A long-duration dihydroorotate dehydrogenase inhibitor (DSM265) for prevention and treatment of malaria.

Malaria is one of the most significant causes of childhood mortality, but disease control efforts are threatened by resistance of the Plasmodium parasite to current therapies. Continued progress in combating malaria requires development of new, easy to administer drug combinations with broad-ranging activity against all manifestations of the disease. DSM265, a triazolopyrimidine-based inhibitor of the pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase (DHODH), is the first DHODH inhibitor to reach clinical development for treatment of malaria. We describe studies profiling the biological activity, pharmacological and pharmacokinetic properties, and safety of DSM265, which supported its advancement to human trials. DSM265 is highly selective toward DHODH of the malaria parasite Plasmodium, efficacious against both blood and liver stages of P. falciparum, and active against drug-resistant parasite isolates. Favorable pharmacokinetic properties of DSM265 are predicted to provide therapeutic concentrations for more than 8 days after a single oral dose in the range of 200 to 400 mg. DSM265 was well tolerated in repeat-dose and cardiovascular safety studies in mice and dogs, was not mutagenic, and was inactive against panels of human enzymes/receptors. The excellent safety profile, blood- and liver-stage activity, and predicted long half-life in humans position DSM265 as a new potential drug combination partner for either single-dose treatment or once-weekly chemoprevention. DSM265 has advantages over current treatment options that are dosed daily or are inactive against the parasite liver stage.

Comparison of electrophysiological data from human-induced pluripotent stem cell-derived cardiomyocytes to functional preclinical safety assays.

Human-induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) are a potential source to develop assays for predictive electrophysiological safety screening. Published studies show that the relevant physiology and pharmacology exist but does not show the translation between stem cell cardiomyocyte assays and other preclinical safety screening assays, which is crucial for drug discovery and safety scientists and the regulators. Our studies are the first to show the pharmacology of ion channel blockade and compare them with existing functional cardiac electrophysiology studies. Ten compounds (a mixture of pure hERG [E-4031 and Cisapride], hERG and sodium [Flecainide, Mexiletine, Quinidine, and Terfenadine], calcium channel blockers [Nifedipine and Verapamil], and two proprietary compounds [GSK A and B]) were tested, and results from hiPSC-CMs studied on multielectrode arrays (MEA) were compared with other preclincial models and clinical drug concentrations and effects using integrated risk assessment plots. All ion channel blockers produced (1) functional effects on repolarization and depolarization around the IC25 and IC50 values and (2) excessive blockade of hERG and/or blockade of sodium current precipitated arrhythmias. Our MEA data show that hiPSC-CMs demonstrate relevant pharmacology and show excellent correlations to current functional cardiac electrophysiological studies. Based on these results, MEA assays using iPSC-CMs offer a reliable, cost effective, and surrogate to preclinical in vitro testing, in addition to the 3Rs (refine, reduce, and replace animals in research) benefit.

Mechanism of vasopeptidase inhibitor-induced plasma extravasation: comparison of omapatrilat and the novel neutral endopeptidase 24.11/angiotensin-converting enzyme inhibitor GW796406.

We describe N-[(2S)-2-(mercaptomethyl)-3-methylbutanoyl]-4-(1H-pyrazol-1-yl)-L-phenylalanine (GW796406), a vasopeptidase inhibitor (VPI) that possessed approximately 3-fold selectivity for neutral endopeptidase 24.11 (NEP) versus angiotensin-converting enzyme (ACE) in in vitro assays using rat and human enzymes. In the same assays, omapatrilat, the most extensively studied VPI, displayed approximately 3-fold selectivity for ACE. The in vivo ACE and NEP inhibition profile and the liability of the compounds to increase plasma extravasation were compared at two (low and high) therapeutically equivalent intravenous doses in the rat. At the low dose, both agents inhibited ACE activity by approximately 85%. Consistent with their in vitro ACE/NEP selectivity, omapatrilat produced 49% inhibition, whereas GW796406 produced >95% inhibition of NEP. Neither compound increased plasma extravasation. When the low dose was administered to rats pretreated with the NEP inhibitor ecadotril to normalize NEP background to <5% of control, only omapatrilat significantly increased plasma extravasation. At the high dose, omapatrilat and GW796406 produced profound, nonselective inhibition of ACE (>90%) and NEP (>95%), and they significantly increased plasma extravasation. The activity of the agents as inhibitors of dipeptidylpeptidase IV (DPP IV) and aminopeptidase P (APP) was also investigated. Neither compound inhibited DPP IV. Interestingly, omapatrilat, but not GW796406, was a relatively potent inhibitor of APP (IC50 = 260 nM). We investigated whether APP inhibition increased the plasma extravasation liability of GW796406. The low dose of GW796406 administered with apstatin, an APP inhibitor, did not increase plasma extravasation. This finding inferred that APP inhibition is not involved in plasma extravasation in the rat and that APP inhibition does not explain the increased plasma extravasation produced by omapatrilat in NEP-inhibited rats.