Clinical and in vitro resistance to GS-9669, a thumb site II nonnucleoside inhibitor of the hepatitis C virus NS5B polymerase.

Treatment with GS-9669, a novel nonnucleoside inhibitor (site II) of hepatitis C virus (HCV) nonstructural 5B (NS5B) polymerase, resulted in significant antiviral activity in HCV genotype (GT) 1 patients dosed at 50 and 500 mg once daily (QD) and at 50, 100, and 500 mg twice daily (BID) for 3 days. This report characterizes the virologic resistance to GS-9669 in vitro and in GT1 HCV-infected patients from a phase I clinical study. An in vitro resistance selection study with GS-9669 revealed substitutions at several NS5B residues that conferred resistance. The M423 variants were selected at low drug concentrations (5× the 50% effective concentration [EC50]), and the L419, R422, and I482 variants were selected at higher drug concentrations (20× the EC50). During the phase I clinical study, substitutions at NS5B residues 419, 422, and 486 were the predominant changes associated with GS-9669 monotherapy. Substitutions at position 423 were observed only in GT1a patients in the low-dose groups (50 and 100 mg BID). Interestingly, four HCV patients had substitutions at position 423 at baseline. Consistent with the low resistance level at this position, three patients with M423I or M423V at baseline achieved >2-log10 reductions of HCV RNA when treated with 100 mg BID or with 500 mg QD or BID of GS-9669. The fourth patient, who had the M423V substitution at baseline, had a 4.4-log10 reduction of HCV RNA with 500 mg BID of GS-9669. Phenotypic analyses demonstrated that the viral isolates with multiple GS-9669 resistance-associated variants have reduced susceptibility to GS-9669 and lomibuvir (VX-222) but are not cross-resistant to other classes of HCV inhibitors. (This study has been registered at ClinicalTrials.gov under registration no. NCT01431898.).

Localized inhibition of platelets and platelet derived growth factor by a matrix targeted glycan mimetic significantly attenuates liver fibrosis.

New therapeutic strategies are needed for the growing unmet clinical needs in liver disease and fibrosis. Platelet activation and PDGF activity are recognized as important therapeutic targets; however, no therapeutic approach has yet addressed these two upstream drivers of liver fibrosis. We therefore designed a matrix-targeting glycan therapeutic, SBR-294, to inhibit collagen-mediated platelet activation while also inhibiting PDGF activity. Herein we describe the synthesis and characterization of SBR-294 and demonstrate its potential therapeutic benefits in vitro and in vivo. In vitro SBR-294 was found to bind collagen (EC50 = 23 nM), thereby inhibiting platelet-collagen engagement (IC50 = 60 nM). Additionally, SBR-294 was found to bind all PDGF homodimeric isoforms and to inhibit PDGF-BB mediated hepatic stellate cell activation and proliferation. Translating these mechanisms in vivo, SBR-294 reduced fibrosis by up to 54% in the CCl4 mouse model (p = 0.0004), as measured by Sirius red histological analysis. Additional fibrosis measurements were also supportive of the therapeutic benefit in this model. These results support the therapeutic benefit of platelet and PDGF antagonism and warrant further investigation of SBR-294 as a potential treatment for liver fibrosis.