Host-based ribavirin resistance influences hepatitis C virus replication and treatment response

Many individuals infected with hepatitis C virus (HCV) develop a chronic infection, and of those who are treated with pegylated interferon and ribavirin (RBV), many do not respond. While the nucleoside analog RBV improves treatment outcome, and will likely be an important component of therapy with next-generation viral inhibitors, RBV's mechanism is controversial. Most of RBV's proposed mechanisms require RBV import into cells. Therefore, we explored whether host-based RBV resistance develops through reduced cellular uptake, akin to chemotherapy resistance in some cancers. We examined the effect of host-based RBV resistance on HCV replication in cultured hepatoma Huh7.5 liver cells and whether RBV resistance develops in HCV patients. When Huh7.5 cells were exposed to RBV, resistance developed through reduced RBV uptake via the ENT1 nucleoside transporter and antiviral efficacy was reduced. The uptake defect in RBV-resistant cells was specific to RBV, since transport of another ENT1 substrate, cytidine, was unaffected. Importantly, RBV uptake significantly declined in HCV patient peripheral blood mononuclear cells (PBMCs) following 4 weeks of therapy. Furthermore, maintenance of RBV uptake correlated with rapid treatment response. Our results uncovered a novel form of antiviral drug resistance and suggest that host-based RBV resistance develops in HCV patients undergoing therapy and that maintenance of RBV uptake may contribute to rapid viral clearance.