Evaluation of efficacy, biodistribution, and inflammation for a potent siRNA nanoparticle: effect of dexamethasone co-treatment

Abstract

Despite recent progress, systemic delivery remains the major hurdle for development of safe and effective small inhibitory RNA (siRNA)-based therapeutics. Encapsulation of siRNA into liposomes is a promising option to overcome obstacles such as low stability in serum and inefficient internalization by target cells. However, a major liability of liposomes is the potential to induce an acute inflammatory response, thereby increasing the risk of numerous adverse effects. In this study, we characterized a liposomal siRNA delivery vehicle, LNP201, which is capable of silencing an mRNA target in mouse liver by over 80%. The biodistribution profile, efficacy after single and multiple doses, mechanism of action, and inflammatory toxicity are characterized for LNP201. Furthermore, we demonstrate that the glucocorticoid receptor (GR) agonist dexamethasone (Dex) inhibits LNP201-induced cytokine release, inflammatory gene induction, and mitogen-activated protein kinase (MAPK) phosphorylation in multiple tissues. These data present a possible clinical strategy for increasing the safety profile of siRNA-based drugs while maintaining the potency of gene silencing.

Figure 1

Lipid composition, siRNA design, and mouse biodistribution profile of LNP201. (a) Lipid components and ratio of the LNP201 assembly. (b) Sequences and chemical modification schemes for Ssb and control siRNAs. (c) Biodistribution of siRNA in mice. CD-1 mice (five/group) were dosed intravenously with LNP201/Ssb siRNA; tissues were collected 2 hours later and [Ssb siRNA] was measured by quantitative PCR as described in Materials and Methods. Values on the chart are reported as mean pg [siRNA] per mg of tissue ± SEM. (d) siRNA kinetics in mouse tissues after intravenous administration of LNP201. Liver and spleen tissue from mice (5/group) was collected at time points ranging from 2 hours to 1 week postdose; [Ssb siRNA] was measured as described. siRNA, small inhibitory RNA.

Figure 2

Administration of LNP201 in vivo results in target mRNA silencing. (a) Reduction of target mRNA in liver after a single intravenous dose of LNP201. Mice were treated with LNP201/Ssb siRNA at the indicated siRNA doses. At the indicated time points, the medial lobe of the liver was sampled and total RNA was isolated. quantitative PCR was performed to measure Ssb mRNA expression relative to a housekeeping gene, Ppib. Values from mice treated with vehicle only (PBS) were fixed to 100. Values are presented as the mean (five/group) ± SEM. (b) LNP potency increases after multiple weekly doses. Mice were treated with LNP201/Ssb siRNA once weekly for 4 weeks. At the indicated time points after the final of 4 doses, liver was collected and [mRNA] was measured as described above. (c), LNP201 loaded with a control siRNA sequence does not cause changes in the target mRNA. Mice were treated with either vehicle only (“PBS”) or LNP201/Control siRNA (“CTRL”) for either 48 hours or 1 week, and relative [Ssb mRNA] was measured as described above. (d), Activity of LNP201 in the spleen. Spleens were collected from mice (five/group) 48 hours after LNP201/Ssb siRNA or LNP201/CTRL siRNA dosed at 9 mg/kg, and mRNA was measured as described above. LNP, lipid nanoparticle; mRNA, messenger RNA; PBS, phosphate buffered saline; siRNA, small inhibitory RNA.

Figure 3

Silencing of target mRNA occurs through an RNA interference mechanism. Liver tissue was collected at the indicated time points after dosing mice with LNP201/Ssb siRNA or vehicle only (labeled “V”). Pooled total liver RNA from (five/group) was subjected to 5′ RACE analysis at each time point indicated. As described in Materials and Methods, 5′ RACE primers were designed to detect the RNA interference cleavage product of the target Ssb mRNA, which is expected to create a species in which the 5′ terminus is complementary to the 11th nucleotide of the siRNA guide strand. Following ligation of a RACE adapter oligonucleotide and s amplification, the resulting DNA products were analyzed via Agilent Bioanalyzer. The pseudogel image is shown. The presence of cleaved Ssb mRNA is confirmed by detection of a 287-bp DNA fragment. bp, base pairs; L, DNA ladder; siRNA, small inhibitory RNA.

Figure 4

LNP201 and CLinDMA cause an acute inflammatory response after systemic administration, independent of the siRNA payload. (a) Plasma was collected 2, 6, or 24 hours after intravenous dosing of LNP201 containing Ssb siRNA, control siRNA, or empty liposomes as indicated. The dose was 3 mg/kg based on siRNA mass, or in the case of empty liposomes a comparable dose of 39 mg/kg based on lipid mass. (b) Plasma was collected 2 hours after intravenous dosing of CLinDMA emulsion (95 mg/kg CLinDMA), or its matched vehicle (0.25% polyethylene glycol-dimyristoylglycerol, 5% sucrose, 9 mmol/l sodium citrate pH 4). A multiplexed enzyme-linked immunosorbent assay was used to measure 12 cytokines (IL-1α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12, IL-13, keratinocyte-derived cytokine, TNF-α, and interferon-γ) at 2, 6, or 24 hours postdose as labeled. Data are shown as mean plasma cytokine concentrations ± SEM, n = 5. Only data for those cytokines which were induced in response to LNP201/siRNA or CLinDMA emulsion are shown. IL, interleukin; siRNA, small inhibitory RNA; TNF, tumor necrosis factor.

Figure 5

LNP201/siRNA induced cytokine response is mitigated by dexamathasone (Dex) pretreatment. Mouse plasma was obtained 3 hours after intravenous dosing. Subjects were pretreated with phosphate-buffered saline or 0.5–8 mg/kg 1 hour prior to lipid nanoparticle (LNP) administration. (a) IL-1α, (b) IL-1β, (c) IL-6, (d) mouse keratinocyte-derived cytokine, (e) IL-10, and (f) TNF-α were measured in plasma by multiplexed ELISA. (g) [mRNA] of the siRNA target, Ssb, was measured (as in Figure 2) 24 hours after LNP dosing ± Dex pretreatment. Values are presented as mean ± SEM (n = 5). IL, interleukin; siRNA, small inhibitory RNA; TNF, tumor necrosis factor.

Figure 6

Effect of Dex pretreatment on serum ALT/AST levels. 5 mice/group were treated with indicated doses of LNP201/siRNA, with or without (phosphate-buffered saline) pretreatment with 3 or 9 mg/kg Dex 1 hour before LNP201 administration. AST/ALT levels were measured 24 hours after LNP201 dosing using standard clinical chemistry methodologies. Values are presented as mean ± SEM. ALT, alanine aminotransferase; AST, aspartate amintransferase; Dex, dexamethasone; siRNA, small inhibitory RNA.

Figure 7

ERK1/2, but not p38 MAPK, is phosphorylated in response to LNP201/siRNA, and inhibited by Dex pretreatment. For two subjects/group treated with 3 mg/kg LNP201/Ssb siRNA ± Dex, total protein from liver and spleen was analyzed by western blot for phosphorylated and total (a) ERK1/2 and (b) p38. Dex, dexamethasone; MAPK, mitogen-activated protein kinase; siRNA, small inhibitory RNA.