Multistage and transmission-blocking targeted antimalarials discovered from the open-source MMV Pandemic Response Box.

Chemical matter is needed to target the divergent biology associated with the different life cycle stages of Plasmodium. Here, we report the parallel de novo screening of the Medicines for Malaria Venture (MMV) Pandemic Response Box against Plasmodium asexual and liver stage parasites, stage IV/V gametocytes, gametes, oocysts and as endectocides. Unique chemotypes were identified with both multistage activity or stage-specific activity, including structurally diverse gametocyte-targeted compounds with potent transmission-blocking activity, such as the JmjC inhibitor ML324 and the antitubercular clinical candidate SQ109. Mechanistic investigations prove that ML324 prevents histone demethylation, resulting in aberrant gene expression and death in gametocytes. Moreover, the selection of parasites resistant to SQ109 implicates the druggable V-type H+-ATPase for the reduced sensitivity. Our data therefore provides an expansive dataset of compounds that could be redirected for antimalarial development and also point towards proteins that can be targeted in multiple parasite life cycle stages.

Identification of a Potential Antimalarial Drug Candidate from a Series of 2-Aminopyrazines by Optimization of Aqueous Solubility and Potency across the Parasite Life Cycle.

Introduction of water-solubilizing groups on the 5-phenyl ring of a 2-aminopyrazine series led to the identification of highly potent compounds against the blood life-cycle stage of the human malaria parasite Plasmodium falciparum. Several compounds displayed high in vivo efficacy in two different mouse models for malaria, P. berghei-infected mice and P. falciparum-infected NOD-scid IL-2Rγnull mice. One of the frontrunners, compound 3, was identified to also have good pharmacokinetics and additionally very potent activity against the liver and gametocyte parasite life-cycle stages.

A Novel Pyrazolopyridine with in Vivo Activity in Plasmodium berghei- and Plasmodium falciparum-Infected Mouse Models from Structure-Activity Relationship Studies around the Core of Recently Identified Antimalarial Imidazopyridazines.

Toward improving pharmacokinetics, in vivo efficacy, and selectivity over hERG, structure-activity relationship studies around the central core of antimalarial imidazopyridazines were conducted. This study led to the identification of potent pyrazolopyridines, which showed good in vivo efficacy and pharmacokinetics profiles. The lead compounds also proved to be very potent in the parasite liver and gametocyte stages, which makes them of high interest.

Structure-Activity Relationship Studies of Orally Active Antimalarial 2,4-Diamino-thienopyrimidines.

Based on the initial optimization of orally active antimalarial 2,4-diamino-thienopyrimidines and with the help of metabolite identification studies, a second generation of derivatives involving changes at the 2- and 4-positions of the thienopyrimidine core were synthesized. Improvements in the physiochemical properties resulted in the identification of 15a, 17a, 32, and 40 as lead molecules with improved in vivo exposure. Furthermore, analogue 40 exhibited excellent in vivo antimalarial activity when dosed orally at 50 mg/kg once daily for 4 days in the Plasmodium berghei mouse model, which is superior to the activity seen with previously reported compounds, and with a slightly improved hERG profile.

Medicinal chemistry optimization of antiplasmodial imidazopyridazine hits from high throughput screening of a softfocus kinase library: part 2.

On the basis of our recent results on a novel series of imidazopyridazine-based antimalarials, we focused on identifying compounds with improved aqueous solubility and hERG profile while maintaining metabolic stability and in vitro potency. Toward this objective, 41 compounds were synthesized and evaluated for antiplasmodial activity against NF54 (sensitive) and K1 (multidrug resistant) strains of the malaria parasite Plasmodium falciparum and evaluated for both aqueous solubility and metabolic stability. Selected compounds were tested for in vitro hERG activity and in vivo efficacy in the P. berghei mouse model. Several compounds were identified with significantly improved aqueous solubility, good metabolic stability, and a clean hERG profile relative to a previous frontrunner lead compound. A sulfoxide-based imidazopyridazine analog 45, arising from a prodrug-like strategy, was completely curative in the Plasmodium berghei mouse model at 4 × 50 mg/kg po.

2,4-Diaminothienopyrimidines as orally active antimalarial agents.

A novel series of 2,4-diaminothienopyrimidines with potential as antimalarials was identified from whole-cell high-throughput screening of a SoftFocus ion channel library. Synthesis and structure-activity relationship studies identified compounds with potent antiplasmodial activity and low in vitro cytotoxicity. Several of these analogues exhibited in vivo activity in the Plasmodium berghei mouse model when administered orally. However, inhibition of the hERG potassium channel was identified as a liability for this series.

Structure-activity relationship studies of orally active antimalarial 3,5-substituted 2-aminopyridines.

In an effort to address potential cardiotoxicity liabilities identified with earlier frontrunner compounds, a number of new 3,5-diaryl-2-aminopyridine derivatives were synthesized. Several compounds exhibited potent antiplasmodial activity against both the multidrug resistant (K1) and sensitive (NF54) strains in the low nanomolar range. Some compounds displayed a significant reduction in potency in the hERG channel inhibition assay compared to previously reported frontrunner analogues. Several of these new analogues demonstrated promising in vivo efficacy in the Plasmodium berghei mouse model and will be further evaluated as potential clinical candidates. The SAR for in vitro antiplasmodial and hERG activity was delineated.

3,5-Diaryl-2-aminopyridines as a novel class of orally active antimalarials demonstrating single dose cure in mice and clinical candidate potential.

A novel class of orally active antimalarial 3,5-diaryl-2-aminopyridines has been identified from phenotypic whole cell high-throughput screening of a commercially available SoftFocus kinase library. The compounds were evaluated in vitro for their antiplasmodial activity against K1 (chloroquine and drug-resistant strain) and NF54 (chloroquine-susceptible strain) as well as for their cytotoxicity. Synthesis and structure-activity studies identified a number of promising compounds with selective antiplasmodial activity. One of these frontrunner compounds, 15, was equipotent across the two strains (K1 = 25.0 nM, NF54 = 28.0 nM) and superior to chloroquine in the K1 strain (chloroquine IC(50) K1 = 194.0 nM). Compound 15 completely cured Plasmodium berghei-infected mice with a single oral dose of 30 mg/kg. Dose-response studies generated ED(50) and ED(90) values of 0.83 and 1.74 mg/kg for 15 in the standard four-dose Peters test. Pharmacokinetic studies in the rat indicated that this compound has good oral bioavailability (51% at 20 mg/kg) and a reasonable half-life (t(1/2) ∼ 7-8 h).