Danoprevir

Danoprevir (0.29 nM) inhibits the reference genotype 1 NS3/4A protease half-maximally, but a high dose of Danoprevir (10 μM) shows no appreciably inhibition in a panel of 79 proteases, ion channels, transporters, and cell surface receptors. Danoprevir remains bound to and inhibits NS3/4A for more than 5 hours after its initial association. Danoprevir (45 nM) eliminates a patient-derived HCV genotype 1b replicon from hepatocyte-derived Huh7 cells with an EC50 of 1.8 nM. ^[1] In HCV subgenomic replicon cell lines containing the individual mutations, V36M, R109K, and V170A substitutions confer little or no resistance to Danoprevir, but the R155K substitution confers a high level (62-fold increase) of resistance to Danoprevir. ^[2] In Huh7.5 cells transfected with chimeric recombinant virus, Danoprevir shows antiviral inhibition effects against HCV genotypes 1, 4 and 6 with IC50 of 2-3 nM, which are >100-fold lower than genotypes 2/3/5 (280-750 nM). ^[3]

Danoprevir (30 mg/kg) administered to rats or monkeys shows that its concentrations in liver 12 hours after dosing exceed the Danoprevir concentration required to eliminate replicon RNA from cells. ^[1]

• Continuous fluorescent resonance energy transfer (FRET) assay

  The assay buffer contains 25 μM NS4A peptide, 50 mM Tris-HCl, pH 7.5, 15% vol/vol, 10 mM dithiothreitol, and 0.5 μM QXL520-labeled FRET substrate {Ac-DE-Dap(QXL520)-EE-Abu-ψ-[COO]-AS-Cys(5-FAMsp)-NH2}. K2040 enzyme (50 pM) is added to initiate the reaction. Reactions are set up in black 96-well plates, and fluorescence data is collected. Control reactions lacking inhibitors and enzyme are included. Initial rates are calculated from the linear phase of the reaction (up to 1 hour) and are used to obtain IC50. Recovery of activity from preformed Danoprevir-NS3/4A complex is assessed by preincubating 10 nM NS3/4A with a two-fold excess of Danoprevir in 1× assay buffer for 15 min, followed by a rapid 200-fold dilution of the preformed complex into assay buffer containing substrate. A control reaction with the same final conditions without preincubation of NS3/4A and Danoprevir is initiated by the addition of enzyme to an otherwise-complete reaction mixture. Additional control reactions lack either Danoprevir or NS3. The progress of the reactions is followed over 5 hours.

• Cell lines

  Huh7 cells harboring HCV replicon

• Concentrations

  5 pM - 100 nM

• Incubation Time

  48 hours

• Method

  Serially diluted Danoprevir is added to Huh7 cells harboring the K2040 replicon 1 day after cell plating. For antiviral assays, after a 48-hour incubation, intracellular RNA is extracted, and the level of HCV replicon RNA is quantified by reverse transcription (RT)-PCR assay with the primers (5'-CACTCCCCTGTGAGGAACTACTG-3' and 5'-AGGCTGCACGACACTCATACT-3') and a probe (5'-6-FAM-CTTCACGCAGAAAGCGTCTAGCCATGG-MGBNFQ-3' using an ABI Prism 7900 sequence detection system. Here, FAM is 6-carboxyfluorescin and MGBNFQ is a molecular-groove binding non-fluorescence quencher specific to the HCV 5' untranslated region. Single-tube reactions are performed using the TaqMan Gold RT-PCR kit. Triplicate reactions for the RNA standards and samples are performed in 50 μL with 5 μL intracellular RNA (50 ng). RT is carried out at 48 °C for 30 min followed by 10 min at 95 °C. The PCR is run as follows: 15 seconds at 95 °C and 1 min at 60 °C for 40 cycles. Each RNA concentration is determined in triplicate. The absolute concentration of replicon RNA is calculated based on its signal relative to that of a standard curve generated by known concentrations of an in vitro-transcribed RNA corresponding to a genotype 1b 5' untranslated region. Replicon levels in the presence of Danoprevir are fitted to a four-parameter logistic function to obtain EC50.

• Animal Models

  Sprague-Dawley rats, Cynomolgus monkeys

• Dosages

  30 mg/kg

• Administration

  Oral gavage