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Millions who live in Latin America and sub-Saharan Africa are at risk of trypanosomatid infections, which cause Chagas disease and human African trypanosomiasis (HAT). Improved HAT treatments are available, but Chagas disease therapies rely on two nitroheterocycles, which suffer from lengthy drug regimens and safety concerns that cause frequent treatment discontinuation. We performed phenotypic screening against trypanosomes and identified a class of cyanotriazoles (CTs) with potent trypanocidal activity both in vitro and in mouse models of Chagas disease and HAT. Cryo-electron microscopy approaches confirmed that CT compounds acted through selective, irreversible inhibition of trypanosomal topoisomerase II by stabilizing double-stranded DNA:enzyme cleavage complexes. These findings suggest a potential approach toward successful therapeutics for the treatment of Chagas disease.

Human African Trypanosomiasis (HAT) is a vector-borne disease caused by kinetoplastid parasites of the Trypanosoma genus. The disease proceeds in two stages, with a hemolymphatic blood stage and a meningo-encephalic brain stage. In the latter stage, the parasite causes irreversible damage to the brain leading to sleep cycle disruption and is fatal if untreated. An orally bioavailable treatment is highly desirable. In this study, we present a brain-penetrant, parasite-selective 20S proteasome inhibitor that was rapidly optimized from an HTS singleton hit to drug candidate compound 7 that showed cure in a stage II mouse efficacy model. Here, we describe hit expansion and lead optimization campaign guided by cryo-electron microscopy and an in silico model to predict the brain-to-plasma partition coefficient K p as an important parameter to prioritize compounds for synthesis. The model combined with in vitro and in vivo experiments allowed us to advance compounds with favorable unbound brain-to-plasma ratios ( K p,uu ) to cure a CNS disease such as HAT.

A series of 5-aryl-2-amino- i midazo t hia d iazole (ITD) derivatives were identified by a phenotype-based high-throughput screening using a blood stage Plasmodium falciparum ( Pf ) growth inhibition assay. A lead optimization program focused on improving antiplasmodium potency, selectivity against human kinases, and absorption, distribution, metabolism, excretion, and toxicity properties and extended pharmacological profiles culminated in the identification of INE963 ( 1 ), which demonstrates potent cellular activity against Pf 3D7 (EC 50 = 0.006 μM) and achieves "artemisinin-like" kill kinetics in vitro with a parasite clearance time of <24 h. A single dose of 30 mg/kg is fully curative in the Pf -humanized severe combined immunodeficient mouse model. INE963 ( 1 ) also exhibits a high barrier to resistance in drug selection studies and a long half-life ( T 1/2 ) across species. These properties suggest the significant potential for INE963 ( 1 ) to provide a curative therapy for uncomplicated malaria with short dosing regimens. For these reasons, INE963 ( 1 ) was progressed through GLP toxicology studies and is now undergoing Ph1 clinical trials.

Dengue virus (DENV) is a mosquito-borne flavivirus that poses a threat to public health, yet no antiviral drug is available. We performed a high-throughput phenotypic screen using the Novartis compound library and identified candidate chemical inhibitors of DENV. This chemical series was optimized to improve properties such as anti-DENV potency and solubility. The lead compound, NITD-688, showed strong potency against all four serotypes of DENV and demonstrated excellent oral efficacy in infected AG129 mice. There was a 1.44-log reduction in viremia when mice were treated orally at 30 milligrams per kilogram twice daily for 3 days starting at the time of infection. NITD-688 treatment also resulted in a 1.16-log reduction in viremia when mice were treated 48 hours after infection. Selection of resistance mutations and binding studies with recombinant proteins indicated that the nonstructural protein 4B is the target of NITD-688. Pharmacokinetic studies in rats and dogs showed a long elimination half-life and good oral bioavailability. Extensive in vitro safety profiling along with exploratory rat and dog toxicology studies showed that NITD-688 was well tolerated after 7-day repeat dosing, demonstrating that NITD-688 may be a promising preclinical candidate for the treatment of dengue., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Monophosphate prodrug analogs of 2'-deoxy-2'-fluoro-2'- C -methylguanosine have been reported as potent inhibitors of hepatitis C virus (HCV) RNA-dependent RNA polymerase. These prodrugs also display potent anti-dengue virus activities in cellular assays although their prodrug moieties were designed to produce high levels of triphosphate in the liver. Since peripheral blood mononuclear cells (PBMCs) are among the major targets of dengue virus, different prodrug moieties were designed to effectively deliver 2'-deoxy-2'-fluoro-2'- C -methylguanosine monophosphate prodrugs and their corresponding triphosphates into PBMCs after oral administration. We identified a cyclic phosphoramidate, prodrug 17, demonstrating well-balanced anti-dengue virus cellular activity and in vitro stability profiles. We further determined the PBMC concentration of active triphosphate needed to inhibit virus replication by 50% (TP 50 ). Compound 17 was assessed in an AG129 mouse model and demonstrated 1.6- and 2.2-log viremia reductions at 100 and 300 mg/kg twice a day (BID), respectively. At 100 mg/kg BID, the terminal triphosphate concentration in PBMCs exceeded the TP 50 value, demonstrating TP 50 as the target exposure for efficacy. In dogs, oral administration of compound 17 resulted in high PBMC triphosphate levels, exceeding the TP 50 at 10 mg/kg. Unfortunately, 2-week dog toxicity studies at 30, 100, and 300 mg/kg/day showed that "no observed adverse effect level" (NOAEL) could not be achieved due to pulmonary inflammation and hemorrhage. The preclinical safety results suspended further development of compound 17. Nevertheless, present work has proven the concept that an efficacious monophosphate nucleoside prodrug could be developed for the potential treatment of dengue virus infection., (Copyright © 2020 American Society for Microbiology.)

The kinetochore is a macromolecular structure that assembles on the centromeres of chromosomes and provides the major attachment point for spindle microtubules during mitosis. In Trypanosoma brucei, the proteins that make up the kinetochore are highly divergent; the inner kinetochore comprises at least 20 distinct and essential proteins (KKT1-20) that include four protein kinases-CLK1 (also known as KKT10), CLK2 (also known as KKT19), KKT2 and KKT3. Here, we report the identification and characterization of the amidobenzimidazoles (AB) protein kinase inhibitors that show nanomolar potency against T. brucei bloodstream forms, Leishmania and Trypanosoma cruzi. We performed target deconvolution analysis using a selection of 29 T. brucei mutants that overexpress known essential protein kinases, and identified CLK1 as a primary target. Biochemical studies and the co-crystal structure of CLK1 in complex with AB1 show that the irreversible competitive inhibition of CLK1 is dependent on a Michael acceptor forming an irreversible bond with Cys 215 in the ATP-binding pocket, a residue that is not present in human CLK1, thereby providing selectivity. Chemical inhibition of CLK1 impairs inner kinetochore recruitment and compromises cell-cycle progression, leading to cell death. This research highlights a unique drug target for trypanosomatid parasitic protozoa and a new chemical tool for investigating the function of their divergent kinetochores.

A phenotypic whole cell high-throughput screen against the asexual blood and liver stages of the malaria parasite identified a benzimidazole chemical series. Among the hits were the antiemetic benzimidazole drug Lerisetron 1 (IC 50 NF54 = 0.81 μM) and its methyl-substituted analogue 2 (IC 50 NF54 = 0.098 μM). A medicinal chemistry hit to lead effort led to the identification of chloro-substituted analogue 3 with high potency against the drug-sensitive NF54 (IC 50 NF54 = 0.062 μM) and multidrug-resistant K1 (IC 50 K1 = 0.054 μM) strains of the human malaria parasite Plasmodium falciparum . Compounds 2 and 3 gratifyingly showed in vivo efficacy in both Plasmodium berghei and P. falciparum mouse models of malaria. Cardiotoxicity risk as expressed in strong inhibition of the human ether-a-go-go-related gene (hERG) potassium channel was identified as a major liability to address. This led to the synthesis and biological assessment of around 60 analogues from which several compounds with improved antiplasmodial potency, relative to the lead compound 3 , were identified., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Current anti-trypanosomal therapies suffer from problems of longer treatment duration, toxicity and inadequate efficacy, hence there is a need for safer, more efficacious and 'easy to use' oral drugs. Previously, we reported the discovery of the triazolopyrimidine (TP) class as selective kinetoplastid proteasome inhibitors with in vivo efficacy in mouse models of leishmaniasis, Chagas Disease and African trypanosomiasis (HAT). For the treatment of HAT, development compounds need to have excellent penetration to the brain to cure the meningoencephalic stage of the disease. Here we describe detailed biological and pharmacological characterization of triazolopyrimidine compounds in HAT specific assays. The TP class of compounds showed single digit nanomolar potency against Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense strains. These compounds are trypanocidal with concentration-time dependent kill and achieved relapse-free cure in vitro. Two compounds, GNF6702 and a new analog NITD689, showed favorable in vivo pharmacokinetics and significant brain penetration, which enabled oral dosing. They also achieved complete cure in both hemolymphatic (blood) and meningoencephalic (brain) infection of human African trypanosomiasis mouse models. Mode of action studies on this series confirmed the 20S proteasome as the target in T. brucei . These proteasome inhibitors have the potential for further development into promising new treatment for human African trypanosomiasis.

Diarrhoeal disease is responsible for 8.6% of global child mortality. Recent epidemiological studies found the protozoan parasite Cryptosporidium to be a leading cause of paediatric diarrhoea, with particularly grave impact on infants and immunocompromised individuals. There is neither a vaccine nor an effective treatment. Here we establish a drug discovery process built on scalable phenotypic assays and mouse models that take advantage of transgenic parasites. Screening a library of compounds with anti-parasitic activity, we identify pyrazolopyridines as inhibitors of Cryptosporidium parvum and Cryptosporidium hominis. Oral treatment with the pyrazolopyridine KDU731 results in a potent reduction in intestinal infection of immunocompromised mice. Treatment also leads to rapid resolution of diarrhoea and dehydration in neonatal calves, a clinical model of cryptosporidiosis that closely resembles human infection. Our results suggest that the Cryptosporidium lipid kinase PI(4)K (phosphatidylinositol-4-OH kinase) is a target for pyrazolopyridines and that KDU731 warrants further preclinical evaluation as a drug candidate for the treatment of cryptosporidiosis.

Two Plasmodium PI4 kinase (PI4K) inhibitors, KDU691 and LMV599, were selected for in vivo testing as causal prophylactic and radical-cure agents for Plasmodium cynomolgi sporozoite-infected rhesus macaques, based on their in vitro activity against liver stages. Animals were infected with P. cynomolgi sporozoites, and compounds were dosed orally. Both the KDU691 and LMV599 compounds were fully protective when administered prophylactically, and the more potent compound LMV599 achieved protection as a single oral dose of 25 mg/kg of body weight. In contrast, when tested for radical cure, five daily doses of 20 mg/kg of KDU691 or 25 mg/kg of LMV599 did not prevent relapse, as all animals experienced a secondary infection due to the reactivation of hypnozoites in the liver. Pharmacokinetic data show that LMV599 achieved plasma exposure that was sufficient to achieve efficacy based on our in vitro data. These findings indicate that Plasmodium PI4K is a potential drug target for malaria prophylaxis but not radical cure. Longer in vitro culture systems will be required to assess these compounds' activity on established hypnozoites and predict radical cure in vivo., (Copyright © 2016 Zeeman et al.)

Poor pharmacokinetic and toxicity profiles are major reasons for the low rate of advancing lead drug candidates into efficacy studies. The In-silico prediction of primary pharmacokinetic and toxicity properties in the drug discovery and development process can be used as guidance in the design of candidates. In-silico parameters can also be used to choose suitable compounds for in-vivo testing thereby reducing the number of animals used in experiments. At the Novartis Institute for Tropical Diseases, a data set has been curated from in-house measurements in the disease areas of Dengue, Tuberculosis and Malaria. Volume of distribution, half-life, total in-vivo clearance, in-vitro human plasma protein binding and in-vivo oral bioavailability have been measured for molecules in the lead optimization stage in each of these three disease areas. Data for the inhibition of the hERG channel using the radio ligand binding dofetilide assay was determined for a set of 300 molecules in these therapeutic areas. Based on this data, Artificial Neural Networks were used to construct In-silico models for each of the properties listed above that can be used to prioritize candidates for lead optimization and to assist in selecting promising molecules for in-vivo pharmacokinetic studies.

Alleviating the burden of tuberculosis (TB) requires an understanding of the genetic basis that determines the emergence of drug-resistant mutants. PA-824 (pretomanid) is a bicyclic nitroimidazole class compound presently undergoing the phase III STAND clinical trial, despite lacking identifiable genetic markers for drug-specific resistant Mycobacterium tuberculosis. In the present study, we aimed to characterize the genetic polymorphisms of spontaneously generated PA-824-resistant mutant strains by surveying drug metabolism genes for potential mutations. Of the 183 independently selected PA-824-resistant M. tuberculosis mutants, 83% harbored a single mutation in one of five nonessential genes associated with either PA-824 prodrug activation (ddn, 29%; fgd1, 7%) or the tangential F420 biosynthetic pathway (fbiA, 19%; fbiB, 2%; fbiC, 26%). Crystal structure analysis indicated that identified mutations were specifically located within the protein catalytic domain that would hinder the activity of the enzymes required for prodrug activation. This systematic analysis conducted of genotypes resistant to PA-824 may contribute to future efforts in monitoring clinical strain susceptibility with this new drug therapy., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

The four serotypes of dengue virus (DENV-1 to -4) represent the most prevalent mosquito-borne viral pathogens in humans. No clinically approved vaccine or antiviral is currently available for DENV. Here we report a spiropyrazolopyridone compound that potently inhibits DENV both in vitro and in vivo. The inhibitor was identified through screening of a 1.8-million-compound library by using a DENV-2 replicon assay. The compound selectively inhibits DENV-2 and -3 (50% effective concentration [EC50], 10 to 80 nM) but not DENV-1 and -4 (EC50,>20 M). Resistance analysis showed that a mutation at amino acid 63 of DENV-2 NS4B (a nonenzymatic transmembrane protein and a component of the viral replication complex) could confer resistance to compound inhibition. Genetic studies demonstrate that variations at amino acid 63 of viral NS4B are responsible for the selective inhibition of DENV-2 and -3. Medicinal chemistry improved the physicochemical properties of the initial “hit” (compound 1), leading to compound 14a, which has good in vivo pharmacokinetics. Treatment of DENV-2-infected AG129 mice with compound 14a suppressed viremia, even when the treatment started after viral infection. The results have proven the concept that inhibitors of NS4B could potentially be developed for clinical treatment of DENV infection. Compound 14a represents a potential preclinical candidate for treatment of DENV-2- and -3-infected patients.

Objectives: The discovery and development of TB drugs has met limited success, with two new drugs approved over the last 40 years. Part of the difficulty resides in the lack of well-established in vitro or in vivo targets of potency and physicochemical and pharmacokinetic parameters. In an attempt to benchmark and compare such properties for anti-TB agents, we have experimentally determined and compiled these parameters for 36 anti-TB compounds, using standardized and centralized assays, thus ensuring direct comparability across drugs and drug classes., Methods: Potency parameters included growth inhibition, cidal activity against growing and non-growing bacteria and activity against intracellular mycobacteria. Pharmacokinetic parameters included basic physicochemical properties, solubility, permeability and metabolic stability. We then attempted to establish correlations between physicochemical, in vitro and in vivo pharmacokinetic and pharmacodynamic indices to tentatively inform future drug discovery efforts., Results: Two-thirds of the compounds tested showed bactericidal and intramacrophage activity. Most compounds exhibited favourable solubility, permeability and metabolic stability in standard in vitro pharmacokinetic assays. An analysis of human pharmacokinetic parameters revealed associations between lipophilicity and volume of distribution, clearance, plasma protein binding and oral bioavailability. Not surprisingly, most compounds with favourable pharmacokinetic properties complied with Lipinski's rule of five., Conclusions: However, most attempts to detect in vitro-in vivo correlations were unsuccessful, emphasizing the challenges of anti-TB drug discovery. The objective of this work is to provide a reference dataset for the TB drug discovery community with a focus on comparative in vitro potency and pharmacokinetics., (© The Author 2014. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Limited information is available on the pharmacokinetic (PK) and pharmacodynamic (PD) parameters driving the efficacy of antimalarial drugs. Our objective in this study was to determine dose-response relationships of a panel of related spiroindolone analogs and identify the PK-PD index that correlates best with the efficacy of KAE609, a selected class representative. The dose-response efficacy studies were conducted in the Plasmodium berghei murine malaria model, and the relationship between dose and efficacy (i.e., reduction in parasitemia) was examined. All spiroindolone analogs studied displayed a maximum reduction in parasitemia, with 90% effective dose (ED90) values ranging between 6 and 38 mg/kg of body weight. Further, dose fractionation studies were conducted for KAE609, and the relationship between PK-PD indices and efficacy was analyzed. The PK-PD indices were calculated using the in vitro potency against P. berghei (2× the 99% inhibitory concentration [IC99]) as a threshold (TRE). The percentage of the time in which KAE609 plasma concentrations remained at >2× the IC99 within 48 h (%T>TRE) and the area under the concentration-time curve from 0 to 48 h (AUC0-48)/TRE ratio correlated well with parasite reduction (R2=0.97 and 0.95, respectively) but less so for the maximum concentration of drug in serum (Cmax)/TRE ratio (R2=0.88). The present results suggest that for KAE609 and, supposedly, for its analogs, the dosing regimens covering a T>TRE of 100%, AUC0-48/TRE ratio of 587, and a Cmax/TRE ratio of 30 are likely to result in the maximum reduction in parasitemia in the P. berghei malaria mouse model. This information could be used to prioritize analogs within the same class of compounds and contribute to the design of efficacy studies, thereby facilitating early drug discovery and lead optimization programs., (Copyright © 2015, Lakshminarayana et al.)

New chemotherapeutic agents are urgently required to combat the global spread of multidrug-resistant tuberculosis (MDR-TB). The mycobacterial enoyl reductase InhA is one of the few clinically validated targets in tuberculosis drug discovery. We report the identification of a new class of direct InhA inhibitors, the 4-hydroxy-2-pyridones, using phenotypic high-throughput whole-cell screening. This class of orally active compounds showed potent bactericidal activity against common isoniazid-resistant TB clinical isolates. Biophysical studies revealed that 4-hydroxy-2-pyridones bound specifically to InhA in an NADH (reduced form of nicotinamide adenine dinucleotide)-dependent manner and blocked the enoyl substrate-binding pocket. The lead compound NITD-916 directly blocked InhA in a dose-dependent manner and showed in vivo efficacy in acute and established mouse models of Mycobacterium tuberculosis infection. Collectively, our structural and biochemical data open up new avenues for rational structure-guided optimization of the 4-hydroxy-2-pyridone class of compounds for the treatment of MDR-TB., (Copyright © 2015, American Association for the Advancement of Science.)

PA-824 is a bicyclic 4-nitroimidazole, currently in phase II clinical trials for the treatment of tuberculosis. Dose fractionation pharmacokinetic-pharmacodynamic studies in mice indicated that the driver of PA-824 in vivo efficacy is the time during which the free drug concentrations in plasma are above the MIC (fT>MIC). In this study, a panel of closely related potent bicyclic 4-nitroimidazoles was profiled in both in vivo PK and efficacy studies. In an established murine TB model, the efficacy of diverse nitroimidazole analogs ranged between 0.5 and 2.3 log CFU reduction compared to untreated controls. Further, a retrospective analysis was performed for a set of seven nitroimidazole analogs to identify the PK parameters that correlate with in vivo efficacy. Our findings show that the in vivo efficacy of bicyclic 4-nitroimidazoles correlated better with lung PK than with plasma PK. Further, nitroimidazole analogs with moderate-to-high volume of distribution and Lung to plasma ratios of >2 showed good efficacy. Among all the PK-PD indices, total lung T>MIC correlated the best with in vivo efficacy (rs = 0.88) followed by lung Cmax/MIC and AUC/MIC. Thus, lung drug distribution studies could potentially be exploited to guide the selection of compounds for efficacy studies, thereby accelerating the drug discovery efforts in finding new nitroimidazole analogs.

Imidazopyridine 1 was identified from a phenotypic screen against P. falciparum (Pf) blood stages and subsequently optimized for activity on liver-stage schizonts of the rodent parasite P. yoelii (Py) as well as hypnozoites of the simian parasite P. cynomolgi (Pc). We applied these various assays to the cell-based lead optimization of the imidazopyrazines, exemplified by 3 (KAI407), and show that optimized compounds within the series with improved pharmacokinetic properties achieve causal prophylactic activity in vivo and may have the potential to target the dormant stages of P. vivax malaria.

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.

Indole-2-carboxamides have been identified as a promising class of antituberculosis agents from phenotypic screening against mycobacteria. One of the hits, indole-2-carboxamide analog (1), had low micromolar potency against Mycobacterium tuberculosis (Mtb), high mouse liver microsomal clearance, and low aqueous solubility. Structure-activity relationship studies revealed that attaching alkyl groups to the cyclohexyl ring significantly improved Mtb activity but reduced solubility. Furthermore, chloro, fluoro, or cyano substitutions on the 4- and 6-positions of the indole ring as well as methyl substitution on the cyclohexyl ring significantly improved metabolic stability. 39 and 41, the lead candidates, displayed improved in vitro activity compared to most of the current standard TB drugs. The low aqueous solubility could not be mitigated because of the positive correlation of lipophilicity with Mtb potency. However, both compounds displayed favorable oral pharmacokinetic properties in rodents and demonstrated in vivo efficacy. Thus, indole-2-carboxamides represent a promising new class of antituberculosis agents.

Tetrahydropyrazolo[1,5-a]pyrimidine scaffold was identified as a hit series from a Mycobacterium tuberculosis (Mtb) whole cell high through-put screening (HTS) campaign. A series of derivatives of this class were synthesized to evaluate their structure-activity relationship (SAR) and structure-property relationship (SPR). Compound 9 had a promising in vivo DMPK profile in mouse and exhibited potent in vivo activity in a mouse efficacy model, achieving a reduction of 3.5 log CFU of Mtb after oral administration to infected mice once a day at 100 mg/kg for 28 days. Thus, compound 9 is a potential candidate for inclusion in combination therapies for both drug-sensitive and drug-resistant TB.

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.

We describe a novel translation inhibitor that has anti-dengue virus (DENV) activity in vitro and in vivo. The inhibitor was identified through a high-throughput screening using a DENV infection assay. The compound contains a benzomorphan core structure. Mode-of-action analysis indicated that the compound inhibits protein translation in a viral RNA sequence-independent manner. Analysis of the stereochemistry demonstrated that only one enantiomer of the racemic compound inhibits viral RNA translation. Medicinal chemistry was performed to eliminate a metabolically labile glucuronidation site of the compound to improve its in vivo stability. Pharmacokinetic analysis showed that upon a single subcutaneous dosing of 25 mg/kg of body weight in mice, plasma levels of the compound reached a C(max) (maximum plasma drug concentration) above the protein-binding-adjusted 90% effective concentration (EC(90)) value of 0.96 μM. In agreement with the in vivo pharmacokinetic results, treatment of DENV-infected mice with 25 mg/kg of compound once per day reduced peak viremia by about 40-fold. However, mice treated with 75 mg/kg of compound per day exhibited adverse effects. Collectively, our results demonstrate that the benzomorphan compounds inhibit DENV through suppression of RNA translation. The therapeutic window of the current compounds needs to be improved for further development.

The (S)-2-nitro-6-(4-(trifluoromethoxy)benzyloxy)-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine named PA-824 (1) has demonstrated antitubercular activity in vitro and in animal models and is currently in clinical trials. We synthesized derivatives at three positions of the 4-(trifluoromethoxy)benzylamino tail, and these were tested for whole-cell activity against both replicating and nonreplicating Mycobacterium tuberculosis (Mtb). In addition, we determined their kinetic parameters as substrates of the deazaflavin-dependent nitroreductase (Ddn) from Mtb that reductively activates these pro-drugs. These studies yielded multiple compounds with 40 nM aerobic whole cell activity and 1.6 μM anaerobic whole cell activity: 10-fold improvements over both characteristics from the parent molecule. Some of these compounds exhibited enhanced solubility with acceptable stability to microsomal and in vivo metabolism. Analysis of the conformational preferences of these analogues using quantum chemistry suggests a preference for a pseudoequatorial orientation of the linker and lipophilic tail., (© 2011 American Chemical Society)

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.

Cellular α-glucosidases I and II are enzymes that sequentially trim the three terminal glucoses in the N-linked oligosaccharides of viral envelope glycoproteins. This process is essential for the proper folding of viral glycoproteins and subsequent assembly of many enveloped viruses, including dengue virus (DENV). Imino sugars are substrate mimics of α-glucosidases I and II. In this report, we show that two oxygenated alkyl imino sugar derivatives, CM-9-78 and CM-10-18, are potent inhibitors of both α-glucosidases I and II in vitro and in treated animals, and efficiently inhibit DENV infection of cultured human cells. Pharmacokinetic studies reveal that both compounds are well tolerated at doses up to 100mg/kg in rats and have favorable pharmacokinetic properties and bioavailability in mice. Moreover, we showed that oral administration of either CM-9-78 or CM-10-18 reduces the peak viremia of DENV in mice. Interestingly, while treatment of DENV infected mice with ribavirin alone did not reduce the viremia, combination therapy of ribavirin with sub-effective dose of CM-10-18 demonstrated a significantly enhanced antiviral activity, as indicated by a profound reduction of the viremia. Our findings thus suggest that combination therapy of two broad-spectrum antiviral agents may provide a practically useful approach for the treatment of DENV infection., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Recent reports of increased tolerance to artemisinin derivatives--the most recently adopted class of antimalarials--have prompted a need for new treatments. The spirotetrahydro-beta-carbolines, or spiroindolones, are potent drugs that kill the blood stages of Plasmodium falciparum and Plasmodium vivax clinical isolates at low nanomolar concentration. Spiroindolones rapidly inhibit protein synthesis in P. falciparum, an effect that is ablated in parasites bearing nonsynonymous mutations in the gene encoding the P-type cation-transporter ATPase4 (PfATP4). The optimized spiroindolone NITD609 shows pharmacokinetic properties compatible with once-daily oral dosing and has single-dose efficacy in a rodent malaria model.

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.

Dengue virus (DENV) is the most prevalent mosquito-borne viral pathogen that infects humans. Neither a vaccine nor an antiviral therapy is currently available for DENV. Here, we report an adenosine nucleoside prodrug that potently inhibits DENV replication both in cell culture and in a DENV mouse model. NITD449 (2'-C-acetylene-7-deaza-7-carbamoyladenosine) was initially identified as a parental compound that inhibits all four serotypes of DENV with low cytotoxicity. However, in vivo pharmacokinetic studies indicated that NITD449 had a low level of exposure in plasma when dosed orally. To increase the oral bioavailability, we covalently linked isobutyric acids to the 3'- and 5'-hydroxyl groups of ribose via ester linkage to NITD449, leading to the prodrug NITD203 (3',5'-O-diisobutyryl-2'-C-acetylene-7-deaza-7-carbamoyl-adenosin). Pharmacokinetic analysis showed that upon oral dosing of the prodrug, NITD203 was readily converted to NITD449, resulting in improved exposure of the parental compound in plasma in both mouse and rat. In DENV-infected AG129 mice, oral dosing of the prodrug at 25 mg/kg of body weight reduced peak viremia by 30-fold. Antiviral spectrum analysis showed that NITD203 inhibited various flaviviruses (DENV, yellow fever virus, and West Nile virus) and hepatitis C virus but not Chikungunya virus (an alphavirus). Mode-of-action analysis, using a luciferase-reporting replicon, indicated that NITD203 inhibited DENV RNA synthesis. Although NITD203 exhibited potent in vitro and in vivo efficacies, the compound could not reach a satisfactory no-observable-adverse-effect level (NOAEL) in a 2-week in vivo toxicity study. Nevertheless, our results demonstrate that a prodrug approach using a nucleoside analog could potentially be developed for flavivirus antiviral therapy.

The antiplasmodial activity of a series of spirotetrahydro beta-carbolines is described. Racemic spiroazepineindole (1) was identified from a phenotypic screen on wild type Plasmodium falciparum with an in vitro IC(50) of 90 nM. Structure-activity relationships for the optimization of 1 to compound 20a (IC(50) = 0.2 nM) including the identification of the active 1R,3S enantiomer and elimination of metabolic liabilities is presented. Improvement of the pharmacokinetic profile of the series translated to exceptional oral efficacy in the P. berghei infected malaria mouse model where full cure was achieved in four of five mice with three daily doses of 30 mg/kg.

Drug resistance against dihydrofolate reductase (DHFR) inhibitors-such as pyrimethamine (PM)-has now spread to almost all regions where malaria is endemic, rendering antifolate-based malaria treatments highly ineffective. We have previously shown that the di-amino quinazoline QN254 [5-chloro-N'6'-(2,5-dimethoxy-benzyl)-quinazoline-2,4,6-triamine] is active against the highly PM-resistant Plasmodium falciparum V1S strain, suggesting that QN254 could be used to treat malaria in regions with a high prevalence of antifolate resistance. Here, we further demonstrate that QN254 is highly active against Plasmodium falciparum clinical isolates, displaying various levels of antifolate drug resistance, and we provide biochemical and structural evidence that QN254 binds and inhibits the function of both the wild-type and the quadruple-mutant (V1S) forms of the DHFR enzyme. In addition, we have assessed QN254 oral bioavailability, efficacy, and safety in vivo. The compound displays favorable pharmacokinetic properties after oral administration in rodents. The drug was remarkably efficacious against Plasmodium berghei and could fully cure infected mice with three daily oral doses of 30 mg/kg. In the course of these efficacy studies, we have uncovered some dose limiting toxicity at higher doses that was confirmed in rats. Thus, despite its relative in vitro selectivity toward the Plasmodium DHFR enzyme, QN254 does not show the adequate therapeutic index to justify its further development as a single agent.

Dengue virus (DENV), a mosquito-borne flavivirus, is a major public health threat. The virus poses risk to 2.5 billion people worldwide and causes 50 to 100 million human infections each year. Neither a vaccine nor an antiviral therapy is currently available for prevention and treatment of DENV infection. Here, we report a previously undescribed adenosine analog, NITD008, that potently inhibits DENV both in vitro and in vivo. In addition to the 4 serotypes of DENV, NITD008 inhibits other flaviviruses, including West Nile virus, yellow fever virus, and Powassan virus. The compound also suppresses hepatitis C virus, but it does not inhibit nonflaviviruses, such as Western equine encephalitis virus and vesicular stomatitis virus. A triphosphate form of NITD008 directly inhibits the RNA-dependent RNA polymerase activity of DENV, indicating that the compound functions as a chain terminator during viral RNA synthesis. NITD008 has good in vivo pharmacokinetic properties and is biologically available through oral administration. Treatment of DENV-infected mice with NITD008 suppressed peak viremia, reduced cytokine elevation, and completely prevented the infected mice from death. No observed adverse effect level (NOAEL) was achieved when rats were orally dosed with NITD008 at 50 mg/kg daily for 1 week. However, NOAEL could not be accomplished when rats and dogs were dosed daily for 2 weeks. Nevertheless, our results have proved the concept that a nucleoside inhibitor could be developed for potential treatment of flavivirus infections.

Accurate predictions of human pharmacokinetic and pharmacodynamic (PK/PD) profiles are critical in early drug development, as safe, efficacious, and "developable" dosing regimens of promising compounds have to be identified. While advantages of successful integration of preclinical PK/PD data in the "anticipation" of human doses (AHD) have been recognized, pharmaceutical scientists have faced difficulties with practical implementation, especially for PK/PD profile projections of compounds with challenging absorption, distribution, metabolism, excretion and formulation properties. In this article, practical projection approaches for formulation-dependent human PK/PD parameters and profiles of Biopharmaceutics Classification System classes I-IV drugs based on preclinical data are described. Case examples for "AHD" demonstrate the utility of preclinical and clinical PK/PD modeling for formulation risk identification, lead candidate differentiation, and prediction of clinical outcome. The application of allometric scaling methods and physiologically based pharmacokinetic approaches for clearance or volume of distribution projections is described using GastroPlus. Methods to enhance prediction confidence such as in vitro-in vivo extrapolations in clearance predictions using in vitro microsomal data are discussed. Examples for integration of clinical PK/PD and formulation data from frontrunner compounds via "reverse pharmacology strategies" that minimize uncertainty with PK/PD predictions are included. The use of integrated softwares such as GastroPlus in combination with established PK projection methods allow the projection of formulation-dependent preclinical and human PK/PD profiles required for compound differentiation and development risk assessments.