In vitro and in vivo antischistosomal activity of ferroquine derivatives
© Keiser et al.; licensee BioMed Central Ltd. 2014
Received: 22 August 2014
Accepted: 27 August 2014
Published: 4 September 2014
Schistosomiasis is a neglected tropical disease and drug-repurposing is a useful strategy to fill its exhausted drug development pipeline. The ferrocenyl analogue of chloroquine, ferroquine, is an antimalarial in late-stage drug development. The aim of the present work was to study the antischistosomal activity of ferroquine against Schistosoma mansoni adult worms and newly transformed schistosomula (NTS) in vitro and in vivo. Hydroxyl-ferroquine and ruthenoquine were included to study the potential role of reactive oxygen species in the antischistosomal activity. Chloroquine and mefloquine, the later described for its antischistosomal properties, served as comparators.
All metal complexes were shown to be moderately cytotoxic on human cervix HeLa cancer cells and human fetal lung fibroblasts MRC-5. 72 hours post-incubation NTS exposed to 33.3 µM ruthenoquine had died, while ferroquine and hydroxyl-ferroquine treated worms were strongly affected. No activity was observed treating NTS with chloroquine at 33.3 µM. Incubation of adult S. mansoni with 33.3 µM of the organometallic derivatives were highly affected in viability but were still alive 72 hours post-incubation. Mefloquine showed the highest activity against NTS and adult S. mansoni. Low total worm burden reductions of 0-36% were observed following oral administration of 200–800 mg/kg of the ferroquine derivatives to S. mansoni-infected mice.
The organometallic compounds evaluated in this study revealed moderate in vitro activity against both larval and adult stages of S. mansoni but low in vivo activity. No correlation can be drawn between the antimalarial and antischistosomal activity of chloroquine analogues and oxidative shock does not seem to play a role in the activity of these compounds against S. mansoni.
KeywordsSchistosoma mansoni Ferroquine Chloroquine Ruthenoquine Hydroxyl-ferroquine In vitro In vivo
Schistosomiasis is a neglected tropical disease, which causes a considerable public health burden . Millions of people require treatment each year to prevent the considerable health effects of schistosomiasis. For example, in 2012 it has been estimated that 249 million people should be treated in preventive chemotherapy programs . Yet, treatment and control of schistosomiasis relies on a single drug, namely praziquantel [1, 3, 4].
The aim of the present work was to study the antischistosomal activities of FQ against S. mansoni in vitro and in vivo. In addition, we investigated whether redox activation plays a role in antischistosomal activity by including the ruthenocenyl analogue of FQ, namely ruthenoquine (RQ, Figure 1), which was shown, contrary to FQ, to be unable to produce reactive oxygen species (ROS) in P. falciparum. This difference in redox activity was assumed to be responsible for the greater antimalarial activity of FQ over RQ. Furthermore, the antischistosomal activity of hydroxyl-ferroquine (FQ-OH, Figure 1) was also studied since FQ-OH is also able to produce hydroxyl radicals and provides reduced cytotoxic effects compared to FQ .
Animals and parasites
In vivo studies were carried out in accordance with Swiss national and cantonal regulations on animal welfare (permission no. 2070) at the Swiss Tropical and Public Health Institute (Basel, Switzerland). Female mice (NMRI strain, n = 31; weight ~ 20–22 g) were purchased from Charles River, Germany, kept under environmentally-controlled conditions (temperature ~ 25°C; humidity ~70%; 12-hour light and 12-hour dark cycle) with free access to water and rodent diet and acclimatized for one week before infection. Cercariae of S. mansoni were obtained from infected intermediate host snails (Biomphalaria glabrata) as described previously .
FQ, FQ-OH and RQ were synthesized according to reported procedures [13, 14, 16]. MQ was kindly obtained from Mepha AG (Aesch, Switzerland). CQ was purchased from Sigma (Buchs, Switzerland). For in vitro studies, compounds were dissolved in DMSO (Fluka, Buchs, Switzerland) to obtain stock solutions of 10 mg/ml. For in vivo studies, compounds were suspended in 7% (v/v) Tween 80 and 3% (v/v) ethanol shortly before oral treatment (10 ml/kg) of mice.
In vitro studies
Newly transformed schistosomula (NTS)
S. mansoni cercariae were mechanically transformed to newly transformed schistosomula (NTS) . A NTS suspension at a concentration of 100 NTS per 50 µl was prepared using Medium 199 (Invitrogen, Carlsbad, CA) [supplemented with 5% inactivated fetal calf serum (iFCS) and 100 U/ml penicillin and 100 mg/mL streptomycin (Invitrogen). NTS were incubated with 10 µM and 33.3 µM of the test compounds for 72 h. Compounds were tested at least in triplicate and the highest concentration of DMSO served as control. Plates were incubated at 37°C, 5% CO2. NTS were evaluated by microscopic readout (Carl Zeiss, Germany, magnification 80x) using a viability scale scoring death, changes in motility, viability, and morphological alterations .
Adult S. mansoni
Adult schistosomes obtained from infected mice were incubated in the presence of 10 µM and 33.3 µM of the test compounds for up to 72 h. Phenotypes were monitored daily based on motility, viability and morphological alterations under an inverse microscope (Carl Zeiss, Germany, magnification 80×).
Cytotoxicity studies were performed on human cervix HeLa cancer cells and non tumorigenic human fetal lung fibroblasts MRC-5 to compare the activity of FQ, RQ, FQ-OH, CQ, MQ and cisplatin. The cell viability was determined via a colorimetric cell-based assay using Resazurin (Promocell GmbH). Briefly, one day before treatment cells were plated in triplicates in 96-well plates at a density of 4 × 103 cells/well in 100 µl. Upon treating cells with increasing concentrations of the target complexes (freshly prepared stock solution in DMSO), cells were incubated at 37°C/6% CO2 for 48 h, the medium was removed, and 100 µl of complete medium containing resazurin (0.2 mg/ml final concentration) was added. After 4 h of incubation at 37°C/6% CO2, the fluorescence of the highly red fluorescent resorufin product was quantified at 590 nm emission with 540 nm excitation wavelength in a SpectraMax M5 microplate Reader.
S. mansoni in vivo studies
Groups of 3–4 NMRI mice were treated orally with single oral doses of 200 mg/kg of FQ, FQ-OH and RQ. In addition, one group of mice was treated with a single oral dose of 800 mg/kg FQ. Untreated mice served as controls in all experiments. At 21 d post-treatment, animals were killed by the CO2 method and dissected. Worms were removed by picking, then sexed and counted as previously described .
Parasite viability values of treated and untreated worms obtained from microscopic evaluation were averaged (means (+/− standard deviation)) using Microsoft Excel software. The Kruskal-Wallis test was applied for in vivo studies, comparing the medians of the worm counts of the treatment and control groups. A difference in median was considered to be significant at a significance level of 5% (StatsDirect statistical software, version 2.7.2.; StatsDirect Ltd., United Kingdom).
Results and discussion
IC 50 values for ferroquine (FQ), hydroxyl-ferroquine (FQ-OH), ruthenoquine (RQ), chloroquine (CQ) and mefloquine (MQ) in non-cancerous MRC-5 and HeLa cancer cells
7.9 ± 1.2
11.5 ± 2.9
24.4 ± 0.9
10.1 ± 0.3
22.6 ± 1.2
16.8 ± 1.5
21.9 ± 2.6
8.8 ± 0.41
55.1 ± 1.3
87.0 ± 1.5
16.7 ± 0.2
6.7 ± 0.7
Activity against NTS and adult S. mansoni in vitro
Exposure to 10 µM of the test drugs resulted in reduced motilities of NTS but the larvae did not die (data not shown).
A similar trend was observed on adult S. mansoni. Incubation of adult S. mansoni with 33.3 µM of MQ resulted in death of worms 24 h post-treatment, while adult S. mansoni exposed to the organometallic derivatives were highly affected in viability but were still alive 72 hours post-incubation (Figure 2b). At 10 µM adults showed strongly reduced viabilities 48–72 hours post-incubation with all derivatives (data not shown).
Activity against adult S. mansoni in vivo
Compounds progressed into in vivo studies despite the fact that in vitro activities were only observed at concentrations that were close to cytotoxic concentrations. However, in our recent studies MQ was well tolerated by mice .
Effect on worm burden of single oral doses of three selected organometallic CQ derivatives administered to mice harboring a 49-day-old adult S. mansoni infection, stratified by sex and worm distribution
No. of mice investigated
No. of mice cured
Mean number of worms (SD)
Total worm burden reduction (%)
Female worm burden reduction (%)
In conclusion, the organometallic compounds evaluated in this study show only weak antischistosomal properties in vivo. Hence, based on our findings an ancillary benefit on schistosomiasis as a result of treating P. falciparum infections with FQ is not expected. Furthermore, no correlation can be drawn between the antimalarial and antischistosomal activity of CQ analogues, which might hint to distinct mechanisms of actions. Despite the low activities of organometallic drugs tested against S. mansoni so far  further derivatives (e.g. organometallic derivatives of MQ) should be studied.
This work was financially supported by the European Research Council (ERC-2013-CoG 614739-A_HERO to J.K.), the Swiss National Science Foundation (SNSF Professorship PP00P2_133568 to G.G.), the University of Zurich (G.G.), the Stiftung für Wissenschaftliche Forschung of the University of Zurich (G.G.), and the Novartis Jubilee Foundation (R.R. and G.G.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Dr. Faustine Dubar is acknowledged for the synthesis of RQ.
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