Therapeutic RNA interference: A novel approach to the treatment of primary hyperoxaluria

Abstract

RNA interference (RNAi) is a natural biological pathway that inhibits gene expression by targeted degradation or translational inhibition of cytoplasmic mRNA by the RNA induced silencing complex. RNAi has long been exploited in laboratory research to study the biological consequences of the reduced expression of a gene of interest. More recently RNAi has been demonstrated as a therapeutic avenue for rare metabolic diseases. This review presents an overview of the cellular RNAi machinery as well as therapeutic RNAi design and delivery. As a clinical example we present primary hyperoxaluria, an ultrarare inherited disease of increased hepatic oxalate production which leads to recurrent calcium oxalate kidney stones. In the most common form of the disease (Type 1), end-stage kidney disease occurs in childhood or young adulthood, often necessitating combined kidney and liver transplantation. In this context we discuss nedosiran (Dicerna Pharmaceuticals, Inc.) and lumasiran (Alnylam Pharmaceuticals), which are both novel RNAi therapies for primary hyperoxaluria that selectively reduce hepatic expression of lactate dehydrogenase and glycolate oxidase respectively, reducing hepatic oxalate production and urinary oxalate levels. Finally, we consider future optimizations advances in RNAi therapies.

Keywords: RNA interference; calcium oxalate; end-stage renal disease; glycolate oxidase; hyperoxaluria; kidney stones; lactate dehydrogenase; micro-RNA; primary hyperoxaluria; small interfering RNAs.

FIGURE 1

Molecular mechanisms of endogenous cellular RNAi. In the nucleus, pre‐micro RNA (pre‐miRNA) are trimmed from large primary micro‐RNA transcripts (pri‐miRNA) by DROSHA/DGCR8 complexes (1). Pre‐miRNA is exported to the cytoplasm associated with EXPORTIN‐5 (2). Exogenous dsRNA molecules enter the cell by endocytosis and cytoplasmic escape (3). dsRNA in the cytoplasm is further processed by DICER/TRBP complexes (4) before recruitment of Argonaut (AGO) and other proteins to form the RISC (5). The RISC unwinds the dsRNA and incorporates the antisense (or guide) strand, releasing the passenger strand for degradation (6). The antisense strand serves as a guide, selecting mRNA targets according to sequence homology, affecting either target mRNA cleavage and degradation (7) or translational repression (8). dsRNA: double‐stranded RNA; DGCR8: DiGeorge syndrome chromosomal region 8; TRBP: TAR RNA‐binding protein; RISC: RNA‐induced silencing complex, AGO: Argonaut protein

FIGURE 2

Hepatic metabolism of oxalate. Metabolic pathways involved in oxalate metabolism depicting the enzymes defective in the 3 major types of primary hyperoxaluria (red boxes and blue text). LDH catalyses the final step in the production of oxalate from glyoxalate for all PH types. The precise mechanisms by which HOGA mutations lead to increased oxalate production are not fully understood (depicted by dotted lines). Hypotheses include inhibition of GRHPR by accumulated HOG and metabolism of HOG in the cytoplasm to glyoxylate by an unidentified aldolase enzyme. 1P5C: 1‐pyrroline‐3‐hydroxy‐5‐carboxylate; E4HG: erythrohydroxyglutamate; HOG: 4‐hydroxy‐2‐oxoglutarate; PH: primary hyperoxaluria; AGXT: alanine glyoxylate aminotransferase; GRHPR: glyoxylate reductase/hydroxypyruvate reductase; HOGA1: hydroxyl‐oxoglutarate aldolase 1; LDH: lactate dehydrogenase

FIGURE 3

Mechanism of action of nedosiran within hepatocytes. Nedosiran is a GalNAc‐dsRNA conjugate. (A) Bound GalNac sugar residues bind to ASGPR receptors prompting endocytosis of the dsRNA. Via an incompletely understood mechanism, the compound undergoes endocytic escape and enters the cytoplasm. (B) Within the cytoplasm, the dsRNA first interacts with endonuclease DICER (orange). DICER then passes the antisense RNA strand to AGO2 (purple). The dsRNA compound is designed to favour the loading of the antisense RNA strand into the RISC complex. (C) RISC is guided to the target mRNA by homology to the RNA strand, cleaving the target RNA. GalNAc: N‐acetylgalactosamine; ASGPR: asialoglycoprotein receptor; RISC: RNA‐induced silencing complex; dsRNA: double‐stranded ribonucleic acid