Background & Aims: Apoptosis signal-regulating kinase 1 (ASK1) plays a key role in hepatocyte injury, inflammation, and fibrosis in non-alcoholic steatohepatitis (NASH). We evaluated the safety and antifibrotic effect of selonsertib, a selective inhibitor of ASK1, in patients with advanced fibrosis due to NASH., Methods: We conducted 2 randomized, double-blind, placebo-controlled, phase III trials of selonsertib in patients with NASH and bridging fibrosis (F3, STELLAR-3) or compensated cirrhosis (F4, STELLAR-4). Patients were randomized 2:2:1 to receive selonsertib 18 mg, selonsertib 6 mg, or placebo once daily for 48 weeks. Liver biopsies were performed at screening and week 48 and non-invasive tests of fibrosis (NITs) were evaluated. The primary efficacy endpoint was the proportion of patients with ≥1-stage improvement in fibrosis without worsening of NASH at week 48. Additional endpoints included changes in NITs, progression to cirrhosis (in STELLAR-3), and liver-related clinical events., Results: Neither trial met the primary efficacy endpoint. In STELLAR-3, fibrosis improvement without worsening of NASH was observed in 10% (31/322, p = 0.49 vs. placebo), 12% (39/321, p = 0.93 vs. placebo), and 13% (21/159) of patients in the selonsertib 18 mg, selonsertib 6 mg, and placebo groups, respectively. In STELLAR-4, the primary endpoint was achieved in 14% (51/354; p = 0.56), 13% (45/351; p = 0.93), and 13% (22/172) of patients, respectively. Although selonsertib led to dose-dependent reductions in hepatic phospho-p38 expression indicative of pharmacodynamic activity, it had no significant effect on liver biochemistry, NITs, progression to cirrhosis, or adjudicated clinical events. The rates and types of adverse events were similar among selonsertib and placebo groups., Conclusions: Forty-eight weeks of selonsertib monotherapy had no antifibrotic effect in patients with bridging fibrosis or compensated cirrhosis due to NASH., Lay Summary: Patients with non-alcoholic steatohepatitis (NASH) can develop scarring of the liver (fibrosis), including cirrhosis, which increases the risks of liver failure and liver cancer. We tested whether 48 weeks of treatment with selonsertib reduced fibrosis in patients with NASH and advanced liver scarring. We did not find that selonsertib reduced fibrosis in these patients., Trial Registration Details: Clinicaltrials.gov numbers NCT03053050 and NCT03053063., Competing Interests: Conflict of interest Dr. Harrison consults for, advises, and has received grants from, and owns stock in Galectin, GENFIT, and Madrigal. He consults for, advises, and has received grants from Axcella, Cirius, CymaBay, Galmed, Gilead, HighTide, Intercept, NGM, Novartis, Novo Nordisk, and Pfizer. He consults for, advises, and owns stock in Akero and Metacrine. He consults for and advises 3V Bio, Albireo, Blade, Bristol-Myers Squibb, CLDF, ContraVir, Consynance, Corcept, Echosens, Gelesis, HistoIndex, Innovate, IQVIA, Perspectum, Poxel, Prometheus, Prometic, Terns, and Lipocine. He is on the speakers' bureau for Alexion. He received grants from Conatus, Immuron, Second Genome, and Tobira/Allergan. Dr. Wong has received honoraria from Echosens and Gilead Sciences; consults for and advises AbbVie, Merck, Gilead Sciences, NovaMedica, Janssen Pharmaceuticals; and has received research funding from Gilead Sciences, Roche; and compensation for travel, accommodations, and other expenses from Gilead Sciences, Otsuka Pharmaceutical. Dr. Okanoue: None. Dr. Bzowej has received grants from Gilead, Bristol-Myers Squibb, Allergan, and Cirius. Dr. Vuppalanchi: None. Dr. Younes advises, is on the speakers' bureau for, and has received grants from Gilead. He is on the speakers' bureau for and received grants from AbbVie. He received grants from Intercept, Bristol-Myers Squibb, NGM, Madrigal, CymaBay, Allergan, Novartis, Axcella, Zydus, Cato, Novo Nordisk, and Cirius. Dr. Kohli received grants from Gilead. Dr. Sarin: None. Dr. Caldwell has received grants from Gilead, Genfit, Galmed, NGM, Conatus, Immuron, VitalTherapy, and Intercept. Dr. Alkhouri advises, is on the speakers' bureau for, and has received grants from Gilead and Intercept. He advises and has received grants from Allergan. He has received grants from GENFIT, Madrigal, and Galmed. Dr. Shiffman advises, is on the speakers' bureau for, and has received grants from Bristol-Myers Squibb, Dova, Gilead, Intercept, and Valeant. He advises and is on the speakers' bureau for AbbVie, Bayer, and Shionogi. He advises and has received grants from HepQuant. He advises Mallinckrodt. He is on the speakers' bureau for Eisai and Daiichi Sankyo. He has received grants from Afimmune, Conatus, CymaBay, Enanta, Exalenz, GENFIT, and Genkyotex. Drs. Camargo, Li, Kersey, Jia, Zhu, Djedjos, Subramanian, Myers are employed by and own stock in Gilead. Drs. Li and Djedjos were employed by Gilead at the time the study was conducted. Dr. Gunn has received research grant support from Conatus, CymaBay, Galectin, Gilead, and Immuron and has received speaker fees from Abbvie, Gilead, and Salix. Dr. Sheikh has served on the advisory board for BMS, Gilead, Intercept, and AbbVie, has performed research for BMS, Gilead, Merck, Intercept, Pfizer, Genentech, Actelion, Theravance, and Cubist, has served as a speaker for BMS, Gilead, and AbbVie, and owns stock in Gilead. Dr. Anstee consults for, is on the speakers' bureau for, and has received grants from Allergan/Tobira. He consults for and is on the speakers' bureau for GENFIT SA and Gilead. He consults for and has received grants from Novartis and Pfizer. He consults for Acuitas, BBN Cardio, Blade, Cirius, CymaBay, EcoR1, E3Bio, Eli Lilly, Galmed, Grunthal, HistoIndex, Indalo, Imperial Innovations, Intercept, Inventiva, IQVIA, Janssen, Kenes, Madrigal, MedImmune, Metacrine, NewGene, NGM, North Sea, Novo Nordisk, Poxel, ProSciento, Raptor, Servier, and Viking. He is on the speakers' bureau for Bristol-Myers Squibb, Clinical Care Options, Falk, Fishawack, Integritas, and Medscape. He has received grants from AstraZeneca, GlaxoSmithKline, Glympse Bio, and Vertex. He has received royalties from Elsevier. Dr. Romero-Gomez consults for, advises, and is on the speakers' bureau for Gilead. He has received restricted and unrestricted research grants from Gilead and Intercept. Dr. Trauner consults for, is on the speakers' bureau for, and has received grants from Falk, Gilead, and MSD. He consults for and has received grants from Intercept and Albireo. He is on the speakers' bureau for and has received grants from Roche. He consults for Phenex, Novartis, Bristol-Myers Squibb, and Regulus. He has received grants from Takeda. Dr. Goodman has received grants from Gilead, Intercept, Novartis, Bristol-Myers Squibb, and Allergan. Dr. Lawitz is on the speakers' bureau for and has received grants from Gilead and AbbVie. Dr. Alkhouri advises, is on the speakers' bureau for, and has received grants from Gilead and Intercept. He advises and has received grants from Allergan. He has received grants from GENFIT, Madrigal, and Galmed. Dr. Younossi consults for Gilead, Intercept, BMS, NovoNordisk, Shinogi, and Novartis. Please refer to the accompanying ICMJE disclosure forms for further details., (Copyright © 2020. Published by Elsevier B.V.)