Ellen Marie Straarup

LNA-mediated microRNA silencing in non-human primates

microRNAs (miRNAs) are small regulatory RNAs that are important in development and disease and therefore represent a potential new class of targets for therapeutic intervention. Despite recent progress in silencing of miRNAs in rodents, the development of effective and safe approaches for sequence-specific antagonism of miRNAs in vivo remains a significant scientific and therapeutic challenge. Moreover, there are no reports of miRNA antagonism in primates. Here we show that the simple systemic delivery of a unconjugated, PBS-formulated locked-nucleic-acid-modified oligonucleotide (LNA-antimiR) effectively antagonizes the liver-expressed miR-122 in non-human primates. Acute administration by intravenous injections of 3 or 10 mg kg-1 LNA-antimiR to African green monkeys resulted in uptake of the LNA-antimiR in the cytoplasm of primate hepatocytes and formation of stable heteroduplexes between the LNA-antimiR and miR-122. This was accompanied by depletion of mature miR-122 and dose-dependent lowering of plasma cholesterol. Efficient silencing of miR-122 was achieved in primates by three doses of 10 mg kg-1 LNA-antimiR, leading to a long-lasting and reversible decrease in total plasma cholesterol without any evidence for LNA-associated toxicities or histopathological changes in the study animals. Our findings demonstrate the utility of systemically administered LNA-antimiRs in exploring miRNA function in rodents and primates, and support the potential of these compounds as a new class of therapeutics for disease-associated miRNAs.

Silencing of microRNA families by seed-targeting tiny LNAs

The challenge of understanding the widespread biological roles of animal microRNAs (miRNAs) has prompted the development of genetic and functional genomics technologies for miRNA loss-of-function studies. However, tools for exploring the functions of entire miRNA families are still limited. We developed a method that enables antagonism of miRNA function using seed-targeting 8-mer locked nucleic acid (LNA) oligonucleotides, termed tiny LNAs. Transfection of tiny LNAs into cells resulted in simultaneous inhibition of miRNAs within families sharing the same seed with concomitant upregulation of direct targets. In addition, systemically delivered, unconjugated tiny LNAs showed uptake in many normal tissues and in breast tumors in mice, coinciding with long-term miRNA silencing. Transcriptional and proteomic profiling suggested that tiny LNAs have negligible off-target effects, not significantly altering the output from mRNAs with perfect tiny LNA complementary sites. Considered together, these data support the utility of tiny LNAs in elucidating the functions of miRNA families in vivo.

Short locked nucleic acid antisense oligonucleotides potently reduce apolipoprotein B mRNA and serum cholesterol in mice and non-human primates

The potency and specificity of locked nucleic acid (LNA) antisense oligonucleotides was investigated as a function of length and affinity. The oligonucleotides were designed to target apolipoprotein B (apoB) and were investigated both in vitro and in vivo. The high affinity of LNA enabled the design of short antisense oligonucleotides (12- to 13-mers) that possessed high affinity and increased potency both in vitro and in vivo compared to longer oligonucleotides. The short LNA oligonucleotides were more target specific, and they exhibited the same biodistribution and tissue half-life as longer oligonucleotides. Pharmacology studies in both mice and non-human primates were conducted with a 13-mer LNA oligonucleotide against apoB, and the data showed that repeated dosing of the 13-mer at 1–2 mg/kg/week was sufficient to provide a significant and long lasting lowering of non-high-density lipoprotein (non-HDL) cholesterol without increasing serum liver toxicity markers. The data presented here show that oligonucleotide length as a parameter needs to be considered in the design of antisense oligonucleotide and that potent short oligonucleotides with sufficient target affinity can be generated using the LNA chemistry. Conclusively, we present a 13-mer LNA oligonucleotide with therapeutic potential that produce beneficial cholesterol lowering effect in non-human primates.

A Locked Nucleic Acid Antisense Oligonucleotide (LNA) Silences PCSK9 and Enhances LDLR Expression In Vitro and In Vivo

Background The proprotein convertase subtilisin/kexin type 9 (PCSK9) is an important factor in the etiology of familial hypercholesterolemia (FH) and is also an attractive therapeutic target to reduce low density lipoprotein (LDL) cholesterol. PCSK9 accelerates the degradation of hepatic low density lipoprotein receptor (LDLR) and low levels of hepatic PCSK9 activity are associated with reduced levels of circulating LDL-cholesterol. Methodology/Principal Findings The present study presents the first evidence for the efficacy of a locked nucleic acid (LNA) antisense oligonucleotide (LNA ASO) that targets both human and mouse PCSK9. We employed human hepatocytes derived cell lines HepG2 and HuH7 and a pancreatic mouse β-TC3 cell line known to express high endogenous levels of PCSK9. LNA ASO efficiently reduced the mRNA and protein levels of PCSK9 with a concomitant increase in LDLR protein levels after transfection in these cells. In vivo efficacy of LNA ASO was further investigated in mice by tail vein intravenous administration of LNA ASO in saline solution. The level of PCSK9 mRNA was reduced by ∼60%, an effect lasting more than 16 days. Hepatic LDLR protein levels were significantly up-regulated by 2.5–3 folds for at least 8 days and ∼2 fold for 16 days. Finally, measurement of liver alanine aminotransferase (ALT) levels revealed that long term LNA ASO treatment (7 weeks) does not cause hepatotoxicity. Conclusion/Significance LNA-mediated PCSK9 mRNA inhibition displayed potent reduction of PCSK9 in cell lines and mouse liver. Our data clearly revealed the efficacy and safety of LNA ASO in reducing PCSK9 levels, an approach that is now ready for testing in primates. The major significance and take home message of this work is the development of a novel and promising approach for human therapeutic intervention of the PCSK9 pathway and hence for reducing some of the cardiovascular risk factors associated with the metabolic syndrome.

PCSK9 LNA Antisense Oligonucleotides Induce Sustained Reduction of LDL Cholesterol in Nonhuman Primates

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a therapeutic target for the reduction of low-density lipoprotein cholesterol (LDL-C). PCSK9 increases the degradation of the LDL receptor, resulting in high LDL-C in individuals with high PCSK9 activity. Here, we show that two locked nucleic acid (LNA) antisense oligonucleotides targeting PCSK9 produce sustained reduction of LDL-C in nonhuman primates after a loading dose (20 mg/kg) and four weekly maintenance doses (5 mg/kg). PCSK9 messenger RNA (mRNA) and serum PCSK9 protein were reduced by 85% which resulted in a 50% reduction in circulating LDL-C. Serum total cholesterol (TC) levels were reduced to the same extent as LDL-C with no reduction in high-density lipoprotein levels, demonstrating a specific pharmacological effect on LDL-C. The reduction in hepatic PCSK9 mRNA correlated with liver LNA oligonucleotide content. This verified that anti-PCSK9 LNA oligonucleotides regulated LDL-C through an antisense mechanism. The compounds were well tolerated with no observed effects on toxicological parameters (liver and kidney histology, alanine aminotransferase, aspartate aminotransferase, urea, and creatinine). The pharmacologic evidence and initial safety profile of the compounds used in this study indicate that LNA antisense oligonucleotides targeting PCSK9 provide a viable therapeutic strategy and are potential complements to statins in managing high LDL-C.

Chapter 5:Locked Nucleic Acid: Properties and Therapeutic Aspects

In 1978 Zamecnik and Stephenson1 showed for the first time that messenger RNA (mRNA) repression could be achieved by single-stranded oligonucleotides (ONs). This mechanistic approach for gene inhibition was later called the antisense (AS) principle. The simplicity of this new principle captivated ma...