A randomized phase 1b trial of the active site polymerase inhibitor nucleotide ATI‐2173 in patients with chronic hepatitis B virus infection

ATI‐2173 is an active site polymerase inhibitor nucleotide in development as part of a potentially curative regimen for chronic hepatitis B virus (HBV) infection. This study evaluated the safety, tolerability, pharmacokinetics (PK) and antiviral activity of ATI‐2173. This was a phase 1b, randomized, double‐blind, placebo‐controlled trial in treatment‐naive adults with chronic HBV infection conducted in the Republic of Moldova and Ukraine (ClinicalTrials.gov: NCT04248426). Patients positive for hepatitis B surface antigen were randomized 6:2 to receive once‐daily oral doses of ATI‐2173 10, 25, or 50 mg (n = 6 per dose) or placebo (n = 7) for 28 days, with off‐treatment monitoring for 24 weeks. Endpoints included PK parameters of ATI‐2173 and its metabolite clevudine, maximum reduction from baseline in HBV DNA, and safety and tolerability. Treatment‐emergent adverse events occurred in eight patients (47%) receiving ATI‐2173 and five (71%) receiving placebo; headache was the most common (n = 4). ATI‐2173 PK was generally dose proportional. Systemic clevudine exposure with ATI‐2173 dosing was substantially reduced compared with historical values observed with clevudine administration. On Day 28, mean changes from baseline in HBV DNA were −2.72 to −2.78 log(10) IU/ml with ATI‐2173 and +0.17 log(10) IU/ml with placebo. Off‐treatment sustained viral suppression and decreases in covalently closed circular DNA biomarkers were observed in most patients; one maintained undetectable HBV DNA at 24 weeks off treatment. In this 28‐day monotherapy study, ATI‐2173 demonstrated safety and antiviral activity, with sustained off‐treatment effects and substantially reduced systemic clevudine exposure. These results support evaluation of ATI‐2173 with tenofovir disoproxil fumarate in phase 2 studies.