A First-in-Human Trial of GLS4, a Novel Inhibitor of Hepatitis B Virus Capsid Assembly, following Single- and Multiple-Ascending-Oral-Dose Studies with or without Ritonavir in Healthy Adult Volunteers

GLS4 is a novel inhibitor of the hepatitis B virus (HBV) capsid assembly with inhibitory activities against nucleot(s)ide-resistant HBV strains. This study investigated the pharmacokinetics, safety, and tolerability of GLS4 and the effects of food and ritonavir in healthy adults. GLS4 was administered in a single-ascending-dose study over 1 to 240 mg and multiple-ascending-dose study that ranged from 30 mg once daily to 180 mg three times daily. The drug interaction study included sequential design (day 1 for 120 mg GLS4 alone, day 5 for 100 mg ritonavir alone, followed by 9 days of both drugs) and a placebo control (9 days of both 240 mg GLS4 and 100 mg ritonavir). The results showed that the steady-state trough concentration of multiple dosing of GLS4 alone was significantly lower than the 90% effective concentration of 55.7 ng/ml, even with increasing dosing frequency and dosage. An initial dose of 100 mg ritonavir significantly boosted plasma concentration at 24 h of 120 mg GLS4 from 2.40 to 49.8 ng/ml (geometric mean ratio, 20.7; 90% confidence interval, 17.0 to 25.3), while a milder effect was observed on the area under the curve from 0 to 24 h, with a 7.42-fold increase, and on the maximum concentration, with a 4.82-fold increase. The pharmacokinetics change in GLS4 persisted after 9 days of chronic dosing, with a trough concentration of 182 ng/ml. Both single and multiple doses of GLS4 up to 240 mg with or without ritonavir were well tolerated. These results support the investigation of a novel HBV treatment regimen containing GLS4 with 100 mg ritonavir added solely to enhance GLS4 concentrations in plasma. (This study was registered at the China Platform for Registry and Publicity of Drug Clinical Trials [http://www.chinadrugtrials.org.cn] under numbers CTR20132137 and CTR20150230.).