Targeting the Liver with Nucleic Acid Therapeutics for the Treatment of Systemic Diseases of Liver Origin

Abstract

Systemic diseases of liver origin (SDLO) are complex diseases in multiple organ systems, such as cardiovascular, musculoskeletal, endocrine, renal, respiratory, and sensory organ systems, caused by irregular liver metabolism and production of functional factors. Examples of such diseases discussed in this article include primary hyperoxaluria, familial hypercholesterolemia, acute hepatic porphyria, hereditary transthyretin amyloidosis, hemophilia, atherosclerotic cardiovascular diseases, α-1 antitrypsin deficiency-associated liver disease, and complement-mediated diseases. Nucleic acid therapeutics use nucleic acids and related compounds as therapeutic agents to alter gene expression for therapeutic purposes. The two most promising, fastest-growing classes of nucleic acid therapeutics are antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs). For each listed SDLO disease, this article discusses epidemiology, symptoms, genetic causes, current treatment options, and advantages and disadvantages of nucleic acid therapeutics by either ASO or siRNA drugs approved or under development. Furthermore, challenges and future perspectives on adverse drug reactions and toxicity of ASO and siRNA drugs for the treatment of SDLO diseases are also discussed. In summary, this review article will highlight the clinical advantages of nucleic acid therapeutics in targeting the liver for the treatment of SDLO diseases. SIGNIFICANCE STATEMENT: Systemic diseases of liver origin (SDLO) contain rare and common complex diseases caused by irregular functions of the liver. Nucleic acid therapeutics have shown promising clinical advantages to treat SDLO. This article aims to provide the most updated information on targeting the liver with antisense oligonucleotides and small interfering RNA drugs. The generated knowledge may stimulate further investigations in this growing field of new therapeutic entities for the treatment of SDLO, which currently have no or limited options for treatment.

Graphical abstract

Fig. 1

Systemic diseases of liver origin (SDLO) and its associated irregular productions in the liver. (A) SDLO are diseases diagnosed in other organs due to abnormal liver productions. The irregularly produced compounds are released from the liver and deposited to other organs or tissue systems, including but not limited to nervous, cardiovascular, endocrine, respiratory, gastrointestinal, integumentary, and renal systems, causing systemic diseases. (B) Irregular productions of small chemical compounds in the liver are associated with SDLO. PH is caused by excessive production of oxalate in the liver and overaccumulation in kidneys and urine to form kidney stones and damage. FH is caused by genetic defects in the LDL-R for irregular production of cholesterol in the liver and overaccumulation in blood to form plaques and lead to coronary artery disease. AHP is caused by irregular production of heme in the liver and overaccumulation in blood with neurologic attacks, resulting in nerve pain, vomiting, neuropathy, and seizures. (C) Irregular productions of proteins in the liver are associated with SDLO. TTR hATTR is caused by expression of an abnormal TTR protein in the liver and over-deposit of the abnormal TTR as amyloid in various organs and peripheral nerves in the body with cardiomyopathy or neuropathy. Hemophilia is caused by production of mutant coagulation factors F-VIII and F-IX proteins in the liver, resulting in X-linked bleeding disorders. ASCVD is caused by Lp(a) in the liver and overaccumulation in arteries with a high risk of heart attack and strokes; AATLD is caused by irregular production of AAT with wrong shape in the liver and deficient in lung with a high risk of developing hepatocellular carcinoma and lung diseases. CMD, including PNH, aHUS, and IgAN, is caused by hyperactivation of C5 protein in the liver and over deposit in blood and the kidneys, causing inflammation that damages red blood cells and kidney tissues. ANS, autonomic nervous system; CNS, central nervous system; PNS, peripheral nervous system.

Fig. 2

Principle of drug action of ASO and siRNA drugs. (A) ASO drugs use an RNase H–mediated mRNA degradation process. An ASO drug, such as mipomersen and inotersen with a gapmer design, gets into a cell through endocytosis and is first stored in the endosome, then undergoes an endosomal release. By complementary base pairing with the target mRNA, ASO and mRNA form a DNA:RNA heteroduplex that can be recognized by RNase H. In the heteroduplex, the mRNA is degraded while the ASO remains intact and can be reused. (B) siRNA drugs use RISC-mediated mRNA degradation process. The GalNAc-conjugated siRNA binds to ASGPR with high affinity and helps this siRNA to be taken up by endocytosis. Then, ASGPR is released by endosome and recycled on the cell membrane. At the same time, siRNA is released to load into a RISC. The antisense strand is activated by selective removal of the sense strand. The antisense strand then guides the RISC to bind to the target mRNA sequence, leading the Argonaute protein in the RISC to cleave the target mRNA sequence​​.

Fig. 3

Chemical modifications and delivery systems for the seven FDA-approved ASO and siRNA drugs. Mipomersen and inotersen are ASO drugs with 20 nucleotides. They share the exact same chemical modifications beyond the phosphate backbone and bases. Five 2’-MOE moieties are added at the 5′ and 3′ ends and phosphorothioate (S^-) modifications throughout the backbone. Substitution at the 5-position of the cytosine (C) and uracil (U) bases with a methyl group is indicated by ^Me. Patisiran is the first siRNA drug approved by FDA with 11 2’-OMe–modified sugar residues in between and two 2’-deoxythymidine residues added to the 3′ ends of both strands. Givosiran is chemically modified with 28 2’-OMe and 16 2’-F groups in the ribose sugar moieties, and two S^- modifications are added at the 5′ end of the sense strand as well as both ends of the antisense strand. Lumasiran has 34 2’-OMe and 10 2’-F groups in the ribose sugar moieties, and two S^- modifications are added at the 5′ end of the sense strand as well as both ends of the antisense strand. Inclisiran has been chemically modified with 31 2’-OMe and 12 2’-F groups in the ribose sugar moieties, and two S^- modifications are added at the 5′ end of the sense strand and both ends of the antisense strand. Notably, there is a deoxyribonucleotide in the middle of its sense strand. Vutrisiran has 35 2’-OMe and nine 2’-F groups in the ribose sugar moieties, and two S^- modifications are added at the 5′ end of the sense strand as well as both ends of the antisense strand. Patisiran is encapsulated in an LNP for optimum circulation time and efficient delivery into cells. Unlike patisiran, the other four approved siRNA drugs are all connected with a GalNAc (L96) at the end of 3′ ends of their sense strands, increasing potency, stability, and uptake into hepatocyte cells.

Fig. 4

Binding positions of the FDA-approved ASO and siRNA drugs on their targeting mRNAs. Mipomersen is designed to selectively interact with the conjoined region of exon 20 and exon 21 within the mRNA sequence of APOB, encompassing one nucleotide from exon 20 and 19 nucleotides from exon 21. In contrast, Inotersen exerts its mechanism by directly binding to the 3′-UTR of the TTR mRNA. Notably, both Inotersen and vutrisiran share a common targeting site excepting the presence of an additional nucleotide at the 3′ terminus of vutrisiran. Patisiran likewise directs its therapeutic effect toward TTR, with a partially overlapping sequence section shared with both inotersen and vutrisiran. Givosiran binds to exon 5 of the 5′- ALAS1 mRNA. Lumasiran and inclisiran elicit their effects by interacting with the 3′-UTR regions of their respective target mRNAs, HAO1 and PCSK9, each within their distinct contexts.