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.

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.

Growing evidence suggests that the presence of a subpopulation of hypoxic non-replicating, phenotypically drug-tolerant mycobacteria is responsible for the prolonged duration of tuberculosis treatment. The discovery of new antitubercular agents active against this subpopulation may help in developing new strategies to shorten the time of tuberculosis therapy. Recently, the maintenance of a low level of bacterial respiration was shown to be a point of metabolic vulnerability in Mycobacterium tuberculosis. Here, we describe the development of a hypoxic model to identify compounds targeting mycobacterial respiratory functions and ATP homeostasis in whole mycobacteria. The model was adapted to 1,536-well plate format and successfully used to screen over 600,000 compounds. Approximately 800 compounds were confirmed to reduce intracellular ATP levels in a dose-dependent manner in Mycobacterium bovis BCG. One hundred and forty non-cytotoxic compounds with activity against hypoxic non-replicating M. tuberculosis were further validated. The resulting collection of compounds that disrupt ATP homeostasis in M. tuberculosis represents a valuable resource to decipher the biology of persistent mycobacteria.

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-observableadverse-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.Dengue virus (DENV), the causative agent for dengue fever, is a mosquito-borne pathogen with significant impacts on public health and economy. It was confined to South East Asia in the 1950s, but since then, DENV has increased in its spread in geographic areas and in the number of infected patients (6). It is now estimated that 2.5 billion people are at risk for DENV infection, with about 50 million to 100 million human infections, leading to over 20,000 deaths each year. The disease spectrum ranges from mild undifferentiated fever to lifethreatening dengue hemorrhage fever (DHF) and dengue shock syndrome (DSS) (18). There is no clinically approved vaccine or antiviral therapy for DENV. Thus, DENV presents an increasingly unmet medical need to develop anti-DENV therapeutics.DENV belongs to the family of Flaviviridae, which contains three genera, Hepacivirus, Pestivirus, and Flavivirus. The genus Flavivirus contains many important human pathogens, such as West Nile virus (WNV), yellow fever virus (YFV), Japanese encephalitis virus (JEV), tick-borne encephalitis virus (TBEV), and DENV (4). Dengue virus is further subdivided into four serologically distinct serotypes, named dengue virus serotypes 1 to 4. The DENV genome consists of a positivestrand ...

We recently reported that (2R,3R,4R,5R)-2-(4-amino-pyrrolo[2,3-d]pyrimidin-7-yl)-3-ethynyl-5-hydroxymethyl-tetrahydro-furan-3,4-diol is a potent inhibitor of dengue virus (DENV), with 50% effective concentration (EC 50 ) and cytotoxic concentration (CC 50 ) values of 0.7 M and >100 M, respectively. Here we describe the synthesis, structure-activity relationship, and antiviral characterization of the inhibitor. In an AG129 mouse model, a single-dose treatment of DENV-infected mice with the compound suppressed peak viremia and completely prevented death. Mode-of-action analysis using a DENV replicon indicated that the compound blocks viral RNA synthesis. Recombinant adenosine kinase could convert the compound to a monophosphate form. Suppression of host adenosine kinase, using a specific inhibitor (iodotubercidin) or small interfering RNA (siRNA), abolished or reduced the compound's antiviral activity in cell culture. Studies of rats showed that 14 C-labeled compound was converted to mono-, di-, and triphosphate metabolites in vivo. Collectively, the results suggest that this adenosine inhibitor is phosphorylated to an active (triphosphate) form which functions as a chain terminator for viral RNA synthesis.The family Flaviviridae consists of three genera, Flavivirus, Pestivirus, and Hepacivirus. Many viruses from the genus Flavivirus are arthropod-borne and cause significant human diseases. The four serotypes of dengue virus (DENV) alone pose a health threat to 2.5 billion people worldwide, leading to 50 to 100 million human infections and 500,000 cases of dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) each year (11). Besides DENV, other flaviviruses, such as West Nile virus (WNV), Japanese encephalitis virus (JEV), yellow fever virus (YFV), and tick-borne encephalitis virus (TBEV), also cause frequent outbreaks throughout the world. No clinically approved antiviral therapy is currently available for treatment of flavivirus infections. Human vaccines are available only for YFV, JEV, and TBEV. The development of a successful DENV vaccine has been challenging due to the facts that (i) the vaccine should simultaneously induce a long-lasting protection against all four DENV serotypes and (ii) an incompletely immunized individual may be sensitized to the lifethreatening DHF or DSS. The challenge associated with the development of a vaccine underlines the importance of antiviral development for DENV and other flaviviruses.The flavivirus genome is a single-strand RNA of plus-sense polarity. The single open reading frame from the 11-kb viral genome encodes three structural proteins (capsid [C], premembrane [prM], and envelope [E]) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). Nonstructural proteins are responsible for viral replication. Of those, NS3 and NS5 have enzymatic activities. The N-terminal domain of NS3 (with NS2B as a cofactor) functions as a serine protease, and the C-terminal domain acts as an RNA helicase, an RNA triphosphatase, and an NTPase (10,34,35). The N-...

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