Study of GS-4321 in Healthy Participants and Participants With Chronic Hepatitis Delta Virus

Phase 1/2 Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Antiviral Activity of GS-4321 in Healthy Participants and Participants With Chronic Hepatitis Delta

The goals of this clinical study are to first learn more about safety and dosing of the study drug GS-4321 in healthy participants. The study will then learn about the safety and effectiveness of GS-4321 in participants with chronic hepatitis delta (CHD).

The primary objective of Phase 1 of this study is to evaluate the safety, tolerability and Pharmacokinetics (PK) of the escalating single doses of GS-4321 administered in healthy participants.

The primary objective of Phase 2 of this study is to evaluate the efficacy and safety of the multiple escalating doses of GS-4321 in participants with CHD.

Key Inclusion Criteria:

Part A:

• Participants assigned male or female at birth who are of childbearing potential and engage in heterosexual intercourse must agree to use protocol-specified method(s) of contraception.
• Have a body mass index (BMI) of ≤ 30.0 kg/m2 at screening and at admission.

Part B:

• Participants assigned male or female at birth who are of childbearing potential and engage in heterosexual intercourse must agree to use protocol-specified method(s) of contraception.
• Chronic hepatitis delta (CHD) for ≥ 6 months prior to screening, documented by prior medical history.
• Must be receiving a commercially available entecavir, TAF, or TDF for the treatment of hepatitis B virus (HBV) infection at or prior to enrollment. Coformulation as part of a fixed-dose combination for the treatment of HIV is permitted.
• Non-cirrhotic or compensated cirrhosis.
• Hepatitis delta virus ribonucleic acid (HDV RNA ) > 500 IU/mL at screening.
• Alanine aminotransferase (ALT) level > 1 × Upper limit of normal (ULN), but < 10 × ULN at screening.

Key Exclusion Criteria:

Part A:

• Positive serum or urine pregnancy test.
• Participants with plans to breastfeed during the study period.

Part B:

• Positive serum or urine pregnancy test.
• Participants with plans to breastfeed during the study period.
• Current or previous clinically decompensated liver disease, including coagulopathy, hepatic encephalopathy, and esophageal varices hemorrhage due to HDV or HBV.
• Child-Turcotte-Pugh (CTP)-B or -C or a CTP score of ≥ 7.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.