Pharmacokinetics of ferroquine, a novel 4-aminoquinoline, in asymptomatic carriers of Plasmodium falciparum infections.

Ferroquine (SSR97193), a ferrocene-quinoline conjugate, is a promising novel antimalarial currently undergoing clinical evaluation. This study characterizes its pharmacokinetic properties. Young male African volunteers with asymptomatic Plasmodium falciparum infection were administered a single oral dose (n = 40) or a repeated oral dose (n = 26) given over 3 days of ferroquine in two dose-escalation, double-blind, randomized, placebo-controlled clinical trials. In addition, a food interaction study was performed in a subsample of participants (n = 16). The studies were carried out in Lambaréné, Gabon. After single-dose administration of ferroquine, dose linearity was demonstrated in a dose range of 400 to 1,200 mg for maximum mean blood concentrations ([C(max)] 82 to 270 ng/ml) and in a dose range of 400 to 1,600 mg for overall exposure to ferroquine (area under the concentration-time curve [AUC], 13,100 to 49,200 ng · h/ml). Overall mean estimate for blood apparent terminal half-life of ferroquine was 16 days and 31 days for its active and major metabolite desmethylferroquine (SSR97213). In the 3-day repeated-dose study, C(max) and overall cumulated exposure to ferroquine (AUC(cum)) increased in proportion with the dose from day 1 to day 3 between 400 and 800 mg. No major food effect on ferroquine pharmacokinetics was observed after single administration of 100 mg of ferroquine except for a slight delay of time to maximum blood concentration (t(max)) by approximately 3 h. The pharmacokinetics of ferroquine and its active main metabolite are characterized by sustained levels in blood, and the properties of ferroquine as a partner drug in antimalarial combination therapy should be evaluated.

Var Gene promoter activation in clonal Plasmodium falciparum isolates follows a hierarchy and suggests a conserved switching program that is independent of genetic background.

Antigenic variation of Plasmodium falciparum is mediated by a mutually exclusive expression mechanism that limits expression to an individual member of the multicopy var gene family. This process determines the antigenic and adhesive phenotype of the infected red blood cell. Previously, we showed that var gene switching is influenced by chromosomal position. Here, we address whether var gene transcription follows a general conserved pattern in long-term laboratory parasites and in recently culture-adapted field parasites. Activation of the var gene family was monitored in biological replicates in each parasite isolate every 3-5 generations for up to 3 months. We used transgenic parasites carrying a drug-selectable marker at a defined var locus to characterize var gene activation after the exclusive expression of the transgene. Transgenic parasites exhibited a repeatable hierarchy of var gene activation and a fluctuating transcriptional activity of the transgenic var locus. Transcriptional profiling of wild-type laboratory and field parasites showed a universal bias toward transcription of UpsC var genes and a fluctuating transcriptional activity of the dominant var promoter. The data suggest the existence of an intrinsic var gene transcription program that is independent of genetic background.

Phase I randomized dose-ascending placebo-controlled trials of ferroquine--a candidate anti-malarial drug--in adults with asymptomatic Plasmodium falciparum infection.

BACKGROUND: The development and spread of drug resistant Plasmodium falciparum strains is a major concern and novel anti-malarial drugs are, therefore, needed. Ferroquine is a ferrocenic derivative of chloroquine with proven anti-malarial activity against chloroquine-resistant and -sensitive P. falciparum laboratory strains. METHODS: Adult young male aged 18 to 45 years, asymptomatic carriers of P. falciparum, were included in two-dose escalation, double-blind, randomized, placebo-controlled Phase I trials, a single dose study and a multiple dose study aiming to evaluate oral doses of ferroquine from 400 to 1,600 mg. RESULTS: Overall, 54/66 patients (40 and 26 treated in the single and multiple dose studies, respectively) experienced at least one adverse event, 15 were under placebo. Adverse events were mainly gastrointestinal symptoms such as abdominal pain (16), diarrhoea (5), nausea (13), and vomiting (9), but also headache (11), and dizziness (5). A few patients had slightly elevated liver parameters (10/66) including two patients under placebo. Moderate changes in QTc and morphological changes in T waves were observed in the course of the study. However, no adverse cardiac effects with clinical relevance were observed. CONCLUSIONS: These phase I trials showed that clinically, ferroquine was generally well-tolerated up to 1,600 mg as single dose and up to 800 mg as repeated dose in asymptomatic young male with P. falciparum infection. Further clinical development of ferroquine, either alone or in combination with another anti-malarial, is highly warranted and currently underway.

A thirteen-year analysis of Plasmodium falciparum populations reveals high conservation of the mutant pfcrt haplotype despite the withdrawal of chloroquine from national treatment guidelines in Gabon.

BACKGROUND: Chloroquine resistance (CR) decreased after the removal of chloroquine from national treatment guidelines in Malawi, Kenia and Tanzania. In this investigation the prevalence of the chloroquine resistance (CQR) conferring mutant pfcrt allele and its associated chromosomal haplotype were determined before and after the change in Gabonese national treatment guidelines from chloroquine (CQ) to artesunate plus amodiaquine (AQ) in 2003. METHODS: The prevalence of the wild type pfcrt allele was assessed in 144 isolates from the years 2005 - 07 by PCR fragment restriction digest and direct sequencing. For haplotype analysis of the chromosomal regions flanking the pfcrt locus, microsatellite analysis was done on a total of 145 isolates obtained in 1995/96 (43 isolates), 2002 (47 isolates) and 2005 - 07 (55 isolates). RESULTS: The prevalence of the mutant pfcrt allele decreased from 100% in the years 1995/96 and 2002 to 97% in 2005 - 07. Haplotype analysis showed that in 1995/96 79% of the isolates carried the same microsatellite alleles in a chromosomal fragment spanning 39 kb surrounding the pfcrt locus. In 2002 and 2005 - 07 the prevalence of this haplotype was 62% and 58%, respectively. Pfcrt haplotype analysis showed that all wild type alleles were CVMNK. CONCLUSION: Four years after the withdrawal of CQ from national treatment guidelines the prevalence of the mutant pfcrt allele remains at 97%. The data suggest that the combination of artesunate plus AQ may result in continued selection for the mutant pfcrt haplotype even after discontinuance of CQ usage.

High prevalence of asymptomatic Plasmodium falciparum infection in Gabonese adults.

Plasmodium falciparum, the most common malarial parasite in sub-Saharan Africa, accounts for a high number of deaths in children less than five years of age. In malaria-endemic countries with stable transmission, semi-immunity is usually acquired after childhood. For adults, severe malaria is rare. Infected adults have either uncomplicated malaria or asymptomatic parasitemia. During a period of one year, we screened 497 afebrile males to investigate the prevalence of asymptomatic P. falciparum parasitemia in villages near Lambaréné, Gabon by use of three different methods. A total of 52% of the individuals had parasites detected by a subtelomeric variable open reading frame polymerase chain reaction (stevor-PCR), 27% of the rapid diagnostic test results were positive, and 12% of the thick blood smears with low parasitemias had P. falciparum. Most positive cases were only detected by the stevor-PCR. Asymptomatic P. falciparum parasitemia in adults living in a malaria-endemic country is frequent.