Modulation of lipoprotein metabolism by antisense technology: preclinical drug discovery methodology

Improvements in the Tolerability Profile of 2'-O-Methoxyethyl Chimeric Antisense Oligonucleotides in Parallel with Advances in Design, Screening, and Other Methods

The development process of antisense oligonucleotides (ASOs) as therapeutic agents in humans has advanced through the implementation of chemical compound modifications as well as increasingly sophisticated toxicological preclinical screening techniques. The Ionis Integrated Safety Database was utilized to determine if advances in ASO screening and clinical lead identification methods have improved the tolerability profiles of 2′-O-methoxyethyl (2′MOE)-modified ASOs as a class, relative to the first 2′MOE ASO approved for use in humans, mipomersen. Tolerability was assessed by the incidence and percentage of subcutaneous doses leading to adverse events at the injection site or flu-like reactions (FLRs), as well as by the incidence of dose discontinuations due to these events. In randomized placebo-controlled phase 1 and phase 2 trials, the incidence of each measure of tolerability was lower in the test group of 12 ASOs (713 ASO-treated subjects) compared with the reference, mipomersen (266 ASO-treated subjects); with the most marked reduction in the incidence of FLRs (0.6% vs. 9.4%). A similar reduction in the incidence of dose discontinuation due to FLRs was also observed (0.2% vs. 0.9%). When compared with mipomersen, 8 of 12 ASOs showed significant improvements in their respective mean percentage of doses leading to adverse events at the injection site, whereas 7 ASOs showed a significant improvement in mean percentage of doses leading to FLRs. These results support an overall improvement in the tolerability profile in 2′MOE ASOs that entered development after mipomersen, in parallel with advances in the drug discovery screening process as well as the gains in clinical experience during development of each ASO.

Well-Defined DNA-Polymer Miktoarm Stars for Enzyme-Resistant Nanoflares and Carrier-Free Gene Regulation

Herein, we report a star-architectured poly(ethylene glycol) (PEG)-oligonucleotide nanoconjugate of a well-defined molecular structure. Based upon fullerene C₆₀ cores, each star bears precisely 1 DNA strand and 11 polymer chains. The elevated PEG density provides the DNA with steric selectivity: the DNA is significantly more resistant to nuclease digestion while remaining able to hybridize with a complementary sequence. The degree of resistance increases as the centers of mass for the DNA and fullerene are closer together. Such steric selectivity reduces protein-related background signals of the nanoflares synthesized from these miktoarm star polymers. Importantly, the stars improve cellular uptake and regulate gene expression as a non-cytotoxic, single-entity antisense agent without the need for a transfection carrier.

IONIS-PKKRx a Novel Antisense Inhibitor of Prekallikrein and Bradykinin Production

Kallikrein is the key contact system mediator responsible for the conversion of high-molecular-weight kininogen into the inflammatory vasodilator peptide bradykinin, a process regulated by C1-esterase inhibitor (C1-INH). In hereditary angioedema (HAE), genetic mutations result in deficient or dysfunctional C1-INH and dysregulation of the contact system leading to recurrent, sometimes fatal, angioedema attacks. IONIS-PKK_Rx is a second-generation 2'-O-(2-methoxyethyl)-modified chimeric antisense oligonucleotide, designed to bind and selectively reduce prekallikrein (PKK) mRNA in the liver. IONIS-PKK_Rx demonstrated dose-dependent reduction of human prekallikrein hepatic mRNA and plasma protein in transgenic mice and dose- and time-dependent reductions of plasma PKK in Cynomolgus monkeys. Similar dose-dependent reductions of plasma PKK levels were observed in healthy human volunteers accompanied by decreases in bradykinin generation capacity with an acceptable safety and tolerability profile. These results highlight a novel and specific approach to target PKK for the treatment of HAE and other diseases involving contact system activation and overproduction of bradykinin.

Integrated Safety Assessment of 2'-O-Methoxyethyl Chimeric Antisense Oligonucleotides in NonHuman Primates and Healthy Human Volunteers

The common chemical and biological properties of antisense oligonucleotides provide the opportunity to identify and characterize chemical class effects across species. The chemical class that has proven to be the most versatile and best characterized is the 2′-O-methoxyethyl chimeric antisense oligonucleotides. In this report we present an integrated safety assessment of data obtained from controlled dose-ranging studies in nonhuman primates (macaques) and healthy human volunteers for 12 unique 2′-O-methoxyethyl chimeric antisense oligonucleotides. Safety was assessed by the incidence of safety signals in standardized laboratory tests for kidney and liver function, hematology, and complement activation; as well as by the mean test results as a function of dose level over time. At high doses a number of toxicities were observed in nonhuman primates. However, no class safety effects were identified in healthy human volunteers from this integrated data analysis. Effects on complement in nonhuman primates were not observed in humans. Nonhuman primates predicted safe doses in humans, but over predicted risk of complement activation and effects on platelets. Although limited to a single chemical class, comparisons from this analysis are considered valid and accurate based on the carefully controlled setting for the specified study populations and within the total exposures studied.

Anti-sense oligonucleotide therapies for the treatment of hyperlipidaemia

INTRODUCTION

Anti-sense oligonucleotide (ASO) therapies are a new development in clinical pharmacology offering greater specificity compared to small molecule inhibitors and the ability to target intracellular process' not susceptible to antibody-based therapies.

AREAS COVERED

This article reviews the chemical biology of ASOs and related RNA therapeutics. It then reviews the data on their use to treat hyperlipidaemia. Data on mipomersen - an ASO to apolipoprotein B-100(apoB) licensed for treatment of homozygous familial hypercholesterolaemia (FH) is presented. Few effective therapies are available to reduce atehrogenic lipoprotein (a) levels. An ASO therapy to apolipoprotein(a) (ISIS Apo(a)Rx) specifically reduced lipoprotein (a) levels by up to 78%. Treatment options for patients with familial chylomicronaemia syndrome (lipoprotein lipase deficiency; LPLD) or lipodystrophies are highly limited and often inadequate. Volanesorsen, an ASO to apolipoprotein C-3, shows promise in the treatment of LPLD and severe hypertriglyceridaemia as it increases clearance of triglyceride-rich lipoproteins and can normalise triglycerides in these patients.

EXPERT OPINION

The uptake of the novel ASO therapies is likely to be limited to selected niche groups or orphan diseases. These will include homozygous FH, severe heterozygous FH for mipomersen; LPLD deficiency and lipodystrophy syndromes for volanesorsen and treatment of patients with high elevated Lp(a) levels.

Endogenous microRNA sponges: evidence and controversy

The competitive endogenous RNA (ceRNA) hypothesis proposes that transcripts with shared microRNA (miRNA) binding sites compete for post-transcriptional control. This hypothesis has gained substantial attention as a unifying function for long non-coding RNAs, pseudogene transcripts and circular RNAs, as well as an alternative function for messenger RNAs. Empirical evidence supporting the hypothesis is accumulating but not without attracting scepticism. Recent studies that model transcriptome-wide binding-site abundance suggest that physiological changes in expression of most individual transcripts will not compromise miRNA activity. In this Review, we critically evaluate the evidence for and against the ceRNA hypothesis to assess the impact of endogenous miRNA-sponge interactions.

An overview of drugs currently under investigation for the treatment of transthyretin-related hereditary amyloidosis

INTRODUCTION

Transthyretin (TTR)-related hereditary amyloidosis is an adult-onset, dominantly inherited, systemic neurodegenerative disease endemic in some populations. Stabilization of the native structure of TTR by small-molecule ligands has recently proved effective in slowing neurological progression. Two drugs, tafamidis and diflunisal, are now available for most patients, particularly in the early stage of the disease. However, this disorder remains life threatening with several unmet needs. There are great expectations for a number of novel agents undergoing investigation.

AREAS COVERED

The authors review the current investigational drugs for the treatment of TTR amyloidosis according to the different steps of the fibrillogenesis process they target. Innovative approaches include suppression of TTR secretion, prevention of TTR misfolding by stronger stabilizers identified through structure-based design and high-throughput screening methodologies as well as the redirection of pathogenic aggregates toward nontoxic species and reabsorption of deposits through amyloid disrupters and immunotherapy.

EXPERT OPINION

Suppression of TTR synthesis by antisense oligonucleotides and small-interfering RNA is presently one of the most promising therapeutic approaches. However, well-designed clinical trials are required to establish their safety and efficacy compared with liver transplantation, tafamidis and diflunisal. With a longer time frame, it may be possible to develop combination therapies that target multiple steps of the aggregation process that could provide the best long-life effective treatments for this devastating disease.