The antimalarial trioxaquine derivative DU-1102, synthesized by covalent linkage between aminoquinoline and trioxane moieties, was highly active against Cameroonian isolates (mean 50% inhibitory concentration of 43 nmol/liter) of Plasmodium falciparum. There was no correlation between the responses to DU-1102 and chloroquine and only a low correlation between the responses to DU-1102 and pyrimethamine, suggesting an independent mode of action of the trioxaquine against the parasites.Because of the extensive spread of drug resistance involving primarily 4-aminoquinolines and antifolate drugs in most of the geographic areas where Plasmodium falciparum is endemic, there is a need for a sustained search for promising compounds with new chemical structures and mechanisms of action. In the past 2 decades, only a few compounds belonging to a new class of antimalarial drugs, including aminoalcohols (mefloquine, halofantrine, lumefantrine), sesquiterpene trioxanes (artemisinin derivatives), and naphthoquinones (atovaquone), were developed for commercialization.DU-1102 (Fig. 1a) is a new candidate compound that belongs to a novel chemical class named trioxaquine (7, 11) (Fig. 1b). Trioxaquines are new modular molecules obtained by covalently attaching a trioxane motif, present in artemisinin, to a 4-aminoquinoline entity, contained in chloroquine. As the trioxane moiety is a potential alkylating agent after reductive activation by heme (6,10,(15)(16)(17)(18) and the 4-aminoquinoline entity is known to easily penetrate within infected erythrocytes (9) and then interact with heme, such modular molecules are expected to combine the properties of both fragments. Although it remains to be experimentally confirmed, we hypothesized that trioxaquine is able to penetrate infected red blood cells and then interact with the free heme liberated during the hemoglobin digestion.The in vitro activity of DU-1102 was assessed against clinical isolates of P. falciparum obtained in Yaoundé, Cameroon, where previous in vitro and in vivo studies have shown a high proportion (Ͼ40%) of chloroquine and/or pyrimethamine resistance (3, 14). We also evaluated the potential for in vitro cross-resistance between DU-1102 and chloroquine and pyrimethamine, which are first-and second-line (pyrimethaminesulfadoxine combination) drugs in Cameroon, respectively.Fresh clinical isolates of P. falciparum were obtained before treatment from adult Cameroonian patients attending the Nlongkak Catholic missionary dispensary in Yaoundé in 2000.The patients presented with signs and symptoms of acute uncomplicated malaria and had at least 0.1% asexual parasitemia. The Saker-Solomons colorimetric test for 4-aminoquinolines, quinine, and antifolate drugs in urine was negative for each patient (12). The patients were treated with oral amodiaquine, according to the national antimalarial guidelines set by the Cameroonian Ministry of Public Health. The study was approved by the Cameroonian National Ethics Committee and the Cameroonian Ministry of Public Health.Chloroquine...

The short-term in vitro growth of Plasmodium falciparumparasites in the asexual erythrocytic stage and the in vitro activities of eight standard antimalarial drugs were assessed and compared by using RPMI 1640 medium supplemented with 10% nonimmune human serum, 10% autologous or homologous acute-phase serum, or 0.5% Albumax I (lipid-enriched bovine serum albumin). In general, parasite growth was maximal with autologous (or homologous) serum, followed by Albumax I and nonimmune serum. The 50% inhibitory concentrations (IC50s) varied widely, depending on the serum or serum substitute. The comparison of IC50s between assays with autologous and nonimmune sera showed that monodesethylamodiaquine, halofantrine, pyrimethamine, and cycloguanil had similar IC50s. Although the IC50s of chloroquine, monodesethylamodiaquine, and dihydroartemisinin were similar with Albumax I and autologous sera, the IC50s of all test compounds obtained with Albumax I differed considerably from the corresponding values obtained with nonimmune serum. Our results suggest that Albumax I and autologous and homologous sera from symptomatic, malaria-infected patients may be useful alternative sources of serum for in vitro culture of P. falciparum isolates in the field. However, autologous sera and Albumax I do not seem to be suitable for the standardization of isotopic in vitro assays for all antimalarial drugs.

Abstract. The effects of pyronaridine and chloroquine on mature Plasmodium falciparum gametocytes were compared in 161 patients treated with chloroquine or pyronaridine. Neither pyronaridine nor chloroquine showed gametocytocidal activity. The relative risks of post-treatment gametocytemia after pyronaridine and chloroquine treatment in the presence of chloroquine-resistant isolates were 1.25 and 11.5, respectively, suggesting that the use of chloroquine was associated with a high risk of favoring post-therapeutic gametocytemia in chloroquine-resistant infections.The intense and continuous transmission of Plasmodium falciparum is one of the important factors that maintain the high prevalence of malaria in most of tropical Africa. The available measures to reduce malaria transmission include vector control and the use of gametocytocidal drugs. Vector control in Africa has not had much impact on malaria control, except in pilot programs. 1 The currently available firstor second-line (chloroquine, amodiaquine, sulfadoxine-pyrimethamine) and third-line (quinine) drugs in Africa do not exhibit any direct gametocytocidal action on P. falciparum. 2 Pyronaridine is a new synthetic drug that is undergoing preclinical and clinical evaluation and may replace chloroquine in Africa. 3,4 We studied and compared the effects of pyronaridine and chloroquine on gametocytes in patients with acute uncomplicated falciparum malaria.The study was part of the clinical trials involving 184 symptomatic, malaria-infected African patients (96 adults and 88 children between 5 and 15 years of age) in Yaoundé, Cameroon.4,5 Patients were treated with either 25 mg/kg of chloroquine phosphate (n ϭ 93; 10 mg/kg on days 0 and 1 and 5 mg/kg on day 2) or 32 mg/kg of pyronaridine tetraphosphate (n ϭ 91; 16 mg/kg on day 0 in two divided doses and 8 mg/kg on days 1 and 2) after informed consent was obtained from the patients or their guardians. The study was approved by the Cameroonian National Ethics Committee. Giemsa-stained thick blood smear was examined for the detection and quantification of gametocytes. The clinical conditions and asexual parasitemia were monitored on days 0, 1, 2, 3, 4, 7, and 14 on an out-patient basis. Because of the slower developmental rate of gametocytes (8-10 days), compared with the 48-hr cycle of P. falciparum asexual erythrocytic forms, 6 gametocyte count was monitored on days 0, 3, 7, and 14. Gametocytes were counted against 3,000 white blood cells, and gametocyte density was determined from the white blood cell count and expressed as the number of gametocytes/l of blood.Thick blood smears were considered negative if no gametocyte was seen after counting 3,000 white blood cells. The patients were assigned to one of the following groups for the analysis of parasitologic responses of gametocytes: 1) absence of gametocytes during the 14-day follow-up period, including day 0, 2) pretreatment presence of gametocytes (which allows the evaluation of a possible gametocytocidal effect of antimalarial drugs), and 3) post-treatme...