Vutrisiran: A Review in Polyneuropathy of Hereditary Transthyretin-Mediated Amyloidosis.

Silencing the transthyretin (TTR) gene is an effective strategy in the treatment of hereditary transthyretin-mediated (hATTR) amyloidosis. Vutrisiran (Amvuttra®), an RNA interference (RNAi) therapeutic targeting TTR mRNA, is approved in the USA and EU for the treatment of adults with polyneuropathy of hATTR amyloidosis. N-acetylgalactosamine conjugation and enhanced stabilisation chemistry are utilised to target vutrisiran to the liver and increase stability, respectively, allowing for subcutaneous administration once every 3 months. In a pivotal phase 3 study in patients with hATTR amyloidosis with polyneuropathy, subcutaneous vutrisiran 25 mg every 3 months significantly reduced neuropathy impairment versus external placebo. Vutrisiran was also associated with significant improvements in neuropathy-specific quality of life, gait speed, nutritional status and disability scores. Vutrisiran was generally well tolerated; the only common adverse events to occur at a greater incidence than with external placebo were pain in extremity and arthralgia. Vutrisiran reduces serum vitamin A levels and vitamin A supplementation is recommended. In conclusion, vutrisiran is an efficacious and generally well-tolerated alternative option for the treatment of polyneuropathy of hATTR amyloidosis, which has the potential advantage of infrequent subcutaneous dosage.

Hereditary transthyretin-mediated (hATTR) amyloidosis is a progressive and disabling disease caused by variants in the transthyretin (TTR) gene, which cause destabilisation and misfolding of the TTR protein. Deposition of misfolded TTR protein (amyloid) around nerves causes a range of neuropathic symptoms. Vutrisiran (Amvuttra^®) silences the TTR gene via RNA interference (RNAi). Vutrisiran, administered subcutaneously once every 3 months, is approved in the USA and EU for the treatment of polyneuropathy of hATTR amyloidosis in adults. In a phase 3 study in patients with hATTR amyloidosis with polyneuropathy, vutrisiran significantly reduced neuropathy impairment and improved other disease-related outcomes versus external placebo. Vutrisiran was generally well tolerated, with most adverse events being mild or moderate in severity. As vutrisiran decreases vitamin A levels, patients undergoing vutrisiran treatment should supplement with vitamin A. In conclusion, vutrisiran is an efficacious and generally well-tolerated alternative option for the treatment of polyneuropathy of hATTR amyloidosis, with a convenient dosage regimen.

Transthyretin Amyloid Cardiomyopathy-Current and Future Therapies.

OBJECTIVE: To describe the clinical presentation of transthyretin amyloid cardiomyopathy (ATTR-CM) and discuss current treatments and investigational products and their effect on patient outcomes. DATA SOURCES: A literature search was performed in PubMed (September 2018 to December 2020) using the following keywords: transthyretin amyloidosis, cardiomyopathy, polyneuropathy and transthyretin amyloid cardiomyopathy, monoclonal light-chain, tafamidis, cardiac amyloidosis, ATTR cardiomyopathy, green tea and inhibition of cardiac amyloidosis, AG10, tolcapone, tolcapone and leptomeningeal ATTR, PRX004, NI006, patisiran, inotersen, vutrisiran, AKCEA-TTR-LRx, and NTLA-2001. STUDY SELECTION AND DATA EXTRACTION: Clinical trials were evaluated for evidence supporting pharmacology, safety, efficacy, and measured outcomes. DATA SYNTHESIS: Until 2019, there were no approved treatments for ATTR-CM. Treatment consisted of symptom management and organ transplant. Nonpharmacological and pharmacological treatments focused on the symptoms of heart failure (HF) associated with ATTR-CM. However, there are several emerging therapies recently approved or in development to address the underlying pathophysiology. Treatment classes for ATTR-CM include transthyretin stabilizers, human monoclonal antibodies, gene silencers, and CRISPR/Cas9 gene editing. RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE: ATTR-CM is a complex disease in which amyloidosis causes cardiomyopathy. Underdiagnosis is attributed to the clinical presentation being heterogeneous, indistinguishable from HF caused by other etiologies, and the need for invasive testing modalities, including endomyocardial biopsy. Improved diagnostic approaches along with targeted therapies can slow disease progression and enhance patient quality of life. CONCLUSION: Diagnostic modalities along with biomarker and genetic testing could detect disease earlier and target therapy more accurately. Novel therapies demonstrate potential treatment benefits and can help shape the standard of care for these patients.

Leading RNA Interference Therapeutics Part 1: Silencing Hereditary Transthyretin Amyloidosis, with a Focus on Patisiran.

In 2018, patisiran was the first-ever RNA interference (RNAi)-based drug approved by the US Food and Drug Administration. Now pharmacology textbooks may include a new drug class that results in the effect first described by Fire and Mello 2 decades ago: post-transcriptional gene silencing by a small-interfering RNA (siRNA). Patients with hereditary transthyretin-mediated amyloidosis (hATTR amyloidosis) present with mutations in the transthyretin (TTR) gene that lead to the formation of amyloid deposits in peripheral nerves and heart. The disease may also affect the eye and central nervous system. The formulation of patisiran comprises the RNAi drug encapsulated into a nanoparticle especially developed to deliver the anti-TTR siRNA into the main TTR producer: the liver. Hepatic cells contain apolipoprotein E receptors that recognize ApoE proteins opsonized in the lipid carrier and internalize the drug by endocytosis. Lipid vesicles are disrupted in the cell cytoplasm, and siRNAs are free to trigger the RNAi-based TTR gene silencing. The silencing process involves the binding of siRNA guide strand to 3'-untranslated region sequence of both mutant and wild-type TTR messenger RNA, which culminates in the TTR mRNA cleavage by the RNA-induced silencing complex (RISC) as the first biochemical drug effect. Patisiran 0.3 mg/kg is administered intravenously every 3 weeks. Patients require premedication with anti-inflammatory drugs and antagonists of histamine H1 and H2 receptors to prevent infusion-related reactions and may require vitamin A supplementation. Following patisiran treatment, TTR knockdown remained stable for at least 2 years. Adverse effects were mild to moderate with unchanged hematological, renal, or hepatic parameters. No drug-related severe adverse effects occurred in a 24-month follow-up phase II open-label extension study. At the recommended dosage of patisiran, Cmax and AUC values (mean ± standard deviation) were 7.15 ± 2.14 µg/mL and 184 ± 159 µg·h/mL, respectively. The drug showed stability in circulation with > 95% encapsulated in lipid particles. Metabolization occurred by ribonuclease enzymes, with less than 1% excreted unchanged in the urine. Patisiran ameliorated neuropathy impairment according to the modified Neuropathy Impairment Score + 7 analysis of the phase III study. The Norfolk Quality of Life-Diabetic Neuropathy score and gait speed improved in 51% of the patisiran-treated group in 18 months. Additionally, the modified body mass index showed positive outcomes. Altogether, the data across phase I-III clinical trials points to patisiran as an effective and safe drug for the treatment of hATTR amyloidosis. It is hoped that real-world data from a larger number of patients treated with patisiran will confirm the effectiveness of this first-approved siRNA-based drug.

Evaluation of Therapeutic Oligonucleotides for Familial Amyloid Polyneuropathy in Patient-Derived Hepatocyte-Like Cells.

Familial amyloid polyneuropathy (FAP) is caused by mutations of the transthyretin (TTR) gene, predominantly expressed in the liver. Two compounds that knockdown TTR, comprising a small interfering RNA (siRNA; ALN-TTR-02) and an antisense oligonucleotide (ASO; IONIS-TTRRx), are currently being evaluated in clinical trials. Since primary hepatocytes from FAP patients are rarely available for molecular analysis and commercial tissue culture cells or animal models lack the patient-specific genetic background, this study uses primary cells derived from urine of FAP patients. Urine-derived cells were reprogrammed to induced pluripotent stem cells (iPSCs) with high efficiency. Hepatocyte-like cells (HLCs) showing typical hepatic marker expression were obtained from iPSCs of the FAP patients. TTR mRNA expression of FAP HLCs almost reached levels measured in human hepatocytes. To assess TTR knockdown, siTTR1 and TTR-ASO were introduced to HLCs. A significant downregulation (>80%) of TTR mRNA was induced in the HLCs by both oligonucleotides. TTR protein present in the cell culture supernatant of HLCs was similarly downregulated. Gene expression of other hepatic markers was not affected by the therapeutic oligonucleotides. Our data indicate that urine cells (UCs) after reprogramming and hepatic differentiation represent excellent primary human target cells to assess the efficacy and specificity of novel compounds.

Preclinical evaluation of RNAi as a treatment for transthyretin-mediated amyloidosis.

ATTR amyloidosis is a systemic, debilitating and fatal disease caused by transthyretin (TTR) amyloid accumulation. RNA interference (RNAi) is a clinically validated technology that may be a promising approach to the treatment of ATTR amyloidosis. The vast majority of TTR, the soluble precursor of TTR amyloid, is expressed and synthesized in the liver. RNAi technology enables robust hepatic gene silencing, the goal of which would be to reduce systemic levels of TTR and mitigate many of the clinical manifestations of ATTR that arise from hepatic TTR expression. To test this hypothesis, TTR-targeting siRNAs were evaluated in a murine model of hereditary ATTR amyloidosis. RNAi-mediated silencing of hepatic TTR expression inhibited TTR deposition and facilitated regression of existing TTR deposits in pathologically relevant tissues. Further, the extent of deposit regression correlated with the level of RNAi-mediated knockdown. In comparison to the TTR stabilizer, tafamidis, RNAi-mediated TTR knockdown led to greater regression of TTR deposits across a broader range of affected tissues. Together, the data presented herein support the therapeutic hypothesis behind TTR lowering and highlight the potential of RNAi in the treatment of patients afflicted with ATTR amyloidosis.

Structural stabilization of transthyretin by a new compound, 6-benzoyl-2-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione.

Familial amyloid polyneuropathy (FAP) is a genetic, adult-onset, neurodegenerative disorder caused by amyloid formation of transthyretin (TTR), a thyroxine-binding protein. Mutation in TTR causes a propensity of TTR tetramer to dissociate to monomer, which is the first step to amyloidosis. Thus, a drug that can stabilize the tetramer structure will have therapeutic benefit. Here, by virtual screening and biochemical assays, we identified small molecule 6-benzoyl-2-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione (L6) that can prevent the dissociation of TTR to monomer. X-ray crystallography reveals that L6 binds to the T4 binding pocket of TTR. These findings show that L6 is a candidate TTR stabilizer.

Therapeutic Oligonucleotides Targeting Liver Disease: TTR Amyloidosis.

The liver has become an increasingly interesting target for oligonucleotide therapy. Mutations of the gene encoding transthyretin (TTR), expressed in vast amounts by the liver, result in a complex degenerative disease, termed familial amyloid polyneuropathy (FAP). Misfolded variants of TTR are linked to the establishment of extracellular protein deposition in various tissues, including the heart and the peripheral nervous system. Recent progress in the chemistry and formulation of antisense (ASO) and small interfering RNA (siRNA) designed for a knockdown of TTR mRNA in the liver has allowed to address the issue of gene-specific molecular therapy in a clinical setting of FAP. The two therapeutic oligonucleotides bind to RNA in a sequence specific manner but exploit different mechanisms. Here we describe major developments that have led to the advent of therapeutic oligonucleotides for treatment of TTR-related disease.

Vitreous surgery impact in glaucoma development in liver transplanted familial amyloidosis ATTR V30M Portuguese patients.

PURPOSE: Familial amyloidosis with polyneuropathy (FAP) sometimes courses with vitreous amyloid. The aim of this study was to evaluate the incidence of glaucoma after vitrectomy in FAP patients. METHODS: A total of 79 eyes of 42 liver transplanted FAP patients and 16 eyes of 16 non-FAP patients with rhegmatogenous retina detachment were collected. The patients were divided in to three groups: Group I - FAP patients with vitreous opacities submitted to vitrectomy, Group II - FAP patients without vitreous opacities and not submitted to vitrectomy and, Group III - non-FAP patients with rhegmatogenous retinal detachment submitted to vitrectomy. The Group I was subdivided into: Ia - "complete" vitrectomy; Ib - "incomplete" vitrectomy. The onset of glaucoma was considered when the intraocular pressure level was higher than 21 mmHg, with concomitant visual field abnormalities and optic nerve cupping. RESULTS: Post vitrectomy glaucoma was more frequent in Group I (56.1%) than in Group III (12.5%) and in Group II (10.5%). We observed a higher incidence of glaucoma in the Ia than in the Ib subgroup (86.4 vs. 21.1%) and earlier appearance in subgroup Ia (7.9 ± 3.6 vs. 39.5 ± 6.6 months). CONCLUSION: Vitrectomy induced the development of glaucoma in FAP patients.

Circadian rhythm of blood pressure reflects the severity of cardiac impairment in familial amyloid polyneuropathy.

BACKGROUND: Cardiac amyloidosis due to familial amyloid polyneuropathy (FAP) includes restrictive cardiomyopathy, thickened cardiac walls, conduction disorders and cardiac denervation. Impaired blood pressure variability has been documented in FAP related to the Val30Met mutation. AIMS: To document blood pressure variability in FAP patients with various mutation types and its relationship to the severity of cardiac involvement. METHODS: Blood pressure variability was analysed in 49 consecutive FAP patients and was compared with a matched control population. Cardiac evaluation included echocardiography, right heart catheterization, electrophysiological study, Holter electrocardiogram and metaiodobenzylguanidine (MIBG) scintigraphy. RESULTS: A non-dipping pattern was found in 80% of FAP patients and in 35% of control patients (P<0.0001); this was due to a significantly lower diurnal blood pressure in FAP patients (FAP group, 113 ± 21 mmHg; control group, 124 ± 8 mmHg; P<0.0001), whereas nocturnal blood pressures were similar. Among FAP patients, a non-dipping pattern was significantly associated with haemodynamic involvement, cardiac thickening or conduction disorders. These associations did not depend on the average blood pressure levels. Impaired blood pressure variability was more frequent and more pronounced in patients with multiple criteria for severe cardiac amyloidosis. CONCLUSION: Low blood pressure variability is common in cardiac amyloidosis due to FAP. A non-dipping pattern was more frequently observed in FAP patients with haemodynamic impairment, cardiac thickening or conduction disorders. It is suggested that impairment of circadian rhythm of blood pressure reflects the severity of cardiac amyloidosis due to FAP.

Spinal cord stimulation markedly ameliorated refractory neuropathic pain in transthyretin Val30Met familial amyloid polyneuropathy.

Although spinal cord stimulation has been reported to be effective for controlling neuropathic pain in diabetic neuropathy, it has rarely been investigated in other peripheral neuropathies. We describe, for the first time, the efficacy of spinal cord stimulation for refractory neuropathic pain in a patient with transthyretin Val30Met associated familial amyloid polyneuropathy (FAP ATTR Val30Met). A 72-year-old man was diagnosed as having FAP ATTR Val30Met when he was 70 years old. He had been complained of burning pain in the distal portion of his bilateral lower limbs since he was 69 years old. Because conventional symptomatic therapies, including nonsteroidal anti-inflammatory drugs, antiepileptic drugs, and tricyclic antidepressants did not ameliorate pain, he underwent bilateral lumbar spinal cord electrical stimulation at high frequency and low voltage at the level of Th12 vertebral body and this was markedly effective. Our case expands the application of spinal cord stimulation, which should be considered as an alternative therapeutic approach for relief of neuropathic pain, which can be extremely distressful for patients and may lead to an impaired quality of life.

A case of vitreous amyloidosis without systemic symptoms in familial amyloidotic polyneuropathy.

We describe a case of vitreous amyloidosis without systemic symptoms in familial amyloidotic polyneuropathy (FAP) associated with Val30Met transthyretin mutation. A healthy 74-year-old woman noticed left blurred vision and floaters in 1992. Severe vitreous opacities were identified in the left eye. The patient displayed no systemic symptoms, and Congo red staining of the biopsy samples of the stomach and duodenum revealed no amyloid deposition. A diagnosis of FAP was confirmed following genetic investigation. Vitrectomy and cataract surgery was performed with intraocular lens implantation in April 1998. Histopathological examination of the vitreous material revealed amyloid fibrils. Intraocular pressure (IOP) gradually elevated and cupping of the optic disc enlarged. Trabeculectomy was performed in February 2000, but postoperative IOP was again elevated and a needling procedure was performed in March 2000. No postoperative recurrence of vitreous opacity has been reported and IOP has remained well controlled. In the present case, ocular manifestations were the only symptoms of FAP and systemic symptoms have not developed, after more than 12 years. FAP should be suspected as the cause in cases of vitreous opacities in patients from areas with endemic foci of FAP.