Jacques Chollet

Identification of an antimalarial synthetic trioxolane drug development candidate

The discovery of artemisinin more than 30 years ago provided a completely new antimalarial structural prototype; that is, a molecule with a pharmacophoric peroxide bond in a unique 1,2,4-trioxane heterocycle. Available evidence suggests that artemisinin and related peroxidic antimalarial drugs exert their parasiticidal activity subsequent to reductive activation by haem, released as a result of haemoglobin digestion by the malaria-causing parasite. This irreversible redox reaction produces carbon-centred free radicals, leading to alkylation of haem and proteins (enzymes), one of which—the sarcoplasmic-endoplasmic reticulum ATPase PfATP6 (ref. 7)—may be critical to parasite survival. Notably, there is no evidence of drug resistance to any member of the artemisinin family of drugs. The chemotherapy of malaria has benefited greatly from the semi-synthetic artemisinins artemether and artesunate as they rapidly reduce parasite burden, have good therapeutic indices and provide for successful treatment outcomes. However, as a drug class, the artemisinins suffer from chemical (semi-synthetic availability, purity and cost), biopharmaceutical (poor bioavailability and limiting pharmacokinetics) and treatment (non-compliance with long treatment regimens and recrudescence) issues that limit their therapeutic potential. Here we describe how a synthetic peroxide antimalarial drug development candidate was identified in a collaborative drug discovery project.

Synthetic ozonide drug candidate OZ439 offers new hope for a single-dose cure of uncomplicated malaria

Ozonide OZ439 is a synthetic peroxide antimalarial drug candidate designed to provide a single-dose oral cure in humans. OZ439 has successfully completed Phase I clinical trials, where it was shown to be safe at doses up to 1,600 mg and is currently undergoing Phase IIa trials in malaria patients. Herein, we describe the discovery of OZ439 and the exceptional antimalarial and pharmacokinetic properties that led to its selection as a clinical drug development candidate. In vitro, OZ439 is fast-acting against all asexual erythrocytic Plasmodium falciparum stages with IC50 values comparable to those for the clinically used artemisinin derivatives. Unlike all other synthetic peroxides and semisynthetic artemisinin derivatives, OZ439 completely cures Plasmodium berghei-infected mice with a single oral dose of 20 mg/kg and exhibits prophylactic activity superior to that of the benchmark chemoprophylactic agent, mefloquine. Compared with other peroxide-containing antimalarial agents, such as the artemisinin derivatives and the first-generation ozonide OZ277, OZ439 exhibits a substantial increase in the pharmacokinetic half-life and blood concentration versus time profile in three preclinical species. The outstanding efficacy and prolonged blood concentrations of OZ439 are the result of a design strategy that stabilizes the intrinsically unstable pharmacophoric peroxide bond, thereby reducing clearance yet maintaining the necessary Fe(II)-reactivity to elicit parasite death.

Mefloquine—An Aminoalcohol with Promising Antischistosomal Properties in Mice

Background The treatment and control of schistosomiasis, an often neglected tropical disease that exacerbates poverty, depends on a single drug, praziquantel. The large-scale use of praziquantel might select for drug-resistant parasites, hence there is a need to develop new antischistosomal compounds. Here, we report that the antimalarial drug mefloquine possesses promising antischistosomal properties in mice. Methodology/Principal Findings A single dose of mefloquine (200 or 400 mg/kg) administered orally to mice infected with adult Schistosoma mansoni or adult S. japonicum resulted in high or complete total and female worm burden reductions (72.3%–100%). Importantly, high worm burden reductions were also observed for young developing stages of S. mansoni and S. japonicum harbored in the mouse. Both mefloquine erythro-enantiomers resulted in high and comparable total and female worm burden reductions when given to mice with either a sub-patent or patent S. mansoni infection. Conclusions/Significance Our findings hold promise for the development of a novel antischistosomal drug based on an aminoalcohol functionality. Further in vitro and in vivo studies have been launched to elucidate the possible mechanism of action and to study the effect of mefloquine on S. haematobium and other trematodes. It will be interesting to investigate whether mefloquine, which is widely and effectively used for the treatment of malaria, has an impact on schistosomiasis in areas where both malaria and schistosomiasis co-exist.

In Vitro and In Vivo Activities of Synthetic Trioxolanes against Major Human Schistosome Species

ABSTRACT Schistosomiasis is a parasitic disease that remains of considerable public health significance in tropical and subtropical environments. Since the mainstay of schistosomiasis control is chemotherapy with a single drug, praziquantel, drug resistance is a concern. Here, we present new data on the antischistosomal properties of representative synthetic 1,2,4-trioxolanes (OZs). Exposure of adult Schistosoma mansoni for 24 h to a medium containing 20 μg/ml OZ209 reduced worm motor activity, induced tegumental alterations, and killed worms within 72 h. While exposure of S. mansoni to OZ78 had no apparent effect, addition of hemin reduced worm motor activity and caused tegumental damage. Administration of single 200-mg/kg of body weight oral doses of OZ78, OZ209, and OZ288 to mice harboring a juvenile S. mansoni infection resulted in worm burden reductions of 82.0 to 95.4%. In the adult infection model in mice, single 400-mg/kg doses of these compounds resulted in a maximum total worm burden reduction of 52.2%. High worm burden reductions (71.7 to 86.5%) were observed after administration of single 200-mg/kg doses of OZ78 and OZ288 to hamsters infected with either juvenile or adult S. mansoni. A single 200-mg/kg dose of OZ78 to hamsters infected with adult Schistosoma japonicum resulted in total and female worm burden reductions of 94.2 to 100%. Our results, along with the low toxicity, metabolic stability, and good pharmacokinetic properties of the OZs, indicate the potential for the development of novel broad-spectrum antischistosomal OZ drug candidates.

Recent investigations of artemether, a novel agent for the prevention of schistosomiasis japonica, mansoni and haematobia☆

Two decades ago, a group of Chinese scientists discovered the antischistosomal properties of artemether, a derivative of the antimalarial drug artemisinin. However, it was only recently that the importance of this finding was recognized internationally, following a collaborative effort between Chinese, European and African scientists, who investigated the effects of artemether against the major human schistosome species. Laboratory studies revealed that artemether exhibits the highest activity against juvenile stages of the parasites, while adult worms are significantly less susceptible. There was no indication of neurotoxicity following repeated high doses of artemether given fortnightly for up to 5 months. Randomized controlled clinical trials confirmed that artemether, orally administered at a dose of 6 mg/kg once every 2-3 weeks, results in no drug-related adverse effects, and significantly reduces the incidence and intensity of schistosome infections. The risk that these treatment regimens might select for resistance, particularly for resistant-plasmodia, appears to be low. Combined treatment with artemether and praziquantel, given to animals harbouring juvenile and adult schistosome worms, resulted in significantly higher worm burden reductions than each drug administered singly. In conclusion, artemether-integrated with other control strategies-has considerable potential for reducing the current burden of schistosomiasis in different epidemiological settings.

Preventive effect of artemether in experimental animals infected with Schistosoma mansoni

The effect of artemether, an antimalarial drug developed from the plant Artemisia annua, has been tested against the larval stages of Schistosoma mansoni covering the time from skin penetration to the early adult liver-stage. The results show that the experimental animals used (hamster and mice) do not develop schistosomiasis mansoni if treated with artemether during the first month after infection. The parasite was found to be especially susceptible between the 3rd and 4th week after infection, resulting in worm reductions of 75.3-82.0% compared to non-treated controls. This level was boosted to 97.2-100% when the animals were subjected to various schedules of repeated treatment. Almost complete protection was also reached in parallel experiments with repeated infections carried out to mirror more closely the real situation of trickle infection.

Comparative study of the effects of artemether and artesunate on juvenile and adult Schistosoma mansoni in experimentally infected mice.

Artemether and artesunate, derivatives of the antimalarial artemisinin, also exhibit antischistosomal properties. There is a need to assess comparatively the activity of both compounds against different developmental stages of schistosome parasites. Since artemisinin derivatives will be increasingly used to treat malaria, it is important to study the effects of 7-day monotherapy regimens on schistosome infections. We carried out experiments with mice, infected with juvenile or adult Schistosoma mansoni, and treated with artemether or artesunate at various doses and regimens including those currently used for monotherapy of malaria. Three doses of artemether, at concentrations of 150 or 300 mg/kg, administered to mice with juvenile S. mansoni resulted in worm reductions of 88-97%, which were significantly higher than the 67-77% obtained with artesunate (P < 0.05). Total concentrations of 600 or 800 mg/kg artemether, administered over 2 or 4 consecutive days to mice with adult S. mansoni, reduced the worm burden significantly by 46-51% (P < 0.05). The reduction of the worm burden observed with artesunate was considerably lower, 24-33%, and not significant when compared with untreated control mice. Seven-day monotherapy regimens of artemether or artesunate given at different concentrations to mice with adult S. mansoni showed total worm reductions of 53-61% or 34-49%, respectively. We conclude that artemether and artesunate are efficacious antischistosomal agents, with artemether displaying consistently higher activities. Our findings may contribute to the current strategic discussions on the effect and use of artemisinin derivatives against schistosomes when they are used in malaria chemotherapy in areas of co-endemicity of both parasites.

Artemether administered together with haemin damages schistosomes in vitro

We conducted experiments in vitro to assess the effect of artemether in combination with haemin on adult Schistosoma japonicum, S. mansoni and S. haematobium. When schistosomes were maintained in a medium containing artemether at concentrations of 20 micrograms/mL or less for 72 h, no apparent effect on the schistosomes was seen. When the medium contained 50 or 100 micrograms/mL haemin as well as artemether, the schistosomes showed decreased motor activity 2-24 h after exposure, which was followed by the staining of the whole worm body a reddish-yellow colour, dilatation of the intestine, and extensive vesiculation of the tegument. Some of the schistosomes died 24 h after exposure, and almost all died within 48-72 h. When schistosomes were exposed to the same concentrations of haemin alone, they were stained a light yellow colour but there was no apparent effect on their survival. Our findings suggest that artemether interacts with haemin to exert a toxic effect on the worms, which might be of importance in the further elucidation of the mechanism of action of artemether on schistosomes.

Effect of combined treatment with praziquantel and artemether on Schistosoma japonicum and Schistosoma mansoni in experimentally infected animals

Praziquantel and artemether are safe and efficacious antischistosomal drugs that act against different developmental stages of the parasite: praziquantel against adult worms and artemether against schistosomula. A combined treatment has been suggested as a strategy for transmission control. Recent laboratory experiments with rabbits with a mixed infection of Schistosoma japonicum parasites of different ages confirmed the effectiveness of a combination therapy. In the present work, we assessed the effect of a combined treatment on adult worms of S. japonicum and found significantly higher worm reduction rates than with a single dose of praziquantel. In a next step, we extended the study of the combined treatment to Schistosoma mansoni. A combined treatment with 75 mg/kg praziquantel and 150 mg/kg artemether was administered to hamsters infected with juvenile and adult S. mansoni. The two drugs, administered simultaneously or spaced by 6 h, 1, 3 or 7 days, resulted in significantly higher worm reduction rates than a single treatment with praziquantel. A combination therapy with increased doses of 100 mg/kg praziquantel and 300 mg/kg artemether showed very high worm reduction rates of 90% and above, however, some hamsters died in five different combined treatment experiments, suggesting that these drug concentrations were too high. We conclude that a combined treatment with praziquantel and artemether at the lower doses is safe and more effective than praziquantel alone, which forms a foundation for designing respective clinical trials in humans.

The Structure−Activity Relationship of the Antimalarial Ozonide Arterolane (OZ277)

The structure and stereochemistry of the cyclohexane substituents of analogues of arterolane (OZ277) had little effect on potency against Plasmodium falciparum in vitro. Weak base functional groups were not required for high antimalarial potency, but they were essential for high antimalarial efficacy in P. berghei-infected mice. Five new ozonides with antimalarial efficacy and ADME profiles superior or equal to that of arterolane were identified.