▎ WuXi AppTec content team editor
In recent years, the development of oligonucleotide therapy for silent RNA expression to treat metabolic diseases is becoming a hot topic for new drug research and development. Optimizations in oligonucleotide design and synthetic chemistry, combined with a highly specific and efficient delivery technology platform, make oligonucleotides a new drug type. Five oligonucleotide therapies have been approved for the treatment of rare and common liver-driven metabolic diseases. More therapies under investigation are in clinical development. Recently, a review on Nature Reviews Drug Discovery took stock of the latest developments in this area. The authors also look forward to future opportunities for oligonucleotide therapy.
How oligonucleotide therapy is used in metabolic diseases
At present, a variety of small interfering RNA (siRNA) and antisense oligonucleotide (ASO) therapies have been approved by the FDA to cause degradation of mRNA through different mechanisms. siRNA and ASO can have beneficial effects on metabolic diseases in several ways.
The most obvious application of concept is to inhibit the production of disease-causing proteins. These proteins may have abnormal activity or specificity due to functional acquired mutations, or protein aggregation. ASO/RNAi can specifically target alleles that produce mutations, and if mutations appear on non-essential genes, they can also target both mutant and wild-type alleles. SiRNA therapy for the treatment of transthyroxine protein amyloidosis (ATTR) demonstrates this strategy. They can reduce the production of wild-type and variant transthyroxine protein.
Another application of ASO and siRNAs is to target key components in metabolic or signaling pathways, thereby influencing the cellular stress response. In this case, disease pathways are often upregulated due to environmental or genetic stress, leading to disease phenotypes. Silencing is a key component of highly active signaling pathways that can modulate stress responses and influence disease phenotypes. For example, patients with dysproteinaemias have increased SYNTHESIS of PCSK9 receptors, which can lead to hypercholesterolemia. The expression of silent PCSK9 can downregulate overactive signaling pathways and reduce cholesterol levels in plasma.
ASO and siRNAs can also achieve the effect of treating metabolic diseases by interfering with feedback signaling pathways and reprogramming metabolic pathways.
▲The application mode of ASO and RNAi therapy in metabolic diseases (Image source: Reference[1])
Potential targets for the treatment of chronic metabolic diseases
Studies of metabolic dysfunction have uncovered many promising drug targets. This review takes stock of targets targeted by approved and clinically investigated oligonucleotide therapies.
Dyslipidemia and cardiovascular disease
According to the World Health Organization's estimates, atherosclerotic cardiovascular disease is one of the leading causes of death globally. Changes in low-density lipoprotein cholesterol (LDL-C) are major risk factors for cardiovascular disease events, with other risk factors including high levels of triglyceride-enriched lipoprotein, high levels of lipoprotein (a), and hypertension. In reducing these risk factors, current oligonucleotide therapies target targeting:
PCSK9
PCSK9 is an emerging target for reducing LDL-C. It raises the level of LDL-C in the blood by degrading LDL receptors. Inhibiting the interaction of PCSK9 with LDL receptors or lowering PCSK9 levels allows more LDL receptors to return to the surface of liver cells, thereby removing more LDL-C from the blood and lowering LDL-C levels in the blood. Antibody therapies and RNAi therapies targeting PCSK9 have been approved for marketing. ASO therapies targeting PCSK9 have also entered Phase 2 clinical trials.
▲The mechanism of action of PCSK9 targeted therapy (Image source: Reference[1])
APOC3
ApOC3 protein plays an important role in regulating lipid metabolism by inhibiting hepatocytes from clearing lipoprotein particles rich in triglycerides (TG), leading to elevated triglyceride levels and very low-density lipoprotein (VLDL) levels in the blood, while high-density lipoprotein cholesterol (HDL-C, "good" cholesterol) levels are reduced.
ApOC3 proteins are expressed at high levels in the liver, and the liver itself produces APOC3 proteins specifically, making it an ideal target for RNA silencing techniques. THE ASO therapy volanesorsen, which targets reduced APOC3 expression, has been approved in the European Union, and the RNAi therapy ARO-APOC3 developed by Arrowhead was able to reduce triglyceride levels by more than 90% in clinical trials.
▲The mechanism of ARO-APOC3 (Image source: Arrowhead company official website)
ANGPTL3
ANGPTL3 is a protein secreted by the liver that plays a key role in regulating triglyceride and cholesterol levels. Human genetic studies have shown that individuals who lose function of ANGPTL3 due to genetic mutations can reduce their risk of cardiovascular disease by about 40%. This also makes it an attractive target.
Angiotensinogen (AGT)
High blood pressure is one of the main risk factors for cardiovascular disease. Although treatment modalities including lifestyle changes and multiple antihypertensive drugs are already available, less than 20% of patients are able to successfully control their blood pressure within the recommended range. There are many reasons for uncontrolled hypertension, and inconsistent control effects of therapy and adherence to medication are important factors.
Angiotensin is a precursor to angiotensin and an important component of the renin-angiotensin-aldosterone system (RAAS) that regulates blood pressure and renal sodium retention. RAAS has been a major target for antihypertensive therapies. Reducing the production of pro-angiotensin using oligonucleotide therapy can reduce the level of angiotensin, resulting in a consistent and lasting decrease in blood pressure.
The RNAi therapy zilebesiran (formerly known as ALN-AGT) developed by Alnylam Pharmaceuticals has yielded positive results in preliminary clinical trials and is expected to achieve a lasting control of hypertension with only one injection in half a year.
▲ Zilebesiran's mechanism of action (Image source: Alnylam official website)
NASH and diabetes
Insulin resistance due to underactivity and obesity is one of the important drivers of type 2 diabetes, hyperlipidemia and hypertension, a range of symptoms also known as metabolic syndrome. Globally, metabolic syndrome is increasingly manifesting as nonalcoholic fatty liver disease (NAFLD), which progresses to nonalcoholic steatohepatitis (NASH), which ultimately leads to cirrhosis. Innovative therapies based on oligonucleotides can effectively reduce the expression of disease-causing genes in the liver, so it has also become one of the hot spots for the development of anti-diabetic drugs. Targets that can currently have an impact on insulin resistance, hyperlipidemia, and NAFLD/NASH include:
17-β-hydroxysteroid dehydrogenase 13
17-β-hydroxysteroid dehydrogenase 13 (HSD17B13) is a liver-specific lipid drop protein that plays a key role in regulating liver lipid drop homeostasis. Elevated expression of HSD17B13 leads to activation of fat de novo lipogenesis and enlargement of lipid droplets, promoting the development of hepatic steatosis. Therefore, the use of ASO/siRNA to inhibit the expression of HSD17B13 is a potential strategy for the treatment of NAFLD/NASH. Currently, Arrowhead and Alnylam's RNAi therapies targeting HSD17B13 are both being evaluated in Phase 1 clinical trials.
PNPLA3
PNPLA3 catalyzes the hydrolysis of triglycerides and the transfer of polyunsaturated fatty acids, leading to the remodeling of phospholipids in liver lipid droplets. Genome-wide association studies (GWAS) have found that variants of PNPLA3 are significantly associated with NAFLD. This variant leads to the retention of triglycerides and the formation of lipid droplets enriched with polyunsaturated fatty acids, which may increase the risk of NASH and hepatocellular carcinoma. Preclinical experiments have shown that ASO targeting PNPLA3 reduces liver inflammation and fibrosis in mouse models. Currently, AstraZeneca's ASO therapy for PNPLA3, AZD2693, is being evaluated in a Phase 1 clinical trial.
Diacylglycerol O-acyltransferase 2 (DGAT2)
DGAT2 is one of two isoenzymes that catalyze triglyceride synthesis. Together with DGAT1, it undertakes almost all triglyceride synthesis. Since the synthesis of triglycerides in NASH is mainly driven by the catalytic activity of DGAT2, inhibiting its activity may inhibit the synthesis of triglycerides and delay the disease progression of NAFLD. Currently, ION224, an ASO therapy that targets DGAT2, has entered Phase 2 clinical trials for the treatment of confirmed NASH patients, and it is expected that the primary endpoint data may be available in September this year.
Glucagon receptor (GCGR)
Glucagon is a hormone secreted by islet α cells, which fights the action of insulin and increases the synthesis of glucose in the liver. In patients with type 2 diabetes, glucagon levels increase, leading to hyperglycemia in the case of fasting. Glucagon may also play an important role in lipid metabolism. Therefore, innovative therapies that block the glucagon receptor signaling pathway may inhibit hepatic glucose synthesis and lower hyperglycemia.
Phase 2 clinical trials in patients with type 2 diabetes receiving metformin have shown that ASO therapy IONICS-GCGRRx, which targets glucagon receptors, can significantly reduce glycosylated hemoglobin (HbA1c) levels in patients.
▲Partial treatment of metabolic diseases in the clinical period or approved oligonucleotide therapy (data source: reference [1], the company in parentheses is a joint development company, WuXi AppTec content team mapping, click to see the larger image)
Looking to the future
With advances in ASO/siRNA delivery technology, the dose of administration and off-target effects of oligonucleotide therapy have been significantly reduced, making it possible to construct therapies to target multiple signaling pathways, or multiple genes in the same signaling pathway. This strategy may lead to better therapeutic outcomes. For example, targeting HSD17B13 and PNPLA3 at the same time may have a synergistic effect in the treatment of liver disease. Lowering blood pressure and LDL-C at the same time is expected to achieve better results in reducing cardiovascular risk.
The GEMINI technology platform already being built by Alnylam will link two siRNAs together while effectively inhibiting the expression of two different targets. Currently, the company is developing a research therapy that links siRNA targeting ANGPTL3 with siRNA targeting proantadtensin. This in-research therapy may be injected every 6 months or 1 year to reduce blood pressure by more than 10 mmHg while reducing ~40% LDL cholesterol levels, and can be used to prevent important adverse cardiovascular events in high-risk populations.
▲ RNAi therapy to reduce LDL-C and blood pressure at the same time (Image source: Alnylam official website)