[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 activity profile of this series the clinical candidate KAF156 shows blood schizonticidal activity with IC50 values of 6-17.4 nM against P. falciparum drug-sensitive and drug-resistant strains as well as potent therapeutic activity in a mouse models of malaria with ED50/90/99 values of 0.6/0.9/1.4 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.
Antimicrobial Agents and Chemotherapy 06/2014; · 4.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Preventing relapses of Plasmodium vivax malaria through a radical cure depends on use of the 8-aminoquinoline primaquine, which is associated with safety and compliance issues. For future malaria eradication strategies new, safer radical curative compounds that efficiently kill dormant liver stages (hypnozoites) will be essential. A new compound with potential radical cure activity was identified using a low throughput assay of in vitro cultured hypnozoite-forms of Plasmodium cynomolgi (an excellent and accessible model for P. vivax). In this assay primary rhesus hepatocytes are infected with P. cynomolgi sporozoites, and exoerythrocytic development is monitored in the presence of compounds. Liver stage cultures are fixed after 6 days, stained with anti-Hsp70 antibodies and the relative proportion of small (hypnozoite) and large (schizont) forms relative to the untreated controls are counted. This assay was used to screen a series of 18 known antimalarials and 14 new non-8-aminoquinolines (preselected for blood and/or liver stage activity) in three-point tenfold dilutions (0.1, 1 and 10 μM final concentration). A novel compound, designated KAI407 showed an activity profile similar to primaquine (PQ), efficiently killing the earliest stages of the parasites that become either primary hepatic schizonts or hypnozoites (IC50 for hypnozoites KAI407: 0.69 μM and PQ: 0.84 μM, for developing liver stages KAI407: 0.64 μM and PQ 0.37 μM). When given as causal prophylaxis, a single oral dose of 100 mg/kg prevented blood stage parasitemia in mice. From these results we conclude that KAI407 may represent a new compound class for P. vivax malaria prophylaxis and potentially radical cure.
Antimicrobial Agents and Chemotherapy 12/2013; · 4.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: New chemotherapeutic compounds against multidrug-resistant Mycobacterium tuberculosis (Mtb) are urgently needed to combat drug resistance in tuberculosis (TB). We have identified and characterized the indolcarboxamides as a new class of antitubercular bactericidal agent. Genetic and lipid profiling studies identified the likely molecular target of indolcarboxamides as MmpL3, a transporter of trehalose monomycolate that is essential for mycobacterial cell wall biosynthesis. Two lead candidates, NITD-304 and NITD-349, showed potent activity against both drug-sensitive and multidrug-resistant clinical isolates of Mtb. Promising pharmacokinetic profiles of both compounds after oral dosing in several species enabled further evaluation for efficacy and safety. NITD-304 and NITD-349 were efficacious in treating both acute and chronic Mtb infections in mouse efficacy models. Furthermore, dosing of NITD-304 and NITD-349 for 2 weeks in exploratory rat toxicology studies revealed a promising safety margin. Finally, neither compound inhibited the activity of major cytochrome P-450 enzymes or the hERG (human ether-a-go-go related gene) channel. These results suggest that NITD-304 and NITD-349 should undergo further development as a potential treatment for multidrug-resistant TB.
Science translational medicine 12/2013; 5(214):214ra168. · 14.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: On the basis of the initial success of optimization of a novel series of imidazolopiperazines, a second generation of compounds involving changes in the core piperazine ring was synthesized to improve antimalarial properties. These changes were carried out to further improve the potency and metabolic stability of the compounds by leveraging the outcome of a set of in vitro metabolic identification studies. The optimized 8,8-dimethyl imidazolopiperazine analogues exhibited improved potency, in vitro metabolic stability profile and, as a result, enhanced oral exposure in vivo in mice. The optimized compounds were found to be more efficacious than the current antimalarials in a malaria mouse model. They exhibit moderate oral exposure in rat pharmacokinetic studies to achieve sufficient multiples of the oral exposure at the efficacious dose in toxicology studies.
Journal of Medicinal Chemistry 04/2012; 55(9):4244-73. · 5.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Starting from a hit series from a GNF compound library collection and based on a cell-based proliferation assay of Plasmodium falciparum, a novel imidazolopiperazine scaffold was optimized. SAR for this series of compounds is discussed, focusing on optimization of cellular potency against wild-type and drug resistant parasites and improvement of physiochemical and pharmacokinetic properties. The lead compounds in this series showed good potencies in vitro and decent oral exposure levels in vivo. In a Plasmodium berghei mouse infection model, one lead compound lowered the parasitemia level by 99.4% after administration of 100 mg/kg single oral dose and prolonged mice survival by an average of 17.0 days. The lead compounds were also well-tolerated in the preliminary in vitro toxicity studies and represents an interesting lead for drug development.
Journal of Medicinal Chemistry 06/2011; 54(14):5116-30. · 5.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The efficacy of most marketed antimalarial drugs has been compromised by evolution of parasite resistance, underscoring an urgent need to find new drugs with new mechanisms of action. We have taken a high-throughput approach toward identifying novel antimalarial chemical inhibitors of prioritized drug targets for Plasmodium falciparum, excluding targets which are inhibited by currently used drugs. A screen of commercially available libraries identified 5655 low molecular weight compounds that inhibit growth of P. falciparum cultures with EC(50) values below 1.25μM. These compounds were then tested in 384- or 1536-well biochemical assays for activity against nine Plasmodium enzymes: adenylosuccinate synthetase (AdSS), choline kinase (CK), deoxyuridine triphosphate nucleotidohydrolase (dUTPase), glutamate dehydrogenase (GDH), guanylate kinase (GK), N-myristoyltransferase (NMT), orotidine 5'-monophosphate decarboxylase (OMPDC), farnesyl pyrophosphate synthase (FPPS) and S-adenosylhomocysteine hydrolase (SAHH). These enzymes were selected using TDRtargets.org, and are believed to have excellent potential as drug targets based on criteria such as their likely essentiality, druggability, and amenability to high-throughput biochemical screening. Six of these targets were inhibited by one or more of the antimalarial scaffolds and may have potential use in drug development, further target validation studies and exploration of P. falciparum biochemistry and biology.
Molecular and Biochemical Parasitology 01/2011; 175(1):21-9. · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Candidate antibacterials are usually identified on the basis of their in vitro activity. However, the apparent inhibitory activity of new leads can be misleading because most culture media do not reproduce an environment relevant to infection in vivo. In this study, while screening for novel anti-tuberculars, we uncovered how carbon metabolism can affect antimicrobial activity. Novel pyrimidine-imidazoles (PIs) were identified in a whole-cell screen against Mycobacterium tuberculosis. Lead optimization generated in vitro potent derivatives with desirable pharmacokinetic properties, yet without in vivo efficacy. Mechanism of action studies linked the PI activity to glycerol metabolism, which is not relevant for M. tuberculosis during infection. PIs induced self-poisoning of M. tuberculosis by promoting the accumulation of glycerol phosphate and rapid ATP depletion. This study underlines the importance of understanding central bacterial metabolism in vivo and of developing predictive in vitro culture conditions as a prerequisite for the rational discovery of new antibiotics.
[Show abstract][Hide abstract] ABSTRACT: A novel family of 1H-imidazol-2-yl-pyrimidine-4,6-diamines has been identified with potent activity against the erythrocyte-stage of Plasmodium falciparum (Pf), the most common causative agent of malaria. A systematic SAR study resulted in the identification of compound 40 which exhibits good potency against both wild-type and drug resistant parasites and exhibits good in vivo pharmacokinetic properties.
[Show abstract][Hide abstract] ABSTRACT: Screening our in-house compound collection using a cell based Plasmodium falciparum proliferation assay we discovered a known pan-kinase inhibitor scaffold as a hit. Further optimization of this series led us to a novel benzamide scaffold which was devoid of human kinase activity while retaining its antiplasmodial activity. The evolution of this compound series leading to optimized candidates with good cellular potency against multiple strains as well as decent in vivo profile is described in this Letter.