PSI-6206 (RO 2433) (RO2433) is a selective HCV RNA polymerase inhibitor.

PSI-6206 (RO2433), a deaminated derivative of PSI-6130, a potent and selective inhibitor of HCV NS5B polymerase, has been evaluated for its anti-HCV efficacy employing both a cell-based quantitative real-time RT-PCR assay and surrogate bovine viral diarrhea virus (BVDV) assays. It showed no activity or cytotoxicity in these assays. The formation of 5′-triphosphate (TP) forms of PSI-6130 (PSI-6130-TP) and RO2433 (RO2433-TP) progressively increased, achieving steady state levels after 48 hours. Notably, RO2433-TP effectively inhibits RNA synthesis by both the native HCV replicase from HCV replicon cells and the recombinant HCV polymerase NS5B, highlighting its potential mechanism of action against HCV replication.

Protein Kinase Assays: The in vitro kinase assays are performed in 96-well plates (30 μL) at ambient temperature for 15–45 min using the recombinant glutathione S-transferase-fused kinase domains (4-100 ng, depending on specific activity). [γ33P]ATP is used as phosphate donor and polyGluTyr-(4:1) peptide as acceptor. With the exception of protein kinase C-α, cyclin-dependent kinase 1/cycB and protein kinase A are protamine sulfate (200 μg/mL), histone H1 (100 μg/mL), and the heptapeptide Leu-Arg-Arg-Ala-Ser-Leu-Gly (known as Kemptide Bachem) respectively and are used as peptide substrates. Assays are optimized for each kinase using the following ATP concentrations: 1.0 μM (c-Kit, c-Met, c-Fms, c-Raf-1, and RET), 2.0 μM (EGFR, erbB2, ErbB3, and ErbB4), 5.0 μM (c-abl), 8.0 μM (Flt-1, Flt-3, Flt-4, Flk, KDR, FGFR-1, and Tek), 10.0 μM (PDGFR-β, protein kinase C-α, and cyclin-dependent kinase 1), and 20.0 μM (c-Src and protein kinase A). The reaction is terminated by the addition of 20 μL 125 mM EDTA. Thirty μL (c-abl, c-Src, insulin-like growth factor-1R, RET-Men2A, and RET-Men2B) or 40 μL (all other kinases) of the reaction mixture is transferred onto Immobilon-polyvinylidene difluoride membrane, presoaked with 0.5% H3PO4 and mounted on a vacuum manifold. Vacuum is then applied and each well rinsed with 200 μL 0.5% H3PO4. Membranes are removed and washed four times with 1.0% H3PO4 and once with ethanol. Dried membranes are counted after mounting in a Packard TopCount 96-well frame and with the addition of 10 μL/well of Microscint. IC50 values (±SE) are calculated by linear regression analysis of the percentage inhibition and are averages of at least three determinations.