Characterization of a dengue NS4B inhibitor originating from an HCV small molecule library.

Dengue is the most important mosquito-transmitted viral disease and a major global health concern. Over the last decade, dengue virus (DENV) drug discovery and development has intensified, however, this has not resulted in approved DENV-specific antiviral treatments yet. DENV and hepatitis C virus (HCV) belong to the same Flaviviridae family and, in contrast to DENV, antiviral treatments for HCV have been licensed. Therefore, applying the knowledge gained on anti-HCV drugs may foster the discovery and development of dengue antiviral drugs. Here, we screened a library of compounds with established anti-HCV activity in a DENV-2 sub-genomic replicon inhibition assay and selected compounds with single-digit micromolar activity. These compounds were advanced into a hit-to-lead medicinal chemistry program resulting in lead compound JNJ-1A, which inhibited the DENV-2 sub-genomic replicon at 0.7 µM, in the absence of cytotoxicity. In addition, JNJ-1A showed equipotent antiviral activity against DENV serotypes 1, 2, and 4. In vitro resistance selection experiments with JNJ-1A induced mutation T108I in non-structural protein 4B (NS4B), pointing towards a mechanism of action linked to this protein. Collectively, we described the discovery and characterization of a novel DENV inhibitor potentially targeting NS4B.

Biochemical screening assays to identify HIV-1 integrase inhibitors.

Human immunodeficiency virus type 1 (HIV-1) integrase is, in addition to reverse transcriptase and protease, an important enzymatic target for antiretroviral drug development. Integrase plays a critical role in the HIV-1 life cycle coordinating the integration of the reverse-transcribed viral DNA into the host genome. This integration step is the net result of two consecutive integrase-related processes. First, integrase removes a dinucleotide from the 3' viral DNA ends in a process called 3'-processing. Next, in a process called strand transfer, the viral DNA is integrated into the host genomic DNA. Early on, biochemical assays have played a critical role in understanding the function of HIV-1 integrase and the discovery of small-molecule inhibitors. In this chapter we describe two biochemical assays to identify inhibitors of the 3'-processing and strand transfer process of HIV-1 integrase.

Cell-based antiviral assays for screening and profiling inhibitors against dengue virus.

Dengue, a mosquito-borne virus of the Flaviviridae family, is reemerging as one of the most important human pathogens in tropical and subtropical regions of the world. It is estimated that 2.5 billion people live in areas at risk for transmission of dengue virus (DENV). Furthermore, it causes significant morbidity and mortality with 50-100 million infections per year. Currently, there are no vaccines commercially available and no effective antiviral drugs for treatment of DENV infections. In this chapter, we describe a plaque reduction assay and a cell-based high-throughput antiviral assay for identifying inhibitors against DENV. The latter is a homogeneous high-throughput assay that has been fully validated according to the Food and Drug Administration (FDA) guidelines for assay validation and can be used for screening compound libraries.

A duplex real-time RT-PCR assay for profiling inhibitors of four dengue serotypes.

We have developed a duplex real-time RT-PCR assay for profiling antiviral inhibitors of four dengue virus (DENV) serotypes. In this assay, the primers and the probe for amplifying DENV were designed in the conserved regions of the genome after aligned more than 300 nucleotide sequences of four dengue serotypes deposited in the GeneBank. To discriminate the antiviral activity from the cytotoxicity of compounds, a housekeeping gene of the Vero cells, ß-actin, was used to design the primers and the probe for the second set of PCR as an internal control, which is used to normalize the RNA levels of dengue-specific PCR due to the cellular toxicity of test compounds. For compound profiling, the duplex PCR is performed using LightCycler(®) in a single tube to simultaneously amplify both the dengue target gene and the Vero cell housekeeping gene from the compound-treated Vero cell lysates. This assay was validated against a panel of reference compounds. The results show that the universal primers and probe in this duplex RT-PCR assay can efficiently amplify all four dengue serotypes and that the PCR efficiency for both the dengue target gene and the Vero cells ß-actin gene is 100%.

A combined genotypic and phenotypic human immunodeficiency virus type 1 recombinant virus assay for the reverse transcriptase and integrase genes.

With the approval of the first HIV-1 integrase inhibitor raltegravir and a second one in phase III clinical development (elvitegravir), genotypic and phenotypic resistance assays are required to guide antiretroviral therapy and to investigate treatment failure. In this study, a genotypic and phenotypic recombinant virus assay was validated for determining resistance against integrase inhibitors. The assays are based on the amplification of a region encompassing not only HIV-1 integrase, but also reverse transcriptase and RNAseH. The overall amplification success was 85% (433/513) and increased to 93% (120/129) for samples with a viral load above 3 log(10) copies/ml. Both B and non-B HIV-1 subtypes could be genotyped successfully (93%; 52/56 and 100%; 49/49, respectively) and reproducibly. The phenotypic assay showed a high success rate (96.5%; 139/144) for subtype B (100%; 19/19) and non-B subtypes (92%; 45/49), and was found to be accurate and reproducible as assessed using well-characterized integrase mutants. Using both assays, baseline resistance to raltegravir and elvitegravir in subtype B and non-B HIV-1 strains selected at random was not observed, although integrase polymorphisms were present at varying prevalence. Biological cutoff values were found to be 2.1 and 2.0 for raltegravir and elvitegravir, respectively. In summary, a genotypic and phenotypic integrase resistance assay was validated successfully for accuracy, reproducibility, analytical and clinical sensitivity, and dynamic range.