Danoprevir (RG7227) is a peptidomimetic inhibitor of the NS3/4A protease(IC50=0.2-3.5 nM) of hepatitis C virus (HCV).

HCV NS3/4A protease:0.2 nM-3.5 nM

In rats or monkeys,Danoprevir (30 mg/kg) was administered.

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) glycerol, 0.6 mM lauryldimethylamine N-oxide, 10 mM dithiothreitol, and 0.5 μM fluorescein/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.

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.(Only for Reference)