes containing both the unlabeled antimalarial and the radiolabeled drug (12).Samples were then centrifuged through silicon oil (AnalaR; BDH) and processed (12), and the radioactivity was determined on a Beckman liquid scintillation spectrometer. Uptake was represented as a percentage of control parasitized erythrocytes minus the uptake of drug in uninfected erythrocytes (Ϯ the relative standard deviation). All experiments were repeated at least twice in triplicate.The sensitivities of eight laboratory parasite lines were assessed to a range of antimalarial drugs (Table 1). Overall, three of the parasite lines were CQS, four were CQR, and line 106/1 was moderately CQR. CQ IC...

Role of Known Molecular Markers of Resistance in the Antimalarial Potency of Piperaquine and Dihydroartemisinin In Vitro

“…Interestingly, there was a trend, albeit a slight one, toward a reduced PIP susceptibility in parasites harboring the CVIET PfCRT haplotype. Although no definitive causal relationship was determined, earlier studies have shown a cross-resistance of PIP and CQ (10,34). In our limited panel of parasite lines, genetic modification of the pfmdr1 locus had little effect on parasite susceptibility to PIP (Table 1), despite observations from a number of studies showing a positive correlation between the YYY PfMDR1 haplotype and amodiaquine susceptibility (amodiaquine is structurally related to PIP) (8,11).…”

Pharmacokinetics and Ex Vivo Pharmacodynamic Antimalarial Activity of Dihydroartemisinin-Piperaquine in Patients with Uncomplicated Falciparum Malaria in Vietnam

“…In vitro drug susceptibility testing revealed that dihydroartemisinin was 15-times [mean IC 90 of 4.50 Ϯ 0.25 versus 67.51 Ϯ 1.87 nM (n ϭ 3)] and 25.2-times [IC 90 of 4.85 Ϯ 1.51 versus 122.16 Ϯ 23.69 nM (n ϭ 7)] more active than piperaquine in inhibiting the D6 and K1 lines of P. falciparum, respectively. The IC 50 s for dihydroartemisinin (2.57 Ϯ 1.27 nM) and piperaquine (82.06 Ϯ 35.25 nM) were about twofold higher than previously published data using the K1 line (3,4). A likely explanation for this discordance in IC 50 s is the higher human plasma concentration (50% versus 10%) used in the present study compared with others using standard in vitro methods (M. Chavchich, unpublished data).…”

In Vitro Sensitivities of Plasmodium falciparum Isolates from the China-Myanmar Border to Piperaquine and Association with Polymorphisms in Candidate Genes

“…Moreover, the overall good clinical efficacy of DHA-PPQ in treating falciparum malaria in areas of high prevalence of CQ-resistant parasites argues against a shared resistance mechanism between CQ and PPQ (15,47,48). Besides, most in vitro studies of laboratory strains and field parasite isolates failed to detect marked reductions in PPQ sensitivity in comparison with 3D7 or other laboratory strains (25,27,29,30). In most in vitro and ex vivo studies conducted thus far, there was generally a 3-to 4-fold difference in PPQ sensitivity between the most and least susceptible isolates (Table 2).…”

“…Similarly, significant correlation of response between PPQ and CQ was also observed in ex vivo studies using parasite isolates from Cameroon (23) and Papua New Guinea (24), albeit PPQ was equally active against CQ-sensitive and -resistant parasites. Studies using laboratory CQ-sensitive and -resistant lines further support the existence of cross-resistance between CQ and PPQ (25,26). In contrast, recent ex vivo and in vitro drug assays using parasites of diverse origins (but mostly from Africa) did not notice significant correlation of responses to CQ and PPQ (27)(28)(29)(30) but detected significant positive correlations in some studies between the responses to PPQ and other antimalarials such as DHA, pyronaridine, amodiaquine, or doxycycline.…”

“…It is suspected that cross-resistance might occur between PPQ and other quinoline drugs because of structural similarities of these drugs and possibly shared modes of ac- tion (46). Studies showing correlation between in vitro susceptibilities of parasite isolates to CQ and PPQ (20,22,24,25,32) and demonstration of elevated resistance to PPQ in well-characterized laboratory CQ-resistant parasite lines (25,26) suggest a role of the major CQ-resistant marker pfcrt in PPQ resistance. However, it is noteworthy that the difference between the PPQ responses in CQsensitive and -resistant strains which led to the suggestion of cross-resistance between CQ and PPQ resistance was insignificant and only at 3-to 4-fold (Table 2).…”