[Show abstract][Hide abstract] ABSTRACT: Hematotoxicity in individuals genetically deficient in glucose-6-phosphate dehydrogenase (G6PD) activity is the major limitation
of primaquine (PQ), the only antimalarial drug in clinical use for treatment of relapsing Plasmodium vivax malaria. PQ is currently clinically used in its racemic form. A scalable procedure was developed to resolve racemic PQ, thus
providing pure enantiomers for the first time for detailed preclinical evaluation and potentially for clinical use. These
enantiomers were compared for antiparasitic activity using several mouse models and also for general and hematological toxicities
in mice and dogs. (+)-(S)-PQ showed better suppressive and causal prophylactic activity than (−)-(R)-PQ in mice infected with Plasmodium berghei. Similarly, (+)-(S)-PQ was a more potent suppressive agent than (−)-(R)-PQ in a mouse model of Pneumocystis carinii pneumonia. However, at higher doses, (+)-(S)-PQ also showed more systemic toxicity for mice. In beagle dogs, (+)-(S)-PQ caused more methemoglobinemia and was toxic at 5 mg/kg of body weight/day given orally for 3 days, while (−)-(R)-PQ was well tolerated. In a novel mouse model of hemolytic anemia associated with human G6PD deficiency, it was also demonstrated
that (−)-(R)-PQ was less hemolytic than (+)-(S)-PQ for the G6PD-deficient human red cells engrafted in the NOD-SCID mice. All these data suggest that while (+)-(S)-PQ shows greater potency in terms of antiparasitic efficacy in rodents, it is also more hematotoxic than (−)-(R)-PQ in mice and dogs. Activity and toxicity differences of PQ enantiomers in different species can be attributed to their
different pharmacokinetic and metabolic profiles. Taken together, these studies suggest that (−)-(R)-PQ may have a better safety margin than the racemate in human.
[Show abstract][Hide abstract] ABSTRACT: Renewed global efforts toward malaria eradication have highlighted the need for novel antimalarial agents with activity against
multiple stages of the parasite life cycle. We have previously reported the discovery of a novel class of antimalarial compounds
in the imidazolopiperazine series that have activity in the prevention and treatment of blood stage infection in a mouse model
of malaria. Consistent with the previously reported activity profile of this series, the clinical candidate KAF156 shows blood
schizonticidal activity with 50% inhibitory concentrations of 6 to 17.4 nM against P. falciparum drug-sensitive and drug-resistant strains, as well as potent therapeutic activity in a mouse models of malaria with 50, 90,
and 99% effective doses of 0.6, 0.9, and 1.4 mg/kg, respectively. When administered prophylactically in a sporozoite challenge
mouse model, KAF156 is completely protective as a single oral dose of 10 mg/kg. Finally, KAF156 displays potent Plasmodium transmission blocking activities both in vitro and in vivo. Collectively, our data suggest that KAF156, currently under evaluation in clinical trials, has the potential to treat, prevent,
and block the transmission of malaria.
[Show abstract][Hide abstract] ABSTRACT: Abstract Abstract: Since the 1940s, the large animal model to assess novel causal prophylactic antimalarial agents has been the Plasmodium cynomolgi sporozoite-infected Indian-origin Rhesus monkeys. In 2009, the model was reassessed with three clinical standards: primaquine (PQ), tafenoquine (TQ) and atovaquone-proguanil. Both control monkeys were parasitemic on day 8 post-sporozoite inoculation on day 0. PQ at 1.78 mg base/kg/day on days (-1) to 8 protected one monkey and delayed parasitemia patency of the other monkey to day 49. Tafenoquine at 6 mg base/kg/day on days (-1) to 1 protected both monkeys. However, atovaquone-proguanil at 10 mg atovaquone/kg/day on days (-1) to 8 did not protect either monkey and delayed patency only to days 18-to-19. PQ and TQ at the employed regimens are proposed as appropriate doses of positive control drugs for the model at present.
Journal of Parasitology 04/2014; 100(5). DOI:10.1645/13-480.1 · 1.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A library of diamine quinoline methanols were designed based on the mefloquine scaffold. The systematic variation of the 4-position amino alcohol side chain led to analogues that maintained potency while reducing accumulation in the central nervous system (CNS). Although the mechanism of action remains elusive, these data indicate that the 4-position side chain is critical for activity and that potency (as measured by IC(90)) does not correlate with accumulation in the CNS. A new lead compound, (S)-1-(2,8-bis(trifluoromethyl)quinolin-4-yl)-2-(2-(cyclopropylamino)ethylamino)ethanol (WR621308), was identified with single dose efficacy and substantially lower permeability across MDCK cell monolayers than mefloquine. This compound could be appropriate for intermittent preventative treatment (IPTx) indications or other malaria treatments currently approved for mefloquine.
[Show abstract][Hide abstract] ABSTRACT: WR319691 has been shown to exhibit reasonable Plasmodium falciparum potency in vitro and exhibits reduced permeability across MDCK cell monolayers, which as part of our screening cascade led to further in vivo analysis. Single-dose pharmacokinetics was evaluated after an IV dose of 5 mg/kg in mice. Maximum bound and unbound brain levels of WR319691 were 97 and 0.05 ng/g versus approximately 1,600 and 3.2 ng/g for mefloquine. The half-life of WR319691 in plasma was approximately 13 h versus 23 h for mefloquine. The pharmacokinetics of several N-dealkylated metabolites was also evaluated. Five of six of these metabolites were detected and maximum total and free brain levels were all lower after an IV dose of 5 mg/kg WR319691 compared to mefloquine at the same dose. These data provide proof of concept that it is feasible to substantially lower the brain levels of a 4-position modified quinoline methanol in vivo without substantially decreasing potency against P. falciparum in vitro.
European Journal of Drug Metabolism and Pharmacokinetics 07/2011; 36(3):151-8. DOI:10.1007/s13318-011-0047-8 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Immune sera from volunteers vaccinated in a blinded Phase 3 clinical trial with JE-VAX(®) and a new Japanese encephalitis virus (JEV) vaccine (IC51 or IXIARO), were tested for the ability to protect mice against lethal JEV challenge. Sera from IXIARO vaccinated subjects were pooled into four batches based on neutralizing antibody measured by plaque reduction neutralization test (PRNT(50) titer): high (∼200), medium (∼40-50), low (∼20) and negative (<10). Pooled sera from JE-VAX(®) vaccinated subjects (PRNT(50) titer∼55) and pooled JEV antibody negative pre-vaccination sera were used as controls. Groups of ten 6- to 7-week-old female ICR mice were injected intraperitoneally with 0.5 ml of each serum pool diluted 1:2 or 1:10, challenged approximately 18 h later with a lethal dose of either JEV strain SA14 (genotype III) or strain KE-093 (genotype I) and observed for 21 days. All mice in the non-immune serum groups developed clinical signs consistent with JEV infection or died, whereas high titer sera from both IXIARO and JE-VAX(®) sera protected 90-100% of the animals. Statistical tests showed similar protection against both JEV strains SA14 and KE-093 and protection correlated with the anti-JEV antibody titer of IXIARO sera as measured by PRNT(50). Ex vivo neutralizing antibody titers showed that almost all mice with a titer of 10 or greater were fully protected. In a separate study, analysis of geometric mean titers (GMTs) of the groups of mice vaccinated with different doses of IXIARO and challenged with JEV SA14 provided additional evidence that titers≥10 were protective.
[Show abstract][Hide abstract] ABSTRACT: Utilizing mefloquine as a scaffold, a next generation quinoline methanol (NGQM) library was constructed to identify early lead compounds that possess biological properties consistent with the target product profile for malaria chemoprophylaxis while reducing permeability across the blood-brain barrier. The library of 200 analogs resulted in compounds that inhibit the growth of drug sensitive and resistant strains of Plasmodium falciparum. Herein we report selected chemotypes and the emerging structure-activity relationship for this library of quinoline methanols.
[Show abstract][Hide abstract] ABSTRACT: Mefloquine has been one of the more valuable antimalarial drugs but has never reached its full clinical potential due to concerns about its neurologic side effects, its greater expense than that of other antimalarials, and the emergence of resistance. The commercial development of mefloquine superseded that of another quinolinyl methanol, WR030090, which was used as an experimental antimalarial drug by the U.S. Army in the 1970s. We evaluated a series of related 2-phenyl-substituted alkylaminoquinolinyl methanols (AAQMs) for their potential as mefloquine replacement drugs based on a series of appropriate in vitro and in vivo efficacy and toxicology screens and the theoretical cost of goods. Generally, the AAQMs were less neurotoxic and exhibited greater antimalarial potency, and they are potentially cheaper than mefloquine, but they showed poorer metabolic stability and pharmacokinetics and the potential for phototoxicity. These differences in physiochemical and biological properties are attributable to the "opening" of the piperidine ring of the 4-position side chain. Modification of the most promising compound, WR069878, by substitution of an appropriate N functionality at the 4 position, optimization of quinoline ring substituents at the 6 and 7 positions, and deconjugation of quinoline and phenyl ring systems is anticipated to yield a valuable new antimalarial drug.
[Show abstract][Hide abstract] ABSTRACT: The quinolinyl methanol drug, mefloquine, is an important antimalarial agent with a long half-life in humans, which allows for its use as an effective single dose treament for malaria and as a once weeky dosing for prophylaxis. However, clinical application of mefloquine is limited by its relative costliness and its debilitating neurological side effects. We, therefore, evaluated a series of 2-phenyl substituted alkylaminoquinolinyl-methanols (AAQMs) for their potential as novel anti-malaria agents that retain the efficacy of mefloquine, yet lack neurotoxicity. These AAQMs were obtained from the U.S. Army's Chemical Information System and tested in a series of in vitro and in vivo efficacy and toxicology screens and in a theoretical costs of goods analysis. In general, we found that the AAQMs were less neurotoxic, exhibitted greater anti-malaria potency and are potentially cheaper than mefloquine, but showed poorer metabolic stability and pharmacokinetics and the potential for phototoxicity. From this series we identified a lead compound, referred as WR069878, and determined structural modifications expected to result in a novel anti-malaria agent lacking neurotoxicity and phototoxicity, in particular we anticipate that modification of WR069878 by substitution of an appropriate N functionality at the 4-position, optimization of quinoline and phenyl ring systems should yield a valuable new antimalarial drug.
55th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Marriott, Atlanta, Georgia, USA. November 12-16, 2006; 12/2006
[Show abstract][Hide abstract] ABSTRACT: Febrifugine is the active principal isolated 50 years ago from the Chinese herb chang shan (Dichroa febrifuga Lour), which has been used as an antimalarial in Chinese traditional medicine for more than 2,000 years. However, intensive study of the properties of febrifugine has been hindered for decades due to its side effects. We report new findings on the effects of febrifugine analogs compared with those of febrifugine extracted from the dry roots of D. febrifuga. The properties of the extracted febrifugine were comparable to those obtained from the standard febrifugine provided by our collaborators. A febrifugine structure-based computer search of the Walter Reed Chemical Information System identified 10 analogs that inhibited parasite growth in vitro, with 50% inhibitory concentrations ranging from 0.141 to 290 ng/ml. The host macrophages (J744 cells) were 50 to 100 times less sensitive to the febrifugine analogs than the parasites. Neuronal (NG108) cells were even more insensitive to these drugs (selectivity indices, >1,000), indicating that a feasible therapeutic index for humans could be established. The analogs, particularly halofuginone, notably reduced parasitemias to undetectable levels and displayed curative effects in Plasmodium berghei-infected mice. Recrudescence of the parasites after treatment with the febrifugine analogs was the key factor that caused the death of most of the mice in groups receiving an effective dose. Subcutaneous treatments with the analogs did not cause irritation of the gastrointestinal tract when the animals were treated with doses within the antimalarial dose range. In summary, these analogs appear to be promising lead antimalarial compounds that require intensive study for optimization for further down-selection and development.