Clinical Proof of Concept for a Novel Hepatocyte-Targeting GalNAc-siRNA Conjugate

Abstract

Advancement of RNAi-based therapeutics depends on effective delivery to the site of protein synthesis. Although intravenously administered, multi-component delivery vehicles have enabled small interfering RNA (siRNA) delivery and progression into clinical development, advances of single-component, systemic siRNA delivery have been challenging. In pre-clinical models, attachment of a triantennary N-acetylgalactosamine (GalNAc) ligand to an siRNA mediates hepatocyte uptake via the asialoglycoprotein receptor enabling RNAi-mediated gene silencing. In this phase 1 study, we assessed translation of this delivery approach by evaluating the safety, tolerability, pharmacokinetics, and pharmacodynamics of a GalNAc-siRNA conjugate, revusiran, targeting transthyretin (TTR). Subjects received a placebo or ascending doses of revusiran subcutaneously ranging from 1.25-10 mg/kg in the single and 2.5-10 mg/kg in the multiple ascending dose phases. Revusiran was generally well tolerated, with transient, mild to moderate injection site reactions the most common treatment-emergent adverse events. Doses of 2.5-10 mg/kg revusiran elicited a significant reduction of serum TTR versus the placebo (p < 0.01), with mean TTR reductions of approximately 90% observed with multiple dosing. These results demonstrate translation of this novel delivery platform, enabling clinical development of subcutaneously administered GalNAc-siRNAs for liver-based diseases.

Keywords: GalNAc-siRNA; RNAi; asialoglycoprotein receptor; revusiran.

Figure 1

Mechanism of Hepatocyte Uptake and Action of Revusiran The siRNA targeting TTR mRNA is conjugated with a triantennary GalNAc. GalNAc binds to the ASGPR, which is highly expressed on hepatocytes, thus targeting revusiran to the liver. The revusiran-ASGPR complex is then taken into hepatocytes by clathrin-mediated endocytosis, where the siRNA causes TTR mRNA destruction through the RISC in the cytoplasm. The ASGPR is recycled to the cell surface for multiple rounds of siRNA uptake.

Figure 2

Trial Profile SAD dose cohorts preceded enrollment of the MAD dose cohorts.

Figure 3

Proportionality of Revusiran Plasma C_max and AUC_0–last after a Single Administration of Revusiran (A and B) Proportionality of revusiran plasma observed maximum plasma concentration (C_max) (A) and area under the plasma concentration-time curve from zero to the last measurable time point (AUC_0–last) (B) after a single administration of revusiran.

Figure 4

Pharmacodynamic Effect of Revusiran on Serum TTR Levels (A and B) Mean (± SEM) change in serum TTR over time relative to baseline in the SAD (A) and MAD (B) phase. Arrows indicate days of dosing in the multidose cohorts at 2.5, 5, and 7.5 (QW) and 10 mg/kg revusiran (days 0–4 and then weekly from days 7–35). The alternate MAD 7.5 mg/kg cohort was dosed on days 0–4 and then every other week from days 7–35.