The Nucleoside Analogue NITD008 , Alone or Combined With Ribavirin, Potently Reduces Hepatitis E Virus Infection in Humanised Mice

Background and Aims Hepatitis E virus (HEV) infection is becoming increasingly clinically relevant worldwide, but no approved antiviral therapy currently exists. Ribavirin (RBV) is used off‐label for immunosuppressed patients with chronic hepatitis E, although it is effective in only 80% of patients and linked to side effects. The nucleoside analogue NITD008 was shown to be effective against a broad range of RNA viruses. We aimed to evaluate the efficacy of NITD008, alone or in combination with RBV, in humanised mice stably infected with HEV. Methods Mice received either NITD008 alone (20 mg/Kg/day) by oral gavage for up to 2 weeks, or 5 mg/Kg NITD008 alone or in combination with RBV (50 mg/Kg). Viral changes were determined in faeces, blood and intrahepatically. Results NITD008 efficiently reduced HEV loads to undetectable levels in serum and by > 4log 10 in faeces within 1 week. Intrahepatic analysis showed a ∆log 10 : 2.5 reduction in HEV RNA levels in treated mice compared to controls after 2 weeks. Imaging showed fewer HEV‐RNA‐positive human hepatocytes in treated mice. NITD008 did not increase serum markers of hepatocyte death. Combination therapy induced stronger suppression of HEV RNA in faeces (∆log 10 : 5.02) than RBV monotherapy (∆log 10 : 1.08), despite lower NITD008 doses. Conclusions This study demonstrates the non‐toxicity of NITD008 towards human hepatocytes and more potent antiviral activity compared to RBV in HEV‐infected mice. Combination regimens with RBV showed strong additive activity. The study suggests that HEV clearance may be achieved in immunosuppressed patients by using and further developing this class of direct antiviral drugs.