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'Therapeutic' microRNA The realization that microRNAs play a central role in gene regulation in both normal development and disease, such as cancer, cardiac disease and metabolic disorders, suggests that they might be viable targets for therapeutic intervention. Now, for the first time, efficient, long-lasting and reversible microRNA silencing has been achieved in non-human primates. African green monkeys received intraperitoneal injections of a short modified DNA sequence that binds to and blocks the function of miR-122, a microRNA that regulates genes that influence cholesterol levels. Dose-dependent lowering of blood cholesterol followed, with no signs of toxicity. It is still a giant leap to therapeutic applications and, as microRNAs can act on many genes, toxicity risks are considerable. Small interfering RNAs (siRNAs) can be systemically administered in non-human primates and significantly reduce expression from the mRNA against which they are directed. A therapeutic effect can also be achieved by targeting a microRNA (miRNA). A modified oligonucleotide directed against miR-122 was administered to monkeys, resulting in a reduction in serum cholesterol without detectable toxicity. microRNAs (miRNAs) are small regulatory RNAs that are important in development and disease 1 , 2 , 3 and therefore represent a potential new class of targets for therapeutic intervention 4 . Despite recent progress in silencing of miRNAs in rodents 5 , 6 , 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.

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. 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 beta-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 approximately 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 approximately 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. 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.

Systemic iron homeostasis is mainly controlled by the liver through synthesis of the peptide hormone hepcidin (encoded by Hamp), the key regulator of duodenal iron absorption and macrophage iron release. Here we show that the liver-specific microRNA miR-122 is important for regulating Hamp mRNA expression and tissue iron levels. Efficient and specific depletion of miR-122 by injection of a locked-nucleic-acid-modified (LNA-modified) anti-miR into WT mice caused systemic iron deficiency, characterized by reduced plasma and liver iron levels, mildly impaired hematopoiesis, and increased extramedullary erythropoiesis in the spleen. Moreover, miR-122 inhibition increased the amount of mRNA transcribed by genes that control systemic iron levels, such as hemochromatosis (Hfe), hemojuvelin (Hjv), bone morphogenetic protein receptor type 1A (Bmpr1a), and Hamp. Importantly, miR-122 directly targeted the 3′ untranslated region of 2 mRNAs that encode activators of hepcidin expression, Hfe and Hjv. These data help to explain the increased Hamp mRNA levels and subsequent iron deficiency in mice with reduced miR-122 levels and establish a direct mechanistic link between miR-122 and the regulation of systemic iron metabolism.

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.

N-methyl-D-aspartate (NMDA) glutamate receptors are regulators of fast neurotransmission and synaptic plasticity in the brain. Disruption of NMDA-mediated glutamate signaling has been linked to behavioral deficits displayed in psychiatric disorders such as schizophrenia. Recently, noncoding RNA molecules such as microRNAs (miRNAs) have emerged as critical regulators of neuronal functions. Here we show that pharmacological (dizocilpine) or genetic (NR1 hypomorphism) disruption of NMDA receptor signaling reduces levels of a brain-specific miRNA, miR-219, in the prefrontal cortex (PFC) of mice. Consistent with a role for miR-219 in NMDA receptor signaling, we identify calcium/calmodulin-dependent protein kinase II γ subunit (CaMKIIγ), a component of the NMDA receptor signaling cascade, as a target of miR-219. In vivo inhibition of miR-219 by specific antimiR in the murine brain significantly modulated behavioral responses associated with disrupted NMDA receptor transmission. Furthermore, pretreatment with the antipsychotic drugs haloperidol and clozapine prevented dizocilpine-induced effects on miR-219. Taken together, these data support an integral role for miR-219 in the expression of behavioral aberrations associated with NMDA receptor hypofunction.

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. 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 [beta]-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. 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.

NUCLEIC ACID THERAPY comprises several approaches based on nucleic acid as the active therapeutic component to treat human disease. Antisense and short interfering RNA (siRNA) are two gene-silencing techniques in this category. Based on nucleic acid sequence recognition both techniques inhibit gene expression. This is highly attractive whenever there is deleterious expression of genetic material, as for example in viral diseases or cancer. In many of these diseases effective treatments are limited and/or toxic; therefore there is a need for new alternative therapeutics. We aimed to improve these gene-silencing techniques to facilitate future therapeutic application. We have made efforts in facilitating the use of viral vectors for nucleic acid delivery, but in particular, we have used the synthetic nucleotide analogue locked nucleic acid (LNA) in both antisense oligonucleotides and siRNA. As therapeutic targets we inhibited the human pathogens human immunodeficiency virus type 1 (HIV-1) and severe acute respiratory syndrome-associated corona virus (SARS-CoV) in cell culture. The results demonstrate that LNA is advantageous in both antisense and siRNA techniques.Starting with delivery, as one major obstacle for nucleic acid based therapeutics, we aimed to facilitate the use of recombinant adeno-accosiated virus (AAV). In certain applications viruses can serve as suitable delivery vehicles for gene-silencing techniques. AAV has favourable properties for use as delivery vehicle, however there has been limited use of AAV due to production difficulties. We developed an alternative method for production that utilized baculoviruses for transfer of needed helper genes. We showed expression of the helper genes from the baculovirus and production of infec- tious recombinant AAV. The protocol may lead to improved AAV production and facilitate increased use of recombinant AAV.Continuing with the development of synthetic antisense oligonucleotides, we targeted the conserved HIV-1 dimerization initiation site with LNA modified antisense oligonucleotides, LNA/DNA mix-mers. We showed improved inhibition of dimerization by using LNA/DNA mixmers and activation of RNase H by LNA/DNA mix-mers containing at least six consecutive DNA bases. We subsequently demonstrated inhibition of HIV-1 replication. LNA improves the antisense oligonuleotides and can function on a therapeutic target.Using the more recently discovered gene-silencing technique siRNA, we targeted the SARS-CoV RNA dependent RNA polymerase. The siRNA inhibited SARS-CoV replication both when delivered pre and post infection. This study shows an example of how genetic information on an emerging pathogen can rapidly be converted to an antiviral tool by the means of siRNA.Finally, we combined LNA with siRNA to a compound we term siLNA. We showed siLNA compatibility with the siRNA machinery in association with higher nuclease resistance and enhanced strand bias. siLNA provides a possibility to reduce undesired, off-target effects of siRNA. We also applied siLNA to inhibit SARS-CoV and showed improved efficiency over unmodified siRNA on certain target sites. LNA brings many favourable features to siRNA beneficial to future therapeutic use.Taken together, these studies improve certain technical aspects of genesilencing techniques and show potential applications of nucleic acid based therapeutics.